Arctic Sea Ice : Forum

Cryosphere => Antarctica => Topic started by: AbruptSLR on February 21, 2013, 04:25:06 PM

Title: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 21, 2013, 04:25:06 PM
In the accompanying figure from Vaughan et al. 2011, the researcher postulate that the indicated seaways opened in the WAIS during the Eemian period some 124,000 years ago.  Vaughan et al. proved that for an upper bound that the longest of these seaways formed within less than a thousand years (which is well within the timeframe of the Eemian peak proving that WAIS could have contributed at least 3.4 to 3.8 m to eustatic SLR in that period) .  I propose that by 2100 such seaways could be re-established in the WAIS via a combination of: (a) floatation of ice sheet sections that have thinned sufficiently for them to float; (b) the formation of a network of interconnected subglacial cavities paralleling the seaways identified by Vaughan et al., which (when interconnected) would allow tidally induced flushing of CDW to rapidly melt the basal ice around the expanding interconnected cavities; (c) accelerated caving of both glaciers and ice shelves due to such factors as increasing CDW temperatures, tidal action, periodic subglacial meltwater network lubrication of basal friction (see surge post topic), and increased wave action due to telecommunication from the Topical Pacific Ocean; (d) a melt-pond mechanism collapse of the Ross Ice shelf after 2050; and (e) a change in the currents in the Weddell Sea after 2050 leading to accelerated CDW advection forced retreat of the glaciers grounding lines in that region so that the grounding lines retreat past buttressing ridges that have been supporting those glaciers.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 21, 2013, 04:44:18 PM
It should be noted that WAIS is that remaining marine ice sheet on earth, and that it is unique from all of the other previous marine ice sheets in that the WAIS can retreat from four different regions (the Bellingshausen Sea region, the Amundsen Sea region; the Ross Sea region and the Weddell Sea region) all converging on a common central subglacial basin area (roughly below the WAIS divide).  The accompanying figure from Bingham et al 2012 shows that the West Antarctic with WAIS removed has numerous subglacial troughs that can lead warm ocean water (driven by: advection, currents and tidal action) from all four seas directly into the heart of the WAIS subglacial basins (see the surge topic posts for a similar view of the West Antarctic with WAIS in-place).  In this figure the area for the Ferrigno Glacier is indicated by the black rectangle; which rests in a rift valley that leads directly into the back side of the trough that the PIG rests in thus leading any subglacial cavities extending beneath these two glaciers to interconnect in the future (leading to tidal driven water flushing through the interconnected cavities); and that the glaciers around the Weddell Sea, and the Thwaites Glacier also lead directly into a subglacial basin that would interconnect all of these subglacial cavities into a network similar to the seaways shown by Vaughan et al. 2011 (note that the glaciers around the Ross Ice Shelf as so thin that if they lose the buttress action of the Ross Ice Shelf after 2050 by a meltpond mechanism that more thinning would cause them to float without the need for advective melting via troughs).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 21, 2013, 06:05:43 PM
While there is a fair amount of signal noise in the historical record, the accompanying figure from Rohling et. al. 2007 indicates that the rate of SLR during the Eemian peak ranged from 2.5 to 4 m per century (mean of 3.5 cm/yr).   Specifically, from circa 124.2 to 123.8 kyr ago it is proposed that the collapse of portions of other marine ice sheets resulted in abrupt SLR, while from circa 123.8 to 123.7 kyr ago the current portion of the WAIS collapsed resulting in about 3.5m of eustatic SLR and about 5m of RSLR in the Coral Sea.  Also, note: during the Meltwater Pulse 1A, 14,600 years ago, a collapse of some prior portions (on the current continental shelf) of the WAIS may have contributed to an average of a 4 m per century SLR for 500 years.  As by Rohling's figure by 123.8 kyr ago the WAIS may have been in full active retreat (which promotes internal friction of the glacial ice that then drains to the bottom of the glaciers, which promotes reduction of the basal friction) and the current WAIS is not yet at that level of activation; nevertheless the radiative forcing of SRES A1FI that we are currently trending has much more forcing than what was occurring during the Eemian, and the thermal inertia of the oceans may not delay the anthropogenic induced warming of the CDW water as much as the GCM projections indicate as: (a) the Southern Ocean dominates the ocean heat uptake; and (b) the ocean water heat content between 700 to 2000m, which feeds the CDW temperature, is currently accelerating faster (due to upwelling) than any other portion of the ocean.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 21, 2013, 09:57:15 PM
The accompanying figure from Orsi et al. 2012 reports temperature measurements from a station at the WAIS Divide which indicates that for the 50-year period from 1957 to 2007 the surface temperature at the WAIS Divide increased at a mean rate of 0.231 C/decade; however for the 20-year period that mean rate of surface temperature was 0.804 C/decade.  This means that the WAIS is currently one of the fastest warming locations on Earth, which means that after 2050 surface melting of the ice sheet will be come more frequently a factor that affects both ice sheet (as is the case for GIS now) and ice shelf (as occurred in the Antarctic Peninsula for the Larsen B ice shelf) stability.  Futhermore, strong El Nino events can temporarily raise surface temperatures well above the decade trend line for periods of month, thus increasing the risk of high episodic ice mass loss during future strong El Nino events (which we have not had for over 10 years).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 22, 2013, 02:29:01 AM
The accompany figure is from a Dec. 2011 AGU poster and shows measured Ross Ice Shelf retreat from 2005 to 2010 with the highest face retreat found near of the central zone with rates from 1 to 1.65 km/yr normal to the face.  Presumably with climate change this rate of calving will increase, but even if it does not the ice shelf face would retreat over 60 km by 2050 thus exposing the Ross Ice Shelf from abrupt collapse from a melt pond mechanism similar to that which occurred for the Larsen B ice shelf.  If so, it is likely that the glaciers buttressed by the Ross Ice Shelf would accelerate by about a factor of 5 times, which would thin the leading edges of these glaciers causing the grounding line to retreat rapidly as the leading edge lifts off of the seafloor.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 22, 2013, 05:22:36 PM
The accompanying figure from Hellmer et al. 2012 shows key model results from their state of the art regional circulation model.  This results indicate that due to projected changes in the sea ice by 2075 (using SRES A1B and scientifically conservative assumptions) will lead to a redirection of warm CDW below that Filchner-Ronne Ice Shelf which will gradual impinge upon the ice at the grounding lines of the adjoing glaciers, which has been projected to result in the relatively rapid retreats of these grounding lines due to the inherent instability of many of the glaciers in this area.  While the glaciers in the Weddell Sea region account for only approximately 10% of the WAIS ice mass loss potential, the formation of subglacial cavities beneath these glaciers (see discussion in the "surge" thread), may connect with nearby subglacial cavities from the Bellingshausen and Amundsen Sea regions before the end of this century, given that the world may continue along our current SRES A1FI path and given the fact that ice mass loss from the Bellingshausen and Amundsen Sea glaciers seem to be accelerating both earlier and faster than most researchers are stating publically at the moment.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 22, 2013, 11:26:18 PM
The accompanying figures show both direct measurement of the thickness of the Ross Ice Shelf (which is rapidly thinning) and of how in 2003 tides interacted with the velocity of the ice flow from the adjoining Whillian Ice Stream.  The subsequent reply will illustrate that as calving occurs for the Ross Ice Shelf tidal interaction will accelerate ice flow from the Siple Coast ice streams.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 22, 2013, 11:32:13 PM
The accompanying figure shows finite element model results of how the tidal cycle the horizontal ice flow within the Ross Ice Shelf.  As the Ross Ice Shelf face calves the areas of higher horizontal tidally influenced ice velocities will increasing interact with the adjoining Siple Coast ice streams which will accelerate the rate of ice mass loss from these ice streams.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 12:27:02 AM
The accompanying figures from Vaughan et al. 2012 illustrate how sub-ice-shelf water flows (from either tides, currents, eddies or melt water advective processes) become channelized which then forms grooves on the underside of the ice shelves; and when the ice shelf flexes (see due to tides, barametric pressure changes from storms, or infragravity waves) the induced flexure stresses can lead to the production of crevasses; which inturn can lead to increased calving from the ice shelves.  It is probable that climate change will lead to increase storm activity around West Antarctica and that changes in sea level will induce flexure stresses within the ice shelves.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 01:14:33 AM
The attached figure by Fogt et al 2011 indicates that trends for cyclones storm in both the Ross Sea, and Bellingshausen Sea, Basins has been of increased intensity (ie lower cental pressure) and increase storm frequency.  This will tend to increase calving from ice shelves/tongues in these areas.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 01:45:15 AM
The accompanying figures indicate the present and potential future contributions to SLR from mountain glaciers and ice caps (GIC), the Antarctic Peninsula, GIS, EAIS, and WAIS.  In my proposed collapse scenario the SLR contributions from GIC and GIS play an important role in raising sea levels around Antarctica which contributes to the destabilization of marine ice sheets and marine glaciers.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 01:59:32 AM
The accompanying figures of Envisat altimetry measurements of the trend in elevation changes (m/yr) thru June of 2012 (with detail of PIG for 2008 & 2009) for Antarctica, indicate that ice mass loss from marine ice sheets and glaciers is not only a growing concern for the WAIS but also for the EAIS (however the total ice mass loss for the EAIS for recent years as been masked by several years of unusually high snow fall, which could well only be natural variations).  These measurements indicate that ice mass loss from the WAIS is accelerating non-linearly as compared to previous years.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 02:09:58 AM
The accompanying figure shows modeled cumulative precipitation in eq. meters of SLR for Antarctica for families of ECP (extended RCP scenarios).  These models indicate that precipitation will only increase linearly in the Antarctic until 2100, while as previously noted current ice mass loss trends from marine ice sheet and marine glaciers is already non-linear.  Therefore, it can be expected that ice mass loss from the Antarctic will become an increasing percentage of the total contribution to SLR through 2100.  Also note that some of the future precipitation the West Antarctic may fall as rain before the end of the century.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 02:33:36 AM
Accompanying is GRACE satellite data of measured ice mass loss rates from 2002 to 2011 for different drainage basins in Antarctica, from Sasgen et al. 2012.  While this time frame is too short to filter out the influence of snowfall variability, the information clearly indicates the importance of ice-mass-loss from West Antarctica and inparticular from the Thwaites Drainage basin (which has the highest rate of ice mass loss).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 02:41:45 AM
Accompanying is GRACE satellite data of measured the acceleration of ice mass loss from 2002 to 2011 for different drainage basins in Antarctica, from Sasgen et al. 2012.  While this time frame is too short to filter out the influence of snowfall variability, the information clearly indicates the importance of the acceleration of ice-mass-loss from West Antarctica and inparticular from the Thwaites Drainage basin (which has the highest measured rate of acceleration ice mass loss in Antarctica).  Note that this data does not include the probable surge of ice mass loss from WAIS and from Thwaites inparticular in 2012 discussed in the "Surge" thread.
 As stated previously these rates of accelerations are expected to increase non-linear with continued climate change.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 03:37:08 PM
I forgot where this image came from, but it makes a useful comparison between the ice/ocean interaction for WAIS marine glaciers with ice shelves and GIS marine glaciers (for those who don't already know).  One particular point that I would like to make is that in the image's caption that author makes a clear distinction between the ice/ocean interaction for cold WAIS marine glaciers with ice shelves such as at the Ross Ice Shelf and the Filchner-Ronne Ice Shelf (where the majority of the Antarctic's Bottom Water is produced) and warm WAIS marine glaciers with ice shelves such as PIG.  For the cold WAIS ice shelf case that author shows that the dense, high-salinity shelf water that forms near the ice-shelf front during winter sea-ice growth (which is normally a source of Bottom Water) can get drawn under the cold ice shelf where it can melt the underside of the cold ice shelf thereby diluting the previously high-density shelf water, which would likely prevent much of this self water from sinking further in order to become Bottom Water.  It is noted that the amount of Antarctic Bottom Water has dropped dramatically in recent years; which could be an indication that the melting of the underside of the cold ice shelves is accelerating; which could contribute to accelerated calving of such cold ice shelves relative to prior projections.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 07:35:10 PM
As my proposed WAIS collapse scenario has many similarities as to what may have happened during the Eemian, I provide the accompanying figure from Barnes et al 2010 showing the probable condition of the WAIS at the Eemian peak.  This condition is supported both on the fossil records of Bryozoans and on DNA of existing  family of Antarctic octopus the West Antarctic.  Furthermore, in 2011 based on marine sediments it was found that GIS could only have contributed 1.6-2.2m to Eemian sea level; while in 2012, based on GIS ice core (NEEM) findings, the high-end of this contribution was further limited indicating that the WAIS contributed at least 3.5 to 3.8m at that time.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 09:11:23 PM
As previously cited, Vaughan et al. 2011 clearly identify sea passage ways for ocean water to travel from outlet marine glaciers (e.g. PIG, Thwaites, and Ferrigno, Glaciers) and ice streams (e.g. Bindschadler, Moller and Rutford ice streams) that are at risk of rapid grounding line retreat would convey warm ocean water to the interior basins of the WAIS, frequently through subglacial cavities such as observed for PIG and Thwaites (see the "Surge" thread).  Furthermore, Vaughan et al. 2011 state: "Progressive thinning of coastal ice resting on a bed below sea level will eventually allow it to float.  If such thinning connected two coastal seas, whether or not a float-ing ice shelf remained, seawater would pass freely beneath the ice and between the seas, forming an open seaway. Although the impact of such seaways on the oceanography of the Southern Ocean and Antarctic climate is likely to have been substantial, to date there has been little effort to investigate their importance. The only comparable seaway in existence today, that beneath George VI Ice Shelf on the Antarctic Peninsula, has a strong ocean current flowing through it, which influences considerably oceanography of the nearby continental shelf [Jenkins and Jacobs, 2008]."  This demonstrates that the formation of passage ways (with or without ice above the passage ways) through the WAIS can have strong currents that would accelerate ice sheet collapse. 
Also, the presence of identified subglacial water networks (see the "Surge" thread) can accelerate the collapse of ice sheets as indicated by Branecky et al. 2011 who states in regards to the Pine Island paleo-ice stream: "Paleo-ice thicknesses of less than 1.35 km result in water escape from basins and transport of significant subglacial water into the ocean. The retreat of the Pine Island paleo-ice stream was likely impacted by such discharge events because they have the potential to increase ice flow velocities by reducing bed resistance and change hydrologic flow regimes by affecting subglacial pressures."
Furthermore, the rapid collapse of the WAIS would result in large (multiple meters) of local GIA seafloor rebound resulting in significant tectonic/seismic activity that would have a positive feedback effect on the collapse of the WAIS, as would the basal ice melting from the basal heat generated by the upwell of magma beneath the seafloor crust (beneath the WAIS) causing the meters of GIA rebound (note that as stated previously the basal melting rate measured directly in a drillhole at the WAIS Divide is extraordinarily high, 1.5~cm a-1.
Also, finally for this post, the accompany figure illustrates the risk of the release of subglacial seafloor methane that could occur during a rapid retreat of the grounding lines of marine glaciers in both the WAIS and the EAIS; which would provide a positive feedback by accelerating the advective process by the methane bubbles generated at the face of the grounding line acting like an air-lift to force the syphon effect (this air-lift action would likely occur even if the methane bubbles release from the seafloor hydrates were absorbed by the surrounding seawater before the bubbles made it to the surface as the change in effect water density (averaging both bubbles and adjoining water) would provide momentum to the vertical advective syphon effect within the subglacial cavities.  Note also that methane releases from the seafloor in the Antarctic Peninsula have already been observed.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 11:24:51 PM
The following briefly lists a: Timeline and Key External Events for SLR Contributions According My Scenario for a 50% CL RCP 8.5 Scenario (as stated in the "Forcing Thread" I believe the actual probabilities of occurrence for the RCP 8.5 Scenario to be many times higher than the IPCC publically acknowledges)  for the Collapse of the WAIS:

(1) 2020 - (a)Arctic Sea Ice Absent in September, (b) 1mm/yr SLR contribution from groundwater extraction; (c) Larsen C ice shelf has collapsed.
(2) 2030 Mean global temperature anomaly = 1.2 C
(3) 2040 Mean global temperature anomaly = 1.5 C: Himalayan Glaciers accelerate and some Himalayan Ice Dams rupture which releases the previously impounded water to the ocean.  Carbon dioxide and methane emissions from Northern Hemisphere permanfrost is in the 1.2 to 1.4 Gt/yr range (see accompanying figure)
(4) 2050 Mean global temperature anomaly = 2 C: Ice mass loss form Greenland Marine Terminating Glaciers accelerates.
(5) 2070 Mean global temperature anomaly = 3 C: Degradation of the amazon forest begins to accelerate.
(6) 2080 Mean global temperature anomaly = 3.4 C: ENSO amplitude begins to increase.
(7) 2090 Mean global temperature anomaly = 4.2 C
( 8 ) 2100 Mean global temperature anomaly = 4.9 C
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2013, 11:36:09 PM
The accompanying figure from Vaughan et al. 2011 illustrates how much ice needs to be lost in order for the lower ice to float-up off of the bottom (James Hansen has emphasized that the Antarctic sheet ice does not all need to melt in order to for the sea level to rise, provided that this ice can float-off of the seafloor.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Peter Ellis on February 24, 2013, 12:29:15 AM
Huh?

The point at which the remaining ice floats is the point at which sea level rise stops.  Melting floating ice does not change sea level.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 24, 2013, 12:33:16 AM
I plan to gradually post a series of images superimposed on Vaughen et al 2011 plan and profile of their passageway alignments showing areas of my assumed areas of grounding line retreat and calving for cases based on a 50% Confidence Level, CL, and a 95% CL, RCP 8.5 scenarios for descrete periods from 2040 to 2100.  The attached image is the first of these images for the 50% CL RCP 8.5 case for 2040.  In this paricular scenario it is assumed that: (a) the "surge" observed for the Ferrigno and Thwaites Glaciers repeat in the future until subglacial cavities indicated occur by 2040; (b) Calving reduces the Ross Ice Shelf buttress action to 85% of the 2000 value and the enhanced tidal influence leads to sufficient thinning of the adjoining ice streams to result in floatation of the previously grounded ice in the indicated areas; and (c) the PIG grounding line retreats to the indicated areas in accordance with Gladstone et al. 2012.
The purpose of these images is to help clarify the points that I am trying to make.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 24, 2013, 12:57:52 AM
The attached images is for the 50% CL RCP 8.5 case for 2060.  In this paricular scenario it is assumed that: (a) acceleration of advection (due to increased CDW temperature, and larger subglacial cavity size, and branching of the subglacial cavities beneath the Thwaites Glacier to follow the subglacial melt water network) and accelerated subglacial water flow from melt water flowing down through the glacier due to internal ice friction from more dynamic ice movement) for the Ferrigno and Thwaites Glaciers repeat in the future until subglacial cavities indicated occur by 2060; (b) Calving reduces the Ross Ice Shelf buttress to 65% of 2000 value and the melt pond mechanism then reduces the buttress action to 10% of 2000 value, causing the grounding line to retreat in the indicated areas; (c) the PIG grounding line retreats to the indicated areas in accordance with Gladstone et al. 2012 and (d) Sea ice continues to thin in the Weddell Sea and reduce in extent, and warm CDW enters the Filchner Trough, leading to the grounding line retreat indicated.
The purpose of these images is to help clarify the points that I am trying to make.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 24, 2013, 01:24:47 AM
The attached images is for the 50% CL RCP 8.5 case for 2090.  In this paricular scenario it is assumed that: (a) acceleration of advection (due to increased CDW temperature, and larger subglacial cavity size, and branching of the subglacial cavities beneath the Thwaites Glacier to follow the subglacial melt water network) and accelerated subglacial water flow from melt water flowing down through the glacier due to internal ice friction from more dynamic ice movement) for the Ferrigno, PIG and Thwaites Glaciers repeat in the future until subglacial cavities indicated occur by 2090 with formation of interconnected basal passageways causing tidal induced water to surge through; (b) Continued thinning of the ice streams around the collapsed Ross Ice Shelf  leads to a progressive retreat of the grounding line due to floatation of the ice sheet edge and continued calving of the ice shelf, similar to the behavior observed for the Larsen B shelf after 2002 melt pond collapse and (c) Sea ice continues to degrade in the Weddell Sea and reduce in extent, and warm CDW volumes accelerate through the Filchner Trough,  and the formation of the interconnected basal passageways, and seaways, leads to a partial collapsed shown.
The purpose of these images is to help clarify the points that I am trying to make
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 24, 2013, 01:51:31 AM
My 95% CL RCP 8.5 scenario is modified from the official RCP 8.5 scenario primarily in that it envisions a significant release of nature methane into the environment together with an accelerated antropogenic methane release from increased use of hydrofracting and shale gas.  I plan to post more specifics later about this methane emissions assumption in the "Forcing" thread, but for now I provide the accompanying figure illustrating the temperature scenario that this 95% CL RCP WAIS collapse scenaro assumes.

Furthermore, as the effects of this assumed methane concentration pathway is not expected to become significant for WAIS ice mass loss until after 2040, the 95% CL RCP 8.5 2040 scenario is essentially identical to the 50% CL RCP 8.5 2040 scenario and thus this figure is not repeated here.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 24, 2013, 02:08:13 AM
The attached images is for the 95% CL RCP 8.5 case for 2060.  In this paricular scenario it is assumed that: (a) acceleration of advection (due to increased CDW temperature, and larger subglacial cavity size, and branching of the subglacial cavities beneath the Thwaites Glacier to follow the subglacial melt water network) and accelerated subglacial water flow from melt water flowing down through the glacier due to internal ice friction from more dynamic ice movement) for the Ferrigno and Thwaites Glaciers repeat in the future until subglacial cavities indicated occur by 2060; (b) Continued thinning of the ice streams adjoining the Ross Ice Shelf leads to a progressive retreat of the grounding lines due to floatation of the ice sheet edge and continued calving of the ice shelf, similar to the melt pond behavior observed for the Larsen B shelf after 2002; (c) the PIG grounding line retreats to the indicated areas in accordance with Gladstone et al. 2012 and (d) Sea ice continues to thin in the Weddell Sea and reduce in extent, and warm CDW enters the Filchner Trough, leading to the grounding line retreat indicated.
The purpose of these images is to help clarify the points that I am trying to make and not to precisely project grounding line retreat patterns.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 24, 2013, 02:27:29 AM
As the 95% RCP 8.5 2090 case is inbetween the 50% RCP 8.5 2090 and the 95% RCP 8.5 2100 cases it is not shown.  The accompanying images are for the 50% CL RCP 8.5 case for 2100.  In this paricular scenario it is assumed that by 2090 with formation of interconnected basal passageways causing tidal induced water to surge through leading to such rapid ice mass loss that seismic activity causes the all of the remaining susceptible ice to float by 2100. It is also noted that such a total collapse of the WAIS would active significant portions of the EAIS, as well accelerating ice mass loss from marine terminating glaciers in the GIS. The purpose of these images is to help clarify the points that I am trying to make.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 25, 2013, 02:04:04 PM
ASLR,
Thanks for all the info on WAIS you're posting here. It will take some time to digest it. For now, just a short remark on your reference above to Rohling et al (2007). If I've understood correctly Rohling has lowered his estimates for max rate of SLR (above current sea level) during the Eemian to about at least 0.7 meters/century. See Grant, Rohling et al (2012):
http://www.nature.com/nature/journal/v491/n7426/full/nature11593.html (http://www.nature.com/nature/journal/v491/n7426/full/nature11593.html)

"[R]ates of sea-level rise reached at least 1.2m per century during all major phases of ice-volume reduction, and were typically up to 0.7m per century (possibly higher, given the smoothing in our method) when sea-level exceeded 0m during the LIG".

Since the current/future GHG-forcing is/will probably be much higher than the Eemian insolation-forcing (averaged over the planet) a significantly higher max rate of SLR than this 0.7 m/century seems likely during the coming centuries.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 25, 2013, 03:17:21 PM
Lennart,

Thank you for the very helpful update to Rohling, which I will review in more detail and comment on in a later post.  But for now I will agree that we cannot use any previous period (Eemian or otherwise) as a model for projecting our current case with the historically highest radiative forcing in millions of years.  Nevertheless, I will note here that the quote that you cite: "[R]ates of sea-level rise reached at least 1.2m per century during all major phases of ice-volume reduction, and were typically up to 0.7m per century (possibly higher, given the smoothing in our method) when sea-level exceeded 0m during the LIG"; only discusses minimum and average SLR rates during the LIG (for periods when sea-level was above our current levels) and not the maximum rates.  Saying the the rates of rise were at least 1.2m per century does not preclude higher values.
And while I believe that we need to model our own present case, still the past can be a guide as to what is possible, so please note that the attached information from Alvarez-Solas et al. 2012, that for at least 50 years the Hudson Strait Marine Glacier surged at a velocity of about 4,500 m/yr while the accompanying figure from Rignot 2008 indicates while in 2007 PIG was flowing at a rate of about 4,000 m/yr still in 2007 Thwaites was only flowing at about 2,500 m/yr; which indicates that there is plenty of opportunity for Thwaites to accelerate.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 25, 2013, 05:07:01 PM
ASLR,

The 1.2 meters/century of Grant et al (2012) is for sea levels below present, the 0.7 m/century for up to 5 m above present. I understand the 0.7 m/century to be the max speed averaged over several centuries, so on shorter time scales the max speed could be higher. I do find their wording not entirely clear, however.

In correspondence with Rohling he told me that the 0.7 figure may well be increased again in follow-up work, although probably not as high as the earlier (2007) 1.6 figure. Also in that earlier paper the difference between 'average' and 'peak' rates is not fully clear to me.

Also Blanchon et al (2009) found indications for a rate of SLR of about 2.5 meters in about 50 years during the Eemian, but I don't know how much confidence other paleo-climatologists have in that estimate.

But let's assume that 1-2 meters/century did occur during the Eemian, or even the 3.5 meters/century from the earlier Rohling et al paper. How much faster could sea levels rise during this century and after?

Pfeffer et al (2008) estimate a max possible rise of about 2 meters by 2100:
http://www.sciencemag.org/content/321/5894/1340.full.pdf (http://www.sciencemag.org/content/321/5894/1340.full.pdf)

That would imply a rate of SLR by about 2100 of probably circa 4 cm/yr, so if sustained about 4 m/century. The question is if this would be their estimated max potential rate of SLR, or if it could go even faster later in the next century.

Hansen and Sato (2012) seem to expect an 'iceberg cooling' negative feedback which would keep the max rate of SLR under about 5-6 meters/century (under BAU emissions). They criticize Pfeffer et al for (mainly) not sufficiently taking the instablity of WAIS into account.

Pfeffer et al assume an average outlet glacier velocity for PIG/Thwaites of about 14-15 km/yr from 2020-2100. How fast could we reach that speed and how much faster could those glaciers go?

And how about the assumption of Pfeffer et al for Greenland of an average outlet glacier velocity of about 27 km/yr from 2020-2100? How likely is that and how much faster could it go, if at all?

I'm very interested to hear your opinion on Pfeffer et al.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 25, 2013, 06:13:54 PM
Lennart,

I very much appreciate you getting to the heart of the matter so directly (and framing the issue so well).  A full response to your questions may take me some days (or weeks) to unfold, but I will make the following brief points now (to be elaborated later): (a) on an expert opinion level I clearly side with Hansen and Sato 2012 and I do criticize Pfeffer et al 2008 for being dated and too narrow, but I do agree with Pfeffer that specific mechanisms need to be identified (which I have started in my other threads [see my latest post in the "surge" thread]); and (b) as I state in the "philosophy" thread ice believe that it will take several decades for computer ice models to fully capture the mechanisms that I am proposing and for now I suggest that a "Hazard Analysis" be conducted using something like Bayesian methodology.
To give approximate answers to your questions about Pfeffer et al 2008 I offer the following criticisms: (a) Pfeffer's high ice velocities are applied to too narrow of gateways: (i) as shown by Rignot 2008 the 2007 ice velocities of 2,500 m/yr is only applied over a narrow ice stream of 5 to 8 km; (b) I suspect that now that the subglacial cavity has extended to the lip of the BSB this this surge flow width may have expanded to 30 to 40 km before being currently pinned on the sides by the submarine mounts, but once the ice in this area thins so that it can float over the submarine mounts to the East (at El -650m) this throat should further widen to 50 to 60 km, and once the ice thins to float at El -450m this throat width widens to almost 100km. (b) Pfeffer disregards the branching that I propose will happen to the subglacial cavity once it reaches the bottom of the negative slope leading to the BSB, thus after 2040 local icebergs could calve off of multiple branches and float out of the 50 to 100 km wide throat; (c) Pfeffer ignores the activation of the Weddell Sea Coastal glaciers by the introduction of warm CDW beneath the Filchner-Ronne Ice Shelf circa 2060, and he ignores the risk of the activation of the Siple Coast glaciers/ice streams by the accelerated calving and probably ice melt pond mechanism (which in this tread I cite could begin circa 2050 to 2070; (d) Pfeffer ignores my proposed mechanism that the subglacial cavities may link together after 2070 leading to a very rapid surge of ice sheet disintergation from tidal water flow through the interconnected subglacial cavities; plus (e) as Hansen and Sato point out for SLR to rise all of the ice does not need to melt, it only needs to float so seismic activity associated with large ice mass loss circa 2070 to 2080 could cause accelerated floatation of multiple icebergs out form all four fronts (Amundsen Sea, Bellingshausen Sea, Weddell Sea, and Ross Sea) of the WAIS.  I believe that with these assumptions that limiting the ice average ice flow velocities to 4,500 to 6,000 m/yr is more than sufficient.  Furthermore, Pfeffer has ignored (failed to update) his case for GIS due to melt water from Albedo change including BC which caused ice mass loss for GIS of 700 Gt from January to Sept 2012 (while Pfeffer is only talking about ice flow/calving).  That is all for now, but please re-look as all the various mechanisms that I present in various different posts/threads.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 25, 2013, 08:13:00 PM
Lennart,

In response to your first post about Rohling (both in 2007 & Grant et al 2012) I provide the two attached figures.  First from Grant et al 2012, in the timeframe of interest from over 125 kyr ago (when sea-level was higher than now) all that I can say is that several of the blue crosses appear to be between 6m to 8m higher than today indicating the potential for brief spikes of collapsed ice mass loss on the order of 50 to 100-years (in any event Grant's data does not rule out such spikes).  The second figure from Muhs et al 2012, shows that for California sea-level rapidly increased to just over 6m above today's sea level (which matches my graphs in the philosophical thread) and then was flat for a long prior.  Therefore, I suggest that one should be very careful when performing a "Hazard Analysis" of using averaged data that includes rapid rises together with long period of little or no rise (also Grant et al 2012 average over at least 1000 years which much to coarse to see a 50 to 100-yr spike).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 26, 2013, 12:41:30 AM
Lennart,

I would like to supplement my earlier post about my criticism of Pfeffer's assumptions for the glaciers in the ASE to note that: (a) he did know about ice mass loss through advection through subglacial cavities and in my drawings of these cavities for the Thwaites Basin I show that this could be a very large area, and further I note that this subglacial ice melting would be accelerated by the geothermal heat coming up through the crust (which I presume to be commonly plugged from high volumes of release by a sediment plug at the base of the gateway to Thwaites).  Also I note that the Ross Ice Shelf (which is a cold ice shelf without warm CDW) loses a lot of thickness to sub-iceshelf melting which does not add to SLR because it is floating, but for any new Thwaites Ice Shelf formed above the BSB this would all contribute to SLR as all of this ice is now grounded; (b) Pfeffer takes a combined gateway cross-section for both PIG and Thwaites to be 120 sq km which is reasonable, but if we get a lot of subglacial advective ice melting within subglacial cavities in the BSB then ice may float out of this gateway.  Also, for those not familiar with Pfeffer et al 2008 I attach a pdf.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 26, 2013, 01:35:44 AM
With regard to ice mass loss from the glaciers around the Filchner-Ronne Ice Shelf: The Alfred Wegener Institute is now studying the potential impact on sea levels of the risk of ice mass loss from the Weddell Sea sector of the WAIS, identified by Hellmer et al. 2012.   However, if the ice sheet flow toward the sea is as great as the ice loss projected for the shelf itself, the institute stated that global sea levels would rise by and additional 4.3 mm per year, before the end of the century.  It is noted here that Hellmer et al. 2012 examined scenarios less aggressive than those for both RCP 8.5 and for the SBEHA corrected RCP 8.5, which implies that the indicated ice mass loss could begin to accelerate closer to 2050 rather than the 2070 date cited by Hellmer et al. 2012.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 26, 2013, 01:49:47 AM
For those not familar with the melt pond mechanism I provide the accompanying figure related to the collapse of the Larsen A & B Ice Shelf in 2002
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 26, 2013, 12:17:28 PM
ASLR,
Thanks for your views on Pfeffer et al (2008) and the reference to Muhs et al (2012). I don't have access to this last paper, but abstract and figures are here:
http://www.sciencedirect.com/science/article/pii/S0277379112000224 (http://www.sciencedirect.com/science/article/pii/S0277379112000224)

Spikes of very fast SLR over 50-100 yrs seem very hard to extract from the Eemian data, but I agree that they may very well have occurred.

I also support your risk hazard approach and find your overview of potential mechanisms that could contribute to collapse very useful.

Expert elicitation seems to be an important way of getting more insight into the potential risk of WAIS-collapse. Bamber & Aspinall (2013) gave some useful data from their survey amongst 13 experts (out of 26 invited) in 2010 and 2012:
http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1778.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1778.html)

In their supplementary Table S1 (p.8 last column) they apparently show that the rate of SLR in 2100 from the ice sheets is estimated on average to be 5-7 mm/yr, with a 5% risk of more than circa 17 mm/yr, and a very small chance of almost 4 cm/yr in the most extreme scenario. That last scenario would seem to be about the same as the most extreme scenario by Pfeffer et al. On p.10 (bottom) of the supplementary info they also seem to give an even more extreme estimate for the max rate of (total) SLR in 2100 of almost 5 cm/yr, but I don't understand the technical details of these different estimates.

The 13 experts surveyed were (p.11 supplementary info):
Richard Alley, Richard Hindmarsh, Philippe Huybrechts, Ian Joughin, Shawn Marshall, Frank Pattyn, Jeff Ridley, Eric Rignot, Catherine Ritz, Robert Thomas, Michiel van den Broeke, Roderik van de Wal, David Vaughan.

I'm wondering what you make of these outcomes and what your own best guess for max rate of SLR around 2100 would be.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 26, 2013, 05:24:32 PM
Lennart,

When I have time I will open a new thread on why the IPCC WG1 (not just Pfeffer) at the moment do not recognize the risk of abupt SLR this century (and I agree that timing is the primary question here).  But in general terms Bamber & Aspinall 2013 is the "tip of the iceberg" of a growing trend to at least formally recognize this risk of abrupt SLR from ice mass loss from ice sheets (IS), see the attached figure with a thin tail for the risk of abrupt SLR.  While B & A at least acknowledge the risk of abrupt SLR, ASLR, they are stuck in the officially recognized scenarios developed by the IPCC which limits its estimates of probabilities to what can be proven deductively by GCM projection give the RCP set of assumptions.  B&A's panel of experts all appear to accept this methodology while experts such as Hansen and Sato appear to try to look out side of the box using inductive reasoning to present the risk of 5m of SLR by 2100, which is to say that the fatten the tail of the IS ice mass lose curves presented by B&A to include factors such as ice from the WAIS thinning sufficiently to lift of the bottom and to float away much faster than Pfeffer and the IPCC WG1 are prepare to even acknowledge. 
Regarding my projections of SLR by 2100, they have been posted in the "philosophy" thread for many days now.  Again, I will open a new thread to try to clarify each out of the box hazard factor that will contribute layer by layer to fatten the trail of the probability curve for ASLR.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 26, 2013, 11:06:30 PM
ASLR,

I wasn't sure how to read those graphs. Do I understand correctly that under RCP 8.5 you think almost 4 meters of (globally averaged) SLR around 2100 not only possible, but likely? And that between circa 2070 and 2090 you think about 2 meters not only possible, but likely? Or should I read this differently?

If so, and if that's a real risk, or even a probability, what adaptation options should we think of in that case, in your view?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 27, 2013, 12:03:31 AM
Lennart,

The way that I mean for these graphs to be read, is that one would either design a new feature of infrastructure to what ever standard that has jurisdiction, or one would re-examine the design of an existing structure; and then one would use these graphs to determine ocean elevations for RSLR (for infrastructure in California) for a resiliency (or maximum credible) case similar to a maximum credible earthquake.  Note that the US Federal Emergency Management Agency, FEMA, requires a similar resiliency check case for the current risk of a 0.2% exceedance probability (one in 500-yr) inundation case.  I propose this MCE RSLR to be a similar resilency check case for future conditions at the end of the infrastructure features design life, rather than for the present case resiliency check.  I believe that what adaptive engineering provisions should be considered for such an MCE check case depends on the consequence of failure of the infrastructure feature and on its importance.  Note that the MCE check case would not include only the probability of a future sea level but also all storm and other short-term load combinations.
Examples of adaptive measures include: (a) design for a shorter service life; (b) design the feature to survive the short-term loading and be suitable for restoration; (c) retreat from the high risk area; (d) cover some risk with insurance; (e) design the feature to be upgradable as the RSLR goes up; or (f) be prepared to accept the loses.  Most militaries around the world are performing hazard analysis for abrupt climate change and they plan accordingly.  While it is more comfortable not to think about such possible hazard cases; it is still better to have resilient infrastructure as we enter our new age of climate change consequences.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 27, 2013, 12:36:45 PM
ASLR,

Thanks again for all the info and insights you're posting here. Are you a publishing scientist in this field, or did your learn all this another way?

Just to be sure I repeat my question above: do I understand correctly that under RCP 8.5 you think almost 4 meters of (globally averaged) SLR around 2100 not only possible, but likely? And that between circa 2070 and 2090 you think about 2 meters not only possible, but likely? Or should I read this differently?

And in addition, what is your thought on the risks of SLR after 2100? For example, what do you think of these figures from Meehl et al (2012):
http://www.nature.com/nclimate/journal/v2/n8/fig_tab/nclimate1529_F3.html (http://www.nature.com/nclimate/journal/v2/n8/fig_tab/nclimate1529_F3.html)

At least they seem to take seriously a risk of about 10-12 meters of SLR by 2300, under BAU, which is more than any other explicit projections I've seen so far, such as from the Dutch Delta Committee. But the projection of Meehl et al is based on the semi-empirical method, not including possible non-linear responses of the ice sheets, so it may still be an under-estimate.

So I'm wondering how your collapse scenario would continue after 2200. Do you project one big surge around the end of this century, or beginning of the next, and a slower SLR afterwards? Or could the EAIS also contribute one or more follow-up surges in the coming centuries?

I ask this also in relation to Foster & Rohling (PNAS 2013):
http://www.pnas.org/content/early/2013/01/03/1216073110 (http://www.pnas.org/content/early/2013/01/03/1216073110)

They conclude that at 400 ppm CO2 there's circa 84% chance of at least 9 meters of SLR over the coming centuries/millennia and about 50% chance of circa 24 meters of SLR over this longer term. So even at 400 ppm, which we will reach soon, EAIS will probably start contributing significantly to SLR. It doesn't seem likely we will return below 400 ppm any time soon, although if we would really try it might still be possible.

Also Hansen & Sato 2011 (p.23) pointed to signs that Totten Glacier in EAIS is already starting to lose mass, based on Rignot et al 2008: "satellite gravity and radar interferometry data reveal that the Totten Glacier of East Antarctica, which fronts a large ice mass grounded below sea level, is already beginning to lose mass". Pfeffer et al did not take Totten Glacier into account.

For the record: I'm just a lay-man interested in and concerned about the risk of rapid and large SLR, among other climate risks, working for a local environmental ngo in The Hague, Netherlands, and trained in public administration/political science. I'm trying to understand the science as well as I can, but the technical details are often too hard to follow. So bear with me if I sometimes seem to ask for the obvious.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 27, 2013, 03:22:30 PM
Lennart,

Thanks for the continued dialogue.  I will provide brief answers so that I can expand on the other threads in this forum.
First, I am an engineer (not a scientist), and I have published one paper on abupt SLR in a marine engineering conference proceeds that is not widely distributed.  I am to busy to prepare a peer reviewed paper by myself on this topic (so I am posting on this forum instead); however, if others want include this information in their own papers then well & good; or is they want my assistance with a peer reviewed paper in a scientific journal then they can e-mail me.  I learned all that I have put into this forum on the internet, since the Spring of 2011 (after Rignot's paper made the risks clear to me); and while researcher have done a great job of developing the facts that I have learned from the internet; it seems to me that the scientific community at large (with many promient exceptions) and the IPCC in particular have done a very poor job of communicating the actual risks (probability times consequences) to the public at large.
Second, I believe that if we continue on our current path then there is a "good" probability that we will see multiple meters (3m to 5m eustatically and upto 6.5m regionally) by 2100.  Also, I concur with Hansen et al's position that this WAIS ice mass loss contribution will be non-linear with the lion's share coming after 2050 (as clearly indicated numerically on my graphs in the philosophical discuss, and note that I put this graphes in the philosophical section because I believe that resiliency is more important than prescience, and that getting an MCE check case for abrupt SLR now is much more important than spending decades (which what it will take) to get highly accurate ice mechanisms that can project abrupt ice mass loss with GCM projections and I think that risk based hazard analyses run by hand now can make clear what magnitude of resiliency that we need to guard against multi-trillion dollar losses to our coastal cities using things such as storm surge barrier [which could have prevented well over half of the economic losses from Superstorm Sandy).
Third, in the scenario that I envision after the WAIS collapses by the end of this century or the beginning of the next century that SLR will slow-down  (as shown clearly in my graphs in the philosophical thread), for at least 50 to 100-yr (with EAIS and GIS still making significant but not abrupt contributions to SLR); then what happens after 2150 to 2200 depend very much on what anthopogenic forcing and/or what natural methane releases occur; but in general terms I see both EAIS and GIS as being more stable than the WAIS and that they will likely follow behaviors more like Meehl et al 2012 until 2500 (I believe it likely that nature methane releases will drive SLR for at least this long into the 9 to 12m range).
Fourth, I have never read anything yet published by Hansen and Sato that I disagree with, and I clearly see signs since Hansen and Sato's 2011 paper that indicate that the rapid dynamic ice mass loss from EAIS is accelerating and that this accelerating mass loss has been temporarily masked from the GRACE satellite results by some probably temporary heavy years of snow fall.  Also, when the WAIS collapses this will activate many EAIS glaciers adjoining WAIS (such as the Byrd Glacier); but while these EAIS will make significant contribution by the end of this century and times their after, I would call these contributions rapid dynamic contributions and not abrupt.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 27, 2013, 05:43:17 PM
ASLR,

Very clear, and I agree on the importance of resilient adaptative measures based on your risk-based approach, and on the need for much clearer communication of those risks.

I also have a question on mitigation though: suppose we do work together globally and succeed in following not RCP 8.5, but one of the lower scenario's, to what extent would that reduce or eliminate the risk of ASLR, in your view/estimation? Or does that risk remain high enough even in the lower scenario's to require significant adaptive measures (since we're already about to cross 400 ppm and will probably not go below that level during this century, even in a very optimistic scenario)?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 27, 2013, 08:04:12 PM
Lennart,

I estimate that if we can follow the RCP 4.5 50% CL path this will give SLR behavior similar to that shown in the graph in my Feb 25th 6:30am post on the "Philosophical" thread for the blue SBEHA Eustatic 5% curve (note that SBEHA means Scenario Based Engineering Hazard Analysis), which effectively does not have ASLR but does almost follows the semi-empirical projections (such as by Rahmstorf et al).  While it may be possible to follow RCP 4.5 with regard to anthropogenic GHG emissions, I am not very optimistic that we will be able to follow the radiative forcing for RCP 4.5 with regards to both Black Carbon and Natural Methane emissions (permafrost, ocean hydrates etc).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 27, 2013, 10:02:36 PM
ASLR,

That would mean the worst-case scenario of the Delta Committee (2008) could actually be about our best-case scenario:
http://www.deltacommissie.com/doc/deltareport_full.pdf (http://www.deltacommissie.com/doc/deltareport_full.pdf)

That would be... alarming, right? How many knowledgeable people do you know, who share your views on this, apart from Hansen? How could these people work together to wake the rest of the scientific and wider community up? Any suggestions?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 27, 2013, 11:53:47 PM
Lannert,

Your are correct that in my opinion by 2100 about the best that we can hope for is a eustatic SLR of about 1m which is at the upper bound of the accompanying figure including the 2008 Delta report finding.  The people that I know who think as I do, would not be interested in putting anything in writing until after the AR6 report is issued in 2020 to 2021 as they seem to what to have computer codes worked out, and do not want to rely on the hazard analysis approach.

Regarding a solution to this problem all that I can suggest is that the solution to the "Tyranny of the Commons" was to privatize the Commons, thus my only recommendation would be to legistate the use of Public Private Partnerships for flood control projects, and in the legislation make the private part legally responsible for the consequence of the possible failure of the infrastructure feature.  I believe that this topic is too complex to be addressed by the government (representing the people) alone, and until the private financial sector has direct legal liability then all parties (government, insurance, business) will continue to take advantage of the Commons without properly taking care of it.  Note that New York & New Jersey where bailed out by federal emergency aid and now they have little or no interest of taking anything but the easiest defensive measure (eg moving their generators from their basements to somewhere above the first floor) as they are expecting the federal government to bail them out again after a future Sandy event.  This is the "moral hazard" associated with most climate change related measures, that so long as they can "short or hedge" their risks/hazards at someone else's expense, why would they ever face the hard work that they need to face to solve this problem.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 28, 2013, 01:04:57 PM
In addition to the last figure with several sea level rise estimates: the WBGU-estimate for 2300 was by no means a worst-case since their scenario assumed 3 degrees warming with 560 ppm CO2e. See pp.36-37 of:
http://www.wbgu.de/fileadmin/templates/dateien/veroeffentlichungen/sondergutachten/sn2006/wbgu_sn2006_en.pdf (http://www.wbgu.de/fileadmin/templates/dateien/veroeffentlichungen/sondergutachten/sn2006/wbgu_sn2006_en.pdf)

For a BAU-scenario their high estimate of 5 meters in 2300 could maybe be doubled to about 10 meters.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 28, 2013, 02:28:08 PM
Lennart,

Thanks for the input from 2006.  When developing projections (or hazard analyses) for the future, it is always good to look back to see where you came from.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 08, 2013, 05:08:52 PM
Regarding looking back from where we came from, while many of you will have already seen this first image, nevertheless some will not have, so I am posting the attached figure of historical global temperatures relative to peak Holocene temperature. (per Hansen and Sato, 2011).  This image illustrates that the peak temperature during the Eemain was only about 0.75 C above the peak temperature during the Holocene and I note here that the earth will returned to those temperatures levels during the Holocene peak by 2020 and to the Eemain peak temperatures by about 2035 if we keep following RCP 8.5 50% CL (see the second image)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 11, 2013, 12:05:39 PM
The following few selected extracts are taken from the attached fact sheet for the University of Washington's: 2012 Program on Climate Change, PCC, Summer Institute "Atmosphere-Ocean-Ice Shelf Interactions" Sunday, September 16, 2012 to Tuesday, September 18, 2012 Friday Harbor Labs, Friday Harbor, San Juan Island.  Note that all of the following observations related to the West Antarctic were made before the postulated "Surge" was observed, but they are all consistent with the initiation conditions assumed by the WAIS collapse scenario presented in many threads here:
(1) Christina Hulbe: "The Ross Sea sector of the West Antarctic Ice Sheet has the potential for rapid and significant change due to its marine character and fast-flowing ice streams. This makes modern change detection of particular interest and indeed, evidence for past ice flow variability is easy to find. The interest here is how changes observed today are to be interpreted: are modern changes a response to recent climate forcing, part of an ongoing response to warming after the last glacial maximum, or something else entirely? An example on the Ross Ice Shelf will be examined and used as a springboard for wider ranging speculation."
(2) Laurie Padman (padman@esr.org) and Scott Springer: "The now-standard paradigm of ice-shelf importance is that "ocean heat flux into the sub-ice-shelf cavity increases; ice shelf thins (and calves); buttressed glaciers accelerate; sea level rises". However, the ice shelves are not just middlemen, but actively participate in establishing the environment that determines their state. That is, feedbacks from the ice shelf to the ocean and sea ice are important to a full system model of ice shelves."
(3) Sarah G. Purkey & Gregory C. Johnson: "Complex processes that are difficult to model fully or parameterize well in coarse resolution numerical climate projections are numerous around Antarctica, including ice sheet dynamics, ocean circulation and water mass formation, and the incursion of relatively warm Circumpolar Deep Water (CDW) onto the shelf and under ice sheets. We discuss observations of changes in several of these processes. First we review warming and freshening of Antarctic Bottom Water (AABW) and estimate a rate of its contraction in recent decades from changes in water-mass inventories. We show that the contracting AABW is associated with a southward expansion of CDW in the Southern Ocean. We speculate that this expansion may allow increased intrusion of warmer northerly CDW across the slope onto the Antarctic continental shelves, in turn allowing basal ice sheet melt. We note that these processes, along with possible ice dynamic feedbacks discussed by previous speakers, have the potential to form a positive feed-back loop."
(4) Brian Rose, brose@atmos.washington.edu, and David Ferreira and John Marshall: "The coupled climate dynamics underlying large, rapid and potentially irreversible changes in ice cover are studied. A global atmosphere-ocean-sea ice general circulation model with idealized aquaplanet geometry is forced by gradual multi-kyr variations in solar luminosity. The model traverses a hysteresis loop between warm ice-free conditions and cold glacial conditions in response to ±5 W/m^2 variations in global, annual mean insolation. Comparison of several model configurations confirms the importance of polar ocean processes in setting the sensitivity and timescales of the transitions. A “sawtooth” character is found with faster warming and slower cooling, reflecting the opposing effects of surface heating and cooling on upper ocean buoyancy and thus effective heat capacity. The transition from glacial to warm, equable climate occurs in about 200 years."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Bruce Steele on March 11, 2013, 10:30:41 PM
ASLR, Purkey et al 2012 is available open source. Thanks to NOAA PMEL. Thanks for the tip.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 11, 2013, 11:20:39 PM
Bruce,

Here is another tip:
Check out the WAIS Intiative website at: http://www.waisworkshop.org/documentation/toc.html (http://www.waisworkshop.org/documentation/toc.html)
and the two WAIS Initiative conference summaries for 2010 & 2011.  All of these researchers have done excellent work; and I believe that my WAIS collapse scenarios are consistent with all of their findings.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 12, 2013, 12:08:22 AM
Bruce,

Also, if you are into ice shelves then attached is a conference abstract compulation for the:

26th International Forum for Research into Ice Shelf Processes - FRISP -
June 12- 14, 2012
Utö Värdshus
Stockholm Archipelago, Sweden
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Bruce Steele on March 12, 2013, 07:17:42 AM
ASLR, the Purkey paper gets into more detail on the AABW reduction. Purkey et al 2012 shows an 8 SV drop in the volume of water colder than 0 degrees C. Also " the water-mass freshening of AABW in the Indian and Pacific sectors is equivalent to roughly half the recent mass loss of the WAIS."    A lot to read and absorb but it backs up much of your thread. Warmer and fresher water just doesn't sink the way it used to and warmer CDW being pushed onto the shelf is undercutting the base of the ice . It took me awhile to get a grip on the arctic topography and currents. Learning which areas of the Antarctic have sills that trap saline waters during seasonal sea ice freeze-up will be something I need to better understand. Thanks again for all your work. If I read correctly you have concentrated on the Antarctic for < 5 years, I have been trying to study carbonate chemistry for 9 years . It takes about 100,000 years for terrestrially  supplied alkalinity to rebalance large perturbations in the pH balance of the worlds oceans . I saw a graph of former ice sheet collapse events in deep time, it looks like the time it takes for the ice sheets to rebound after a collapse is also in the 100,000 year range. Just speculating ,there may be a connection.       
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 12, 2013, 02:08:54 PM
Bruce,

I agree that Purkey et al 2012 is a great reference, and I agree that getting to understand the Antarctic ocean, atmosphere, bathymetry, ice, topology, feedbacks, boundary conditions, and forcing functions is complicated, and non-stationary, and takes time (note that I am a full-time civil engineering and have only been looking at the Antarctic in my spare time for the past year and a half; which has the advantage that I have been focusing on primarily the most recent research available on the internet).  As I feel that I have not provided adequate discussion about the complex ocean/ice interactions/mechanisms for my postulated collapse scenario the FRIS and RIS I plan to open another thread soon to focus on this important matter (which is quite different from the collapse scenario for the Bellingshausen/Amundsen Sea marine ice sheets).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 13, 2013, 12:49:54 AM
As I decided that the information that I provide regarding Antarctic methane hydrates seem inadequate I provide the following abstract from Potential methane reservoirs beneath Antarctica by Wadham et al 2012:
"Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 1015 g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage."

Also an internet article states:

"Half the West Antarctic ice sheet and a quarter of the East Antarctic sheet lie on pre-glacial sedimentary basins containing around 21,000bn tonnes of carbon, said the scientists, writing in the journal Nature.
British co-author Prof Jemma Wadham, from the University of Bristol, said: "This is an immense amount of organic carbon, more than 10 times the size of carbon stocks in northern permafrost regions.
"Our laboratory experiments tell us that these sub-ice environments are also biologically active, meaning that this organic carbon is probably being metabolised into carbon dioxide and methane gas by microbes."
The amount of frozen and free methane gas beneath the ice sheets could amount to 4bn tonnes, the researchers estimate."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 04, 2013, 12:16:15 AM
In order to effectively implement the scenario based hazard analysis recommended in all of my threads in this folder into a format that policy maker can accept/utilize; I recommend that the scientific community invest in a stacked knowledge managment software approach such as is commercially available from Palantir Technologies (see the following website):

http://www.palantir.com/technologies/ (http://www.palantir.com/technologies/)

Such an approach would allow for a much more dynamic knowledge management environment, where the input information could be kept in one stack; the GCM analysis could be in another stack; the post-processing software related to risk analysis could be in another stack and the top stack could handle graphics and presentations.

Panatir's approach has been very successful in managing other complex problems including terrorist threats.  I think that both government agencies and the scientific community need to get serious about managing the available information/projections on climate change and SLR risks in a more effective manner, rather than acting in a business as unusual manner.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 04, 2013, 08:06:08 PM
Perhaps my prior post was not very clear about the roles Palantir's different stacks (Data Integration, Search & Discovery; Knowledge Management, and Collaboration) facilitate the analysis of complex issues (such as the potential abrupt collapse of the WAIS and/ or the SLR contribution from the AIS); and allows collaboration across various disciplines and between researchers.  I am very concerned that the risks from the Antarctic fall into the case of "out of sight, out of mind" and that the difficulties and expense of gaining information from this critical and complex area, makes it difficult to just keep track of the dots, let alone to connect them; while use of a software tool such as that offered by Palantir could greatly increase the effective evaluation of what data there is, in order to more fully present the true risks from this arena.

For one important example:  As I previously posted about, an Antarctic study (by Wadham et al 2012 in Nature) has found that half the West Antarctic ice sheet and a quarter of the East Antarctic sheet lie on pre-glacial sedimentary basins containing around 21,000bn tonnes of carbon.  British co-author Prof Jemma Wadham, from the University of Bristol, said: "This is an immense amount of organic carbon, more than 10 times the size of carbon stocks in northern permafrost regions.
"Our laboratory experiments tell us that these sub-ice environments are also biologically active, meaning that this organic carbon is probably being metabolised into carbon dioxide and methane gas by microbes."  The amount of frozen and free methane gas beneath the ice sheets could amount to 4bn tonnes, the researchers estimate.  Wadham also said: “Depending on where that hydrate is, and how much there is, if the ice thins in those regions, some of that hydrate could come out with a possible feedback on climate”.   This implies that some of these methane from destabilized hydrates below the WAIS and the EAIS could be released via the methane saturated basal meltwater just by pressure reduction associated with the thinning of the ice sheets, without the subglacial sediments being exposed by either subglacial cavities due to the advection of warm CDW, or other grounding line retreat.

Furthermore, these estimates do not include the methane hydrates in the seafloor of the Southern Ocean that could be destabilized by with warming of the CDW in the ACC; which may already be occurring depending on how to interpret the atmospheric methane content over the Antarctic posted by A4R in the "Antarctic Methane" thread.

Accessing the true risk from these massive Antarctic carbon/methane stores is a complicated task suitable for the Palantir software as part of a larger effort to evaluate the larger risks of changes in the Antarctic.


Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 05, 2013, 08:59:04 PM
I thought that I would post this image from: Reconstructions before rifting and drifting reveal the geological connections between Antarctica and its conjugates in Gondwanaland, by J.J. Veevers, Earth-Science Reviews, Volume 111, Issues 3–4, March 2012, Pages 249–318;
because it indicates how complex the tectonics are for the West Antarctic, which could activate both earthquakes and volcanic action with sufficient ice mass loss from the WAIS.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 14, 2013, 08:05:26 PM
I thought that I would post the first attached image to should how significant the isostatic rebound would be for the Antarctic if all the ice were to melt, as compared to the second image showing the current bed elevations (per BedMap2).  Note that as most all of this rebound occurs underwater, it contibutes directly to the observed sea level of the future.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 30, 2013, 03:35:22 PM
I have commented repeatedly about the need to both update and augment the GCM projections about the risks of abrupt SLR primarily from the potential collapse of the WAIS this century, to include both the most recent observations and to include consideration of factors not addressed within the traditional methodology adopted by the IPCC for projecting the risks of SLR (abrupt or otherwise).

Therefore, I plan to make several posts in this thread to try to clarify the approach that I am proposing to iteratively (as new information becomes available) identify the true risks of this possible abrupt SLR event (see the PDF's in the "Philosophical" thread and the discussion in all other threads).   I am posting in this thread both because it contains prior posts that present an overview of the issues that justify making updates to the traditional (IPCC) SLR projections, and because it contains discussions of both "big data" software such as Palantir's systems for process the large about of data and a on the new commercial quantum computers (such as recently bought by NASA) that are very good at running the types of calculations that I will be discussing/presenting.

I propose to generally follow a Bayesian Learning approach in order to upgrade  prior PDF's to better capture the risks beyond those identified by the GCM's projections, using Event Trees (Fault Trees) of specific un-captured cases together with Markov Chain and Monte Carlo (MCMC) analyses to quantify the probability of the SLR contributions for the specific cases.  Furthermore, I plan to divide the discussion of this topic into two categories: (a) that focused on updating the forcing scenarios (including climate sensitivity); and (b) updating ice mass loss mechanisms/scenarios related to the risk of abrupt SLR.

Therefore, I will conclude this post by presenting results of a recent exercise by Bodman et al 2013 to update the uncertainties/risks of mean global temperature projections in order to induce numerous carbon cycle and climate observations (Earth Systems).  While, I do not believe that Bodman et al 2013's findings are comprehensive, I fully support their methodology for updating the forcing scenarios (note that I will not discuss updates to ice mass loss mechanisms/scenarios related to SLR until later posts), and I plan to discuss a variation of this methodology when I discuss SLR risks.

Bodman et al 2013's exercise is summarized by the following (including at the link below):
http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1903.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1903.html)
"Uncertainty in temperature projections reduced using carbon cycle and climate observations
Roger W. Bodman, Peter J. Rayner & David J. Karoly, Nature Climate Change; 2013, doi:10.1038/nclimate1903, 26 May 2013

Abstract:
The future behaviour of the carbon cycle is a major contributor to uncertainty in temperature projections for the twenty-first century. Using a simplified climate model, we show that, for a given emission scenario, it is the second most important contributor to this uncertainty after climate sensitivity, followed by aerosol impacts. Historical measurements of carbon dioxide concentrations4 have been used along with global temperature observations to help reduce this uncertainty. This results in an increased probability of exceeding a 2 °C global–mean temperature increase by 2100 while reducing the probability of surpassing a 6 °C threshold for non-mitigation scenarios such as the Special Report on Emissions Scenarios A1B and A1FI scenarios, as compared with projections from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Climate sensitivity, the response of the carbon cycle and aerosol effects remain highly uncertain but historical observations of temperature and carbon dioxide imply a trade–off between them so that temperature projections are more certain than they would be considering each factor in isolation. As well as pointing out the promise from the formal use of observational constraints in climate projection, this also highlights the need for an holistic view of uncertainty."

Further discuss of this paper can be found at:
http://www.futurity.org/earth-environment/new-estimate-narrows-global-warming-range/ (http://www.futurity.org/earth-environment/new-estimate-narrows-global-warming-range/)
"Team leader Bodman says while continuing to narrow the range even further was possible, significant uncertainty in warming predictions would always remain due to the complexity of climate change drivers.
“This study ultimately shows why waiting for certainty will fail as a strategy,” he says. “Some uncertainty will always remain, meaning that we need to manage the risks of warming with the knowledge we have.”
The study found 63 percent of uncertainty in projected warming was due to single sources—such as climate sensitivity, followed by future behavior of the carbon cycle, and the cooling effect of aerosols—while 37 percent of uncertainty came from the combination of these sources.
“This means that if any single uncertainty is reduced—even the most important, climate sensitivity—significant uncertainty will remain,” Bodman says.
Karoly says the study reinforced the importance of strong action on climate change.
“Our results reconfirm the need for urgent and substantial reductions in greenhouse gas emissions if the world is to avoid exceeding the global warming target of 2 degrees needed to minimize dangerous climate change,” he says."

The Bodman et al 2013 exercise used the computer program MAGICC to calculate the new projected mean global temperatures for SRES A1B, A1FI, and A2 (see the first attached image comparing the new MAGICC projections with the old IPCC projections).

The second attached image presents table of priors and posteriors (see my pervious posts on Bayesian methodology or Google it) for eleven key carbon cycle forcing parameters/mechanism (as related to Earth Systems Modeling), that were used as input to the MAGICC program.

The third attached image presents an example of a Monte Carlo Metropolis-Hastings (MCMH) algorithm which is a type of Markov Chain Monte Carlo (MCMC) analysis.   Per Bodman et al 201s: "The Monte Carlo Metropolis–Hastings (MCMH) algorithm is a data assimilation method that combines observational data with prior probability density functions (PDFs) in order to obtain a posterior parameter distribution. It is a technique that has been applied in a number of other studies for calibrating both simple and intermediate complexity Earth system models."

The fourth attached image presents the joint probability distributions for these eleven key parameters/mechanisms used in the MAGICC analyses.  Per Bodman et al 2013: "Joint distribution of the eleven key MAGICC parameters used with the MCMH algorithm. The diagonal elements show the histograms for the individual prior (black line) and posterior (shaded region) distributions. The off–diagonal contour plots indicate the joint marginal distributions between any pair of these parameters."
As I have run out of time and space, I will conclude by saying that Bodman et al's 2013 findings should be updated to include the risks associated with such possible forcing functions as: (a) Arctic Sea Ice "albedo flip", (b) recent black carbon findings; (c) the risks of wildfires in the Arctic permafrost regions; (d) natural and hydro-fracking related releases of methane; (d) see other factors discussed in the "Forcing" thread.  Again in subsequent posts I will present discussions using Event Tree (Fault Tree) and MCMC (or MCMH) analyses related to the risks of abrupt SLR (which is a different approach than that used by the RAND Corps and PennState; which I presented/discussed previously).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Laurent on May 30, 2013, 04:14:22 PM
When you say iso-static rebound, you mean that while the Antarctic will loose some weigh, it will also go up because lighter...if what i understand is correct then, that should be added to the volume of ice that will sent away to increase the sea level rise. Have you an estimate of that volume of sea water added ? should be around 63 meter + something ?

Thanks AbruptSLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 30, 2013, 04:39:45 PM
Laurent,

The iso-static rebound will vary across the WAIS area depending on the local conditions, varying from a few 10's of meters to several hundreds of meters (eventually).  The images that I posted on page 1 of this 2 page thread from Vaughan et al 2011 provides a dotted line along several different cross-sections through the WAIS area that show the various potential iso-static rebounds.  Also, to the degree that the magma causing the rebound flows out from under adjoining landmasses (such as the EAIS) rather than the adjoining seafloor, then yes this rebound will clearly add (eventually) to SLR.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 30, 2013, 04:41:33 PM
Before I leave the topic of updating forcing input for ice mass loss, I would like to note here that all of the GCM's have been calibrated to match the scientific community's prior understanding of paleo-responses during previous interglacial period; however, recent new paleo-evidence (eg see the "WAIS Divide" borehole thread and the Arctic Sea Ice Blog discussion of the Lake El'gygytgyn boreholes) indicates that the earth system responses in the past exhibited short periods of abrupt climate change; to which the GCMs (ESMs) need to be recalibrated.  Furthermore, the WAIS Divide core demonstrates that the WAIS was absent during the Eemian (MIS 5e) period, and the following 2013 summary about the Lake El'gygytgyn ice cores indicates multiple times when the WAIS was absent during "super interglacials"; and the GCMs (ESMs) need to be re-calibrated to match these finding of periods when the WAIS was absent in the past.

"Millennial scale change from Lake El’gygytgyn, NE Russia: Did we step or leap out of the Warm Pliocene into the Pleistocene?
Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel 
The Pliocene-Pleistocene climate evolution of the Arctic must have modulated the glacial history of Greenland and the onset of Northern Hemisphere glaciation. What is known from the terrestrial stratigraphy of Arctic climate change comes from sites that are spatially and temporally fragmented. In 2009, International Continental Deep drilling at Lake El’gygytgyn (67o30’ N, 172 o 05’ E) recovered lacustrine sediments dating back to 3.58 Ma that provide the first time-continuous Pliocene-Pleistocene Arctic paleoclimate record of alternating glacial-interglacial change. The warmest/wettest Pliocene interval of the lake record occurs from ~3.58-3.34 Ma and is dominated by exceptional tree pollen implying July temperatures nearly 7-8o C warmer than today with nearly ~3 times the annual precipitation. Atmospheric CO2 levels are estimated to have been 360 to 400 ppm implying exceptionally high climate sensitivity and polar amplification. In fact, pollen spectra and modern analog analysis show an unbroken persistence of summers much warmer and wetter than the last interglacial, MIS 5e until nearly 2.2 Ma. Extreme warmth in the Mid Pliocene Arctic occurs at the same time ANDRILL results suggest the West Antarctic Ice Sheet was non-existent.
Using physical, chemical, and biological proxies we find pronounced glacial episodes commenced ~2.6 Ma ago, but the full range of typical Pleistocene glacial/interglacial change wasn’t established until ~1.8 Ma ago. Greenland must have also responded to numerous “super interglacials” during the Quaternary record, with maximum summer temperatures and annual precipitation, especially during MIS 9,11 and 31, at Lake El’gygytgyn exceeding that documented for MIS 5e. The correspondence of many of these super-interglacials with retreat of the West Antarctic Ice Sheet (Naish et al. 2009) could coincide with intervals when the Greenland Ice was reduced in size. The climate record from Lake El’gygytgyn, especially the history of past interglacials, provides a fresh means of testing the evolving magnitude of polar amplification over time, and the sensitivity of the Greenland Ice Sheet to extreme warmth in the rest of the Arctic."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Laurent on May 30, 2013, 05:33:50 PM
If the west Antarctic Ice shelve wasn't were in the Eemian (-130.000 year), it wasn't were with a CO2 level of 300 ppm (or not far) !? Do you confirm ?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 31, 2013, 01:57:02 AM
Laurent,

At the peak, I believe that Eemian CO2 levels were about 300 ppm; however, as the Earth was more tilted then than at the present, I believe that insolation was more significant during the Eemian than now.  Therefore, as I discuss in the "paleo-evidence" thread, the Eemiam may not be the best example to parallel the Earth's present conditions.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 31, 2013, 02:48:04 AM
Laurent,

To expand slightly on my last post, attached please find two attached images from a 2011 article by Steve Brown comparing the Eemian to the Holocene>
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sg_smith on May 31, 2013, 07:35:45 AM
Hi,

I  have tried to read all the posts but I have not understood most of them.  Sorry if you have already covered this and I missed it (I am sure you did somewhere) but if the Antarctic started rebounding, volcanoes, already known to exist, and earthquakes etc could help to speed the collapsing ice shelves on their way. 
That would be even more fun (:

Cheers
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 31, 2013, 04:55:52 PM
sg_smith,

Thanks for taking the time to read all of the hundreds of posts.  You are absolutely right that the iso-static rebound will mean a lot of guaranteed seismic and volcanic activity (and associated ice mass loss) particularly in the Western Antarctic.  The only remaining question is how fast this will occur: decades, or centuries.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 31, 2013, 04:57:50 PM
Before I redirect my posts to ice mass loss accounting, I would like to make another post about the risk of climate change forcing from wildfires in the newly defrosting permafrost regions, or Tundra.  As I previously posted, James Hansen has reported that recent biomass growth (largely in the Tundra, see the first attached figure) has temporarily slowed some of the recently observed vs. the GCM projected increases in mean global temperature.  I (and many others) have also reported that this biomass growth is decreasing the local (northern land areas) albedo resulting in earlier snow melts in the Tundra.  But James Hansen has called this temporary increase in CO2 sequestration in biomass a Faustian Bargain; as this CO2 will likely be released as global temperatures continue to increase as indicated by the last three attached images  (related to the risks of wildfires releasing this temporarily biomass sequestered CO2) from:

Moritz, M. A., M.-A. Parisien, E. Batllori, M. A. Krawchuk, J. Van Dorn, D. J. Ganz, and K. Hayhoe. 2012. Climate change and disruptions to global fire activity. Ecosphere 3(6):49. http://dx.doi.org/10.1890/ES11-00345.1 (http://dx.doi.org/10.1890/ES11-00345.1)

The second image shows the factors contributing to the increasing risk of wildfires, indicating that for the initial period this risk is relatively low while the new biomass is growing (particularly as the Tundra is warming/defrosting).

The third image shows maps of projections from an ensemble of GCM analyses on wildfire risks with climate change to 2100.  These maps show the increasing wildfire hazard in the Tundra.

The fourth attached image show the risk of actual biomass loss to wildfires; which highlights the risk from the Tundra in the future, not only from increased CO2 emissions but also from future enhanced degradation of the permafrost and the future enhanced emissions of black carbon into the particularly sensitive northern areas.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 01, 2013, 07:41:47 PM
In a prior post in this thread, I suggested that it would be good for researchers to re-calibrate their GCM ice mass loss projections to reconsider recent new paleo-evidence that the WAIS is less stable than was generally thought even one or two years ago.  While I am unaware that such an exercise has performed focused on the WAIS; I am aware of such an exercise that was recently performed focused on the GIS (or GrIS, for Greenland Ice Sheet) findings of which were published in:
Quantification of the Greenland ice sheet contribution to Last Interglacial sea level rise, E. J. Stone, D. J. Lunt, J. D. Annan, and J. C. Hargreaves; Clim. Past, 9, 621–639, 2013 www.clim-past.net/9/621/2013/; (http://www.clim-past.net/9/621/2013/;) doi:10.5194/cp-9-621-2013

Supplementary material related to this article is available online at: http://www.clim-past.net/9/621/2013/ (http://www.clim-past.net/9/621/2013/) cp-9-621-2013-supplement.pdf.


Abstract. During the Last Interglacial period (~130–115 thousand years ago) the Arctic climate was warmer than today and global mean sea level was probably more than 6.6m higher. However, there are large discrepancies in the estimated contributions to this sea level change from various sources (the Greenland and Antarctic ice sheets and smaller ice caps).  Here, we determine probabilistically the likely contribution of Greenland ice sheet melt to Last Interglacial sea level rise, taking into account ice sheet model parametric uncertainty.  We perform an ensemble of 500 Glimmer ice sheet model simulations forced with climatologies from the climate model HadCM3, and constrain the results with palaeodata from Greenland ice cores. Our results suggest a 90% probability that Greenland ice melt contributed at least 0.6 m, but less than 10% probability that it exceeded 3.5 m, a value which is lower than several recent estimates. Many of these previous estimates, however, did not include a full general circulation climate model that can capture atmospheric circulation and precipitation changes in response to changes in insolation forcing and orographic height. Our combined modeling and palaeodata approach suggests that the Greenland ice sheet is less sensitive to orbital forcing than previously thought, and it implicates Antarctic melt as providing a substantial contribution to Last Interglacial sea level rise. Future work should assess additional uncertainty due to inclusion of basal sliding and the direct effect of insolation on surface melt. In addition, the effect of uncertainty arising from climate model structural design should be taken into account by performing a multi-climate-model comparison."

The first attached image (Figure 9 from Stone et al 2013) shows a PDF (probability density function) for eustatic sea level during the Eemian (LIG or MIS5e); from which an idea of AIS SLR contribution can be estimated by subtracting the information in panel c&d of the third attached image (Figure 10 from Stone et al 2013), and accounting for steric (ocean temperature and salinity) and GIC (mountain glaciers and ice caps) SLR contributions.

The second and fourth attached images together shown Figure 11 from Stone et al 2013; which provide an idea of the sensitivity of Stone et al 2013's analysis to the various indicated parameters.

As a side note: while I have recently stated that the Eemian (or MIS 5e, or Last Interglacial [LIG]) is not the best interglacial to calibrate to (in the paleo-evidence thread I suggest that calibrating to the Holsteinian may be more appropriate), still there is a lot more paleo-evidence available for the Eemian period (such as from the NEEM ice core project) and calibrating GCM projections to the Eemian is very instructive; as is indicated by the conclusions that the AIS contribution to eustatic SLR during the Eemian (LIG) was substantial; which implies that the current risk of abrupt SLR contribution for the WAIS is more significant that was appreciated as recently as two years ago.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 01, 2013, 08:47:35 PM
While perhaps I should have posted the information in the "Antarctic Peninsula" thread; I am posting it here because I believe that this evaluation of potential Antarctic Peninsula Ice Sheet, APIS, contribution to SLR is very relevant to methodology for updating the risk of abrupt SLR contribution from the WAIS this century:

Computing the volume response of the Antarctic Peninsula ice sheet to warming scenarios to 2200 by Nicholas E. BARRAND, Richard C.A. HINDMARSH, Robert J. ARTHERN, C. Rosie WILLIAMS, Je´re´mie MOUGINOT, Bernd SCHEUCHL, Eric RIGNOT, Stefan R.M. LIGTENBERG, Michiel R. VAN DEN BROEKE, Tamsin L. EDWARDS, Alison J. COOK, Sebastian B. SIMONSEN; 2013; Journal of Glaciology, Vol. 59, No. 215, 2013 doi:10.3189/2013JoG12J139

"ABSTRACT. The contribution to sea level to 2200 from the grounded, mainland Antarctic Peninsula ice sheet (APIS) was calculated using an ice-sheet model initialized with a new technique computing ice fluxes based on observed surface velocities, altimetry and surface mass balance, and computing volume response using a linearized method. Volume change estimates of the APIS resulting from surface massbalance anomalies calculated by the regional model RACMO2, forced by A1B and E1 scenarios of the global models ECHAM5 and HadCM3, predicted net negative sea-level contributions between –0.5 and –12mm sea-level equivalent (SLE) by 2200. Increased glacier flow due to ice thickening returned ~15% of the increased accumulation to the sea by 2100 and ~30% by 2200. The likely change in volume of the APIS by 2200 in response to imposed 10 and 20km retreats of the grounding line at individual large outlet glaciers in Palmer Land, southern Antarctic Peninsula, ranged between 0.5 and 3.5mm SLE per drainage basin. Ensemble calculations of APIS volume change resulting from imposed grounding-line retreat due to ice-shelf break-up scenarios applied to all 20 of the largest drainage basins in Palmer Land (covering ~40% of the total area of APIS) resulted in net sea-level contributions of 7–16mm SLE by 2100, and 10–25mm SLE by 2200. Inclusion of basins in the northern peninsula and realistic simulation of grounding-line movement for AP outlet glaciers will improve future projections."

This first image shows the various Antarctic Peninsula Ice Sheet, APIS, drainages basins; while the second attached image show a table with key parameters for these drainage basins.
Now as noted in the abstract for this paper; the GCM projections for APIS SLR contributions to 2200 were all negative due to the GCM's assumptions that all future precipitation in the Antarctic Peninsula (AP) would occur as snowfall with all the ice shelves remaining intact.  As much of the austral summer precipitation in the AP is currently occurring as rainfall, and inconsideration of the weakening conditions of the AP ice shelves, the authors prepared ensemble calculation of APIS volume changes due to assumed imposed grounding-line retreat and ice-shelf break-up scenarios; which resulted in the significant APIS SLR rise contributions by 2100 as indicated in the third and fourth attached images.

In subsequent posts I expect to eventually provide meaningful discussion of how decision makers can use related methodology to evaluate the risks of abrupt SLR contributions from the WAIS by 2100 in order to correct for obvious short-coming in current GCM SLR projections.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 02, 2013, 05:31:00 AM
Again, before proceeding to posts about methodology for clarifying the risk of abrupt sea level rise, I would like to point out regarding the following research that: (a) as the new research indicates that the SLR contribution from mountain glaciers and ice caps is lower than previously feared; this implies that more of the observed SLR from 2003 to 2009 came from ice sheets than some researchers previously thought; and (b) the ice mass loss mechanism from relative small mountain glaciers and ice caps is different from that for ice sheets, so the fact that ice mass loss from mountain glaciers and ice caps is less than some researchers previously feared, is not evidence that future ice mass loss from ice sheets will not increase non-linearly from current levels.

"A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009; Alex S. Gardner, Geir Moholdt, J. Graham Cogley, Bert Wouters, Anthony A. Arendt, John Wahr, Etienne Berthier, Regine Hock, W. Tad Pfeffer, Georg Kaser, Stefan R. M. Ligtenberg, Tobias Bolch, Martin J. Sharp, Jon Ove Hagen, Michiel R. van den Broeke, Frank Paul; Science 17 May 2013: Vol. 340 no. 6134 pp. 852-857; DOI: 10.1126/science.1234532
From:
https://www.sciencemag.org/content/340/6134/852.full (https://www.sciencemag.org/content/340/6134/852.full)

"Our consensus estimate of glacier mass wastage between 2003 and 2009 implies a sea-level contribution of 0.71 ± 0.08 mm of sea level equivalent (SLE) year−1, accounting for 29 ± 13% of the observed sea-level rise (2.50 ± 0.54 mm year-1) for the same period. The total glacier mass loss is comparable to a recent estimate for the whole of Greenland and Antarctica (peripheral glaciers + ice sheets) for the period 2003–2008. To avoid double counting, we subtracted our estimates for peripheral glacier mass loss from this total to obtain a total ice-sheet mass budget of –290 ± 50 Gt year−1 and a total land ice (all glaciers + ice sheets) mass budget of –549 ± 57 Gt year−1, amounting to a sea level rise of 1.51 ± 0.16 mm of SLE year−1, which is 61 ± 19% of the total global sea level rise. "

Also, the following related summary is from:

http://www.jpl.nasa.gov/news/news.php?release=2013-164 (http://www.jpl.nasa.gov/news/news.php?release=2013-164)

"NASA Helps Pinpoint Glaciers' Role in Sea Level Rise
May 16, 2013
PASADENA, Calif. - A new study of glaciers worldwide using observations from two NASA satellites has helped resolve differences in estimates of how fast glaciers are disappearing and contributing to sea level rise.

The new research found glaciers outside of the Greenland and Antarctic ice sheets, repositories of 1 percent of all land ice, lost an average of 571 trillion pounds (259 trillion kilograms) of mass every year during the six-year study period, making the ocean rise 0.03 inches (0.7 millimeters) per year. This is equal to about 30 percent of the total observed global sea level rise during the same period and matches the combined contribution to sea level from the Greenland and Antarctica ice sheets.

The study compares traditional ground measurements to satellite data from NASA's Ice, Cloud, and Land Elevation Satellite (ICESat) and Gravity Recovery and Climate Experiment (GRACE) missions to estimate ice loss for glaciers in all regions of the planet. The study period spans 2003 to 2009, the years when the two missions overlapped.

"For the first time, we have been able to very precisely constrain how much these glaciers as a whole are contributing to sea level rise," said Alex Gardner, Earth scientist at Clark University in Worcester, Mass., and lead author of the study. "These smaller ice bodies are currently losing about as much mass as the ice sheets."

The study was published Thursday in the journal Science.

ICESat, which stopped operating in 2009, measured glacier change through laser altimetry, which bounces lasers pulses off the ice surface to inform the satellite of changes in the height of the ice cover. ICESat's successor, ICESat-2, is scheduled to launch in 2016. GRACE, still operational, detects variations in Earth's gravity field resulting from changes in the planet's mass distribution, including ice displacements.

The new research found all glacial regions lost mass from 2003 to 2009, with the biggest ice losses occurring in Arctic Canada, Alaska, coastal Greenland, the southern Andes and the Himalayas. In contrast, Antarctica's peripheral glaciers -- small ice bodies not connected to the main ice sheet -- contributed little to sea level rise during that period. The study builds on a 2012 study using only GRACE data that also found glacier ice loss was less than estimates derived from ground-based measurements.

Current estimates predict all the glaciers in the world contain enough water to raise sea level by as much as 24 inches (about 60 centimeters). In comparison, the entire Greenland ice sheet has the potential to contribute about 20 feet (about 6 meters) to sea level rise and the Antarctic ice sheet just less than 200 feet (about 60 meters).

"Because the global glacier ice mass is relatively small in comparison with the huge ice sheets covering Greenland and Antarctica, people tend to not worry about it," said study co-author Tad Pfeffer, a glaciologist at the University of Colorado in Boulder. "But it's like a little bucket with a huge hole in the bottom: it may not last for very long, just a century or two, but while there's ice in those glaciers, it's a major contributor to sea level rise."

To make ground-based estimates of glacier mass changes, glaciologists perform on-site measurements along a line from a glacier's summit to its edge. Scientists extrapolate these measurements to the entire glacier area and carry them out for several years to estimate the glacier's overall mass change over time. While this type of measurement does well for small, individual glaciers, it tends to overestimate ice loss when the findings are extrapolated to larger regions, such as entire mountain ranges.

"Ground observations often can only be collected for the more accessible glaciers, where it turns out thinning is occurring more rapidly than the regional averages," Gardner said. "That means when those measurements are used to estimate the mass change of the entire region, you end up with regional losses that are too great."

GRACE does not have fine enough resolution and ICESat does not have sufficient sampling density to study small glaciers, but the two satellites' estimates of mass change for large glaciered regions agree well, the study concluded.

"We now have a lot more data for the glacier-covered regions because of GRACE and ICESat," said Gardner. "Without having these independent observations, there was no way to tell that the ground observations were biased." "

The three attached images present information related to Antarctic peripheral glaciers from this research.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 02, 2013, 10:57:29 PM
In my previous post I noted that I hope to shortly present methodology that will help decision makers to appreciate the true risks of abrupt sea level rise, ASLR, from the potential collapse of the WAIS this century.  However, first I would like to briefly discuss a few related issues:

1.  Uncertainty that unavoidable consequences is coming from ASLR is at the heart of decision makers' failure to take stronger actions; particularly when they have so many other challenges to address; however, ASLR is different from other threats in that: (a) its impact on the economic underpinning of modern society will be so significant that no one will be able to avoid significant consequences; which is unacceptable even for low probabilities; (b) the consequences will be irreversible for several thousands of years; and (c) the tipping point for those consequences will likely be passed before the decision makers are aware that the point has been passed.

2.  Decision makers are used to being able to procure insurance, or hedges, against the consequences of the uncertainties that they face; but considering the level of potential consequences from ASLR, some degree of consequences will be exacted up on the decision makers themselves for failing to recognize and address these risks in a timely manner.  Indeed, currently almost all decision makers so heavily discount the hazards of ASLR that they decline to even invest a few extra percentages of the total cost of the infrastructure at risk in order to make it more robust to the combined threat of ASLR and weather based events (such as hurricanes).

3.  There is a threshold of recognition of the true hazards of ASLR from the potential collapse of the WAIS this century that must be overcome within the symbiotic relationship between decision makers and the scientific community, before appropriate actions can be taken.  In a rational world, high uncertainty of a potentially catastrophic consequence, would be sufficient reason alone for taking precautionary action; however, in this world a paradigm shift in public opinion which can only happen by straight talk about the true risks that we are facing.  In short people need to realize that as the last remaining marine ice sheet in the world, the WAIS represents a unique threat that is currently poorly understood by the public, and more scientists and decision makers need to first identify these risks (possibly using the methodology I hope to describe in subsequent posts), and then to communicate their concerns on this matter to the public. 

Let me be clear that I am not talking about re-inventing the wheel here; but rather I am talking using pre-existing analysis tools to conduct scenario based engineering hazard assessments, SBEHA, to complement pre-existing GCM/RCM/LCM (global/regional/local circulation model) projections of ice mass loss contributions to SLR focused on the AIS (and particularly on the WAIS); together with sufficient discussion of SLR contributions from GIC (isolated glaciers and ice caps); the GIS (Greenland Ice Sheet); terrestrial storage; and ocean thermal/density (steric) changes.  Furthermore, I will only talk about forcing for the RCP 8.5 95% CL (or the A1FI 95% CL) scenario (others can detail lower consequence scenarios); also I propose to use the NRC 2012 West Coast SLR projections (see the first two attached figures and discussion in the "Critique" thread) as my base analysis (for lower consequence scenarios).  Furthermore, for the fingerprint assessment I only plan to look at RSLR in the San Francisco area of California (see the third attached figure).  Specifically, I only intend to look at hazard scenarios beyond the NRC 2012 business-as-usual scenarios (omitting SLR contributions considered by NRC 2012 in order to avoid double counting).  If future base cases become available (possibly AR5) which are more advanced than NRC 2012, then I may re-calibrate the hazard scenarios to match the new base case (if adopted).

Furthermore, my scenario based engineering hazard assessments, SBEHAs, will focus on the physical credibility/probability of the hazard scenarios considered; and well as in presenting the findings in a format useful to the engineers who need to deal with the SLR hazards identified.  In this regard, it is valuable to note that currently scientist (including IPCC researchers) discretely cite disclaimers for factors not considered in their analysis; and currently policy makers frequently pass along these uncertainties to engineers, without clarifying how to address these hazardous uncertainties.
As an indication of need/appropriateness of this type of SBEHA I present the fourth attached image from:
Expert judgement assessment: Quantifying uncertainty on thin ice;
R. M. Cooke; 2013, Nature Climate Change; 3,311–312; doi:10.1038/nclimate1860
In this fourth image, experts and combined experts present 5th, 50th and 95th CL percentiles for the contribution of the West Antarctic Ice Sheet (WAIS) to SLR in 2100 (in mm/yr), elicited in 2010 (blue) and 2012 (red). M indicates that the expert is a modeler, and O denotes observationalist. Triangles represent individual expert estimates, rectangles indicate self and equal weights (filled and open rectangles, respectively) and circles show performance-based weighting.  This figure indicates that in only 2-years almost all of the experts increased their assessments of SLR contributions from the WAIS, with one modeler increasing his 95% CL from under 7 mm/yr to about 30 mm/yr.  I can assure the readers that this incremental upward creep in expert assessment of WAIS SLR contribution will continue for two to three more decades, as more evidence becomes available.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 03, 2013, 02:36:17 AM
NOAA's advice to decision makers from the website linked below is: "So do you want a conservative or liberal sea level rise scenario?  Choose wisely.  Unfortunately you will have to wait until 2100 to see if you were right."

http://www.csc.noaa.gov/digitalcoast/geozone/whats-the-scenario (http://www.csc.noaa.gov/digitalcoast/geozone/whats-the-scenario)

Hopefully, some of the discussion in this, and following, posts may help some decision makers to choice wisely:

The first image as an example of an event tree (considering seismic hazards) appropriate for use in Monte Carlo models, that I plan to talk about in later posts. Furthermore, probability ranges and PDFs (probability distribution functions) will also be used in an expert risk analyses to portray the variation of certainty by the expert.  There are a number of ways that probability PDFs can be incorporated into the analysis to understand and convey the level of uncertainty and the potential benefit of additional study, with varying levels of complexity.  In facilitated expert risk analyses, the uncertainty in the overall failure probability and risk is usually evaluated using a Monte Carlo analysis that calculates the risk numerous times (typically 10,000), with each branch probability sampled at random according to its PDF. This produces a large set of equally likely results that can show the expert's level of certainty about the risk and may also show areas where additional study may be advantageous for better decision making.

It is important to capture the uncertainty for all event outcomes of the event tree in order for the Monte-Carlo results to be meaningful. For example, if distributions representing ranges of probabilities are input for the ice mass loss response outcomes, but only a single value is input for a given forcing parameter range probability, the full range of uncertainty is not captured, and the results will not have as much meaning. Therefore, it is important to clearly document what was included in the uncertainty analysis and how.

For relatively complex risk models, it is sometimes helpful to define a "fragility curve," (see an example in the second image) which gives the conditional probability of failure as a function of some measure of loading (such as that shown for a cantilever model of an ice shelf in the third image). The detailed engineering analysis and event decomposition are performed for a number of different values of the loading. These results are then fitted to a curve that allows interpolation of probabilities between the analyzed cases instead of estimating them separately for each iteration of a Monte Carlo model or each end node of a complex event tree with many similar paths leading to failure.

Selecting the appropriate number of forcing ranges, and the appropriate forcing ranges themselves is not a trivial matter. Forcing ranges typically centered around the specific loads for which analyses have been performed. Forcing risk analysis can be expensive and time consuming. Therefore, results from forcing response analyses are typically only available for a few sets of parameter selections and forcing levels.  It is important to identify the threshold forcing, below which collapse probability is negligible. This becomes the bottom end of the lowest forcing range for which risks are estimated. While simple in concept, the selected value(s) can have a significant effect on the calculated annual failure probability.  This is often an iterative process, and it may be necessary to perform additional analyses at small forcing levels, or at least perform sufficient analyses that the results can be extrapolated to smaller forcing levels. Care must also be exercised in defining what constitutes the threshold of collapse, and ensuring the collapse probabilities associated with the lowest forcing range are consistent with the threshold definition.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on June 03, 2013, 05:14:44 AM
Gardner(2013) at 549 GT/yr total ice mass loss for 2003-2009 is outstripped by reality. Mass waste from GIS _alone_ was 574GT in 2012.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 09, 2013, 06:17:19 PM
Sidd,

I agree with you that the very high ice mass loss from the GIS in 2012 is very disturbing; but many traditional experts will warn that one year's data does not make a trend.  Unfortunately, by the time that we have sufficient data to make a well-calibrated projection, the damage will already have been done; which is why decision makers need to use the "Precautionary Principle" as a wise choice.  Unfortunately, to quote Herman Hesse's 1922 novel "Siddhartha":

"Knowledge can be communicated, but not wisdom.  One can find it, live it, do wonders through it, but one cannot communicate and teach it."

Thus until the world's decision makers wise-up through their own effort, the best that we can do here is to continue to present food for their thought.

Best, ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 09, 2013, 06:28:06 PM
In the way of food for thought, I present the attached image from:

From Ice to High Seas: Sea-level rise and European coastlines,
The ice2sea Consortium, Cambridge, United Kingdom, (2013).

This report/image finds that the Filchner Ronne Ice Shelf, FRIS, is particularly at risk of collapse circa 2150 (due to high rates of base ice melting by that time).  However, the user of such information should make allowances for considerations such as: (a) the ice2sea model assumed a constant ice shelf area (which is non-conservative from a safety point of view); (b) the ice2sea model does not include the possible effects of the Larsen C ice shelf collapsing soon and changing the local weather patterns; (c) the influence of the warm spur of CDW entering the Weddell Gyre which currently being directed beneath the FRIS via the Filchner Trough; and (d) the model that ice2sea is using cannot accommodate abrupt changes and thus is incapable of providing any guidance on the risk that the FRIS might collapse prior to 2100.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 10, 2013, 04:25:10 PM
In my June 3rd, 2:36am, post I state that:

Selecting the appropriate number of forcing ranges, and the appropriate forcing ranges themselves is not a trivial matter. Forcing ranges typically centered around the specific loads for which analyses have been performed. Forcing risk analysis can be expensive and time consuming. Therefore, results from forcing response analyses are typically only available for a few sets of parameter selections and forcing levels.  It is important to identify the threshold forcing, below which collapse probability is negligible. This becomes the bottom end of the lowest forcing range for which risks are estimated. While simple in concept, the selected value(s) can have a significant effect on the calculated annual failure probability.  This is often an iterative process, and it may be necessary to perform additional analyses at small forcing levels, or at least perform sufficient analyses that the results can be extrapolated to smaller forcing levels. Care must also be exercised in defining what constitutes the threshold of collapse, and ensuring the collapse probabilities associated with the lowest forcing range are consistent with the threshold definition.

The forcing that I am referring to here is that which directly causes ice mass loss that contributes to SLR (as contrasted to radiative forcing, which primarily acts indirectly on ice mass loss from the AIS).  Furthermore, as I said that I will use the NRC 2012 SLR projections as the base case; this automatically defines the threshold forcing for abrupt (collapse) contributions to SLR; as it would then be any forcing above the NRC 2012 traditional net rapid ice mass loss.  As the traditional net rapid ice mass loss rate is essentially taken to be a linear multiple (determined by expert opinion) of the current observed AIS ice mass loss rate less the future trend for snow accummulation in Antarctica.  While (as defined here) the abrupt/collapse contribution to SLR would be the non-linear contribution above that cited in NRC 2012.

I note here that most people, including scientists, are wary of non-linear functions as: who knows which function to use, who knows when and where the non-linear behavior begins to dominate the linear behavior; and who accurately knows what the forcing inputs will be for these non-linear functions that will amplify input errors?  Therefore, currently most traditional scientists assume that the non-linearity of the ice mass loss will be off-set by the non-linear ice mass gain due to snow accumulation, resulting in a net rate of ice mass loss contribution to SLR that is a simple linear multiple of current observed behavior.

Nevertheless, in my over 500 posts I have identified numerous forcing mechanisms for future ice mass loss that could (for at least the next one years) result in such non-linear ice mass loss, that it could well dominate the ice mass gain from snowfall over that time period.  Therefore, I will try to quantify the non-linear ice mass loss mechanisms that I am most concerned about, and possible scenarios (for timing and feed-back mechanisms with other trends); which could be useful (in a Bayesian Learning sense) to help decision makers to include these abrupt forcing mechanism within their threshold of recognized risk.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 12, 2013, 03:23:46 PM
Of the potential sources of non-linear contributions to SLR, certainly that potentially coming from the Thwaities Glacier is perhaps the source that concerns knowledgeable researchers the most.  Therefore, I present the following abstract on this topic, from:

Dynamic (in)stability of Thwaites Glacier, West Antarctica,
by B. R. Parizek, K. Christianson, S. Anandakrishnan, R. B. Alley, R. T. Walker, R. A. Edwards, D. S. Wolfe, G. T. Bertini, S. K. Rinehart, R. A. Bindschadler, S. M. J. Nowicki, Article first published online: 16 MAY 2013, DOI: 10.1002/jgrf.20044;  Journal of Geophysical Research

ABSTRACT:
"Thwaites Glacier, West Antarctica, has the potential to directly contribute ~1 m to sea level and currently is losing mass and thinning rapidly. Here, we report on regional results for the Sea-level Response to Ice Sheet Evolution (SeaRISE) experiments and investigate the impact of i) spatial resolution within existing data sets, ii) grounding-zone processes, and iii) till rheology on the dynamics of this outlet glacier. In addition to the SeaRISE data sets, we use detailed aerogeophysical and satellite data from Thwaites Glacier as input to a coupled ice stream/ice-shelf/ocean-plume model that includes oceanic influences across a several kilometers wide grounding zone suggested by new, high-resolution data. Our results indicate that the ice tongue provides limited stability, and that while future atmospheric warming will likely add mass to the surface of the glacier, strong ice stream stabilization on bedrock highs narrower than the length of the grounding zone may be ephemeral if circulating waters substantially reduce basal resistance and enhance melting beneath grounded ice within this zone. However, we find that stability is significantly enhanced by effectively plastic till beds. Accurate projections of future sea level change relies on correct understanding of the till rheology as well as local basal processes near the grounding line."

This paper clearly documents the effectiveness of the advection/circulation of relatively warm ocean water in the Thwaites gateway; which can "... substantially reduce basal resistance and enhance melting beneath grounded ice within this zone."  However, in future posts I plan to examine the additional de-stabilizing influence of such factors as: (a) the end of the El Nino hiatus period bring additional warm ocean water in contact with the Thwaites gateway grounding line zone; (b) the influence of the outflow of basal meltwater from the entire drainage basin through the trough in the gateway; (c) the influence of the subglacial lake located in the gateway itself; (d) the influence of ice thinning in the ice stream; (e) the potential for increased ice calving along the ice face in the gateway; (f) influence of the possible properties of the glacial till; (g) the influence of the"softness" of the basal ice in the ice stream; (h) the local influence of the projected increase in local snowfall on the driving force and velocity of the ice stream; and (i) parallels between the Jakobshavn Effect and the situation for the Thwaites gateway ice stream.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 13, 2013, 03:44:03 PM
As the immediately previous post regarding Parizek et al 2013, indicates that the circulation of warming CDW need the Thwaites Gateway grounding line could easily un-pin this key glacier; the only remaining question is how fast could this un-pinning occur. In this regard:

1.  As discussed in the "Surge" thread it appears that the possible subglacial cavity in the Thwaites trough identified by Tinto & Bell 2011 was at least infilled by glacial ice when the fall of 2012 surge of the local ice stream occurred, which formed a new section of the Thwaites Ice Tongue.
2.  The first attached image re-posted from MacGregor et al 2012, summarizes the evolution of the recent history of the ASE coastline; and indicates that the Thwaites Ice Tongue has historically sustained a number of surges of the local ice stream out through the Thwaites trough.  This image indicates that the last surge (prior to 2012) possibly occurred in 2002 (when iceberg B-22 broke away from the Thwaites Ice Tongue).  If so this implies that the advective process in the Thwaites trough may be so active as to form a sufficiently large subglacial cavity to trigger a surge (due to the local reduction in basal friction) within a nominally 10-year period (from 2002 to 2012 during the El Nino hiatus period).
3.  With continued warming and expansion of the warm CDW in the ACC, and the likely end of the El Nino hiatus period, shortly, the advective process within the Thwaites trough may accelerate, that could lead to another local ice stream surge in less than ten years.
4.  Each new local ice stream surge (through the Thwaites trough) thins the local ice thickness, which could lead to accelerated: (a) local calving of the ice face; (b) ice flow velocity, resulting in more thinning; and (b) grounding line retreat down the trough due to the ease of local floatation.
5.  As discussed in the "PIG-Thwaites 2012-2060" thread, once the groundling line retreats sufficiently southward along the Thwaite trough it should intercept a sub-glacial lake on the northside of a submerged mount in the Thwaites gateway, that could then facilate the un-pinning of the Thwaites Glacier.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 14, 2013, 01:22:34 AM
In my previous post I mentioned that ocean water advection could effective un-pin the Thwaites Glacier in the next ten or more years.  Once it is un-pinned, I believe that it could initially behave somewhat like what has been observed for the Jakobshavn Glacier in Greenland for the past ten to fifteen years.  In this regard the following abstract about the Jakobshavn Effect (or mechanism for glacial grounding line retreat acceleration), the authors find that softening of the basal ice near the leading face of the Jakobshavn Glacier, and both due to ocean warming, increased basal friction heat, and the measured high basal melt rate for the Thwaites Glacier, I believe that the Thwaites Glacier could also accelerate due to basal ice softening, once it is un-pinned:

"Changing basal conditions during the speed-up of Jakobshavn Isbræ, Greenland
by: M. Habermann, M. Truffer, and D. Maxwell
The Cryosphere Discuss., 7, 2153–2190, 2013 www.the-cryosphere-discuss.net/7/2153/2013/; (http://www.the-cryosphere-discuss.net/7/2153/2013/;) doi:10.5194/tcd-7-2153-2013

Abstract
Ice-sheet outlet glaciers can undergo dynamic changes such as the rapid speed-up of Jakobshavn Isbræ following the disintegration of its floating ice tongue. These changes are associated with stress changes on the boundary of the ice mass. We investigate  the basal conditions throughout a well-observed period of rapid change and evaluate parameterizations currently used in ice-sheet models. A Tikhonov inverse method with a Shallow Shelf Approximation forward model is used for diagnostic inversions for the years 1985, 2000, 2005, 2006 and 2008. Our ice softness, model norm, and regularization parameter choices are justified using the data-model misfit metric and the L-curve method. The sensitivity of the inversion results to these parameter choices is explored.  We find a lowering of basal yield stress in the first 7 km of the 2008 grounding line and no significant changes higher upstream. The temporal evolution in the fast flow area is in broad agreement with a Mohr–Coulomb parameterization of basal shear stress, but with a till friction angle much lower than has been measured for till samples. The lowering of basal yield stress is significant within the uncertainties of the inversion, but it cannot be ruled out that there are other significant contributors to the acceleration of the glacier."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 14, 2013, 02:34:05 AM
This summary and attached image indicate the importance of the warming of ocean currents on ice mass loss in Antarctica.


Science DOI: 10.1126/science.1235798 , June 2013
"Ice Shelf Melting Around Antarctica
1.   E. Rignot,
2.   S. Jacobs,
3.   J. Mouginot,
4.   B. Scheuchl
We compare the volume flux divergence of Antarctic ice shelves in 2007–2008 with 1979–2010 surface accumulation and 2003–2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 14, 2013, 03:51:56 PM
To expand on the point that I was making in my June 14, 2013 1:22am post about the potential future softening of the basal ice near the grounding line of Thwaites Glacier in its gateway area:

(a) as the ice thins in the gateway due to both: (i) spreading from ice flow and ice surges; and (ii) advective re-formation of a subglacial cavity (particularly in the trough); the leading edge can become subject to floatation on high tides, which can circulate warm CDW beneath the ice stream form some distance (a kilometer or more); which can progressively soften the basal ice in the leading edge area, which can promote a Jakobshavn Effect.
(b) the mechanism cited in item (a) could become much more significant if the advectively re-formed subglacial cavity in the trough extends (in 5 to 10 years) to intercept the subglacial lake at the northern side of the submerged mount in the middle of the Thwaites gateway (which divides the western and eastern ice streams in the Thwaites gateway, see the "Surge" thread.
(c) once the Jakobshavn Effect is established I have speculated that it could progress into what I have called the Thwaites Effect (see the PIG-Thwaites 2012-2060" thread); where the ice stream velocities in the Thwaites gateway could become several times that that has been recorded for the Jakobshavn Glacier (see the first attached image from Van der Veen et al 2011, and the second image comparing Thwaites to Jakobshavn Glacier).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 15, 2013, 01:56:38 AM
Other non-linear interactions not accounted for in NRC 2012 that should be considered with regards to ice mass loss from the Thwaites Glacier include:

(1) The advective CDW interaction between PIG and the Thwaites Glacier, TG, which appears to have directed CDW into a pre-existing towards the TG gateway. 

(2) The recently measured high subglacial basal melt rate in the BSB.

(3) The West Antarctic CDW temperatures appears to be increasing faster than previously projected possibly due to: (a) telecommunication of heat content from the tropical ocean regions (particularly for the Pacific Ocean) into the CDW; (b) reduced mixing with the AABW at the break to the continental slope, due to the reduced volume of AABW being produced; and (c) possible insulation of upwelling CDW near the West Antarctic coastline by the above average amounts of recent sea ice extent.

(4) A combination of advective growth of a subglacial cavity in the Thwaites trough and thinning of the ice stream thickness (associated with what is assumed to be increasingly frequent and active surges of the ice steam) allows Thwaites Glacier to become un-pinned from the submerged sea mount in the TG gateway by 2025, thus allowing the east and west ice streams to merge into one ice stream and to allow the associated gateway grounding line to retreat about 100 km down into the BSB by 2050, to the location of a recently identified ridge is damming a subglacial lake (and where the TG subglacial meltwater network branches upstream).  During the 25 year period from 2025 to 2050, the rate of grounding line retreat is taken to be: 1.75 (the average rate of groundling line retreat for PIG) x 1.5 (due to CDW temp increase) x 1.5 (due to the basal meltwater effect for TG) = 4 km/yr or equal to 100 km in 25 years.

(5) For the period from 2050 to 2070, the TG groundling line retreats are assumed to accelerate by an additional factor of 3.0 (above the 2050 rate) as follows: 1.7 (Jakobshavn Effect)x1.1 (CDW temp rise effect)x1.1(Zwally Effect)x1.1(basal meltwater increase effect)x1.1(storm activity effect)x 1.1 (albedo effect) x 1.1(methane hydrate emission effect) = 3.0.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 16, 2013, 05:44:33 PM
The following 2013 abstract helps to frame the risks that as we exist the current El Nino hiatus period, with regard to the risk that a series of strong El Nino events could accelerate the introduction of warm CDW into the ASE, thereby accelerating ice mass loss from this area, and inparticular from the Thwaites Glacier Basin.  I have underlined key sentences/phrase for emphasis:

"Tropical forcing of Circumpolar Deep Water Inflow and outlet glacier thinning in the Amundsen Sea Embayment, West Antarctica
By Jenkins, Adrian; Steig, Eric; Ding, Qinghua; Battisti, David.; April 2013.
Abstract/Summary
The part of the West Antarctic Ice Sheet that drains into the Amundsen Sea Embayment (ASE) is currently thinning at such a rate that it contributes nearly 10% of the observed rise in global mean sea level. Acceleration of the outlet glaciers appears to be caused by thinning at their downstream ends, where the ice goes afloat, indicating that the changes are probably being forced from the ocean. Observations made since the mid-1990s on the Amundsen Sea continental shelf have revealed that the deep troughs, carved by previous glacial advances, are flooded by almost unmodified Circumpolar Deep Water (CDW) with temperatures around 3-4°C above the freezing point, and that this water mass drives rapid melting of the floating ice. Quantifying these processes and the changes that may have occurred in the past is a critical step in improving our understanding of the ice sheet’s current behaviour and how it will contribute to sea level rise into the future. An ocean model forced with climate reanalysis data has shown that, beginning in the early 1990s, an increase in westerly wind stress near the continental shelf edge drove an increase in CDW inflow onto the Amundsen Sea continental shelf. The change in local wind stress occurred predominantly in autumn and early winter, associated with anomalously high sea-level pressure (SLP) to the north of the ASE and an increase in sea surface temperature (SST) in the central tropical Pacific Ocean. The SLP change is associated with geopotential height anomalies in the middle and upper troposphere, characteristic of a stationary Rossby wave response to tropical SST forcing, rather than with changes in the zonally symmetric circulation around Antarctica characterised by the Southern Annular Mode. Tropical Pacific warming similar to that of the 1990s occurred in the 1940s, and thus is a candidate for initiating the current period of ASE glacier retreat."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on June 16, 2013, 11:05:33 PM
Rignot (2013) is interesting, confirming a long held suspicion of mine. East Antarctica is a player. Amery, Totten, Moscow University and Shackleton, all grounded at around 2Km below sea level, are melting from below. At those depths the pressure melting point is around -3C and CDW is around 0C. Hot water indeed, and we are all in it.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 17, 2013, 03:07:09 AM
Sidd,

Thanks for keeping people thinking about the risk of SLR contributions from the EAIS, and I agree that these EAIS areas appear to currently be very active as indicated by the attached image from Purkey and Johnson 2013 which shows a large amount of "Water Mass" largely due to ice shelf meltwater; which when combined with the local AABW warming results in a relatively high rate of local (Southern Ocean) SLR which further helps to promote grounding line retreat for grounded glaciers in these areas (particularly in the EAIS).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 18, 2013, 01:58:24 AM
In order to emphasize my point that coming El Nino events present at rise for future accelerated ice mass loss from glaciers around the the ASE I present the attached image from:  CentralWest Antarctica among most rapidly warming regions on Earth - Supplementary Information, in: Nature Geoscience; DOI: 10.1038/NGEO1671

In this image the black star represents the location of the Byrd Station temperature reading that indicate that the surface temperatures during the indicated DJF 1997-1998 El Nino event were highest measured readings since recordings began in 1957.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 25, 2013, 05:17:24 PM
The following abstract from SCAR 2012 Session 7, supports the position that the Thwaites Glacier could retreat at least one hundred kilometers this century:

The Dynamic Instability of Thwaites Glacier, West Antarctica
by: Christianson, Knut; Parizek, Byron; Horgan, Huw; Anandakrishnan, Sridhar; Alley, Richard; Walker, Ryan; Edwards, Rebecca; Wolfe, Derek; Bertini, Gabriel; Reinhart, Samantha;

Thwaites Glacier, West Antarctica has the potential to directly contribute approximately 1 m to sea level, and is currently losing mass and thinning rapidly. Due to the geometry of the geometry of the glacier’s bed, which is below sea level and deepens inland, it is also subject to the marine ice sheet instability, and thus, possibly, to rapid deglaciation. Here we integrate recent kinematic GPS, GLAS ICESat laser altimetry, and aerogeophysical data (collected by Operation IceBridge) to present a comprehensive geophysical picture of both the grounding zone of Thwaites Glacier and highlight recent changes in inland dynamics, which include acceleration of inland thinning up to 100 km from the current grounding line. These data are used in a coupled ice-stream/ice-shelf/ocean-plume model that includes oceanic influences across a several-kilometers-wide grounding zone (a possible interpretation of the geophysical data). Our results suggest that ice-stream stabilization on grounding-line highs may be ephemeral, and that Thwaites Glacier has the potential to retreat on the order of a hundred kilometers on century to millennial timescales. Thus, accurate projections of future sea-level change will require both improved grounding-zone data and important revisions to ice-sheet models, which now consider ice-sheet grounding to occur at a single point along flow."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 05, 2013, 07:07:07 PM
The accompanying 2011 figure (from the following article) is slightly out of date, but very clearly presents the point that I want to make in this post, that the largest input to the increase of CDW in the Southern Ocean comes from the Indian Ocean, and that this heat input source has the shortest possible path for the increased CDW to reach Amundsen/Bellingshausen Seas coast; which is the soft underbelly of the WAIS.  This path is sufficient short that heat input from the Indian Ocean at the beginning of the current El Nino hiatus period should have already reached the Amundsen/Bellingshausen Seas coast; which is supported by direct measurement.  The fact there is over a decade of El Nino hiatus period heat already in the pipeline from the Indian Ocean tropics directed directly via CDW towards the Amundsen/Bellingshausen Seas coast, provides additional support to my previously statement position that the soft underbelly of the WAIS is an area of major concern (regarding acceleration of ice mass loss) in the near-term (within the next 20-years):

Trends in Observation and Research of Deep Ocean Circulation and Heat Transport
By: Takeshi KAWANO; QUARTERLY R E V I E W N o. 3 9 / A p r i l 2 0 1 1

Caption for the attached image is:
"Pattern Diagram of Thermohaline Circulation:  The circulation that sinks in the North Atlantic Ocean and moves northward along the upper layer of water is called Atlantic overturn, and the circulation that sinks around the Antarctica area, moves northward along the bottom layers and then moves southward along the deep layer of water is called Antarctic overturn (which exists in the Pacific, Atlantic and Indian oceans). Although the sea surface temperature in low latitudes rises close to 30 degrees C, temperature in deep layer is about 1 degree C as seawater cooled near the poles is constantly supplied to the deep layer of the ocean."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 07, 2013, 03:34:09 AM
The following reference provides evidence that the is a long-term (ie natural) Antarctic contribution to SLR; which must be added on top of the anthropogenically induced Antarctic contribution to SLR.  Whether natural or anthropogenic; both factors contribute to the risk of abrupt sea level rise, ASLR:

Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts?
By: Gregory, J. M., et al, 2013;  J. Climate, 26, 4476–4499.  doi: http://dx.doi.org/10.1175/JCLI-D-12-00319.1 (http://dx.doi.org/10.1175/JCLI-D-12-00319.1)

Abstract:
"Confidence in projections of global-mean sea level rise (GMSLR) depends on an ability to account for GMSLR during the twentieth century. There are contributions from ocean thermal expansion, mass loss from glaciers and ice sheets, groundwater extraction, and reservoir impoundment. Progress has been made toward solving the “enigma” of twentieth-century GMSLR, which is that the observed GMSLR has previously been found to exceed the sum of estimated contributions, especially for the earlier decades. The authors propose the following: thermal expansion simulated by climate models may previously have been underestimated because of their not including volcanic forcing in their control state; the rate of glacier mass loss was larger than previously estimated and was not smaller in the first half than in the second half of the century; the Greenland ice sheet could have made a positive contribution throughout the century; and groundwater depletion and reservoir impoundment, which are of opposite sign, may have been approximately equal in magnitude. It is possible to reconstruct the time series of GMSLR from the quantified contributions, apart from a constant residual term, which is small enough to be explained as a long-term contribution from the Antarctic ice sheet. The reconstructions account for the observation that the rate of GMSLR was not much larger during the last 50 years than during the twentieth century as a whole, despite the increasing anthropogenic forcing. Semiempirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of the authors' closure of the budget is that such a relationship is weak or absent during the twentieth century."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on July 07, 2013, 04:57:09 AM
Gregory(2013) seems interesting enough from a century perspective, but to me the last ten years of GRACE and other satellite data combined with ground and submarine observation, together with the theories from the seventies beginning with Weertman and Mercer, indicate something particularly large and nasty moving in the WAIS. (Not that EAIS doesn't have worrisome areas but WAIS is the one more likely to keep me up at night. ) The recent data are quite difficult to reconcile with that last hundred years or so, unless we add instabilities not previously seen in the hundred to two hundred year record, or indeed, perhaps since MWP1A or even further, since the Eemian.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on July 07, 2013, 06:36:50 AM
Lots here after about minute 32 on Arctic dynamics from Alley:

climatestate.com/2013/07/06/state-of-the-climate-system-2013-by-richard-alley/
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 07, 2013, 06:00:04 PM
Sidd,

I agree that the recent anthropogenically induced non-linear trends for ice mass loss from the WAIS are much more important than the long-term slow natural ice mass loss from the AIS; and that it is good to keep focused on the dominate phenomenon; but nevertheless, the long-term slow natural ice mass loss trend could be amplified by the non-linear anthropogenic trend; and therefore, it is at least worth documenting.

Wili,

Thanks for the link to the Alley lecture, his thinking seem to fall right in line with everything that I am posting on risks of ASLR from the WAIS; as noted by the fact that Alley is a co-author in both the papers that I cite in my replies #78 and 88 in this thread regarding papers by Parizek et al 2013 and Christianson et al 2013; both of which cite some of the latest research on the significant risk of the Thwaites Glacier ice mass loss accelerating rapidly once the warm ocean water un-pins the current choke point in the Thwaites Gateway area (particularly for for scenarios equal to, or above RCP 8.5 50%CL, which we are currently exceeding).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on July 07, 2013, 06:02:51 PM
I've seen him on other video's more specifically directed toward this issue that are also quite good. I'll see if I can track down the links.

(Ah, I see I've just become a 'Full Member"! Yeah me!? ;D )
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 07, 2013, 06:44:34 PM
Wili,

Congrats on becoming a "Full Member"; and the following is my next contribution to bringing this puzzle into focus:

While most of the information discussed in the reference cited below is off topic, I am posting the following quote as it emphasizes the fact that with sufficient high rates of global warming (ie above RCP 8.5 50% CL) that the expected increase in precipitation with global warming could be a positive feedback for ice mass loss contribution to SLR, because much of the precipitation will eventually fall as rain:

"The projected increase in precipitation partly compensates for the mass loss caused by warming, but this compensation is negligible at higher temperature anomalies since an increasing fraction of precipitation at the glacier sites is liquid."

From: Feedbacks and mechanisms affecting the global sensitivity of glaciers to climate change
By: B. Marzeion, A. H. Jarosch, and J. M. Gregory; The Cryosphere Discuss., 7, 2761–2800, 2013; doi:10.5194/tcd-7-2761-2013
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on July 07, 2013, 07:21:07 PM
Thanks for that reference. Feedbacks related to climate are a particular interest/obsession of mine.

I would like to hear your view on the main argument I have heard put forward against the possibility of very abrupt sea level rise from the Antarctic. The claim is that, even if major, rapid calving of the huge ice sheets starts to happen in earnest, most of the larger chunks will get stuck on the continental shelf rather than floating off into the sea to melt. This will substantially slow (so the claim goes) the ability of these big chunks to melt rapidly enough to cause a really abrupt large SLR.

Even typing it out, I can see a number of places where this claim may have weaknesses, but I wanted to know if you have heard such arguments, and what you think of them.

(Apologies ahead of time if you have already addressed this. I'm afraid I have not yet had time to read through all of every one of your well-sourced posts above.)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 08, 2013, 12:09:01 AM
Wili,

This is a good question that I have not yet specifically addressed yet and any of the various threads in this Antarctic folder. Certainly, James Hansen has stated his vision of an armada of icebergs circling around the Southern Ocean for many decades after breaking free from the Antarctic continent; and he did not express a signficant concern that so many of these icebergs would become grounded on the continental shelf that they would choke-off the supply of new icebergs sufficiently to prevent something like a 5m global mean ASLR this century.  While I cannot provide a reference on this matter, I will simply cite some of my thinking on this matter.

(a) To get something like a 5m global mean ASLR this century, a large number of icebergs will need to be formed from the WAIS as there is insufficient heat available to melt this amount of ice inplace by circa 2100.

(b) To get to an ASLR case, the world (including all positive feedbacks) will need to equal or exceed a scenario like RCP 8.5 50% CL; which would mean that the ocean water around the WAIS will be several degrees warmer than today by 2100; which will promote very high rates of basal melt for all ice shelves and icebergs (grounded or otherwise); which means that any grounded icebergs may be grounded for much shorter periods of time than we have observed in the recent past.

(c) I would expect such icebergs to look similar to the melange of floating ice that exited from the Jakobshaven Glacier while it was undergoing the Jakobshaven Effect; which never grounded sufficiently to limit any aspect of the ice mass loss associated with the Jakobshaven Effect.

(d) The shallowest part of the West Antarctic Continental Shelf is in all relevant cases near the current gateways in the Weddell, Bellingshausen and Amundsen Seas; which means that the people raising this issue must believe that current gateways will be the primary choke points that they are talking about; but in all of these relevant gateways advectively driven ocean currents will focus large amounts of warm basal water around any such grounded icebergs, which means that they will become ungrounded much more rapidly than a typical case.

(e) Some people note that with sufficient ice mass loss from the WAIS the sea level will drop locally; which according to this theory would serve to stabilize both the ice remaining in the ice sheets and possibly icebergs trying to exist through the current gateways; however, I do not find this theory particularly compelling for reasons including: (i) the is no need for all icebergs to exit out the gateways as for the local sea level to drop (which has not yet happened at all) the grounding lines would have had to have retreated far from the current gateways, thus providing considerable room for recently calved ice to float in while it is undergoing basal melting to decrease their drafts; (ii) the advective ocean currents would be accelerated by the large amount of ice melting; and would be supplemented by both tidal action (amplified within the newly formed fjords) and redirected local ocean currents; (iii) the increase storm activity associated with RCP 8.5 50%CL after 2050 would provide a large amount of energy for dislodging temporarily grounded icebergs; and (iv) seismic activity and volcanic activity triggered by large ice mass losses from the WAIS would also serve to limit the choking potential of grounded icebergs.


In short I do not find the issue of grounded icebergs choking-off ice mass loss from the WAIS to be very likely; however, I would also invite you to review my discuss related to this matter focused on the Thwaites Glacier (paricularly my replies #12 thru 18) that can be found at:

http://forum.arctic-sea-ice.net/index.php/topic,72.0.html (http://forum.arctic-sea-ice.net/index.php/topic,72.0.html)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on July 08, 2013, 06:52:01 AM
Thanks, ASLR. Those were some of the things I was thinking, too. But you have the background to say them more confidently. I must say that I don't quite understand how Antarctic melting/calving could lower local sea level. But perhaps I am being dense (wouldn't be the first time  :-\ ).

Thanks again for all your thoughts on this important-to-consider possibility.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 08, 2013, 04:37:12 PM
Wili,

While I have addressed the topic of the gravitational attraction of the ice sheets on the adjoining surface of the ocean elsewhere (with better figures); I provide the first attached image to show how the over 3,000 m height Antarctic Ice Sheets attract the adjoining ocean water by gravity thereby raising the adjoining sea level by tens to hundreds of meters (see panel a); thus when these ice sheets sustain ice mass loss the gravitational attraction is weakened and the adjoining ocean water flows away proportionately (see panel b).  The second attached image gives you an idea of how much and where the ocean water and ice meltwater will go when the WAIS loses a unit quantity of ice mass (expressed in equivalent units of SLR).

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on July 09, 2013, 05:57:19 AM
Ah, OK, I have heard of this phenomena--quite counter-intuitive at first. Does it really raise sea level locally be hundreds of meters, though?

On the second graph, is that after melt? Otherwise, it seems to run counter to what you've been saying (unless I am again missing something obvious--the most likely possibility, as usual)?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 09, 2013, 04:20:23 PM
Wili,

I do not have very much time to provide a lot of explanation on this topic so I will provide some links (some to videos), one old pdf, and one reference, on the topic:

http://harvardmagazine.com/2010/05/gravity-of-glacial-melt (http://harvardmagazine.com/2010/05/gravity-of-glacial-melt)

http://piecubed.co.uk/2013/05/31/ice-melt/ (http://piecubed.co.uk/2013/05/31/ice-melt/)

http://citizenschallenge.blogspot.com/2013/04/jerry-mitrovica-fingerprints-of-sea.html (http://citizenschallenge.blogspot.com/2013/04/jerry-mitrovica-fingerprints-of-sea.html)


Tamisiea, M.E., and J.X. Mitrovica. 2011. The moving boundaries of sea level change:
Understanding the origins of geographic variability. Oceanography 24(2):24–39, doi:10.5670/
oceanog.2011.25.

Regarding to my reference to hundreds of meters, this is correct if you consider 1.2 time one hundred as meaning hundreds; as between the condition with absolutely zero ice in Antarctica, versus the case with all the continent worth of ice that there is now; that difference is sufficent to draw-up regional water elevations around Antarctica by about 120m.

You can read though my posts as I discussed the 120m value in one of them; or you can Google this matter for many more papers to read.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 09, 2013, 05:20:16 PM
Wili,

I realize that I may not have address your question about my second attached image, which possibly the attached image here might help to clarify; but in any case, this image show that when an ice sheet melts the local sea level drops, while the far field sea level rises.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 22, 2013, 04:28:08 AM
While I have posted, and with continue to post more, evidence of the trends and risks of anthropogenically induced regional warming in Antarctica (in this and in numerous other threads); it is also important to discuss some of the likely positive feedback mechanisms that are currently not being adequately captured by existing GCM, RCM and LCM projections for Antarctic ice mass loss, due to anthropogenic global warming.  The following is a brief review of three positive feedback mechanisms, as examples of the numerous feedbacks that are not being captured in any current GCG, RCM, or LCM projections:

1.   It is likely that when the Larsen B ice shelf collapsed in 2002 that it sufficiently changed the local barometric pressure system (by local decreased albedo and local increased evaporation) in the Weddell Sea area to increase the frequency of the periodic redirection of warm CDW from the Weddell Gyre underneath the FRIS via the Filchner Trough.  Current field measurements indicate that this feedback by itself has accelerated basal ice melting beneath FRIS, which is also increasing the rate of calving of the Filchner Ice Shelf.  But as important as this positive feedback is; I am much more concerned that when (not if) the much larger Larsen C ice shelf collapses within the next decade (possibly triggered by the end of the current El Nino hiatus period); that then feedback mechanism discussed above for the Larsen B ice shelf will trigger a much stronger positive feedback for ice mass loss from FRIS; which may be strong enough to contribute to both the early retreat of regional sea ice and the associated  virtual collapse of the FRIS by about 2060.
2.   In the "FRIS/RIS" thread I have noted that should the advective CDW induced basal ice melting accelerate (says due the end of the current El Nino hiatus period) for the Getz Ice Shelf sufficient for it to collapse, then a positive feedback could occur in that the increase in regional surface seawater salinity could result in a decrease in the local ice thickness, & extent, in the local sea ice; which in turn could change the wind to sea drag, thus redirecting local currents beneath RIS and thus possible contributing to the collapse of RIS by about.
3.   The GIA date from the ASE glaciers indicate that almost certainly about 40% more ice mass is being lost from these glaciers than was included (as recently as last year) in the GRACE SLR contribution estimates for the WAIS.  As satellite altimetry data does not indicate that this extra 40% in ice mass loss is associated with 40% higher ice velocities; it is therefore logical that this ice mass loss is coming from geothermally driven basal ice melting in the BSB.  If this is the case then when the EL Nino hiatus period ends, and more warm CDW current is driven towards the Thwaites Glacier grounding line; then the outflow of basal ice melt water along this groundling line should interact with the warm CDW to provide a positive feedback to accelerate: (a) the collapse of the Thwaites Ice Tongue; (b) calving along the length of the Thwaites Gateway; and (c) extension of a subglacial cavity beneath the ice in the Thwaites Trough.

As I will be traveling this coming week, I will limit myself to these three examples of important positive feedback mechanisms that are currently not being captured by LCM, RCM or GCM projections, and all of which could has major impacts on the probability that the WAIS will collapse this century.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 22, 2013, 02:34:23 PM
While I wait for my flight, I have time to post about another positive feedback mechanism particular to the Antarctic that is not being captured by any current GCM, RCM or LCM projections which is the feedback between the recent increase in warm CDW volume and the recent increase upper tropospheric methane concentration over East Antarctica (also see discussion in several other threads including the "Methane" thread and the "Southern Ocean" thread).

 As I have posted on in multiple threads: (a) the current El Nino hiatus period is delivering more deep water Ocean Heat Content, OHC, to the Southern Ocean; which is contributing to increasing the volume of warm CDW; (b) the current ozone hole frequency over Antarctica is driving circumpolar winds and associated circumpolar currents to the south thus inducing more upwelling of warm CDW onto the continental shelf; and (c) the reduced production of AABW is entraining a smaller volume of CDW thus resulting in an increased age of the CDW.  The result of the increase volume of warm CDW crowed toward the south means that the thickness of the CDW water layer flowing on to the continental shelf is increasing, resulting in an increasing amount of methane hydrate decomposition.

As shown in the attached figure, unlike the Arctic that has a convex geopotential height topology which tends to disperse local methane emissions; the Antarctic has a concave geopotential height topology which tends to concentrate any local methane emissions (such as the marine methane hydrate emissions cited above).  Furthermore, the extreme cold over the East Antarctic reduces the rate of chemical oxidation of the methane to carbon dioxide thus resulting in a further concentration of methane in the troposphere over the East Antarctic.  However, as GHG contributes to the concavity of the geopotential height topology over Antarctica; this provides a positive feedback mechanism to further accelerate (or at least maintain) the velocity of the circumpolar winds, which should increase the circumpolar current velocity (as well as moving it to the south); which should push more warm CDW onto the Antarctic continental shelf thus decomposing more methane hydrate; resulting in an increased rate of local ice sheet mass loss and an increased probability of the collapse of the WAIS this century than what is current projected by any LCM, RCM or GCM.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 23, 2013, 03:13:02 AM
Some other possible positive feedback mechanisms associated with Antarctic that are not fully captured by current LCM, RCM or GCM ice mass loss projections, include:

1.   As ice streams (eg within the Thwaites Glacier) thin relative to the adjoining , less active ice/land, basal crevasses will form that will promote calving; which will reduce buttressing; which will accelerate the ice stream velocities; which will promote ice stream thinning; which completes this positive feedback mechanism (note that no LCM models basal crevasses effectively yet).
2.   Increasing ice mass loss (including from ice shelves) result in less AABW production; which results in less entrainment of adjoining CDW; which results in more accumulation of CDW; which results in more ice mass loss from advection of the warm CDW; which completes this positive feedback mechanism (note that AABW production is poorly understood and even less well modeled).
3.    As increased upwell occurs around Antarctica (e.g. due to increased GHG concentration over Antarctica inducing higher winds and currents), more previously sequestered carbon (of organic origin); which may contribute to more upwelling (e.g. possibly by increasing the activity of El Nino events) ;  thus completing a positive feedback mechanism.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 24, 2013, 03:23:29 AM
The concerns that the authors of the following article express about the PIG and the Thwaites Glacier are very similar to what I have expressed in the "PIG/Thwaites 2012 to 2040-2060 Time Frame" thread; indicating that SLR this century will likely be higer than many researchers previously thought possible:


http://www.sciencecodex.com/sea_level_rise_new_iceberg_theory_points_to_areas_at_risk_of_rapid_disintegration-116161 (http://www.sciencecodex.com/sea_level_rise_new_iceberg_theory_points_to_areas_at_risk_of_rapid_disintegration-116161)

"Sea level rise: New iceberg theory points to areas at risk of rapid disintegration
Posted By News On July 22, 2013 - 5:00pm
ANN ARBOR—In events that could exacerbate sea level rise over the coming decades, stretches of ice on the coasts of Antarctica and Greenland are at risk of rapidly cracking apart and falling into the ocean, according to new iceberg calving simulations from the University of Michigan.
"If this starts to happen and we're right, we might be closer to the higher end of sea level rise estimates for the next 100 years," said Jeremy Bassis, assistant professor of atmospheric, oceanic and space sciences at the U-M College of Engineering, and first author of a paper on the new model published in the current issue of Nature Geoscience.
Iceberg calving, or the formation of icebergs, occurs when ice chunks break off larger shelves or glaciers and float away, eventually melting in warmer waters. Although iceberg calving accounts for roughly half of the mass lost from ice sheets, it isn't reflected in any models of how climate change affects the ice sheets and could lead to additional sea level rise, Bassis said.
"Fifty percent of the total mass loss from the ice sheets, we just don't understand. We essentially haven't been able to predict that, so events such as rapid disintegration aren't included in those estimates," Bassis said. "Our new model helps us understand the different parameters, and that gives us hope that we can better predict how things will change in the future."
The researchers have found the physics at the heart of iceberg calving, and their model is the first that can simulate the different processes that occur on both ends of the Earth. It can show why in northern latitudes—where glaciers rest on solid ground—icebergs tend to form in relatively small, vertical slivers that rotate onto their sides as they dislodge. It can also illustrate why in the southernmost places—where vast ice shelves float in the Antarctic Ocean—icebergs form in larger, more horizontal plank shapes.
The model treats ice sheets—both floating shelves and grounded glaciers—like loosely cemented collections of boulders. Such a description reflects how scientists in the field have described what iceberg calving actually looks like. The model allows those loose bonds to break when the boulders are pulled apart or rub against one another.
The simulations showed that calving is a two-step process driven primarily by the thickness of the ice.
"Essentially, everything is driven by gravity," Bassis said. "We identified a critical threshold of one kilometer where it seems like everything should break up. You can think of it in terms of a kid building a tower. The taller the tower is, the more unstable it gets."
Icebergs do have a tendency to form before that threshold though, Bassis suspects, due to cracks that are already there—either formed when capsizing bergs crash into the water and send shockwaves through the surrounding ice, or when melted water on the surface cuts through. The former is believed to have led to the Helheim Glacier collapse in 2003. The glacier had begun to retreat slowly in 2002, but suddenly gave way the following year when the thinner ice had broken away, exposing a thicker ice coast.
The latter—melted water pools—are occurring more frequently due to climate change, and they're believed to have played a role in the rapid disintegration of the Antarctica's Larsen B ice shelf, which crumbled over about six weeks in 2002.
When the researchers added random cracks to their model, it could mirror both Helheim and Larsen B.
A third feature is also required for the most dramatic ice collapses to occur. Icebergs can't float away and make room for more icebergs to break off the main sheet unless the system has access to open water. So areas that border deep, unobstructed ocean rather than fjords or other waterways are at greater risk of rapid ice loss. The researchers point to the Thwaites and Pine Island glaciers in Antarctica and the Jakobshavn Glacier in Greenland, which is already retreating rapidly, as places vulnerable to "catastrophic disintegration" because they have all three components.
"The ice in those places gets thicker as you go back. If our threshold is right, then if these places start to retreat as you expose the thicker calving font, they're susceptible to catastrophic breakup," Bassis said.
Retreat of the current ice coasts in these places areas could occur via melting or iceberg calving."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 03, 2013, 01:19:23 AM
In their assessment of the risks of ASLR, Lempert et al. 2012 approximate future mean annual sea level using the equation in the attached image.

Where the term a is the sea-level anomaly at time zero (2011), b is a constant rate [mm/year], and c is an acceleration term [mm/year2]. These first three terms represent the effects of relatively well understood processes, such as thermal expansion of the oceans due to rising temperatures and the melting of small glaciers, that are well-constrained by past observations. The fourth term represents currently poorly understood and poorly constrained processes, for example potentially abrupt changes in the dynamics of ice flow (cf. Alley et al, 2007), which Lempert et al. 2012  parameterize by an increase in the rate of sea-level rise c* [mm/a] that occurs after some time t*.

It is possible to Lempert et al 2012's methodology and to develop different formulae for individual WAIS (or GIS) ice drainage basins (with unique initiation periods and conditions) in order to estimate the risks of ASLR this century; which is the approach that I used in developing the ASLR hazard curves that I have posted in several threads (including initially in the "Philosophical" thread).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on August 03, 2013, 06:01:26 AM
The Bassis paper is disturbing, since Fig 1b) indicates that once ice thickness at grounding line hits 1Km the front is unconditionally unstable.

"Minimum fraction of randomly broken bonds at which given ice thicknesses become unstable for any water depth" (the caption for Fig 1b) hits zero at thickness of 1Km.

PIG, Thwaites, Byrd, Amery are all bedded below 1Km. Not to speak of Jacoshawn, Peterman, Nioghalvfjerdsfjorden (Glacier 79N at the mouth of NEGIS) at the other end of the world.

I am not a young man, but I do believe I wil see many beloved places drowned before I die.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 03, 2013, 06:46:03 PM
Sidd,

I think that you are right to point to calving of thick ice sheets as the greatest risk for ASLR this century, as is supported by the discussion provided in the University of Washington document in the following link:

http://www.atmos.washington.edu/~bitz/514_2013/RecentChangesInGreenlandAntarctica_2013.pdf (http://www.atmos.washington.edu/~bitz/514_2013/RecentChangesInGreenlandAntarctica_2013.pdf)

It is my belief that the Thwaites Glacier grounding line is close to the Bassis criteria now, and that with a collapse of the buttressing from the Thwaites Ice Tongue and slight increase in adjoining ocean water temperatures (such as the end of the El Nino hiatus period would certainly provide); it seems highly believable that the Thwaites Glacier could become "unconditionally unstable" within three to ten years.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on August 04, 2013, 06:14:03 AM
Thanks for the link to the Poinar presentation.  I attach a slide from there that is curiously reminiscent of the ANDRILL/Pollard/DeConto results. I see 3 odd meter of SLR from the picture, but I am surprised that the Northern ice shelves east of the peninsula survive. I note that the referenced paper from that slide is from 2009. And I also note that Poinar and Joughin lower the Pfeffer estimate for SLR from PIG, which I doubt very much. PIG will surprise when Thwaites goes.

Poinar is optimistic.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 04, 2013, 12:11:30 PM
Sidd,

My interpretation of the image that you post is that as the ice shelves do not contribute to SLR, the authors did not both indicating that the ice shelves (particularly those east of the penisula) probably did not survive the collapse of the rest of the WAIS.

ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 18, 2013, 06:06:32 PM
I do not think that I have adequately documented the following reference which clearly indicates evidence that the GIS was more stable during the Eemian than was previously believed; which indicates that the WAIS is less stable then was previously believed; which indicates that the risk of ASLR this century is higher than previously believed:

http://www.nature.com/nature/journal/v493/n7433/full/nature11789.html (http://www.nature.com/nature/journal/v493/n7433/full/nature11789.html)

Eemian interglacial reconstructed from a Greenland folded ice core; by the NEEM Community Members; Nature; 493, pp: 489–494; (24 January 2013); doi:10.1038/nature11789

Abstract:
"Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 28, 2013, 12:47:28 AM
The Wikipedia write-up on the WAIS (see following link) is very explicit about its potentially "rapid disintegration" as indicated in the following extract:

http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet (http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet)


"Large parts of the WAIS sit on a bed which is below sea level and slopes downward inland. This slope, and the low isostatic head, mean that the ice sheet is theoretically unstable: a small retreat could in theory destabilize the entire WAIS leading to rapid disintegration. Current computer models do not include the physics necessary to simulate this process, and observations do not provide guidance, so predictions as to its rate of retreat remain uncertain. This has been known for decades."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on August 28, 2013, 09:06:06 PM
Wikipedia is too harsh. Schoof et seq. is certainly an advance on the 70's when Weertman and Mercer were sounding the alarm.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 29, 2013, 01:33:17 AM
Sidd,

As it is currently not possible to make calculations to specifically predict the rate of ice mass loss from either the WAIS or the EAIS; we are all (including Wikipedia) going to have different opinions on how aggressive, or not, to be about discussing this risk.  While I admit that being alarmist can be counter-productive; I also believe that being too reticent can be dangerous. 

Personnally, I doubt very much that any decision makers will take adequate precautionary measures to prevent significant SLR this century; and I also believe that sufficient evidence will not be available until after we have crossed a tipping point with regard to the WAIS.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: nukefix on August 29, 2013, 03:27:59 PM
How would one stop the potential collapse from happening? I have the feeling that even stopping greenhouse-gas emissions completely doesn't necessarily stop it. That leaves us with terraforming.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 29, 2013, 04:01:31 PM
Nukefix,

While stopping GHG emissions (if possible) immediately would be the single best thing to do; I do not think that this will happen therefore as I think that atmospheric geoengineering will be too dangerous to use for a long time, I think that: (a) populated areas could prepare better inundation defenses and (b) I presented a novel solution to stabilize the glaciers at the following link:

http://forum.arctic-sea-ice.net/index.php/topic,288.0.html (http://forum.arctic-sea-ice.net/index.php/topic,288.0.html)

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 03, 2013, 12:34:02 PM
The following linked reference provides new evidence (subject to verification) that since 1950 mid-depth ocean water temperatures in the Pacific have risen an order of magnitude faster than at any time in the past 10,000 years, and as discussed previously such warm ocean water can migrate to the Southern Ocean relatively rapidly:

http://www.sciencemag.org/content/342/6158/617.full (http://www.sciencemag.org/content/342/6158/617.full)

Rosenthal, Y., Linsley, B.K., and Oppo, D.W., (2013), "Pacific Ocean Heat Content During the Past 10,000 Years", Science 1 November 2013: Vol. 342 no. 6158 pp. 617-621, DOI: 10.1126/science.1240837

Abstract:
"Observed increases in ocean heat content (OHC) and temperature are robust indicators of global warming during the past several decades. We used high-resolution proxy records from sediment cores to extend these observations in the Pacific 10,000 years beyond the instrumental record. We show that water masses linked to North Pacific and Antarctic intermediate waters were warmer by 2.1 ± 0.4°C and 1.5 ± 0.4°C, respectively, during the middle Holocene Thermal Maximum than over the past century. Both water masses were ~0.9°C warmer during the Medieval Warm period than during the Little Ice Age and ~0.65° warmer than in recent decades. Although documented changes in global surface temperatures during the Holocene and Common era are relatively small, the concomitant changes in OHC are large."

A key passage from the article states:

"It is clear that much of the heat that humans have put into the atmosphere through greenhouse gas emissions will be absorbed by the ocean. But the absorption time takes hundreds of years, much longer than the current rate of warming and the planet will keep warming. Our study puts the modern observations into a long-term context. Our reconstruction of Pacific Ocean temperatures suggests that in the last 10,000 years, the Pacific mid-depths have generally been cooling by about 2 degrees centigrade until a minimum about 300 years during the period known as the Little Ice Age.

After that, mid-depth temperatures started warming but at a very slow rate. Then, since about 1950, temperatures from just below the sea surface to ~1000 meter, increased by 0.18 degrees C. This seemingly small increase occurred an order of magnitude faster than suggested by the gradual change during the last 10,000 years thereby providing another indication for global warming. But our results also show the temperature of the ocean interior is still much colder than at any time in the past 10,000 years thus, lagging the changes we see at the ocean surface."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: JimD on November 03, 2013, 03:16:56 PM
ASLR

Do we know with any precision what the high and low temperatures of the ocean were in relation to the high and low air temperatures during the last couple of ice ages.  Your post above got me wondering about what the lead/lag times were in the past absent human interference. 
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 03, 2013, 04:26:22 PM
JimD,

First, let me state that in regards to paleoevidence of ocean and atmospheric temperature, "precison" is a fuzzy term, and that different authors get different numbers.  That said, I like Hansen et al 2013's answers that you can find in the following like to a free pdf:

http://rsta.royalsocietypublishing.org/content/371/2001/20120294.full.pdf+html (http://rsta.royalsocietypublishing.org/content/371/2001/20120294.full.pdf+html)

The reference for this publication is:

Hansen, J., Sato, M., Russell, G. and Kharecha, P., (2013), "Climate sensitivity, sea level, and atmospheric carbon dioxide", Phil. Trans. R. Soc. A, 371, 20120294, doi:10.1098/rsta.2012.0294.

Furthermore, it is a bit misleading to think that increases in atmospheric temperatures from global warming drives heat into the ocean.  It is better to think in terms of the thermal inertia of the ocean causing its temperature increase to lag the increases in radiative forcing (particularly radiative forcing from increases in GHGs, particularly carbon dioxide).  In this last regard, a rule of thumb is that the thermal equilibrium response of the ocean lags by about 50 years behind the increase in radiative forcing.  However, the Pacific Ocean feeds temperature increases more quickly to the seas of of Western Antarctica, and this 50-year rule of thumb is just a generality.  Also, it is particularly important to realize that the Amundsen Sea Embayment, ASE, glaciers are particularly influenced by the warm Circumpolar Deep Water, CDW, which can be driven to upwell more actively into the ASE by El Nino events (due to the Amundsen-Bellingshausen Seas Low); therefore, when the current El Nino hiatus period ends, one can expect the ASE glaciers to lose ice mass faster than by the 50-year rule of thumb.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 03, 2013, 07:34:02 PM
The following link discusses the findings of a new NRC report on Abrupt climate change:

http://news.nationalgeographic.com/news/2013/12/131203-abrupt-climate-change-science-early-warning-report/ (http://news.nationalgeographic.com/news/2013/12/131203-abrupt-climate-change-science-early-warning-report/)

The linked article includes the following quote, which precisely supports the position that I have taken in my various posts in this folder:

"An abrupt slide of the vast West Antarctic Ice Sheet into the ocean would suddenly sink coasts worldwide under 10 to 13 feet (3 to 4 meters) of water. The report rates the risk of this calamity as "unknown" although probably low for this century.
"Unknown means we should be studying this question intently, not pretending it isn't there," White says."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Andreas T on December 03, 2013, 09:53:54 PM
The following linked reference provides new evidence (subject to verification) that since 1950 mid-depth ocean water temperatures in the Pacific have risen an order of magnitude faster than at any time in the past 10,000 years, and as discussed previously such warm ocean water can migrate to the Southern Ocean relatively rapidly:

http://www.sciencemag.org/content/342/6158/617.full (http://www.sciencemag.org/content/342/6158/617.full)

Rosenthal, Y., Linsley, B.K., and Oppo, D.W., (2013), "Pacific Ocean Heat Content During the Past 10,000 Years", Science 1 November 2013: Vol. 342 no. 6158 pp. 617-621, DOI: 10.1126/science.1240837

....

A key passage from the article states:
....
 But our results also show the temperature of the ocean interior is still much colder than at any time in the past 10,000 years thus, lagging the changes we see at the ocean surface."

do you see this as a contradiction of the findings of Johnson et al 2007 ? http://www.pmel.noaa.gov/pubs/outstand/john3037/john3037.shtml (http://www.pmel.noaa.gov/pubs/outstand/john3037/john3037.shtml)
from what depth are these sediment cores and how do they resolve such a large area?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 03, 2013, 11:00:03 PM
Andreas,

It is my belief that the water depths evaluated in the Rosenthal et al 2013 and the Johnson et al 2007 are at different depths, so there may not be a contradiction.  I cannot comment further on the Rosenthal et al 2013 finding; other than to say that they are subject to vertification.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: JimD on December 06, 2013, 05:50:14 PM
The following link discusses the findings of a new NRC report on Abrupt climate change:

http://news.nationalgeographic.com/news/2013/12/131203-abrupt-climate-change-science-early-warning-report/ (http://news.nationalgeographic.com/news/2013/12/131203-abrupt-climate-change-science-early-warning-report/)

The linked article includes the following quote, which precisely supports the position that I have taken in my various posts in this folder:

"An abrupt slide of the vast West Antarctic Ice Sheet into the ocean would suddenly sink coasts worldwide under 10 to 13 feet (3 to 4 meters) of water. The report rates the risk of this calamity as "unknown" although probably low for this century.
"Unknown means we should be studying this question intently, not pretending it isn't there," White says."

ASLR 

In that paragraph the report also states that collapse of the WAIS is "plausible" this century.   That statement should have a substantial impact on risk analysis for policy makers.  But will it.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: TeaPotty on December 07, 2013, 07:27:35 AM
Hey AbruptSLR & JimD,

I reccommend hearing the report's video discussion, or at least the part where they discuss WAIS collapse [16:27]:
http://www.youtube.com/watch?v=uh3auNaQbhc#t=987 (http://www.youtube.com/watch?v=uh3auNaQbhc#t=987)
[http://www.youtube.com/watch?v=uh3auNaQbhc#t=987]
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 07, 2013, 11:58:41 AM
JimD,
Until you acknowledge a problem it is not possible to develop a solution.  At least now that the NRC acknowledges the plausiblity of the collapse of the WAIS planners now can at least talk about a topic that they effectively could not even talk about before.  Whether "solutions" are developed fast enough to avoid the worst consequences is uncertain, but certainly it is better to open ones eyes rather than not.  At least with SLR groups can at locally to make a very real difference to themselves (without the problem of the "Tyranny of the Commons" associated with global warming).

TeaPotty,

Thanks for the video link, I think that the NRC committee did a great job to raise general awareness on a topic that has been clear to some since at least the 1980's.  My biggest concern about the possible collapse of the WAIS is that the Amundsen-Bellingshausen Seas Low will likely shift back towards the east (due to both the Pacific Decadal Oscillation, PDO, cycle and the healing of the Antarctic Ozone layer) where it would telecommunicate both atmospheric and oceanic energy directly into the Amundsen Sea Embayment, ASE, within the next 10 years; which would have consequences that are not being modeled correctly by any researchers that I am aware of.

Best,
ASLR

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 15, 2014, 05:37:52 AM
Following links and abstract discusses a recent article about a deep trough (see attached image) in the Ellsworth Subglacial Highland with implications on the inception and retreat of the WAIS:

http://www.sci-news.com/othersciences/geography/science-ellsworth-trough-antarctica-01687.html (http://www.sci-news.com/othersciences/geography/science-ellsworth-trough-antarctica-01687.html)


http://gsabulletin.gsapubs.org/content/126/1-2/3.abstract (http://gsabulletin.gsapubs.org/content/126/1-2/3.abstract)


Neil Ross, Tom A. Jordan, Robert G. Bingham, Hugh F.J. Corr, Fausto Ferraccioli, Anne Le Brocq, David M. Rippin, Andrew P. Wright and Martin J. Siegert, (2014), "The Ellsworth Subglacial Highlands: Inception and retreat of the West Antarctic Ice Sheet" Geological Society of America, v. 126 no. 1-2 p. 3-15, first published on line: September 19, 2013, doi: 10.1130/B30794.1

"Abstract
Antarctic subglacial highlands are where the Antarctic ice sheets first developed and the “pinning points” where retreat phases of the marine-based sectors of the ice sheet are impeded. Due to low ice velocities and limited present-day change in the ice-sheet interior, West Antarctic subglacial highlands have been overlooked for detailed study. These regions have considerable potential, however, for establishing the locations from which the West Antarctic Ice Sheet originated and grew, and its likely response to warming climates. Here, we characterize the subglacial morphology of the Ellsworth Subglacial Highlands, West Antarctica, from ground-based and aerogeophysical radio-echo sounding (RES) surveys and the Moderate-Resolution Imaging Spectroradiometer (MODIS) Mosaic of Antarctica. We document well-preserved classic landforms associated with restricted, dynamic, marine-proximal alpine glaciation, with hanging tributary valleys feeding a significant overdeepened trough (the Ellsworth Trough) cut by valley (tidewater) glaciers. Fjord-mouth threshold bars down-ice of two overdeepenings define both the northwest and southeast termini of paleo-outlet glaciers, which cut and occupied the Ellsworth Trough. Satellite imagery reveals numerous other glaciated valleys, terminating at the edge of deep former marine basins (e.g., Bentley Subglacial Trench), throughout the Ellsworth Subglacial Highlands. These geomorphic data can be used to reconstruct the glaciology of the ice masses that formed the proto–West Antarctic Ice Sheet. The landscape predates the present ice sheet and was formed by a small dynamic ice field(s), similar to those of the present-day Antarctic Peninsula, at times when the marine sections of the West Antarctic Ice Sheet were absent. The Ellsworth Subglacial Highlands represent a major seeding center of the paleo–West Antarctic Ice Sheet, and its margins represent the pinning point at which future retreat of the marine-based West Antarctic Ice Sheet would be arrested."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 09, 2014, 03:04:39 AM
I liked this summary figure from Scripps and the British Antarctic Survey (see the linked press release) so I thought that I post it here as it makes it clear how the ocean around the ASE and how much ice mass loss from grounded ice is occurring in that area.  The following is the caption for the figure:

Antarctic ice-shelf ice-thickness change rate DT/Dt, 2003–2008. Seaward of the ice shelves, estimated average sea-floor potential temperatures (in uC) from the World Ocean Circulation Experiment Southern Ocean Atlas (pink to blue) are overlaid on continental-shelf bathymetry (in metres) 30 (greyscale, landward of the continental-shelf break, CSB) Grey circles show relative ice losses for ice-sheet drainage basins (outlined in grey) that lost mass between 1992 and 2006 (from Scripps & the British Antarctic Survey)

http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=1799 (http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=1799)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 02, 2014, 02:56:01 PM
At a recent (April 2014) conference in New South Wales, NSW, the co-chair of the IPCC working group on SLR, Dr Church said:
 
“There is concern by scientists and others around the world that the West Antarctic Ice Sheet is potentially unstable and will melt away."
“We are not clear on whether this will happen in the 21st century, but there is reason for concern.”

Dr Church is very conservative in all of his SLR projections, and for him to acknowledge that there is reason for concern that the WAIS is potentially unstable and could possibly "melt away" in the 21st century is not to be taken lightly.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 11, 2014, 01:43:48 AM
The linked reference (with a free access pdf) adds additional evidences from an ice core between the PIG and Ferrigno Glacier, that the WAIS has been subject to dramatic warming trends over at least the past 300-yrs and that this area is currently undergoing such a dramatic warming trend:

Thomas, Elizabeth R; Bracegirdle, Thomas J; Turner, John; Wolff, Eric W. 2013 A 308-year record of climate variability in West Antarctica. Geophysical Research Letters, 40 (20). 5492-5496. 10.1002/2013GL057782

http://nora.nerc.ac.uk/503527/ (http://nora.nerc.ac.uk/503527/)

Abstract "We present a new stable isotope record from Ellsworth Land which provides a valuable 308-year record (1702-2009) of climate variability from coastal West Antarctica. Climate variability at this site is strongly forced by sea surface temperatures (SSTs) and atmospheric pressure in the tropical Pacific and related to local sea ice conditions. The record shows that this region has warmed since the late 1950s, at a similar magnitude to that observed in the Antarctic Peninsula and central West Antarctica, however, this warming trend is not unique. More dramatic isotopic warming (and cooling) trends occurred in the mid-19th and 18th centuries, suggesting that at present the effect of anthropogenic climate drivers at this location has not exceeded the natural range of climate variability in the context of the past ~300 years."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 11, 2014, 10:53:42 PM
I would like to note here that the scenarios that I present near the beginning of this thread illustrating how the WAIS might collapse by the end of this century (assuming that we stay on a BAU pathway until at least 2050); are contingent upon the near-term end of the approximately 15-year El Nino hiatus period (1999-2014).  This is so because the ABSL is predominate from October through March, and during El Nino years it is generally position to direct warm Circumpolar Deep Water, CDW, into the Amundsen Sea Embayment, ASE; where this warm CDW can dramatically accelerate ice mass loss from key ice shelves and glaciers in this key portion of the WAIS.

As discussed in the linked thread in the Consequence folder regarding the possibility of an El Nino event in 2014-15; it is currently noted that NOAA now given such an event at least an 80% chance of occurrence, and the current positive trends for both the PDO and the IPO indices, indicate that it is likely that the prior El Nino hiatus period will likely end for at least the coming 15-years (until about 2030).  Therefore, the scenarios presented in the first tab of this thread still remain reasonable:

http://forum.arctic-sea-ice.net/index.php/topic,730.800.html (http://forum.arctic-sea-ice.net/index.php/topic,730.800.html)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 12, 2014, 02:23:01 AM
The following link leads to a longer article of an interview in New Zealand with two top Antarctic scientists, indicating the risks of the potential collapse of the WAIS:

http://www.scoop.co.nz/stories/PO1404/S00306/lisa-owen-interviews-experts-on-antacrtica.htm (http://www.scoop.co.nz/stories/PO1404/S00306/lisa-owen-interviews-experts-on-antacrtica.htm)

"Top Antarctic scientists warns New Zealand "not ready" for worst as ice shelves and sea ice in Antarctica retreat and the climate changes

Gary Wilson: "Can we mitigate this or are we planning to adapt? I guess we're adapting... we're committed to some kind of [climate] change at this point"

Last time the world had CO2 levels as high as today, the West Antarctic ice shelf collapsed; a shelf containing 20m worth of sea level rise. So "we know the end game" we just don't how fast it might happen.

Wilson: "We're certainly heading into the danger level".

If global temperature increases continue along the same path as now, we will see more ice melt and the impact on Antarctica will be "much worse"

That impacts the New Zealand economy, which is dependent on ocean and climate conditions driven by Antarctica

Chuck Kennicutt: China, Russia and other countries have a "clear eye" on oil, gas and fisheries in Antarctica and "it's not clear" whether the Antarctic Treaty will protect the continent from exploitation."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 12, 2014, 07:59:02 PM
The link leads to a discussion of two new studies supporting the idea that the WAIS has crossed a tipping point and will continue to lose ice mass (the site has nice videos of the problem):


http://www.nbcnews.com/science/environment/west-antarctic-ice-sheets-collapse-triggers-sea-level-warning-n103221 (http://www.nbcnews.com/science/environment/west-antarctic-ice-sheets-collapse-triggers-sea-level-warning-n103221)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on May 12, 2014, 08:29:29 PM
This does seem to be getting a fair deal of MSM coverage. NYT has picked it up, too:

http://www.nytimes.com/2014/05/13/science/earth/collapse-of-parts-of-west-antarctica-ice-sheet-has-begun-scientists-say.html?_r=0 (http://www.nytimes.com/2014/05/13/science/earth/collapse-of-parts-of-west-antarctica-ice-sheet-has-begun-scientists-say.html?_r=0)

Scientists Warn of Rising Oceans as Antarctic Ice Melts

Quote
The collapse of large parts of the ice sheet in West Antarctica appears to have begun and is almost certainly unstoppable, with global warming accelerating the pace of the disintegration, two groups of scientists reported Monday.

The finding, which had been feared by some scientists for decades, means that a rise in global sea level of at least 10 feet may now be inevitable. The rise may continue to be relatively slow for at least the next century or so, the scientists said, but sometime after that it will probably speed up so sharply as to become a crisis.

“This is really happening,” said Thomas P. Wagner, who runs NASA’s programs on polar ice and helped oversee some of the research. “There’s nothing to stop it now. But you are still limited by the physics of how fast the ice can flow.”

ASLR, your article mentions a positive feedback mechanism. Is that mostly the loss of elevation bringing the melt surface to ever lower/warmer levels? Or is there something else?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 12, 2014, 11:02:03 PM
wili,

I am not sure what the positive feedback is, but I suspect that it is related more to the gravitational stability (not to mention reduced basal friction) of the glaciers, rather than to any surface temperature issue related to elevation.  I also post below the two abstracts and links for the two referenced studies:


E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi andB. Scheuchl, (2014), "Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011", Geophysical Research Letter, DOI: 10.1002/2014GL060140

http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/abstract)

"Abstract: We measure the grounding line retreat of glaciers draining the Amundsen Sea Embayment of West Antarctica using Earth Remote Sensing (ERS-1/2) satellite radar interferometry from 1992 to 2011. Pine Island Glacier retreated 31 km at its center, with most retreat in 2005–2009 when the glacier un-grounded from its ice plain. Thwaites Glacier retreated 14 km along its fast-flow core and 1 to 9 km along the sides. Haynes Glacier retreated 10 km along its flanks. Smith/Kohler glaciers retreated the most, 35 km along its ice plain, and its ice shelf pinning points are vanishing. These rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique (MC) that removes residual ambiguities from prior mappings. Upstream of the 2011 grounding line positions, we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin."


Ian Joughin, Benjamin E. Smith, & Brooke Medley, (2014), "Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica", Science DOI: 10.1126/science.1249055

http://www.sciencemag.org/content/early/2014/05/12/science.1249055 (http://www.sciencemag.org/content/early/2014/05/12/science.1249055)

Abstract: "Resting atop a deep marine basin, the West Antarctic Ice Sheet has long been considered prone to instability. Using a numerical model, we investigate the sensitivity of Thwaites Glacier to ocean melt and whether unstable retreat is already underway. Our model reproduces observed losses when forced with ocean melt comparable to estimates. Simulated losses are moderate (<0.25 mm per year sea level) over the 21st Century, but generally increase thereafter. Except possibly for the lowest-melt scenario, the simulations indicate early-stage collapse has begun. Less certain is the timescale, with onset of rapid (> 1 mm per year of sea-level rise) collapse for the different simulations within the range of two to nine centuries."

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Clare on May 14, 2014, 01:54:09 AM
This has to be an eye-catching headline is ever there was one (spotted by my hubby)

"Antarctic ice melts and California's response is ... a bullet train?"

http://www.latimes.com/opinion/opinion-la/la-ol-climate-change-sea-levels-antarctica-20140512-story.html (http://www.latimes.com/opinion/opinion-la/la-ol-climate-change-sea-levels-antarctica-20140512-story.html)

"It has to make one wonder why, with billions of dollars a year coming in to California from the state’s cap-and-trade program for greenhouse gases, Gov. Jerry Brown wants to spend 30% of it on the high-speed rail project. The train wouldn’t be ready to run for about a decade, and its ability to reduce vehicle miles driven remains to be seen."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on May 14, 2014, 06:57:09 AM
Mr. Wili,

Antarctica has little surface melt (so far), so the elevation melt feedback as outlined in Gregoire(2012)

doi:10.1038/nature11257
 
will operate more in Greenland, first at the saddle between north and south dome at 67N. But that is best discussed on a Greenland thread.

The feedbacks in Antarctica as outlined by Joughin (10.1126/science.1249055)

"melt-induced ice-shelf thinning reduces buttressing, causing an initial speedup. In turn, this initial speedup causes the grounding line to retreat, resulting in loss of traction and far greater speedup and retreat."

But this is not the most scary part. Joughin model indicates

"onset of rapid(decades) collapse as the grounding line reaches the deepest regions of the marine basin"

grounding line will reach deepest parts according to Joughin will be on the order of centuries

But I see the Rignot paper stating

"As shown here, the glacier grounding lines retreat rapidly, at km/yr, over the entire sector. On Smith/Kohler, the retreat rate of 1.8 km/yr is even greater than its rate of horizontal motion of 1.1 km/yr."

At these rates, the grounding lines reach the deepest sections of beds in decades, not centuries. The scales on Fig 3 in Rignot are in tens of kilometers, not hundreds.
 
The Joughin model does states it's own limitations:

"Our simulations also assume that there is no retreat of the ice-shelf front. Full or partial ice-shelf collapse should produce more rapid retreat than we have simulated. In addition, we have not modeled ocean-driven melt that extends immediately upstream of the grounding line, which could also accelerate retreat"

and

"Such rapid collapse likely would spill over to adjacent catchments, undermining much of West Antarctica"

I guess the world is behaving like it feels lucky. I have remarked that i was privileged to see the Everglades before they were gone. I suppose the current residents of Bangladesh might feel differently  about my privilege, which involved burning a buncha carbon on a road trip.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: TeaPotty on May 15, 2014, 04:35:31 AM
I guess the world is behaving like it feels lucky. I have remarked that i was privileged to see the Everglades before they were gone. I suppose the current residents of Bangladesh might feel differently  about my privilege, which involved burning a buncha carbon on a road trip.

sidd

Yep, barely anyone noticed this news.

But, our less intelligent scientists are on their usual anti-alarmist crusade:

So collapse isn't really collapse, or something...
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on May 15, 2014, 09:13:24 AM
Revkin is a shill, and dotearth is a sewer. Excuse me for being frank.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: TeaPotty on May 15, 2014, 03:21:59 PM
I tweeted him and told him he deserves imprisonment:
https://twitter.com/Tea_Potty/status/466206140809101312
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 15, 2014, 05:27:24 PM
wili,

While I like sidd's discussion in Reply #137, nevertheless, I thought that I would post two images from NASA's video (see YouTube link) of their model and to provide the following comments:


Animation - Loss of West Antarctic Glaciers Appears Unstoppable (http://www.youtube.com/watch?v=Adh86ma3oxw#ws)

(1) As sidd point's out and the images/video make clear, this NASA model does not account for possible major calving of both the ASE ice shelves, or eventually the ASE glacial faces in a Jakobshavn Effect manner.  This is a major short-coming of the NASA model.
(2) The basal heating in the BSB will almost certainly be higher than used in NASA model, due to magma moving rapidly beneath the thin crust in this area.
(3) The model does not account for the increase in warm CDW associated with the ABSL being pinned in a location to circulate the CDW into the ASE during El Nino events, which will happen this year (with the ABSL being influenced from October to March), and with increase frequency throughout the 15 to 30-yr positive phase of the PDO/IPO (we should not forget that we are just leaving a 15-yr hiatus period [1999-2014] which suppressed ice mass loss from the ASE, and many point to this slow/hiatus period and say that it might continue forever, but I think not).  This is a major short-coming of the NASA model, as it will lead to extensive grounding-line retreat that will accelerate the destabilization of the ASE marine glaciers.
(4) The NASA model does not fully account for the influence of the subglacial hydrological systems that have been documented to exist beneath the ASE marine glaciers.
(5) The NASA model cannot fully account for the full interaction between glacial basins, and in-particular between the PIG and the Thwaites Basins, particularly with regard to activating the eastern shear margin of the Thwaites ice stream due to a retreat of the PIIS ice face (see MacGregor et al 2014), and an activation of the SW tributary that feeds into the PIIS from the Thwaites basin.
(6) The NASA model cannot account for what I have called synergistic horizontal advection between the PIG and the Thwaites Glacier; where I believe that during the current (and future El Ninos) the advection from PIG will be strong enough to convey excess warm CDW towards the grounding line of the Thwaites Glacier..

I have made all of these points before (and others in the various threads), but they bear repeating.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on May 15, 2014, 10:09:10 PM
Thanks, ASLR. And yes, all those points do bear repeating.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Stephen on May 16, 2014, 07:54:44 AM
Mr. Wili,

Antarctica has little surface melt (so far), so the elevation melt feedback as outlined in Gregoire(2012)

doi:10.1038/nature11257
 
will operate more in Greenland, first at the saddle between north and south dome at 67N. But that is best discussed on a Greenland thread.

The feedbacks in Antarctica as outlined by Joughin (10.1126/science.1249055)

"melt-induced ice-shelf thinning reduces buttressing, causing an initial speedup. In turn, this initial speedup causes the grounding line to retreat, resulting in loss of traction and far greater speedup and retreat."

But this is not the most scary part. Joughin model indicates

"onset of rapid(decades) collapse as the grounding line reaches the deepest regions of the marine basin"

grounding line will reach deepest parts according to Joughin will be on the order of centuries

But I see the Rignot paper stating

"As shown here, the glacier grounding lines retreat rapidly, at km/yr, over the entire sector. On Smith/Kohler, the retreat rate of 1.8 km/yr is even greater than its rate of horizontal motion of 1.1 km/yr."

At these rates, the grounding lines reach the deepest sections of beds in decades, not centuries. The scales on Fig 3 in Rignot are in tens of kilometers, not hundreds.
 
The Joughin model does states it's own limitations:

"Our simulations also assume that there is no retreat of the ice-shelf front. Full or partial ice-shelf collapse should produce more rapid retreat than we have simulated. In addition, we have not modeled ocean-driven melt that extends immediately upstream of the grounding line, which could also accelerate retreat"

and

"Such rapid collapse likely would spill over to adjacent catchments, undermining much of West Antarctica"

I guess the world is behaving like it feels lucky. I have remarked that i was privileged to see the Everglades before they were gone. I suppose the current residents of Bangladesh might feel differently  about my privilege, which involved burning a buncha carbon on a road trip.

sidd

Another fact to consider - (not so much a feedback as that implies coming from within the same system) - is the effect that the first metre of GIS melt will have on the WAIS

Richard Alley talks about in this [urlhttp://www.youtube.com/watch?v=o4oMsfa_30Q]video[/url] (I hope I've linked the correct video)

Essentially he is suggesting that while 1 metre of Sea level rise from the GIS will be bad enough, the biggest effect of GIS melt will be on the WAIS.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 16, 2014, 05:56:32 PM
Stephen,

Thanks for raising the issue of the impact SLR contribution from the GIS on the WAIS, which clearly very important for ice mass loss on the scale of centuries, and I believe that it is also an important consideration for "fat-tailed" scenarios where the WAIS could partially collapse this century.

Also, I would like to note that Alley has also commented that he believes that ice sheet modelers should be given more freedom w.r.t. to the selection of forcing functions rather than being limited to the IPCC official RCP scenarios. For example two of my recent posts in the "Forcing" thread (see link below) have documented Earth System Sensitivities as high as 9.6 degrees C within the past 4 million years with CO2 levels as low as 415ppm (however, I do acknowledge that no one knows how fast the "slow response" feedback mechanisms may kick-in during our current extremely fast rate of warming (several times faster than during the PETM)):

http://forum.arctic-sea-ice.net/index.php/topic,41.150.html (http://forum.arctic-sea-ice.net/index.php/topic,41.150.html)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 17, 2014, 10:51:58 PM
The linked reference indicates that from January to June the ASL (also call the ABSL) typically moves from about 110 degrees W (where it is in position to help direct warm CDW into the ASE) to about 150 degrees W (where it does not help to direct warm CDW into the ASE).  I note also that: (a) as the SAM has become more positive due to AGW the ASL has become more intensity and has tended to drift more to the west than previously; and (b) starting in October the occurrence of an El Nino can tend to accelerate the eastward migration of the ASL (or ABSL) where it can help to direct more warm CDW  than typical into the ASE (also note that as we are now entering a positive phase of the PDO/IPO El Nino events should become more frequent than during the past 15-yr period of negative IPO; which should serve to accelerate ice mass loss from the ASE):

Turner, J., Phillips, T., Hosking, J. S., Marshall, G. J. and Orr, A. (2013), The Amundsen Sea low. Int. J. Climatol., 33: 1818–1829. doi: 10.1002/joc.3558

http://onlinelibrary.wiley.com/doi/10.1002/joc.3558/abstract (http://onlinelibrary.wiley.com/doi/10.1002/joc.3558/abstract)

Abstract: "We develop a climatology of the Amundsen Sea low (ASL) covering the period 1979–2008 using ECMWF operational and reanalysis fields. The depth of the ASL is strongly influenced by the phase of the Southern annular mode (SAM) with positive (negative) mean sea level pressure anomalies when the SAM is negative (positive). The zonal location of the ASL is linked to the phase of the mid-tropospheric planetary waves and the low moves west from close to 110°W in January to near 150°W in June as planetary waves 1 to 3 amplify and their phases shift westwards. The ASL is deeper by a small, but significant amount, during the La Niña phase of El Niño-Southern Oscillation (ENSO) compared to El Niño. The difference in depth of the low between the two states of ENSO is greatest in winter. There is no statistically significant difference in the zonal location of the ASL between the different phases of ENSO. Over 1979–2008 the low has deepened in January by 1.7 hPa dec−1 as the SAM has become more positive. It has also deepened in spring and autumn as the semi-annual oscillation has increase in amplitude over the last 30 years. An increase in central pressure and eastward shift in March has occurred as a result of a cooling of tropical Pacific SSTs that altered the strength of the polar front jet."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Clare on May 18, 2014, 03:14:41 AM
This week:
http://live.huffingtonpost.com/r/segment/west-antarctica-melting-ice-climate-change-/53725e5c78c90a228500004c (http://live.huffingtonpost.com/r/segment/west-antarctica-melting-ice-climate-change-/53725e5c78c90a228500004c)
Discussion is with:
Chuck Kennicutt (Mayfield, NY) Professor Emeritus of Oceanography at Texas A&M University
Julien Nicolas (Columbus, OH) Post-Doctoral Researcher at Byrd Polar Research Center, Ohio State University
Timothy Naish (Christchurch, New Zealand) Director, Antarctic Research Centre
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 18, 2014, 05:30:28 PM
I like the linked reference by Rovere et al 2014 (with a free access pdf) very much, and it should help to determine more accurately true paleo eustatic sea levels from the Mid-Pliocene to the Holocene; which in turn will give a more accurate idea of the stability of the WAIS over this time period.  This is important because as in the video that Clare posted (see Reply #146), most mainstream scientists are only willing to admit that the most recent collapse of the WAIS was about 3 million years ago during the Mid-Pliocene; however, I have presented numerous references in multiple threads indicating that the WAIS at least partially collapsed during the peak of the Eemian as indicated in: O'Leary, M.J., Hearty, P.J., Thompson, W.G., Raymo, M.E., Mitrovica, J.X., and Webster, J.M., (2013), "Ice sheet collapse following a prolonged period of stable sea level during the last interglacial", Nature Geoscience;  doi:10.1038/ngeo1890

Rovere, A., M. E. Raymo, J. X. Mitrovica, P. J. Hearty, M. J. O'Leary, and J. D. Inglis. 2014. “The Mid-Pliocene sea-level conundrum: Glacial isostasy, eustasy and dynamic topography.” Earth and Planetary Science Letters 387: 27-33

http://www.sciencedirect.com/science/article/pii/S0012821X13006006 (http://www.sciencedirect.com/science/article/pii/S0012821X13006006)

Abstract: "Determining eustatic sea level during the Mid-Pliocene warm period (∼3.3 to 2.9 Ma) has been a central but elusive goal in the study of past warm climates. Estimates of eustatic sea level based on geologic data span a broad range; variation that we now recognize is due in part to geographically varying post-depositional displacement caused by glacial isostatic adjustment and dynamic topography. In this study, we combine field observations and glacial isostatic adjustment modeling to estimate the dynamic topography signal in three areas that are important to paleo-sea level studies of the Mid-Pliocene warm period (South Africa, West Australia and southeastern United States). We show that dynamic topography played a significant role in the post-depositional displacement of Pliocene, and even younger Pleistocene, shorelines. In this regard, we provide a robust paleo-sea level elevation data set, corrected for glacial isostatic adjustment, that can be used to evaluate predictions from mantle flow models of dynamic topography."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: idunno on May 18, 2014, 05:57:00 PM
Rignot in today's Observer...

http://www.theguardian.com/commentisfree/2014/may/17/climate-change-antarctica-glaciers-melting-global-warming-nasa?commentpage=4 (http://www.theguardian.com/commentisfree/2014/may/17/climate-change-antarctica-glaciers-melting-global-warming-nasa?commentpage=4)

Last week saw a 'holy shit' moment in climate change science. A landmark report revealed that the collapse of a large part of Antarctica is now unstoppable
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on May 18, 2014, 07:37:43 PM
Thanks idunno,

One line struck me.

Rignot: "Two centuries – if that is what it takes –"

Finally the hedged comments have been put into perspective for the public. But one has to wonder, was this article cleared with NASA's bureaucracy before publication?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 18, 2014, 08:02:00 PM
The article states in several places that the timescale for the collapse of the Amundsen Sea Embayment, ASE, marine glaciers is difficult to determine, and then goes on to state:

"At the current rate, a large fraction of the basin will be gone in 200 years, but recent modelling studies indicate that the retreat rate will increase in the future."

This statement clarifies that the 200-yr period is an upper bound for the collapse of the ASE marine glaciers, and that as the "... retreat rate will increase in the future"; that this period will absolutely be shorter than 200-yrs and possibly much shorter, depending on the rate of acceleration of retreat.

Focusing on the upper bound 200-yr period is like putting lipstick on a PIG (Pine Island Glacier).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 18, 2014, 08:41:26 PM
In my last post I pointed out that focusing on the consideration that it could conceivably take as long as 200-yrs for the ASE glaciers to collapse, rather than on the fact that this period to ASE collapse will almost certainly be shorter (and possibly much shorter), is like putting "Lipstick on a PIG (Pine Island Glacier)".  Indeed, the past 40-yr period considered by the NASA was dominated by many temporary climate change "masking factors", that cannot be counted on to continue for an extended period of time as partially pointed out by Michael Mann in his April 2014 SciAm article: "False Hope: The rate of global temperature rise may have hit a plateau, but a climate crisis still looms in the near future":

Mann, M.E., False Hope: The rate of global temperature rise may have hit a plateau, but a climate crisis still looms in the near future, Scientific American, p. 78-81, April 2014.

Further to the SciAm article Michael Mann points out that a significant portion of the "Faux Pause" from 1999 to 2014 was associated with a cooling phase of the NAO, which will reverse soon enough (see reference below):
Mann, M.E., Steinman, B.A., Miller, S.K., On Forced Temperature Changes, Internal Variability and the AMO, Geophys. Res. Lett. (“Frontier” article), doi:10.1002/2014GL059233;  May1, 2014

http://www.meteo.psu.edu/holocene/public_html/Mann/articles/articles/MannEtAlGRLOnline14.pdf (http://www.meteo.psu.edu/holocene/public_html/Mann/articles/articles/MannEtAlGRLOnline14.pdf)

Abstract: "We estimate the low-frequency internal variability of Northern Hemisphere (NH) mean temperature using observed temperature variations, which include both forced and internal variability components, and several alternative model simulations of the (natural + anthropogenic) forced component alone. We then generate an ensemble of alternative historical temperature histories based on the statistics of the estimated internal variability. Using this ensemble, we show, first, that recent NH mean temperatures fall within the range of expected multidecadal variability. Using the synthetic temperature histories, we also show that certain procedures used in past studies to estimate internal variability, and in particular, an internal multidecadal oscillation termed the “Atlantic Multidecadal Oscillation” or “AMO”, fail to isolate the true internal variability when it is a priori known. Such procedures yield an AMO signal with an inflated amplitude and biased phase, attributing some of the recent NH mean temperature rise to the AMO. The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming. Claims of multidecadal “stadium wave” patterns of variation across multiple climate indices are also shown to likely be an artifact of this flawed procedure for isolating putative climate oscillations."



Furthermore, while the "Forcing" thread contains many references that cite mechanisms that indicate that climate change forcing is probably higher than that used in most GCMs/RCMs that project ice mass loss from WAIS; the following is a partial list of factors that are currently masking the full consequences of many of these climate change forcings:
(1) Aerosols (eg sulfates from burning coal) have masked the build-up of GHGs which will be felt when the air pollution is reduced (as China has pledged to do).
(2) Volcanic eruptions have masked many of the impacts of the last negative phase of the IPO/PDO (El Nino hiatus). For example: in 1991 Mt Pinatubo erupted in the Philippines; and in 1963 Mt. Agung erupted in Bali; however, such events are relatively rare and cannot be counted on to reoccur in the near future.
(3) The thinning of Arctic sea ice is delaying consequences of the coming albedo change, which could come as soon as 2017 +/- 2 yrs.
(4) Thermal inertia of the permafrost is delaying the coming CO₂ & methane emissions; which is starting to accelerate already.
(5) Thermal inertia of the ocean delays most changes in mean global temperature by up to 50-years; meaning that we cannot stop the acceleration of the loss of the ASE glaciers and the WAIS.
(6) We were slowly entering an ice age when AGW began; which temporarily slowed the rate of warming.
(7) Vegetation can accommodate a certain amount of climate change before suffering from stress, and while there has been a recent temporary increase in vegetation worldwide, this trend is likely to stop within the next could of decades, and as indicated by the following two references, vegetation has been emitting aerosol precursors that has been temporarily slowing the rate of AGW, but when the vegetation cannot keep up with the rate of AGW (or more likely declines due to AGW induced stress), we can expect AGW to further accelerate:

In a study by Salo, et.al, 2011, the authors argue that climate sensitivity could be ‘greater than previously believed’ because in the initial phases of the current CO2-induced warming plant life has emitted larger amounts of precursor gases that lead to the formation of reflective or blocking secondary organic aerosols (SOA) in the atmosphere, thereby acting as a negative climate feedback, and masking part of the ‘warming’ that’s occurring underneath.
Salo, K., Hallquist, M., Jonsson, A.M., Saathoff, H., Naumann, K.-H., Spindler, C., Tillmann, R., Bohn, B., Rubach, R., Mentel, Th.F., Muller, L., Hoffmann, T., and Donahue, N.M. (2011); "Volatility of secondary organic aerosol during OH radical induced ageing"; Atmos. Chem. Phys., 11, 11055-11067, 2011; doi: 10.5194/acp-11-11055-2011.

Pauli Paasonen et al, (2013), "Warming-induced increase in aerosol number concentration likely to moderate climate change", Nature Geoscience, 6,pp: 438–442 (2013)doi:10.1038/ngeo1800

http://www.nature.com/ngeo/journal/v6/n6/full/ngeo1800.html (http://www.nature.com/ngeo/journal/v6/n6/full/ngeo1800.html)

Abstract: "Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. Apart from black carbon aerosol, aerosols cause a negative radiative forcing at the top of the atmosphere and substantially mitigate the warming caused by greenhouse gases. In the future, tightening of controls on anthropogenic aerosol and precursor vapour emissions to achieve higher air quality may weaken this beneficial effect. Natural aerosols, too, might affect future warming. Here we analyse long-term observations of concentrations and compositions of aerosol particles and their biogenic precursor vapours in continental mid- and high-latitude environments. We use measurements of particle number size distribution together with boundary layer heights derived from reanalysis data to show that the boundary layer burden of cloud condensation nuclei increases exponentially with temperature. Our results confirm a negative feedback mechanism between the continental biosphere, aerosols and climate: aerosol cooling effects are strengthened by rising biogenic organic vapour emissions in response to warming, which in turn enhance condensation on particles and their growth to the size of cloud condensation nuclei. This natural growth mechanism produces roughly 50% of particles at the size of cloud condensation nuclei across Europe. We conclude that biosphere–atmosphere interactions are crucial for aerosol climate effects and can significantly influence the effects of anthropogenic aerosol emission controls, both on climate and air quality."


Robert J. Allen, Joel R. Norris & Mahesh Kovilakam, (2014), "Influence of anthropogenic aerosols and the Pacific Decadal Oscillation on tropical belt width", Nature Geoscience, 7, 270–274, doi:10.1038/ngeo2091


http://www.nature.com/ngeo/journal/v7/n4/full/ngeo2091.html (http://www.nature.com/ngeo/journal/v7/n4/full/ngeo2091.html)


Abstract: "The tropical belt has widened by several degrees latitude since 1979, as evidenced by shifts in atmospheric circulation and climate zones. Global climate models also simulate tropical belt widening, but less so than observed. Reasons for this discrepancy and the mechanisms driving the expansion are uncertain. Here we analyse multidecadal variability in tropical belt width since 1950 using the Coupled Model Intercomparison Project Phase 5 climate model runs and find that simulated rates of tropical expansion over the past 30 years—particularly in the Northern Hemisphere—are in better agreement with observations than previous models. We find that models driven by observed sea surface temperatures over this interval yield the largest rate of tropical expansion. We link the tropical expansion in the Northern Hemisphere to the leading pattern of sea surface temperature variability in the North Pacific, the Pacific Decadal Oscillation. We also find, both from models and observations, that the tropical belt contracted in the Northern Hemisphere from 1950 to 1979, coincident with the reversal of the Pacific Decadal Oscillation trend. In both time periods, anthropogenic aerosols act to modify the Pacific Decadal Oscillation and therefore contribute to the width of the tropical belt. We conclude that tropical expansion and contraction are influenced by multidecadal sea surface temperature variability associated with both the Pacific Decadal Oscillation and anthropogenic aerosols."

To repeat, as currently estimates of "climate sensitivity" do not include this vegetation aerosol precursor negative feedback; in order for Global Circulation Models, GCM's including this negative feedback to match historical records they will need to utilize higher effective "climate sensitivity" values; which should resulting in higher projections of global temperature increase, if plant growth/activity does not keep path with the rate of future greenhouse gas, GHC, emissions.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on May 18, 2014, 08:47:54 PM
ASLR, it's all in the phrasing. Or maybe the timing. Having facts is not the issue; using them is.

This new article was written for the popular press. Almost all comments I have seen in the popular press have downplayed the term "collapse". NASA has made no statements to the contrary. With this new Rignot put into the popular mind that collapse means collapse. The comment will probably shift the discussion in the popular press.

The article had to have been written by Rignot in the last week. If it was cleared by NASA, this signals a policy shift at high levels in the government. Or maybe last week's press conference indicated a shift. If not, Rignot put his career at risk.

Good deal either way for the ASLR problem's recognition. Doesn't matter that the technical report said the same thing in different words. Previously the time frame could be overlooked by pundits -- not so readily now.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 19, 2014, 12:42:21 AM
steve s,

In Reply #121, I link to an article about the December 2013 NRC report on abrupt climate change that includes the following quote that supports the position that I have taken in my various posts in this folder:

"An abrupt slide of the vast West Antarctic Ice Sheet into the ocean would suddenly sink coasts worldwide under 10 to 13 feet (3 to 4 meters) of water. The report rates the risk of this calamity as "unknown" although probably low for this century.
"Unknown means we should be studying this question intently, not pretending it isn't there," White says."

With the gold-standard of science in the US (the NRC) formally acknowledging the ASLR risk from the WAIS, not only does Rignot not need to fear for his job for talking about the risk of the collapse of the ASE, but those scientists who deny this possibility, run the risk of going against the formal doctrine of the top-tier of the US scientific establishment.  Soon the public will get used to this concept.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 19, 2014, 01:09:43 AM
While some readers may think that I am overstating the fact that the US scientific establishment formally acknowledges the risk of the partial collapse of the WAIS this century, then please read the quote from the linked NOAA 2012 SLR guidance document (with a free access pdf) that cites an "Highest Scenario" with a SLR of 2m by 2100, and they acknowledge that the possibility exists that SLR could exceed this "limit".  I also note that it would be difficult to achieve a SLR of 2m by 2100 without a partial collapse of the WAIS starting no later than 2070:

http://cpo.noaa.gov/sites/cpo/Reports/2012/NOAA_SLR_r3.pdf (http://cpo.noaa.gov/sites/cpo/Reports/2012/NOAA_SLR_r3.pdf)

Quote: "Our Highest Scenario is an upper limit for SLR by 2100, but the possibility exists that SLR could exceed this limit beyond this timeframe (Pfeffer et al 2008).
…..
Most of the ice loss in Antarctica has come from the West Antarctic ice sheet (WAIS; Rignot et al. 2008).  A significant portion of the WAIS is floating at or grounded below sea level, as are relatively smaller parts of the ice sheets in East Antarctica and Greenland.  Floating ice shelves support land-based ice sheets. Current and future ocean warming below the surface make ice shelves susceptible to catastrophic collapse, which in turn can trigger increased ice discharge to the ocean (Rignot et al. 2004, Scambos et al. 2004, Jacobs et al. 2011, Joughlin and Alley 2011, Yin et al. 2011).  Better understanding of how the polar ice sheets will respond to further changes in climatic conditions over the 21st century requires continued development of physical models (Price et al. 2011)."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: CraigsIsland on May 19, 2014, 07:33:55 AM
steve s,

In Reply #121, I link to an article about the December 2013 NRC report on abrupt climate change that includes the following quote that supports the position that I have taken in my various posts in this folder:

"An abrupt slide of the vast West Antarctic Ice Sheet into the ocean would suddenly sink coasts worldwide under 10 to 13 feet (3 to 4 meters) of water. The report rates the risk of this calamity as "unknown" although probably low for this century.
"Unknown means we should be studying this question intently, not pretending it isn't there," White says."

With the gold-standard of science in the US (the NRC) formally acknowledging the ASLR risk from the WAIS, not only does Rignot not need to fear for his job for talking about the risk of the collapse of the ASE, but those scientists who deny this possibility, run the risk of going against the formal doctrine of the top-tier of the US scientific establishment.  Soon the public will get used to this concept.

Best,
ASLR

Thanks ASLR; without your contributions here, I wouldn't have been as "surprised" with the coverage than most uninformed (at least in regards to general risk that melting has on their livelihoods, etc) people have appeared to be. Very real and sobering. Yes, I'm happy that people seem to be understanding that the risk is real and is being talked about without being as polarizing as the "debate" as our imprint has had and so on. Thanks again for providing the time and effort towards your posts.

Craig
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on May 19, 2014, 08:21:49 AM
Here is an amusing semilog plot of my estimate of time to icesheet collapse as it evolved.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 19, 2014, 04:12:47 PM
sidd,

Your semi-log plot is both amusing and instructive.  If by "collapse" you mean the beginning of the rapid acceleration phase of the ASE marine glacier, and given the 15 to over 20-year positive IPO/PDO phase that we are now entering; then your recognition of 2035 collapse date by 2025 seems believable.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on May 19, 2014, 10:33:09 PM
Talking of growth rates, anyone want to estimate what year the Thwaites Glacier is going to be recognized as contributing more to SLR than the Pine Island Glacier?

Steve
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 19, 2014, 10:59:18 PM
steve s,

It can be difficult to second guess two moving targets; but nevertheless, I will put in my guess now for January 2035 (see also my Reply #21).  Of course this assumes that we stay on our current BAU pathway for the next twenty years (but even if we start backing away from our current BAU, I think that this will only delay Thwaites passing PIG by five to ten years).  This is based on my belief that the CDW inflow to the ASE will generally accelerate during the coming positive phase of the PDO, and that calving of both the PIIS and the Eastern Thwaites Ice Shelf will accelerate (and provide less buttressing) during this period.  As another caveat, I not that due to natural variability it is possible that both the PIG and the Thwaites Glacier could switch back and forth for first place for ice mass loss, for a few years until Thwaties finally pulls ahead.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 30, 2014, 01:56:29 AM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

Pritchard 2014 provides evidence that current dynamic ice discharge rates in Antarctica are historically abnormal, indicating that it may be induced by anthropogenic global warming, and may be unstable:

70A1077
A long-term history of Antarctic grounding line change
Hamish PRITCHARD
Corresponding author: Hamish Pritchard
Corresponding author e-mail: hprit@bas.ac.uk

Abstract: "Rapid grounding line retreat is underway along several sections of the Antarctic ice sheet margin, forced by the arrival of warm water at the coast and leading to the continent’s significant ongoing contribution to sea-level rise. Even an ice sheet stable to grounding line perturbations will continue to lose mass if this forcing is sustained, but the forcing is poorly understood. Is it unusual? Will it continue or increase? We can start to answer these questions by looking for evidence of coastal dynamic change stored within the ice itself. Fortunately, a record of flow dynamics along the ice-sheet margins – the glacial response to grounding line change – is preserved within ice divides. ‘Raymond bumps’ in the internal ice stratigraphy form over a long (and calculable) time under an unmoving divide, hence their presence indicates a sustained, unchanging flow regime. A present-day divide that is offset from its underlying Raymond bump indicates a long spell of unchanged flow perturbed at some time in the more recent past. I present here a map, derived from both ground and satellite radar remote sensing, of this Antarctic flow history spanning centuries to millennia that serves as a proxy for changes at the grounding line. This reveals a surprising picture of prolonged stasis where we now see rapid and recent change, implying a new and abnormal shift in the coastal regime."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 30, 2014, 02:16:35 AM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

The insight of Bassis 2014's simple ice damage model that the current acceleration of glaciers like PIG and Thwaites Glacier is accumulating internal damage within these ice streams that will likely lead to accelerated future instability of such marine glaciers, is fundamental:

70A1126
A simple damage evolution law for ice shelves
Jeremy BASSIS
Corresponding author: Jeremy Bassis
Corresponding author e-mail: jbassis@umich.edu

Abstract: "Basal melting and iceberg calving are the primary mechanisms responsible for transferring mass from the ice shelves to the ocean. Although the connection between basal melting and ocean forcing is clear, the effect of ocean forcing on iceberg calving remains more controversial with conflicting hypothesis about whether a warming ocean will increase or decrease future iceberg production. Previous theories of iceberg calving have either invoked fracture mechanics to explain the fracture process that precedes calving or sought to use damage mechanics to simulate the bulk behavior of fractures within the ice. Here we use a perturbation analysis to link the creep deformation of brittle crevasses after failure to bulk ‘damage’ within the ice shelf. This allows us to derive a damage evolution law that links brittle failure with creep failure and can be directly applied to simulate the progressive increase or decrease of damage within ice shelves. One of the advantages of this formalism is that it accounts for the effect of surface meltwater related hydrofracturing on damage progression. Moreover, the theory provides an explicit link between damage accumulation and the large-scale melting or refreezing regime of the ice shelf. For example, we find that marine ice accretion within crevasses substantially diminishes damage. In contrast, we find that large basal melt rates can slowly increase damage, but over decadal and longer timescales. This suggests that regions like Pine Island and Thwaites Glaciers that have experienced enhanced basal melt may also experience enhanced calving in the coming decades. Crucially, our results are sensitive to melt/accumulation rates at the scale of an individual crevasses, suggesting that small-scale thermodynamic interaction between crevasses and the ocean may play a pivotal role in the stability of ice shelves."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 30, 2014, 02:21:57 AM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

Rignot 2014 presents progress on a big data approach to advanced ice-sheet modelling that are likely to provide significant advances in projecting ice-sheet and glacier evolution:

70A1140
Big data for advanced ice-sheet modeling
Eric RIGNOT
Corresponding author: Eric Rignot
Corresponding author e-mail: erignot@uci.edu

Abstract: :Current uncertainties in projections of sea-level rise from ice sheets and glaciers are embarrassingly large because we are lacking large-scale, high-resolution models coupled with the ocean, sea ice and the atmosphere, and constrained by massive data assimilation to minimize the impact of unresolved physics. Progress is being made in those directions, however, under the impetus of new remote-sensing observations that reveal rapid, significant changes affecting the outlet glaciers and that help constrain ice-sheet models in a new, effective way; furthermore, high-resolution, higher-order physics ice-sheet models are being developed and applied to ice-sheet-wide problems with encouraging results; ice–ocean–sea-ice–atmosphere coupled models are also starting to emerge; and efforts are made on the remote-sensing side to alleviate our most significant knowledge gaps such as bed topography and ice thickness, and sea-floor bathymetry beneath ice shelves, along glacial fjords and on continental shelves, to name a few. While one might easily argue that ice sheets and glaciers will remain fundamentally unpredictable, I will discuss current progress and frameworks that are likely to provide significant advances in projecting ice-sheet and glacier evolution. A most fundamental aspect of this new framework, however, is that the problem is of a multidisciplinary nature, beyond glaciology."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 08, 2014, 08:10:27 PM
The following link leads to a very nice Part 1 summary of the recent research history (from about 1968 to about the late 1990's) on the stability of the WAIS, and which includes a very nice video by NASA about Rignot et al's 2014 research on this topic:

https://etherwave.wordpress.com/2014/05/22/a-historical-primer-on-wais-collapse-part-1-early-history/#comment-7466

I look forward to seeing Part 2 of this summary when it is posted.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on June 09, 2014, 05:46:20 PM
SkS has a nice commentary on the new Climate Crocks video on WAIS collapse, which has appearances by Archer, Alley, Rignot, Hansen and others.

https://www.skepticalscience.com/new-video-meltwater-pulse-2b.html (https://www.skepticalscience.com/new-video-meltwater-pulse-2b.html)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Neven on June 09, 2014, 06:30:11 PM
Very nice video indeed:

https://www.youtube.com/watch?v=71l9lzLsBRc (https://www.youtube.com/watch?v=71l9lzLsBRc)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Anne on June 10, 2014, 07:31:35 PM
A search on the forum suggests this hasn't been posted before. This from Science Daily suggests that Thwaites Glacier is also subject to variable geothermal heat from below:
Quote
The UTIG researchers had previously used ice-penetrating airborne radar sounding data to image two vast interacting subglacial water systems under Thwaites Glacier. The results from this earlier work on water systems (also published in the Proceedings of the National Academy of Sciences) formed the foundation for the new work, which used the distribution of water beneath the glacier to determine the levels and locations of heat flow.
In each case, Schroeder, who received his Ph.D. in May, used techniques he had developed to pull information out of data collected by the radar developed at UTIG.
According to his findings, the minimum average geothermal heat flow beneath Thwaites Glacier is about 100 milliwatts per square meter, with hotspots over 200 milliwatts per square meter. For comparison, the average heat flow of the Earth's continents is less than 65 milliwatts per square meter.
The presence of water and heat present researchers with significant challenges.
"The combination of variable subglacial geothermal heat flow and the interacting subglacial water system could threaten the stability of Thwaites Glacier in ways that we never before imagined," Schroeder said.
Science Daily report here: Link (http://www.sciencedaily.com/releases/2014/06/140609153425.htm)

Full paper:
Dustin M. Schroeder, Donald D. Blankenship, Duncan A. Young, and Enrica Quartini. Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet. PNAS, June 9, 2014 DOI: 10.1073/pnas.1405184111
http://www.pnas.org/content/early/2014/06/04/1405184111 (http://www.pnas.org/content/early/2014/06/04/1405184111)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 10, 2014, 08:28:15 PM
Anne,

Thanks for the post.  I made a parallel post in Reply #37 of the "Subglacial Lake and Meltwater Drainage System" thread at:

http://forum.arctic-sea-ice.net/index.php/topic,404.0.html (http://forum.arctic-sea-ice.net/index.php/topic,404.0.html)

However, this is an important reference and posts about it belong in this thread and the PIG/Thwaites 2012 to 2040-2060 thread.

Obviously, as more ice mass is lost and more magma flows in beneath the BSB, and as the Thwaites ice velocities increase, the subglacial meltwater drainage system will become a critical factor, which I believe directly contributed to the Fall 2012 "Surge" event for the Thwaites Ice Tongue (see the Surge thread, Reply #73 and the link below):

http://forum.arctic-sea-ice.net/index.php/topic,21.100.html (http://forum.arctic-sea-ice.net/index.php/topic,21.100.html)

Thanks again,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on June 10, 2014, 08:59:41 PM
(Please see my question about this on the other thread.)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 07, 2014, 07:36:48 PM
Reply #77 in the "Risks and Changes of RCMs for the Southern Ocean" thread (see link below), references recent model results confirming that projected changes in the Southern Hemisphere Westerly winds will bring warm CDW to the grounding lines of many Antarctic marine glaciers, including those in the ASE:

http://forum.arctic-sea-ice.net/index.php?topic=281.msg30862#msg30862 (http://forum.arctic-sea-ice.net/index.php?topic=281.msg30862#msg30862)

Also see (and the associated extract):

http://www.natureworldnews.com/articles/7938/20140707/changing-arctic-winds-threaten-to-raise-global-sea-levels.htm (http://www.natureworldnews.com/articles/7938/20140707/changing-arctic-winds-threaten-to-raise-global-sea-levels.htm)

Extract: "The sub-surface warming revealed in this research is on average twice as large as previously estimated with almost all of coastal Antarctica affected. This relatively warm water provides a huge reservoir of melt potential right near the grounding lines of ice shelves around Antarctica. It could lead to a massive increase in the rate of ice sheet melt, with direct consequences for global sea level rise."
Prior studies focused on rising sea levels and the rate of ice shelf melting due to the general warming of the ocean over large areas. This time, researchers examined in great detail the impact of changing winds on currents down to 700 meters around the coastline.
With the help of supercomputers at Australia's National Computational Infrastructure (NCI) Facility, they found that changes in the Antarctic coastal winds from climate change could be linked more closely to melting of the ice shelves, compared to broader warming of the ocean.
"It is very plausible that the mechanism revealed by this research will push parts of the West Antarctic Ice Sheet beyond a point of no return," explained Dr. Axel Timmerman, a professor of Oceanography at University of Hawaii.
Additionally, this research may help to explain a number of sudden and unexplained increases in global sea levels that have happened in the past.
"This work suggests the Antarctic ice sheets may be less stable to future climate change than previously assumed," Timmerman concluded.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 23, 2014, 05:49:51 PM
The following link leads to a further discussion of the Spence et al 2014 findings discussed in Reply #169 (and in the Trends of the Southern Ocean thread):


http://www.abc.net.au/lateline/content/2014/s4041192.htm (http://www.abc.net.au/lateline/content/2014/s4041192.htm)

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 15, 2014, 11:29:33 AM
Using methodology that is likely to be accepted by IPCC for AR6 (ie meaning very conservative), the linked reference (with a free access PDF) estimates that Antarctica alone may contribute up to 37 cm (14.5 inches) to global seas by 2100; which is more than triple previous IPCC worst-case estimates for a likely Antarctic SLR contribution by 2100 (see attached image).  However, assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5.  While some may view this as an upper bound; I am of the opinion that it more likely represents a lower bound.

Levermann, A., Winkelmann, R., Nowicki, S., Fastook, J. L., Frieler, K., Greve, R., Hellmer, H. H., Martin, M. A., Meinshausen, M., Mengel, M., Payne, A. J., Pollard, D., Sato, T., Timmermann, R., Wang, W. L., and Bindschadler, R. A., (2014), "Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models", Earth Syst. Dynam., 5, 271-293, doi:10.5194/esd-5-271-2014

http://www.earth-syst-dynam.net/5/271/2014/esd-5-271-2014.pdf (http://www.earth-syst-dynam.net/5/271/2014/esd-5-271-2014.pdf)

Abstract: "The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02–0.14 m; 90% range: 0.0–0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04–0.21 m; 90% range: 0.01–0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04–0.17 m; 90% range: 0.02–0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 21, 2014, 05:41:58 PM
According to Dr Nancy Bertler, of Victoria University's Antarctic Research Centre, this month, she and her team finished processing ice cores, taken from a depth of 763m at the bottom of the Roosevelt Island, on the eastern limits of the Ross Ice Shelf, as part of the RICE project.  The record contained in the ice was much longer than Dr Bertler had expected, and appeared to stretch back to the critical time in question, where the Ross Ice Shelf last collapsed abruptly.  Hopefully, we should see published findings in a year, or so.

See:
http://climatechange.umaine.edu/roosevelt_island_climate_evolution_rice (http://climatechange.umaine.edu/roosevelt_island_climate_evolution_rice)

http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11310259 (http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11310259)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 25, 2014, 12:15:14 AM
In the two linked internet articles, Will Thomas presents a historical primer on the coming WAIS collapse.  This excellent primer illustrates just how recent our understanding of the risks of the WAIS collapse, and it is very clear that there is so much more to learn about this risk, that I believe that most of the WAIS collapse will be actively occurring before the researchers have a full understanding of that risk.  Note that in the video of Rignot in the second link, Rignot states that if the ASE marine glaciers keep retreating at their present rate of retreat this portion of the WASI will be actively collapsing within two hundred years; however, the rate of the ASE marine glacier retreat is accelerating, which is why I believe that this portion of the WAIS will be actively collapsing sometime after 2040.


https://etherwave.wordpress.com/2014/05/22/a-historical-primer-on-wais-collapse-part-1-early-history/


https://etherwave.wordpress.com/2014/08/04/a-historical-primer-on-wais-collapse-pt-2-recent-history/

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 25, 2014, 12:22:10 AM
The following link leads to a March 2014 internet article by Bruce Milton, summarizing the nature and risks of abrupt climate change, including a discussion of the risks of a WAIS collapse:

http://truth-out.org/news/item/22469-abrupt-climate-change-no-bioperturbation (http://truth-out.org/news/item/22469-abrupt-climate-change-no-bioperturbation)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 28, 2014, 04:25:09 PM
While I posted about the findings of Weber et al 2014 in the Paleo-Evidence thread (see Reply #119 in the Paleo-Evidence thread), the following link to a New Zealand Herald article shows that the Antarctic Ice Sheet is capable of contributing at least one meter of sea level rise to the global total by 2100:

M. E. Weber, P. U. Clark, G. Kuhn, A. Timmermann, D. Sprenk, R. Gladstone, X. Zhang, G. Lohmann, L. Menviel, M. O. Chikamoto, T. Friedrich & C. Ohlwein, (2014), "Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation", Nature, (2014), doi:10.1038/nature13397


http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11315512 (http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11315512)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on September 12, 2014, 10:05:15 PM
The following reference provides a new reconstruction of Antarctic near-surface temperatures from 1958 – 2012 (see also Reply #3); and this reconstruction indicates that the recent positive trend for the SAM (partially due to both the ozone hole and the recent negative [La Nina dominated] phase of the ENSO), has been recently had a cooling effect on West Antarctica; however, I note that as we enter a positive [El Nino dominated] phase of the ENSO, and as the ozone hole heals itself, we can expect an acceleration of the rate of increase of the West Antarctic near-surface temperatures; which of course will serve to accelerate the rate of collapse of the WAIS:


Julien P. Nicolas and David H. Bromwich, (2014), "New reconstruction of Antarctic near-surface temperatures: Multidecadal trends and reliability of global reanalyses", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-13-00733.1 (http://dx.doi.org/10.1175/JCLI-D-13-00733.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00733.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00733.1)

Abstract: "A reconstruction of Antarctic monthly mean near-surface temperatures spanning 1958–2012 is presented. Its primary goal is to take advantage of a recently revised key temperature record from West Antarctica (Byrd) to shed further light on multidecadal temperature changes in this region. The spatial interpolation relies on a kriging technique aided by spatio-temporal temperature covariances derived from three global reanalyses (ERA-Interim, MERRA, and CFSR). For the full extent of the reconstruction, we find statistically significant annual warming in the Antarctic Peninsula and virtually all of West Antarctica, but no significant temperature change in East Antarctica. Importantly, the warming is of comparable magnitude both in central West Antarctica and in most of the Peninsula, rather than concentrated either in one or the other region as previous reconstructions have suggested. The Transantarctic Mountains act, for the temperature trends, as a clear dividing line between East and West Antarctica, reflecting the topographic constraint on warm air advection from the Amundsen Sea basin. The reconstruction also serves to highlight spurious changes in the 1979–2009 time series of the three reanalyses that reduces the reliability of their trends, illustrating a long-standing issue in high southern latitudes. The study concludes with an examination of the influence of the Southern Annular Mode (SAM) on Antarctic temperature trends. Our results suggest that the trend of the SAM toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in East Antarctica (as already well documented) and but also (only in fall) in West Antarctica."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on September 13, 2014, 01:13:22 AM
The linked reference, with an open access pdf, indicates that at the moment the grounding line zone for the  Union Glacier (in the WAIS) is in near-equilibrium, but that if the rate of ice mass loss were to accelerate in the future (say due to climate change) then this glacier has the potential for significant grounding line retreat:

Rivera, A., Zamora, R., Uribe, J. A., Jaña, R., and Oberreuter, J. , (2014), "Recent ice dynamic and surface mass balance of Union Glacier in the West Antarctic Ice Sheet", The Cryosphere, 8, 1445-1456, doi:10.5194/tc-8-1445-2014.

http://www.the-cryosphere.net/8/1445/2014/tc-8-1445-2014.html (http://www.the-cryosphere.net/8/1445/2014/tc-8-1445-2014.html)

Abstract: "Here we present the results of a comprehensive glaciological investigation of Union Glacier (79°46' S/83°24' W) in the West Antarctic Ice Sheet (WAIS), a major outlet glacier within the Ellsworth Mountains. Union Glacier flows into the Ronne Ice Shelf, where recent models have indicated the potential for significant grounding line zone (GLZ) migrations in response to changing climate and ocean conditions. To elaborate a glaciological base line that can help to evaluate the potential impact of this GLZ change scenario, we installed an array of stakes on Union Glacier in 2007. The stake network has been surveyed repeatedly for elevation, velocity, and net surface mass balance. The region of the stake measurements is in near-equilibrium, and ice speeds are 10 to 33 m a−1. Ground-penetrating radars (GPR) have been used to map the subglacial topography, internal structure, and crevasse frequency and depth along surveyed tracks in the stake site area. The bedrock in this area has a minimum elevation of −858 m a.s.l., significantly deeper than shown by BEDMAP2 data. However, between this deeper area and the local GLZ, there is a threshold where the subglacial topography shows a maximum altitude of 190 m. This subglacial condition implies that an upstream migration of the GLZ will not have strong effects on Union Glacier until it passes beyond this shallow ice pinning point."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on September 14, 2014, 06:34:49 AM
Feldmann and Levermann, Postsdam, with the PISM model
pull a plug on one unstable icesheet and you drain more than one ...

http://www.the-cryosphere-discuss.net/8/4885/2014/tcd-8-4885-2014.pdf (http://www.the-cryosphere-discuss.net/8/4885/2014/tcd-8-4885-2014.pdf)

and pollard and diconto are pessimistic also, they previously had nice ANDRILL related stuff

http://adsabs.harvard.edu/abs/2014EGUGA..1613539D (http://adsabs.harvard.edu/abs/2014EGUGA..1613539D)

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on September 14, 2014, 08:04:53 AM
Feldmann and Levermann, Postsdam, with the PISM model
pull a plug on one unstable icesheet and you drain more than one ...

http://www.the-cryosphere-discuss.net/8/4885/2014/tcd-8-4885-2014.pdf (http://www.the-cryosphere-discuss.net/8/4885/2014/tcd-8-4885-2014.pdf)

and pollard and diconto are pessimistic also, they previously had nice ANDRILL related stuff

http://adsabs.harvard.edu/abs/2014EGUGA..1613539D (http://adsabs.harvard.edu/abs/2014EGUGA..1613539D)

sidd

"pessimistic" is relativistic
The IPCC is self censoring so ANY line of reason that boarders on "realistic"
sounds "pessimistic"

The simple fact is that the IPCC working group WGI suffers from a FATAL TYPE I ERROR AVOIDANCE BIAS.

The report is inherently conservative and the authors know this.  There is going to be no other last chance for humanity than this next 2 years.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on September 14, 2014, 09:10:54 AM
DeConto and Pollard write:
"In the most extreme RCP scenarios, subsequent retreat of the Siple Coast margin results in the near-total collapse of the West Antarctic Ice Sheet (WAIS) within a few centuries, followed by retreat into the deep subglacial basins underlying the East Antarctic Ice Sheet (EAIS). Antarctica is shown to contribute up to 9m of sea level rise within the next five centuries. Under such high greenhouse gas conditions, atmospheric warming alone is sufficient to cause substantial ice retreat, without any influence from ocean warming and sub-ice melt. Conversely, in the absence of increasing atmospheric temperatures, very little ocean warming (<0.5 C) is required to trigger substantial WAIS retreat, even if present-day atmospheric temperatures are held constant. Given current rates of ocean heat uptake, this has serious implications for future commitment to sea level rise regardless of future greenhouse gas emissions."

So what are we talking about here? A risk of about maybe 15m total SLR by 2500, including about a 4m contribution from GIS? That would be more than double the current IPCC-worst case based on physical models, and in line with some estimates based on semi-empirical models.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on September 14, 2014, 08:42:47 PM
I must agree with jai that "pessimistic" is a relative term, and I view both the Feldmann & Levermann, and the DeConto & Pollard, findings as representing lower-bound solutions to the non-stoppable ASLR risks that the world is facing at the moment.

I am deeply concerned that the coming (starting now and accelerating for at least the next 25 to 30-years) synergy between the North Atlantic (due to the AMO), and the North Pacific (due to the PDO/IPO), Oceans (see the "Forcing" thread); will guarantee an acceleration of both mean global warming, and SLR contribution from the WAIS, over the coming decades.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on September 14, 2014, 11:51:34 PM
"The IPCC is self censoring ..."

The papers i linked to were published long after IPCC AR5 review period. I want to clarify that my last post does not support such a notion in the least.

As to the judgements of the IPCC, take it to a different thread please. I will defer to AbrptSLR, since he started this thread, but i was under the impression we were discussing the _latest_ research into WAIS collapse here and not the putative motivations of the IPCC.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on September 15, 2014, 04:31:23 AM
All,

While I do believe that the IPCC has consistently erred on the side of least drama (as I believe that the majority of scientists have also done), with regard to SLR; I concur with sidd that in this thread it is best to try to focus on discussing the latest research about the potential collapse of the WAIS; whether those estimates are conservative, or not. 

I certainly keep learning from everyone's posts in this thread; but when I want to discuss policy I try to post in other threads (such as the "Philosophical" or the "Challenging Misconceptions", threads)  in this "Antarctica" folder, or else in the "Policy & solutions", or the "Consequences" folders.

Certainly, the rate (high or low) of expected SLR is a fully legitimate topic for this thread, so long as a logical case is presented.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on September 21, 2014, 05:33:50 PM
I felt bad that I requested that jai provide logical evidence that the IPCC was biased, if he was going to state as much in this thread, and then I stated that I believe that the IPCC (and most scientist) err on the side of least drama, without providing any logical supporting evidence.

Therefore, I provide the following link to a free access PDF of the Brysse et al (2012) paper that presents evidence that most scientists (and the IPCC in particular) are biased toward cautious estimates that the authors define as "erring on the side of least drama", ESLD.  ESLD distorts projections particularly with regard to the SLR risks from the possible collapse of the WAIS as discussed in the second linked 2014 reference by the New Yorker magazine.

Keynyn Brysse, Naomi Oreskes, Jessica O’Reilly, and Michael Oppenheimer, (2012), "Climate change prediction: Erring on the side of least drama?", Global Environmental Change, 23: 327-337

https://www.wageningenur.nl/upload_mm/2/0/b/f2601035-3fa4-41cb-b0f5-77de713695fc_erring.pdf (https://www.wageningenur.nl/upload_mm/2/0/b/f2601035-3fa4-41cb-b0f5-77de713695fc_erring.pdf)

Abstract: "Over the past two decades, skeptics of the reality and significance of anthropogenic climate change have frequently accused climate scientists of ‘‘alarmism’’: of over-interpreting or overreacting to evidence of human impacts on the climate system. However, the available evidence suggests that scientists have in fact been conservative in their projections of the impacts of climate change. In particular, we discuss recent studies showing that at least some of the key attributes of global warming from increased atmospheric greenhouse gases have been under-predicted, particularly in IPCC assessments of the physical science, by Working Group I. We also note the less frequent manifestation of over-prediction of key characteristics of climate in such assessments. We suggest, therefore, that scientists are biased not toward alarmism but rather the reverse: toward cautious estimates, where we define caution as erring on the side of less rather than more alarming predictions. We call this tendency ‘‘erring on the side of least drama (ESLD).’’ We explore some cases of ESLD at work, including predictions of Arctic ozone depletion and the possible disintegration of the West Antarctic ice sheet, and suggest some possible causes of this directional bias, including adherence to the scientific norms of restraint, objectivity, skepticism, rationality, dispassion, and moderation. We conclude with suggestions for further work to identify and explore ESLD."

See also:

http://www.newyorker.com/tech/elements/the-west-antarctic-ice-sheet-melt-defending-the-drama (http://www.newyorker.com/tech/elements/the-west-antarctic-ice-sheet-melt-defending-the-drama)

&

http://environment.harvard.edu/about/faculty/naomi-oreskes (http://environment.harvard.edu/about/faculty/naomi-oreskes)

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on October 05, 2014, 03:32:17 PM
While not new, I thought that I would provide the following link to the National Academy of Sciences, NAS, website on their 2013 report on abrupt climate change, which includes the attached image indicating that a partial collapse of the WAIS is plausible this century and that if it did it could triple the current projections for SLR by 2100 to roughly over 3m.

http://nas-sites.org/americasclimatechoices/other-reports-on-climate-change/2013-2/abrupt-impacts-of-climate-change/ (http://nas-sites.org/americasclimatechoices/other-reports-on-climate-change/2013-2/abrupt-impacts-of-climate-change/)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on October 05, 2014, 03:52:10 PM
While the linked GOCE ice mass loss findings issued by the ESA (see the following link) was discussed in the PIG/Thwaites 2012 - 2040-2060 thread, I think that it is good to post in this thread as this findings are key to the potential collapse of the WAIS.

http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_reveals_gravity_dip_from_ice_loss (http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_reveals_gravity_dip_from_ice_loss)

Furthermore, I note that the ESA is now working to extend the GOCE to the entire Antarctic continent, and as indicated by the attached Cryosat plot, it is likely that the extended GOCE study will find significant ice mass loss near the Totten Glacier in the EAIS.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 02, 2014, 01:56:13 AM
While I have previously posted about the following reference (when it was published in the Spring of 2014), the following provides a link to an open access pdf, and I provide the four attached images from this reference.  The first image provides a table of ice flux for the years and ASE marine glaciers listed.  This table indicates that the total annual ice flux from the ASE is comparable to the annual ice mass loss from the Greenland Ice Sheet (see the following link and extract to the Arctic Report Card Update for 2013: Greenland Ice Sheet).  The second attached image graphically shows the individual and total ice fluxes from the ASE marine glaciers; indicating that the flux from Thwaites Glacier is continuing accelerate, while the other marine glaciers have temporarily plateaued (possible due to the recent La Nina and ENSO neutral conditions).  The third and fourth attached images show different representations of the ice velocities for these marine glaciers (as noted on the images).  Again, I am concerned that a strong El Nino in 2015 could trigger an acceleration of ice flux from all of the ASE marine glaciers (but particularly from the PIG and the Thwaites Glacier):

Mouginot, J., E. Rignot, and B. Scheuchl, (2014), "Sustained increase in ice discharge from the Amundsen Sea Embayment, West Antarctica, from 1973 to 2013", Geophys. Res. Lett., 41, doi:10.1002/2013GL059069.

http://www.ess.uci.edu/researchgrp/erignot/files/grl51433.pdf (http://www.ess.uci.edu/researchgrp/erignot/files/grl51433.pdf)

Abstract:  "We combine measurements of ice velocity from Landsat feature tracking and satellite radar interferometry, and ice thickness from existing compilations to document 41 years of mass flux from the Amundsen Sea Embayment (ASE) of West Antarctica. The total ice discharge has increased by 77% since 1973. Half of the increase occurred between 2003 and 2009. Grounding-line ice speeds of Pine Island Glacier stabilized between 2009 and 2013, following a decade of rapid acceleration, but that acceleration reached far inland and occurred at a rate faster than predicted by advective processes. Flow speeds across Thwaites Glacier increased rapidly after 2006, following a decade of near-stability, leading to a 33% increase in flux between 2006 and 2013. Haynes, Smith, Pope, and Kohler Glaciers all accelerated during the entire study period. The sustained increase in ice discharge is a possible indicator of the development of a marine ice sheet instability in this part of Antarctica."

Arctic Report Card Update for 2013: Greenland Ice Sheet:
http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html (http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html)

Extract: "From the end of April 2012 through the end of April 2013, which corresponds reasonably well to the period between the beginning of the 2012 and 2013 melt seasons, the cumulative ice sheet loss was 570 Gt, over twice the average annual loss rate of 260 Gt y-1 during 2003-2012. The 2012-2013 mass loss is the largest annual loss rate for Greenland in the GRACE record, mostly reflecting the large mass loss during the summer of 2012 (Tedesco et al. 2013b). "
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 02, 2015, 02:34:43 AM
Nice talk and simulation of potential collapse of WAIS by Tony Payne of University of Bristol, starting with the simulation at 30m41s:
http://youtu.be/NXjYpilWtQs?t=30m41s (http://youtu.be/NXjYpilWtQs?t=30m41s)

In this simulation it takes 400 years for a big part of WAIS to collapse, mainly because Thwaites stays pretty stable for about 200 years.

But Payne shows earlier in the talk how much this apparent stability of the glaciers in models depends on the resolution of these models. So I don't know what forcing scenario was used in this particular simulation, but it had a mixed resolution with 150m per grid cell as the highest. What would happen with even higher resolution? And how complete are these models apart from the resolution?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 02, 2015, 03:48:45 AM
Lennart,

Thank you very much.  I liked the part where he talks about the SW Tributary Glacier that currently feeds into the PIIS, can trigger the acceleration of the Thwaites Glacier.  Also, as this conference was held in Sept 2013, it occurred well before Eric Rignot's papers and comments that large parts of the WAIS could be lost in the next 100 to 200 years.  It will be interesting to watch as more research refines our understanding of this complex topic.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 02, 2015, 11:07:10 AM
ASLR,
Yes, as a matter of fact I asked Rignot what he thinks of this simulation and he thinks it's still quite limited. He said this model is no better than the others. It is intrinsically very difficult for such models to collapse an ice sheet quickly: no calving, no melt at the grounding line, no 3D treatment of the grounding line, and bed with erroneous mountain peaks that should not be there.

I'll also ask Richard Alley what he thinks of it. He said earlier he has two papers on Thwaites coming out soon, in the coming week, together with Pollard and DeConto.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 03, 2015, 05:05:45 PM
Lennart,

Of course I agree with all of Rignot's points, and I look forward to seeing the Alley, Pollard & DeConto papers on Thwaites.  However, as you are well aware from all of my prior posts (in this thread and others), there are additional points that these excellent researchers are not yet able to include in their projections that could still further accelerate the degradation of the WAIS (beyond the 1/3rd level of degradation projected by Rignot within the next 100 years), which to repeat myself, include:

1.  The ice flow velocity of the Southwest (SW) Tributary Glacier to the PIIS could double as soon as the next austral summer due to a possible major calving event of the PIIS (which is currently buttressing the SW Tributary Glacier) as discussed in Reply #261 of the "PIG has Calved" thread:

http://forum.arctic-sea-ice.net/index.php/topic,429.250.html (http://forum.arctic-sea-ice.net/index.php/topic,429.250.html)

2.  As can be seen in the attached plot, the current NOAA ENSO forecast gives a high probability of a strong El Nino event in 2015; and as you know a strong El Nino event can accelerate the volume of warm CDW advected into the ASE due to the interaction of El Nino events with the Amundsen (Bellingshausen) Sea Low.

3.  The majority of the observed decay rate of the WAIS glaciers has been taken during the negative phase of the PDO cycle, which favor La Nina events; and as we have now entere a positive phase of the PDO cycle we can expect an increase in the number and intensity of El Nino events relative to La Nina events.

4.  The ECS (equilibrium climate sensitivity) may exceed 4 C rather than the currently assumed 3 C; and by 2100 the effective climate sensitivity may well exceed 6 C if we continue on a BAU pathway which will activate numerous positive feedbacks.  If so the chances of increased surface ice melting (and or rainfall) in the WAIS perimeter areas increases dramatically.  Also, note that a BAU pathway would markedly increase the seafloor ocean water temperatures in both the Southern Ocean and the Arctic Sea.

5.  It is likely that before 2070 the Antarctic Sea Ice extent will decrease sharply, which will promote wind driven ocean currents to carry even more warm CDW to further accelerate the retreat of the grounding lines of key WAIS marine glaciers.

6.  The geothermal basal heat effect has not yet been adequately modeled in any WAIS glacial models and particularly not for the Thwaites Glacier.

7.  The likely accelerated ice mass loss from the Greenland Ice Sheet in the coming decades (see the Greenland folder) will at least temporarily raise sea levels around Antarctica; which will at least temporarily serve to reduce the stability of the WAIS marine glaciers.

I could go on but I have nothing new to add to the points that I have made previously in all of the various threads of the Antarctic folder. 

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 03, 2015, 10:43:17 PM
The following abstract from DeConto & Pollard (2014) confirms the disturbing message that I have been conveying by saying:
 
"… the same model shows the potential for massive ice and freshwater discharge beginning in the second half of this century.
 …
In the more aggressive (and arguably more likely) RCP8.5 scenario, Pine Island Bay retreat is followed by more massive retreat of the entire WAIS, and eventual ice retreat into deep East Antarctic basins.

Here, we demonstrate that large portions of the Antarctic Ice Sheet (in West and East Antarctica) can retreat on relatively short (decadal to centennial) timescales, posing a serious threat to global populations."


DeConto R, and Pollard D., (2014), "Antarctica's potential contribution to future sea-level rise", SCAR - COMNAP Symposium

http://www.scar2014.com/assets/SCAR_and_COMNAP_2014_Abstract_Document.pdf (http://www.scar2014.com/assets/SCAR_and_COMNAP_2014_Abstract_Document.pdf)

Abstract: "A hybrid ice sheet-shelf model with freely migrating grounding lines is improved by accounting for 1) surface meltwater enhancement of ice shelf calving; and 2) the structural stability of thick (>800 m), marine-terminating (tidewater) grounding lines. When coupled to a high-resolution atmospheric model with imposed or simulated ocean temperatures, the new model is demonstrated to do a good job simulating past geologic intervals with high (albeit uncertain) sea levels including the Pliocene (3Ma; +20 ±10m) and the Last Interglacial (130-115ka; +4-9m).  When applied to future IPCC CMIP5 RCP greenhouse gas forcing scenarios with ocean temperatures provided by the NCAR CCSM4, the same model shows the potential for massive ice and freshwater discharge beginning in the second half of this century. In both RCP2.6 and 8.5 scenarios considerable retreat begins in the Pine Island Bay region of West Antarctica. In the more aggressive (and arguably more likely) RCP8.5 scenario, Pine Island Bay retreat is followed by more massive retreat of the entire WAIS, and eventual ice retreat into deep East Antarctic basins. During peak rates of retreat, freshwater discharge exceeds 1 Sv and exceeds 0.2 Sv for several centuries with potential to disrupt ocean circulation in addition to contributing between 2m and 9m sea level rise within the next 500 years. Here, we demonstrate that large portions of the Antarctic Ice Sheet (in West and East Antarctica) can retreat on relatively short (decadal to centennial) timescales, posing a serious threat to global populations."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 03, 2015, 11:36:14 PM
ASLR,

You've probably seen this before, but here's what Jim Hansen said in the documentary Earth Under Water (at 36m07s):
http://youtu.be/baGrtqyWSRM?t=36m7s (http://youtu.be/baGrtqyWSRM?t=36m7s)

If we go to 1000 ppm then he thinks we could melt all the ice on the planet in less than 1000 years, so 70-75m in total.

In that documentary Harold Wanless speaks of a worst-case scenario of 1.5 meter/decade, so 15 meter/century. That would be about 20 times faster than the average rate of SLR during interglacials, according to Rohling et al 2013. Assuming a forcing of about 4.5 W/m2 per century, averaged over 2000-2300, this would be at least 30x stronger than the 0.15 W/m2 maximum forcing per century during interglacials.

In that scenario SLR by 2100 would be 2m (7 feet), by 2200 it would be 7m (22 feet), and by 2300 it would be 22m (72 feet), according to the documentary.

At that speed (15 meter/century) all the ice would be gone before 2700. Do you think that would really be possible, if we go beyond 1000 ppm? And not only possible, but likely, as Hansen believes?

Or could there also be negative feedbacks, such as an iceberg cooling effect (Hansen & Sato) and kinematic constraints (Pfeffer), that would make SLR rate-limited?

I asked Rignot, Alley and David Vaughan if they think 3-4 meters in 3-4 decades is possible, but they apparently don't like to give a direct answer. Rignot thinks 5 meter/century cannot be excluded. Alley is more cautious, but doesn't seem to fully exclude 5 meter/century either. Vaughan thinks a few meters per century may be possible.

Rignot and Vaughan do seem to think 3-4 meters in less than a decade is impossible. Alley just said to wait for his new paper in the pipeline. Rignot also seems to think 1 meter/decade is not possible.

But maybe thery're all just more cautious or reticent or conservative than Hansen and Wanless?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 04, 2015, 12:00:26 AM
Lennart,

Thanks.  I have seen this 2013 video before.  My biggest concern is that surface meltwater will enter crevasses upstream of the calving face of thick (more than 800m) marine ice streams, which could rapidly launch a fleet of icebergs.  I believe we might see this in the Jakobshavn Glacier within the next ten years, and possibly in the WAIS (Thwaites) sometime after 2070 (at the earliest on a BAU pathway).  We will need to wait for more sophisticated models before we know the specific timing.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 04, 2015, 12:38:20 AM
ASLR,

Great find, that abstract by DeConto & Pollard. So 9m from Antarctica by 2500 would make maybe 14m by 2500 in total, so 3-4 meters/century? Looks like their model is pretty good, but maybe not complete yet.

Alley also pointed to Bassis & Jacobs 2013, so a question is if DeConto & Pollard have included the findings of that paper into their model, amongst other processes.

Interesting times, with plenty of reason for concern.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 04, 2015, 02:09:28 AM
ASLR,

Great find, that abstract by DeConto & Pollard. So 9m from Antarctica by 2500 would make maybe 14m by 2500 in total, so 3-4 meters/century? Looks like their model is pretty good, but maybe not complete yet.

Alley also pointed to Bassis & Jacobs 2013, so a question is if DeConto & Pollard have included the findings of that paper into their model, amongst other processes.

Interesting times, with plenty of reason for concern.

Lennart,

I suspected that the instability work of Bassis & Jacobs 2013 would be involved in any rapid rate of calving of ice bergs from thick marine glaciers like Thwaites.

Also, as sea level rise due to melting glaciers is about ~ 0.01 Sv, and as glaciers currently contribute about 0.71mm/year to SLR; thus the peak 1.0 Sv discharge that DeConto & Pollard 2014 cite is equal to a rate of SLR of about 0.071meters per year, or about 1/30th the rate that Jackson cited.

Best,
ASLR

Edit: I fixed a math error
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 04, 2015, 07:43:39 AM
ooo, tanx, bassis was the paper i could not recall in the other thread

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 04, 2015, 10:07:57 AM
as sea level rise due to melting glaciers is about ~ 0.01 Sv, and as glaciers currently contribute about 0.71mm/year to SLR; thus the peak 1.0 Sv discharge that DeConto & Pollard 2014 cite is equal to a rate of SLR of about 0.071meters per year, or about 1/30th the rate that Jackson cited.

ALSR,

Thanks, I'd not realized yet that 1 Sv of meltwater sustained for a year contributes about 86 mm to SLR. So add in thermal expansion and meltwater from GIS, and about 100 mm/yr of SLR would be possible as a peak rate, according to DeConto & Pollard. This is also the maximum rate of SLR thought plausible in Rohling et al 2013, based only on geological evidence. Sustained for a decade that would be 1 meter/decade. Still about an order of magnitude smaller than Jackson's remark, but plenty abrupt enough for human societies, it seems.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 04, 2015, 11:19:39 AM
Lennart,

I agree that while 1 m/decade of SLR (for RCP 8.5) is about an order of magnitude slower than Jackson's remark, it is certainly plenty abrupt for society if this were to occur before the end of this century (but after 2050).  Nevertheless, in the following quote DeConto & Pollard cite that the peak freshwater discharge exceeds 1 Sv before slowing down to 0.2 Sv for several centuries, and may contribute 9m to SLR in the next 500 years.  As 0.2 Sv is 1.72 meters of SLR per century, and if we take several centuries to mean 4 centuries, then this would mean 6.88m of SLR from 2100 to 2500; which would leave 2.12m of SLR from 2015 to 2100 (only coming from Antarctica).  If you add in contributions from the GIS, mountain glaciers, and steric sources it would seem that following RCP 8.5 we could be near 3m of eustatic SLR by 2100, based on DeConto & Pollard.

DeConto & Pollard 2014 Quote: "During peak rates of retreat, freshwater discharge exceeds 1 Sv and exceeds 0.2 Sv for several centuries with potential to disrupt ocean circulation in addition to contributing between 2m and 9m sea level rise within the next 500 years. Here, we demonstrate that large portions of the Antarctic Ice Sheet (in West and East Antarctica) can retreat on relatively short (decadal to centennial) timescales, posing a serious threat to global populations."

However, as Hansen warns about the possibility of 5m of SLR in the next century, we should all note that DeConto & Pollard (2014) may be state-of-the-art, it certainly is not definitive, and other possible sources of accelerated ice mass loss from the WAIS include:

1. The high geothermal basal heat in the BSB will likely reduce basal friction, which according to the Jakobshavn Effect would possibly increase calving beyond that assumed in the Bassis & Jacobs 2013 model.
2.  As the seaways through the WAIS open, the ocean currents will change directions; which should increase ice mass loss.
3. As global warming continues, the storms in the Southern Ocean will become more severe which could accelerate calving rates still further.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 04, 2015, 03:47:15 PM
ASLR,
That would be one possibility. Another would be that peak discharge would occur somewhere between 2100-2200. But the potential risk that 1 meter/decade would be reached even before 2100 is indeed what counts most from a risk-management perspective. I wonder when peak discharge is reached in the model of DeConto & Pollard, and under what assumptions.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 04, 2015, 03:58:03 PM
Lennart,

Hopefully when the Alley, DeConto & Pollard paper(s) come-out next week we will get more information, not only about when the peak discharge is projected to occur, but also whether their model is for all of Antarctica (in which case I question what their resolution is) or just for the WAIS and immediately adjoining EAIS (in which case I question what is the projected contribution to SLR from the un-modeled portions of the EAIS).  In any event, given the rapid rate of change in projected AIS & GIS contributions to SLR, I will not be convinced that we have a reasonably accurate projection for SLR until the end of the Earth System Model - ACME program (or possibly later).

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 04, 2015, 04:41:46 PM
Good points, ASLR. In the Payne-model referred to earlier they had modelled WAIS with a combination of six different resolutions, with 150m the highest. For a timescale of five centuries we would really need to know how the rest of EAIS behaves to put the maximum 9m contribution in the model of DeConto & Pollard into perspective.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 05, 2015, 11:27:24 AM
Pollard & DeConto 2012 describes a model for Antarctica with 10-40 km grid resolution:
http://www.geosci-model-dev.net/5/1273/2012/gmd-5-1273-2012.pdf (http://www.geosci-model-dev.net/5/1273/2012/gmd-5-1273-2012.pdf)

If that's the same model and resolution used in their model mentioned above, then it seems higher resolutions could produce even faster SLR, based on the example of Payne's model.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 06, 2015, 09:16:24 PM
The linked article provides evidence that geothermal heat flux is probably contributing to relatively high rates of basal ice melting beneath the Thwaites Glacier; which if true (and there are multiple lines of evidence of this) this basal meltwater would almost certainly contribute to the reduced stability of the marine ice sheet above the Byrd Subglacial Basin, and by extension the rest of the WAIS:

Theresa M. Damiani, Tom A. Jordan, Fausto Ferraccioli, Duncan A. Young, Donald D. Blankenship, (2014), "Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica", Earth and Planetary Science Letters, Volume 407, 1 December 2014, Pages 109–122, doi:10.1016/j.epsl.2014.09.023


http://www.sciencedirect.com/science/article/pii/S0012821X14005780 (http://www.sciencedirect.com/science/article/pii/S0012821X14005780)


Abstract: "Thwaites Glacier has one of the largest glacial catchments in West Antarctica. The future stability of Thwaites Glacier's catchment is of great concern, as this part of the West Antarctic Ice Sheet has recently been hypothesized to already be en route towards collapse. Although an oceanic trigger is thought to be responsible for current change at the grounding line of Thwaites Glacier, in order to determine the effects of this coastal change further in the interior of the West Antarctic Ice Sheet it is essential to also better constrain basal conditions that control the dynamics of fast glacial flow within the catchment itself. One major contributor to fast glacial flow is the presence of subglacial water, the production of which is a result of both glaciological shear heating and geothermal heat flux. The primary goal of our study is to investigate the crustal thickness beneath Thwaites Glacier, which is an important contributor to regional-scale geothermal heat flux patterns. Crustal structure is an indicator of past tectonic events and hence provides a geophysical proxy for the thermal status of the crust and mantle. Terrain-corrected Bouguer gravity disturbances are used here to estimate depths to the Moho and mid-crustal boundary. The thin continental crust we reveal beneath Thwaites Glacier supports the hypothesis that the West Antarctic Rift System underlies the region and is expressed topographically as the Byrd Subglacial Basin. This rifted crust is of similar thickness to that calculated from airborne gravity data beneath neighboring Pine Island Glacier, and is more extended than crust in the adjacent Siple Coast sector of the Ross Sea Embayment. A zone of thinner crust is also identified near the area's subaerial volcanoes lending support to a recent interpretation predicting that this part of Marie Byrd Land is a major volcanic dome, likely within the West Antarctic Rift System itself. Near-zero Bouguer gravity disturbances for the subglacial highlands and subaerial volcanoes indicate the absence of supporting crustal roots, suggesting either (1) thermal support from a warm lithosphere or alternatively, and arguably less likely; (2) flexural support of the topography by a cool and rigid lithosphere, or (3) Pratt-like compensation. Although forward modeling of gravity data is non-unique in respect to these alternative possibilities, we prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself. Our new crustal thickness estimates and geothermal heat flux inferences in the Thwaites Glacier region are significant both for studies of the structure of the broader West Antarctic Rift System and for assessments of geological influences on West Antarctic Ice Sheet dynamics and glacial isostatic adjustment models."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 06, 2015, 09:26:45 PM
The following link leads to a very nice Part 1 summary of the recent research history (from about 1968 to about the late 1990's) on the stability of the WAIS, and which includes a very nice video by NASA about Rignot et al's 2014 research on this topic:

https://etherwave.wordpress.com/2014/05/22/a-historical-primer-on-wais-collapse-part-1-early-history/#comment-7466

I look forward to seeing Part 2 of this summary when it is posted.

Nice overview!
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 06, 2015, 10:01:32 PM
In the two linked internet articles, Will Thomas presents a historical primer on the coming WAIS collapse.  This excellent primer illustrates just how recent our understanding of the risks of the WAIS collapse, and it is very clear that there is so much more to learn about this risk, that I believe that most of the WAIS collapse will be actively occurring before the researchers have a full understanding of that risk.  Note that in the video of Rignot in the second link, Rignot states that if the ASE marine glaciers keep retreating at their present rate of retreat this portion of the WASI will be actively collapsing within two hundred years; however, the rate of the ASE marine glacier retreat is accelerating, which is why I believe that this portion of the WAIS will be actively collapsing sometime after 2040.

https://etherwave.wordpress.com/2014/05/22/a-historical-primer-on-wais-collapse-part-1-early-history/

https://etherwave.wordpress.com/2014/08/04/a-historical-primer-on-wais-collapse-pt-2-recent-history/

And thanks for posting part 2 as well.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 06, 2015, 10:23:41 PM
While I posted about the findings of Weber et al 2014 in the Paleo-Evidence thread (see Reply #119 in the Paleo-Evidence thread), the following link to a New Zealand Herald article shows that the Antarctic Ice Sheet is capable of contributing at least one meter of sea level rise to the global total by 2100:

M. E. Weber, P. U. Clark, G. Kuhn, A. Timmermann, D. Sprenk, R. Gladstone, X. Zhang, G. Lohmann, L. Menviel, M. O. Chikamoto, T. Friedrich & C. Ohlwein, (2014), "Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation", Nature, (2014), doi:10.1038/nature13397

http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11315512 (http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11315512)

Melt events could occur in just a decade, syas this quote from the article:
Quote
The research revealed that Antarctica's vast ice sheet collapsed at least eight times during a period between 9000 and 20,000 years ago. Sediment preserved in drill cores retrieved from the ice showed that while these mass collapses had happened every couple of hundred years, the melt events could occur in just a decade. "It's like an earthquake - for a long time, nothing happens, but when it does, boom - it happens all at the same time,"
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 07, 2015, 12:08:23 AM
The linked article focuses on the coming collapse of the WAIS; however, I like the quote from Kevin Trenberth concerning the question of whether we are currently in a climate crisis or not, as I agree that our greatest crisis is a lack of human will power to address climate change in a manner commensurate with the magnitude of the problem.  Until society shows both the wisdom  and the backbone necessary to properly address our current/coming climate situation, I will continue to contend that we are currently experiencing a Climate Crisis (unless one is over 50 years old and does not care what happens to future generations, at least from a collapse of the WAIS):

http://blogs.discovermagazine.com/imageo/2014/12/05/west-antarctic-ice-sheet-not-collapsed-new-findings-concerning-indicate-climate-crisis/ (http://blogs.discovermagazine.com/imageo/2014/12/05/west-antarctic-ice-sheet-not-collapsed-new-findings-concerning-indicate-climate-crisis/)

Extract: "3:10 p.m. MST, 12/5/14: For the second story under the “Climate in Crisis” headline in Discover’s Year in Science issue, I interviewed Kevin Trenberth, a senior scientist at the National. He shared these comments with me by email:

Quote
We do not have to solve the problem today, but we have to start, and the crisis is that we have not really started.  Or we have not started in a way that is commensurate with the magnitude of the problem, yet. I add the “yet” with optimism that maybe we will get going. And of course there are at least two aspects to this.  The first is emissions [of carbon dioxide and other greenhouse gases] and their mitigation. And the second is adaptation and adequately planning for the consequences, given that mitigation will not suffice.  But mitigation may make the consequences much more manageable.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 07, 2015, 12:38:18 AM
Here's the new paper by Pollard, DeConto & Alley 2015:
http://www.sciencedirect.com/science/article/pii/S0012821X14007961 (http://www.sciencedirect.com/science/article/pii/S0012821X14007961)

Abstract
"Geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last ∼25 million years, at times reaching 20 m or more above modern. If correct, this implies substantial variations in the size of the East Antarctic Ice Sheet (EAIS). However, most climate and ice sheet models have not been able to simulate significant EAIS retreat from continental size, given that atmospheric CO2 levels were relatively low throughout this period. Here, we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model–data conflict. In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. The mechanisms are highly parameterized and should be tested by further process studies. But if accurate, they offer one explanation for past sea-level high stands, and suggest that Antarctica may be more vulnerable to warm climates than in most previous studies."

So that could be 3m within a century from WAIS alone, and 5m by 2200 from AIS. So maybe 7-8m  by 2200 including GIS, GIC and thermal expansion?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 07, 2015, 01:07:43 AM
Lennart,

Great catch.  The attached figure 4 from Pollard, DeConto & Alley (2015) clearly shows that (as an approximation) with both hydrofracturing and cliff failures, the WAIS could contribute 2m to 3m to SLR by 2100.

Caption: "Fig. 4. Global mean equivalent sea level rise in warm-climate simulations. Time series of global mean sea level rise above modern are shown, implied by reduced Antarctic ice volumes. The calculation takes into account the lesser effect of melting ice that is originally grounded below sea level. Cyan: with neither cliff failure nor melt-driven hydrofracturing active. Blue: with cliff failure active. Green: with melt-driven hydrofracturing active. Red: with both these mechanisms active. Geographic ice distributions for the latter run are shown in Fig. 3, and for the other runs in Fig. 5."

Edit: I note that the values given in the attached image are for a simple Pliocene-like warming scenario, and not for any RCP or SRES pathways.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 07, 2015, 04:54:18 PM
Pollard et al say:
"The equivalent eustatic sea level rise reaches 5 m after ∼200 yr and 17 m after ∼3000 yr (Fig. 4, red curve), similar in magnitude to albeit uncertain proxy estimates of past sea-level variations mentioned above. About 3 mesl comes from West Antarctica, and the remaining ∼14 mesl comes from East Antarctic basins."

And:
"To investigate the impact of the cliff-failure and melt-driven hydrofracture mechanisms, the ice-sheet model is run forward in time, forced by climate representative of past warm periods. Simulations are started from a previous spin-up of modern Antarctica using observed climatology. An instantaneous change to a warmer climate is applied, broadly representative of a warm Pliocene period. The past warm atmospheric climate is obtained from the RegCM3 Regional Climate Model (Pal et al., 2007) applied over Antarctica with some physical adaptations for polar regions, and with 400 ppmv CO2 and an orbit yielding particularly strong austral summers (DeConto et al., 2012). Detailed simulation of ocean warming beneath Antarctic ice shelves is currently not feasible on these time scales, so a simple uniform increment of View the MathML source is added to modern observed ocean temperatures, broadly consistent with circum-Antarctic warming in Pliocene paleo-oceanic reconstructions (Dowsett et al., 2009)."

And:
"For simplicity, this paper uses step-function climate forcing representative of generalized warming episodes during the late Cenozoic. A natural next step will be to use time-dependent forcing to model specific warm events or periods of the past and compare with available data, such as warm Pliocene intervals ∼5–3 Ma, MIS-31 at ∼1.08 Ma, and strong Pleistocene interglacials (Naish et al., 2009, Raymo and Mitrovica, 2012 and O'Leary et al., 2013). Another important step will be the use of regional ocean models to resolve different oceanic responses in different Antarctic embayments (Hellmer et al., 2012)...
The main aim of adding hydrofracturing and cliff failure was to produce total Antarctic retreat consistent with albeit poorly constrained past sea-level data, and no effort was made to adjust the rate of retreat. The time scale that emerges for West Antarctic collapse (∼3 m contribution to global sea-level rise within O(100) years after a step-function warming) is an order of magnitude faster than previous estimates for the next century, which range from ∼0.1 to 0.6 m by 2100 AD (Pfeffer et al., 2008, Levermann et al., 2014 and Joughin et al., 2014). The modeling approaches in Pfeffer et al. and Levermann et al. are very different, and our study is not directly applicable to the future because of our step-function climate change, Pliocene-like climate, and homogeneous ocean warming. But even so, our predicted WAIS retreat rates are much faster than might be expected from the previous work."

So what does this mean?

My understanding: on the one hand it's unlikely that WAIS-collapse will start as fast as in this simulation, because we're not at the Pliocene climate yet. On the other hand, the forcing now and in the future will probably be much stronger than during the Pliocene, except maybe in the strongest mitigation cases. So once collapse does fully set in, say in the second part of this century, it could be very fast, with 3m of SLR within 100 years from WAIS alone. With contributions from GIS of possibly up to 2 meter/century, according to Applegate et al 2014 (see folder What's new in Greenland?), we could get 5-6 meter in 100 years, say from 2100-2200, for a total of maybe 7-8 meter by 2200. That has a 0.1-0.5% chance in Kopp et al 2014, but this may now seem an under-estimate, as Kopp et al already thought possible.

Any other views?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 07, 2015, 09:50:48 PM
Lennart,

For the information that we have in hand your summary is very reasonable.  Maybe the second paper that Alley said was to be released shortly will add more light.  In my mind the first physical evidence that we will see that the collapse of the WAIS will initiate sooner rather than later will be a major calving of the PIIS following by an acceleration of the Southwest Tributary Glacier.  I imagine that the chain of events triggered by a two to five fold acceleration of the SW Tributary Glacier will be difficult to ignore; and in this regard you can track the risk of a major calving event for the PIIS in the "PIG has Calved" thread.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 07, 2015, 10:07:50 PM
Pollard(2014) indicates that the game will be over as soon as we see substantial surface melt on PIG/Thwaites. I am not yet convinced that the absence of surface melt will "stabilize" WAIS for  couple centuries; one weakness in the model is the absence of basal hydrology.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 07, 2015, 10:24:17 PM
The attached figure from Nature Geoscience 2012, DOI: 10.1038/NGEO1671, show in good detail the areas of the Antarctic subject to the indicated number of days of surface ice melting in January 2005.  This figure indicates that both the PIG/Thwaite drainage basins and the Ross Sea Embayment areas are subject to a substantial risk of surface ice melting in the future (as per Pollard's concern).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on January 07, 2015, 11:21:02 PM
3 meters in 35 to 45 years

Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on January 07, 2015, 11:25:58 PM
Pollard et al say:

Any other views?

yes, granted the instantaneous forcing is not possible, however, we don't realize how slower melt dynamics may be setting up the system for this kind of catastrophic collapse on even less than a decadal scale, given the appropriate initial conditions and an 90th percentile period, say 4-5 years, of extreme temperature and precipitation anomalies.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 07, 2015, 11:33:47 PM
Pollard et al say:

Any other views?

yes, granted the instantaneous forcing is not possible, however, we don't realize how slower melt dynamics may be setting up the system for this kind of catastrophic collapse on even less than a decadal scale, given the appropriate initial conditions and an 90th percentile period, say 4-5 years, of extreme temperature and precipitation anomalies.

It is just my opinion but I suspect that if we stay on a BAU pathway to 2100 then the Antarctic ocean and atmospheric conditions may generally match Pliocene-like conditions by about 2065 so we may well see 3m of SLR contribution from the WAIS by 2100 under that assumption.  Of course the world will not end in 2100 and SLR would continue upward for centuries as indicated by Pollard, DeConto & Alley 2015.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 07, 2015, 11:48:27 PM
3 meters in 35 to 45 years

Jai, seems more like 3m in almost 100 years to me.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on January 07, 2015, 11:55:08 PM
oops you are right, it is 3 meters in 70-90 years, just less than 1/2 way on first tic mark on the x-axis. . .
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 08, 2015, 04:25:37 AM
Per Wikipedia:

"The global average temperature in the mid-Pliocene (3.3 Ma–3 Ma) was 2–3 °C higher than today, global sea level 25m higher."

As the only way that Pollard et al 2015 could get adequate SLR contribution from the EAIS was by invoking hydrofracturing, it would seem clear that global warming increase of 2–3 °C can provide sufficient surface ice melting to get the WAIS to at least partially collapse this century.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 08, 2015, 11:34:57 AM
Per Wikipedia:

"The global average temperature in the mid-Pliocene (3.3 Ma–3 Ma) was 2–3 °C higher than today, global sea level 25m higher."

As the only way that Pollard et al 2015 could get adequate SLR contribution from the EAIS was by invoking hydrofracturing, it would seem clear that global warming increase of 2–3 °C can provide sufficient surface ice melting to get the WAIS to at least partially collapse this century.

I posted the following in the Sea Level Rise thread of the Consequence folder:

Quote
If we stay on a BAU to the end of the century then I think that it is reasonable to believe that the WAIS will likely contribute 3m by 2100; however, if we back down to RCP 6 then maybe 2m is reasonable, and if we can get to RCP 4 then maybe 1m is a reasonable contribute to assume from the WAIS.  These are just my opinions; but if you are concerned about The Netherlands, do not forget the fingerprint effect (which I believe is about 1.1 for Holland and up to 1.4 for parts of the USA).

I would like to note that the world could easily blow past the 2 to 3 C global temperature increase (characteristic of the mid-Pliocene) well before the end of this century.  It will be very interesting to see how the ACME program addresses Pollard et al 2015's findings and extends them to a projection of our modern case.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 08, 2015, 10:53:55 PM
In addition to my earlier comments, the following offers a couple more comments about Pollard et al 2015's collapse progression (for a stepped Pliocene condition imposed on modern conditions with both "cliff failures" and hydrofracturing) shown in the first attached image (see caption below); regarding how these initial conditions and collapse condition differ from my expectations for our modern progression following RCP 8.5 this century.

The second attached image shows that the ocean water temperature (averaged from 2004 to 2009) at the grounding line for the PIG is about 3.5 C above freezing.  Thus if Pollard et al assume that the ocean water temperatures around the Antarctic are currently near freezing then the relevant water temperature at the PIG may already be (for non-El Nino years) about 1.5 C (3.5 – 2) above those assumed by Pollard et al.  Thus it may be reasonable to approximate time zero for the PIG/Thwaites catchment basins as about 1980 (when the ozone hole accelerated winds and drove warm CDW into the ASE).  If so it may be reasonable to assume that the collapsed condition for the ASE by 2100 could look like that shown in panel (c) of the first attached image, at 100-years from the Pollard et al initiation.

As it seems to me that the collapse mechanisms for both the FRIS and RIS areas are highly dependent on the regular formation of surface melt ponds, it would seem plausible that for the collapse conditions for the FRIS and RIS areas by 2100, that one could look at panel (b) of the first attached image, at 50-years from the Pollard et al initiation.

Also, if Pollard et al's grid resolution were finer then the projected ice mass loss would likely be higher; and I doubt that the Pollard et al projections include the influence of changing ocean currents as the seaways through the WAIS open circa 2100 (or before).

Thus I still believe that the Pollard et al findings support the case for up to 3m of SLR contribution from the WAIS by 2100, following a BAU pathway, when bearing in mind these points above, together with my earlier comments about:

(a) The potential for relatively high climate sensitivity;
(b) Probable reduced basal friction from basal meltwater in the BSB,
(c) The influence of increased local storm, storm surge and wave activity due to climate change
(d) The possible interaction with GIS SLR contributions (raising sea level around Antarctica), and
(e) The fact that by 2100 following a BAU pathway, mean global surface temperatures will be well above those during the Pliocene, particularly when considering polar amplification.

Caption for the First Image: "Ice distributions in a warm-climate simulation. The simulation starts from modern conditions, with a step-function change to a generic past warm climate applied at year 0. Atmospheric temperatures and precipitation are from a Regional Climate Model simulation with hot austral summer orbit, CO2=400ppmv, and ocean temperatures are increased uniformly by 2◦C above modern. Color scale: Grounded ice elevations, m. Pink scale: floating ice thicknesses, m. The run is initialized from a previous simulation equilibrated to modern climate (panel (a), 0 yr). Both new mechanisms (cliff failure and melt-driven hydrofracturing) are active."

Caption for Second Image: "Mean Water Temperature Above Freezing and Salinity Measurements at the Pine Island Glacier from 2004 to 2009"
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 09, 2015, 11:05:43 PM
While the austral winters have been warming faster in Antarctica than the austral summers, the attached NASA map of surface temperature anomalies on August 29, 2014, illustrates how much of this Antarctic Amplification is occurring in Western Antarctica.  This supports Pollard et al 2015's premise that the WAIS may be subject to hydrofracturing and cliff failures sooner (due to Antarctic Amplification) rather than later as global warming continues:
Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on January 10, 2015, 12:13:08 AM
Quote
influence of changing ocean currents as the seaways through the WAIS open circa 2100 (or before).

Since PIG to Rutford Ice Stream seems the most likely first candidate for this seaway, what rates of annual grounding line retreats would we have to see for this to open by 2100?

how does this compare to today?  It seems that the cliff collapse mechanism would prevent the pathway from opening up under the ice sheet if we were to see grounding line retreats at the rate that you are talking about here (I think).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 12:47:46 AM
Quote
influence of changing ocean currents as the seaways through the WAIS open circa 2100 (or before).

Since PIG to Rutford Ice Stream seems the most likely first candidate for this seaway, what rates of annual grounding line retreats would we have to see for this to open by 2100?

how does this compare to today?  It seems that the cliff collapse mechanism would prevent the pathway from opening up under the ice sheet if we were to see grounding line retreats at the rate that you are talking about here (I think).

As the distance from the PIG to the Rutford groundings lines is something like 500 km, if one assumed grounding line retreats from both sides that would be 250/85 years or about 3 km of grounding line retreat per year on average.  Regarding the cliff failure mechanism, it maybe slower to develop for the PIG as it is confined within a relatively narrow channel which will help to support some ice shelf for sometime.  Nevertheless, any Pine Island Ice Shelf will continue to calve so any subglacial cavity that may (or may not) exist when the seaway between the ASE and the Weddell Sea is formed, may only be a few tens of kilometers long.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 12:48:18 AM
Whether obvious to everyone, or not, I thought that I would like a few positive feedback mechanisms that would accelerated/activated on both local and global scales by the hydrofracturing/cliff failure WAIS collapse scenario described in the Pollard et al 2015 paper, which are:

1. Albedo flip occurs both when melt ponds form on top of pre-existing ice, and when ice gives way to ocean water.  Thus both the postulated Antarctic melt ponds postulated in the hydrofracting mechanism, and the calving of armadas of icebergs into the ocean, would decrease local albedo and increase local temperatures (which would result in a positive feedback for more melt ponds and more calving).

2. The formation of seaways through the WAIS would not only contribute to more ice calving, but would also change the AMOC, resulting in a positive feedback.

3. The ocean water pushed through the Bering Strait by the rapid collapse of the WAIS would contribute to Arctic Amplification and accelerated global warming.

4. A rapid collapse of the WAIS would expose a large amount of Antarctic seafloor methane hydrates to decomposition, which would accelerate global warming.

5.  However, I realize that I should mention that the cooling of the Southern Ocean by the introduction of a large armada of icebergs would serve as a negative feedback until all of the icebergs had melted.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 01:43:03 AM
The linked article indicates that the basal roughness beneath the Institute and Moller Ice Streams have been smoothed by past ice flows and are continuing to be smoothed by current ice movement (thus increase the probability of faster future ice mass loss events):

Rippin, David; Bingham, Robert; Jordan, Tom; Wright, Andrew; Corr, Hugh F. J.; Ferraccioli, F ; Le Brocq, Anne; Ross, Neil; Siegert, Martin J.( 2014), "Basal roughness of the Institute and Möller Ice Streams, West Antarctica: process determination and landscape interpretation",  Geomorphology, Vol. 214, p. 139-147, 10.1016/j.geomorph.2014.01.021

https://pure.york.ac.uk/portal/en/publications/basal-roughness-of-the-institute-and-moeller-ice-streams-west-antarctica-process-determination-and-landscape-interpretation(fe88c0f0-0129-4c81-adcc-fedde7b8cfbe).html

Abstract: "We present a detailed analysis of bed roughness beneath Institute and Möller Ice Streams, west Antarctica, using radio-echo sounding data (RES) acquired in the austral summer of 2010/11. We assess roughness using a two-parameter approach and also assess the directionality of roughness relative to present-day ice flow. Our work highlights the wealth of additional information that resides in analyses of bed roughness. Employing these multiple approaches we show that spatially variable roughness patterns are partly a consequence of the ability of flowing ice not only to smooth the bed but also to redistribute and remove sediments, and to do this along-flow. Accordingly, we identify some fast-flow tributaries underlain by topography that has been streamlined and other tributaries that are underlain by sediments. We also identify locations that are currently protected from erosion, but where more ancient erosion may once have occurred. We conclude that detailed roughness analysis is a useful tool for landscape interpretation; and we suggest that the roughness of an ice-sheet's bed should be viewed not only as the consequence of ancient marine sedimentation, but also as a product of more contemporary erosion and redistribution of sediments, as well as bedrock-smoothing that is ongoing because of continuing dynamic activity. In this way, basal roughness has the potential to evolve continually with ice sheet form and flow, and should not be viewed simply as a snapshot of either present-day or palaeo-basal conditions."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 01:55:18 AM
While the following reference has been previously cited in the EAIS thread, I thought that I would post it here as it is so clearly relevant to the recent Pollard et al 2015 work:

M. Mengel & A. Levermann, (2014), "Ice plug prevents irreversible discharge from East Antarctica", Nature Climate Change, Volume: 4, Pages: 451–455, doi:10.1038/nclimate2226

http://www.nature.com/nclimate/journal/v4/n6/full/nclimate2226.html (http://www.nature.com/nclimate/journal/v4/n6/full/nclimate2226.html)

Abstract: "Changes in ice discharge from Antarctica constitute the largest uncertainty in future sea-level projections, mainly because of the unknown response of its marine basins1. Most of West Antarctica’s marine ice sheet lies on an inland-sloping bed and is thereby prone to a marine ice sheet instability. A similar topographic configuration is found in large parts of East Antarctica, which holds marine ice equivalent to 19 m of global sea-level rise, that is, more than five times that of West Antarctica. Within East Antarctica, the Wilkes Basin holds the largest volume of marine ice that is fully connected by subglacial troughs. This ice body was significantly reduced during the Pliocene epoch. Strong melting underneath adjacent ice shelves with similar bathymetry8 indicates the ice sheet’s sensitivity to climatic perturbations. The stability of the Wilkes marine ice sheet has not been the subject of any comprehensive assessment of future sea level. Using recently improved topographic data in combination with ice-dynamic simulations, we show here that the removal of a specific coastal ice volume equivalent to less than 80 mm of global sea-level rise at the margin of the Wilkes Basin destabilizes the regional ice flow and leads to a self-sustained discharge of the entire basin and a global sea-level rise of 3–4 m. Our results are robust with respect to variation in ice parameters, forcing details and model resolution as well as increased surface mass balance, indicating that East Antarctica may become a large contributor to future sea-level rise on timescales beyond a century."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 10, 2015, 06:34:17 AM
Re: which WAIS seaway opens first
Vaughan(2011) doi:10.1029/2011GC003688


Amundsen to Weddell 1200 yr (Rutford flows into Ronne-Weddell i believe)
                 to Ross      4030
                 to Bellinghausen 910  (the winner)

Bellinghausen to Weddell  1830 yr
Ross to Weddell 85000 yr

I enclose part of fig 1 showing putative seaways

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 10, 2015, 06:39:40 AM
Re:

"the cooling of the Southern Ocean by the introduction of a large armada of icebergs would serve as a negative feedback until all of the icebergs had melted."


Disagree. Freshwater layer will freeze faster and insulate CDW better in polar winter. (This effect may also suppress AABW production, and I will not speculate here on the effect on thermohaline circ.) Cooling of SH ocean surface will suppress evaporation, decreasing snowfall on Antarctica.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on January 10, 2015, 07:39:00 AM
rutford = A-W pathway

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fgeology.gsapubs.org%2Fcontent%2F35%2F2%2F127%2FF1.large.jpg&hash=94a1a749368ca9b686d5a937577ccdfe)

it should be noted that the grounding line retreats for A-W (PIG?) in Vaughn (2011) are about 1/3 (or is it 1/10th of the 2005-2009 retreat rate?!?!) the observed rates in Rignot et. al 2014

http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/abstract)

Quote
from 1992 to 2011. Pine Island Glacier retreated 31 km at its center, with most retreat in 2005–2009 when the glacier ungrounded from its ice plain
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 10, 2015, 08:25:46 AM
agreed that Vaughan(2011) estimates for seaway opening are optimistic (too long, if i have to spell it out)

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 03:36:32 PM
Re:

"the cooling of the Southern Ocean by the introduction of a large armada of icebergs would serve as a negative feedback until all of the icebergs had melted."


Disagree. Freshwater layer will freeze faster and insulate CDW better in polar winter. (This effect may also suppress AABW production, and I will not speculate here on the effect on thermohaline circ.) Cooling of SH ocean surface will suppress evaporation, decreasing snowfall on Antarctica.

sidd

sidd,
You m
ay (or may not) be right about the presence of a large armada of icebergs in the Southern Ocean being positive feedback instead of a negative feedback; I was just quoting the findings of Hansen & Sato 2012's computer simulation:

James Hansen and Makiko Sato, 26 December 2012, "Update of Greenland Ice Sheet Mass Loss: Exponential?"


http://www.columbia.edu/~jeh1/mailings/2012/20121226_GreenlandIceSheetUpdate.pdf (http://www.columbia.edu/~jeh1/mailings/2012/20121226_GreenlandIceSheetUpdate.pdf)

Extract: "However, exponential ice loss, if it occurs, would encounter negative (diminishing) feedbacks. Our simulations (Hansen and Sato, 2012) suggest that a strong negative feedback kicks in when sea level rise reaches meter-scale, as the ice-melt has a large cooling and freshening effect on the regional ocean."

See also:
Hansen, J.E., and M. Sato, 2012: Paleoclimate implications for human-made climate change. In Climate Change: Inferences from Paleoclimate and Regional Aspects. A. Berger, F. Mesinger, and D. Šijački, Eds. Springer, pp. 21-48, doi:10.1007/978-3-7091-0973-1_2.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 04:05:37 PM
agreed that Vaughan(2011) estimates for seaway opening are optimistic (too long, if i have to spell it out)

sidd

In the original post to this thread I discuss how Vaughan et al (2011) was only providing an upper bound on how long it might take to form such seaways during the Eemian, and he proved that such seaways could form during the duration of the peak of the Eemian, this indicating that the WAIS probably largely collapsed during the Eemian and thus is even more susceptible to collapse now as each collapse smoothens the basal topology.

jai,
While I admit/agree that the Pollard et al (2015) findings implies that I should refine/update my WAIS collapse scenario from 2013 (found earlier in this {and other} thread{s}), I believe such a refinement is premature and would require too many different cases of time and locations with different boundary conditions (some with cliff failure configurations, some with limited local ice shelves, some with short temporary subglacial cavities, some with converging ice streams, some calving faces temporarily pinned), that it would be pretentious of me to table refined scenarios maps.  Therefore, I re-post the first three images of some portions of my 2013 scenarios (for 2060 and 2090 with some 50% and some 95% CL for RCP 8.5) in order to support my comments that: (a) on the profiles I did not show the calving face so to determine my implied geometry of calving faces you would need to connect the red calved areas with the associated black grounding line retreat areas, and I admit now that in many cases this would imply a more sloped (less vertical) calving face than the cliff failure mechanisms implies, but I note that due to the bottom topology there many not be cliff faces everywhere; and (b) I never meant to imply that the interconnected subglacial cavities were more than a few tens of kilometers long.

Finally, I post Pollard et al (2015) figure showing their collapse progression sequence (with time) to illustrate their collapse area around Rutford and PIG (between 2050 and 2100)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 04:16:58 PM
Further to my last post, and in order to support my position that the bottom topology beneath the WAIS presents a large number of local conditions with different pinning cases, side shear cases, basal friction cases, etc, I re-post the two attached Bedmap 2 images.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 10, 2015, 04:46:37 PM
New paper by Dutton et al 2015 on WAIS- and/or EIAS-collapse during the Eemian:
http://www.sciencedirect.com/science/article/pii/S0277379114004120 (http://www.sciencedirect.com/science/article/pii/S0277379114004120)

Abstract
"In the search for a record of eustatic sea level change on glacial–interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local—or relative—sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between ∼129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ∼5–8 m of polar ice sheet contribution, relative to today's volume, of which only ∼2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand."

Highlights
• Peak eustatic sea level (ESL) for MIS 5e estimated at ∼7.6 ± 1.7 m above present.
• Polar ice sheets contributed ∼5–8 m of ice-equivalent sea level to this peak.
• Partial collapse of Antarctic ice sheet may have occurred early in MIS 5e.
• Gradual sea-level rise of ∼0.2 m ka−1 recorded between ∼129 and 125 ka.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 10, 2015, 05:02:22 PM
Dutton et al 2015 say:
"We observe a pattern of gradually rising sea level in the Seychelles between ∼129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present... Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand."

In the Highlights it says:
"Gradual sea-level rise of ∼0.2 m ka−1 recorded between ∼129 and 125 ka."

But 7.6-5.9=1.7m in 128.6-125=3.6 ka, so almost 0.5 m/kyr, or 0.5 mm/yr on average.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 05:25:12 PM
The following reference must be the second paper that Alley mentioned to Lennart of the two that came out this week.  This paper complements the Pollard et al 2015 paper (which looked at a simple Pliocene case superimposed on current AIS conditions in a stepped manner).  This reference provides all of the appropriate caveats for making an actual projection of our current case, and notes that the initiation phase of the main collapse phase is still the most difficult to determine.  That said I still like my general collapse scenario that I posted in 2013:

Richard B. Alley, Sridhar Anandakrishnan, Knut Christianson, Huw J. Horgan, Atsu Muto, Byron R. Parizek, David Pollard & Ryan T. Walker, (Volume publication date June 2015), "Oceanic Forcing of Ice-Sheet Retreat: West Antarctica and More", Annual Review of Earth and Planetary Sciences, Vol. 43

Note: Expected final online publication date for the Annual Review of Earth and Planetary Sciences Volume 43 is May 30, 2015. Please see http://www.annualreviews.org/catalog/pubdates.aspx (http://www.annualreviews.org/catalog/pubdates.aspx) for revised estimates.

http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344 (http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344)

Abstract: "Ocean-ice interactions have exerted primary control on the Antarctic Ice Sheet and parts of the Greenland Ice Sheet, and will continue to do so in the near future, especially through melting of ice shelves and calving cliffs. Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed, shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West Antarctica, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state is likely to involve loss of most of the West Antarctic Ice Sheet, causing >3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic Ice Sheets share some of the same vulnerabilities to shrinkage from marine influence."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 06:07:57 PM
Dutton et al 2015 say:
"We observe a pattern of gradually rising sea level in the Seychelles between ∼129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present... Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand."

In the Highlights it says:
"Gradual sea-level rise of ∼0.2 m ka−1 recorded between ∼129 and 125 ka."


But 7.6-5.9=1.7m in 128.6-125=3.6 ka, so almost 0.5 m/kyr, or 0.5 mm/yr on average.

Lennart,

Thanks for the link to:

Andrea Dutton , Jody M. Webster, Dan Zwartz, Kurt Lambeck & Barbara Wohlfarth, (1 January 2015, ), "Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands", Quaternary Science Reviews, Volume 107, Pages 182–196, doi:10.1016/j.quascirev.2014.10.025.

You (or the authors) highlight the fact that when this paleo-evidence is sufficiently averaged it can be made to imply a relatively gradual contribution to SLR from the AIS, during the Eemian peak.  While I admit that a case can be made for a gradual contribution to SLR during the Eemian peak from the AIS, I would like to note (for the benefit of new viewers) that:

1.  Other paleo-evidence such as the attached figure from O'Leary et al (2013) shows that when not averaging, some abrupt contributions to SLR (circa 119kya) are supported by paleo-evidence.
2.  The Eemian conditions are less severe than the Pliocene conditions, and both are less severe than the regional Antarctic conditions projected for 2100 for a RCP 8.5 50% CL scenario.
3. Paleo-forcing is appreciably different than current forcing conditions, and do not include an ozone hole over Antarctic.

Again I note that we will probably need to wait until the ACME project issues projections before we get anything like a reasonable projection of a plausible AIS collapse scenario in the next 100 to 200 years, and even that may only be a lower bound approximation of the true SLR contribution risks.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 10, 2015, 09:56:19 PM
The Alley abstract indicates some commonality between GRIS and EAIS. I do not see this clearly, so i await the full paper. Any thoughts ?

Another interesting bit is that they suggest a delay is possible between the time that the irreversible threshold is crossed and full scale collapse. This suggest hysteresis, as i think we see already in the Pollard paper where they try to regrow the ice in a period of cooler temperature.

The Dutton paper offers a tantalizing hint that AIS may have collapse early, perhaps even before GRIS.

"This additional, more gradual sea-level rise presumably stems from GrIS melt, if our interpretation of partial AIS collapse early in the LIG period is correct ..."

"A critically important observation to note from our dataset in terms of implications for ice-sheet response is that even early in the interglacial, ESL reached 5.9 ± 1.7 m above present sea level, which we have attributed to rapid retreat from an unstable sector(s) within the AIS. This scenario is at odds with other studies that have suggested a collapse of the WAIS near the end of the LIG high-stand immediately prior to glacial inception ... "

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 10, 2015, 10:29:32 PM
sidd,

All interesting observations that you make in Reply #240.  I offer the following brief responses:

1.  Regarding commonalities between the GRIS and EAIS:  They both have large ice fractions of their total ice volumes in land-based glaciers/ice sheets, with smaller but significant fractions of their total ice volumes in marine terminating and marine glaciers.  The land-based ice will take thousands of years to degrade while the marine fraction (in both the GRIS and the EAIS) could contribute to future sea level rise within the next 100 to 200 years (or less).

2.  Your comment about hysteresis is valuable in that when you look at the O'Leary et al (2013) image that I posted in Reply #239 you will see the early ice-sheet contribution to SLR in the early part of the LIG (Eemian) around 127kya, followed by a slow period of sea level drop (hysteresis during a cooling period) to about 119kya, followed by another abrupt ice-sheet contribution to SLR around 119 to 120kya.

3.  I believe that the key lesson is that marine terminating and marine glaciers in the GRIS, the EAIS and the WAIS are all subject to potentially rapid collapse within the next 100 years if society continues to follow a BAU pathway (driven by economic growth in the developing world) through at least 2050.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 10, 2015, 11:16:49 PM
ASLR, sidd,

Also see Kopp et al 2013 on the Eemian:
http://gji.oxfordjournals.org/content/193/2/711.full (http://gji.oxfordjournals.org/content/193/2/711.full)

They estimate maximum SLR during this period was 5 m/ky, but it may have been higher.

It seems the various studies of Eemian SLR do not really agree yet.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 10, 2015, 11:30:55 PM
Also see:
http://people.oregonstate.edu/~carlsand/PALSEA2/Past_Meetings_files/rome_meeting_report.pdf (http://people.oregonstate.edu/~carlsand/PALSEA2/Past_Meetings_files/rome_meeting_report.pdf)

"Reconstructions based on a range of sea level indicators from different regions were presented at the workshop and all support temporal variability within the LIG with millennial average rates ranging from order decimeters per century to order metres per century. The discrepancy in these values relates primarily to limitations in height and time precision of the reconstruction methods use.  Therefore, an important target for the community is the production of more precise records for this period."

Blanchon et al 2009 found indications for very fast SLR about 121 ky ago:
http://www.nature.com/nature/journal/v458/n7240/full/nature07933.html (http://www.nature.com/nature/journal/v458/n7240/full/nature07933.html)

"Here we present a complete reef-crest sequence for the last interglacial highstand and its U-series chronology from the stable northeast Yucatán peninsula, Mexico. We find that reef development during the highstand was punctuated by reef-crest demise at +3 m and back-stepping to +6 m. The abrupt demise of the lower-reef crest, but continuous accretion between the lower-lagoonal unit and the upper-reef crest, allows us to infer that this back-stepping occurred on an ecological timescale and was triggered by a 2–3-m jump in sea level. Using strictly reliable 230Th ages of corals from the upper-reef crest, and improved stratigraphic screening of coral ages from other stable sites, we constrain this jump to have occurred ~121 kyr ago and conclude that it supports an episode of ice-sheet instability during the terminal phase of the last interglacial period."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 10, 2015, 11:50:51 PM
IPCC AR5 WG1 Ch.5, p.426:
http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf)

"Since AR4, there is evidence for meter-scale variability in local LIG sea level between 126 ka and 120 ka (Thompson and Goldstein, 2005; Hearty et al., 2007; Rohling et al., 2008a; Kopp et al., 2009; Thompson et al., 2011). However, there are considerable differences in the timing and amplitude of the reported fluctuations due to regional sea level variability and uncertainties in sea level proxies and their ages... In summary, there is evidence for two intra-LIG sea level peaks (high confidence) during which sea level varied by up to 4 m (medium confidence). The millennial-scale rate of sea level rise during these periods exceeded 2 m kyr–1 (high confidence)."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 11, 2015, 12:37:13 AM
Re; Hansen and Sato on negative feedback from ocean cooling

They may be speaking of surface temperature response, which is not too interesting for me. I am far more interested in overall AIS glacial response ...

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 11, 2015, 04:59:40 AM
ASLR, sidd,

Also see Kopp et al 2013 on the Eemian:
http://gji.oxfordjournals.org/content/193/2/711.full (http://gji.oxfordjournals.org/content/193/2/711.full)

They estimate maximum SLR during this period was 5 m/ky, but it may have been higher.

It seems the various studies of Eemian SLR do not really agree yet.

Lennart,

The 5m/ky that you quote from Kopp et al 2013 has more than a 50% probability of being exceeded (actually closer to 75% chance of being exceeded) as indicated in the attached associated image.  Personally, using such values is far to risky for my tastes where many human lives are at risk.  Also, I do not like averaging rates of SLR over 1,000 years, when the PALSEA2 quotation that you cite warns of the potential for meters of SLR per century.  Furthermore, based on the Pollard et al 2015 findings and the Alley et al 2015 findings, the highest rates of SLR appear to happen relatively early in a collapse event, when there is still relatively large amounts of marine ice sheet mass subjected to cliff failure and hydrofracturing types of accelerated calving.

Robert E. Kopp, Frederik J. Simons, Jerry X. Mitrovica, Adam C. Maloof and Michael Oppenheimer, (2013), "A probabilistic assessment of sea level variations within the last interglacial stage", Geophys. J. Int., 193 (2): 711-716, doi: 10.1093/gji/ggt029

http://gji.oxfordjournals.org/content/193/2/711.full (http://gji.oxfordjournals.org/content/193/2/711.full)

Abstract: "The last interglacial stage (LIG; ca. 130–115 ka) provides a relatively recent example of a world with both poles characterized by greater-than-Holocene temperatures similar to those expected later in this century under a range of greenhouse gas emission scenarios. Previous analyses inferred that LIG mean global sea level (GSL) peaked 6–9 m higher than today. Here, we extend our earlier work to perform a probabilistic assessment of sea level variability within the LIG highstand. Using the terminology for probability employed in the Intergovernmental Panel on Climate Change assessment reports, we find it extremely likely (95 per cent probability) that the palaeo-sea level record allows resolution of at least two intra-LIG sea level peaks and likely (67 per cent probability) that the magnitude of low-to-high swings exceeded 4 m. Moreover, it is likely that there was a period during the LIG in which GSL rose at a 1000-yr average rate exceeding 3 m kyr−1, but unlikely (33 per cent probability) that the rate exceeded 7 m kyr−1 and extremely unlikely (5 per cent probability) that it exceeded 11 m kyr−1. These rate estimates can provide insight into rates of Greenland and/or Antarctic melt under climate conditions partially analogous to those expected in the 21st century."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 11, 2015, 09:49:49 AM
ASLR,
Indeed, up to 11 m/ky during the Eemian is also what Rohling et al 2013 estimate:
http://www.nature.com/srep/2013/131212/srep03461/full/srep03461.html?message-global=remove (http://www.nature.com/srep/2013/131212/srep03461/full/srep03461.html?message-global=remove)

"Initial (Red Sea-based) LIg SLR rate estimates of 1.6 ± 1.0 m cy−1 lacked direct age control. Subsequent studies proposed 1000-year average LIg rates of > 0.26 m cy−1 (ref. 49) and 0.56–0.92 m cy−1 (ref. 47), which is consistent with a 1000-year smoothed estimate of 0.7 ± 0.4 m cy−1 over the −5 to +5 m sea-level range based on improved dating of the Red Sea record. Note that such smoothing masks brief intervals with more rapid rise. Data from western Australia suggest a rapid rise within the LIg at 0.6 m cy−1 (ref. 50). We infer that LIg SLR likely occurred at sustained rates of ~1 m cy−1 or less."

That was based on Grant et al 2012:
http://www.highstand.org/erohling/Rohling-papers/2012-Grant-et-al-nature11593.pdf (http://www.highstand.org/erohling/Rohling-papers/2012-Grant-et-al-nature11593.pdf)

"Our new RSL chronology permits the first robust calculation of rates of relative sea-level change throughout the past 150,000 years (Fig.3c). This reveals that rates of sea-level rise reached at least 1.2m per century during all major phases of ice-volume reduction, and were typically up to 0.7m per century (possibly higher, given the smoothing in our method) when sea-level exceeded 0m during the LIG (Fig.3c); the latter is consistent with independent estimates."

So 1 meter/century seems to be the minimum we can expect for the coming centuries. But since the forcing now is so much stronger than during previous interglacials (or any previous period), it will probably be much more.

How much more? Maybe up to 1 meter/decade and 6 meter/century, would be my guess. Or up to circa 2.5m by 2100, circa 8m by 2200, and circa 13m by 2300, based on the recent papers by Pollard et al and Applegate et al, amongst others.

That would be my very rough worst-case risk assessment for now, but maybe this could still be an under-estimate?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 11, 2015, 01:26:48 PM
Lennart,

I agree more with your line of logic in Reply #247; however, I would like to raise the additional following considerations:

1. Your SLR estimate of 2.5 m by 2100, may not include steric increases (note that due to thermal inertia our modern oceans are still warming, while the paleo-data that you point to almost certainly has oceans that have already warmed).

2.  I believe that based on 2014 findings the unstable portions (both calving and surface melting) of the GRIS (GIS) are capable of contributing about 1m to SLR by 2100.  Thus both you may be underestimating the GRIS contribution and the potential that the GRIS contribution could help to destabilize the AIS marine glaciers.

3.  Not all paleo-data is of equal quality, so when you blend poor quality findings with good quality you can get a dumbed-down finding.  Thus if it turns out that the O'Leary et al 2013 data is better than other research findings then the Eemain peak about 119kya may be more abrupt and more severe than you are assuming (note that Kopp et al 2013 verify that two sea level peaks occurred during the Eemian.

4.  It is also possible that the world is moving into a "perfect-storm" situation (or may be reaching resonance in any otherwise chaotic system), as due to synergy between the PDO and the AMO multi-decadal cycles, and or due to activation of positive feedback mechanisms.  If so we could be moving into a Dragon-King type probability distribution function for SLR, with enhanced "fat-tail" risks.  Thus by 2100 our planetary system could far exceed the Pliocene conditions assumed by Pollard et al 2015.

Climate change is all about risk management.  In my opinion too many policy makers today "manage" risk by denying fat-tail risks, rather than acknowledging that uncertainty inherently implies risk, and then taking appropriate risk management measures.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 11, 2015, 05:56:32 PM
ASLR,
You may be right that it could be more than 2.5m by 2100. I don't know. I guess I'm trying to find the maximum number that I can communicate to policymakers and public while referring them to the best available papers/scientists that make this number plausible. We can speculate about this still being an under-estimate, but if there's no or hardly any scientist who's willing to defend that number, then it may make our speculation less credible.

So I find Kopp et al 2014, table 1, a good starting point for referring people to what scientists are thinking on the risks of SLR:
http://onlinelibrary.wiley.com/doi/10.1002/2014EF000239/full (http://onlinelibrary.wiley.com/doi/10.1002/2014EF000239/full)

They seem to think 2.5m by 2100 is about the worst-case imaginable. However, they estimate a 5% chance of 1.2m by 2100 under RCP8.5, while Horton et al 2014 estimate a 5% chance of 1.5m by 2100 in that case, Rohling et al 2013 estimate a 2.5% chance of 1.8m by 2100, and Jevrejeva et al 2014 estimate a 5% chance of 1.8m by 2100 as a worst-case, while not completely excluding 2.5m by 2100 either (in their fig.3):
http://iopscience.iop.org/1748-9326/9/10/104008/article (http://iopscience.iop.org/1748-9326/9/10/104008/article)

So this is something we can point to, whereas more than 2.5m by 2100 would be (even) more speculative, such as Hansen's 5m by 2100 exponential extrapolation, or some individual answers in Horton et al 2014, fig.2:
https://marine.rutgers.edu/pubs/private/HortonQSR_2013.pdf (https://marine.rutgers.edu/pubs/private/HortonQSR_2013.pdf)

They could be right. I don't know. But can this be enough to convince policymakers? Or judges for that matter?

Also at this point my main interest is still the potential effect of strong mitigation on reducing risks of SLR in the long term. For 2100 this effect will probably by smaller than for 2200 or 2300. If the coming two decades show that 2.5m by 2100 may not be a worst-case, then there'll be still two decades to prepare. If in the coming two decades we don't manage to reduce emissions enough, it will be hard or impossible to still reduce the risk of longer term SLR.

This is my reasoning so far, but again, you may be right, if you think this is still too risky.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 11, 2015, 06:48:45 PM
Lennart,

I fully appreciate your line of logic, as on numerous occasions I have tried to speak truth to power about the risks of ASLR, and you are right that without either: (a) representing a consensus view, and/or (b) presenting undeniable proof, then policymakers will continue taking the path of least resistance, and talking to them about poorly defined risks are a waste of time and energy.

Nevertheless, I would like to point-out that the findings of Kopp et al 2014 were determined before the recent findings of Rignot et al and Pollard et al 2015, as can be seen in the attached image from Kopp et al 2014.  This plot shows a 5 to 95% probability range limit of about a 0.33m contribution to SLR from the AIS by 2100; which clearly could not include any recent Rignot et al or Pollard et al findings.  Therefore, if you approach policymakers now with a 2.5m SLR limit by 2100, you may need to re-approach them much sooner than in 20 years in order to increase this limit as within less than 10-years findings from the ACME program may likely put the cliff failure and hydrofracturing mechanisms into a formal SLR projection (rather than a hypothetical simple Pliocene thought experiment as performed by Pollard et al 2015), and in the meantime many more people/companies will invest in coastal areas that they thought were risk free when in reality they were only risk masked.

Obviously, if you can sell an increase in the regulated/required 2100 SLR value from 2m to 2.5m it is better than nothing; provided that the policymakers understand that you might re-approach in 2 to 10-years with another upper limit based on new consensus science in a highly non-stationary situation.

Edit: I also note that the Kopp et al 2014 probability numbers include RCP2.6 and RCP 4.5; while if Exxon-Mobil's 2014 projection of carbon emissions are reasonable correct, then both of these future scenarios are illusions and considering only RCP 6 and RCP 8.5 would markedly increase the probabilities that Kopp et al 2014 are quoting.

Best,
ASLR

For convenience, I provide the following Kopp et al 2014 reference:

Kopp, R. E., Horton, R. M., Little, C. M., Mitrovica, J. X., Oppenheimer, M., Rasmussen, D. J., Strauss, B. H. and Tebaldi, C. (2014), "Probabilistic 21st and 22nd century sea-level projections at a global network of tide-gauge sites", Earth's Future, 2: 383–406. doi: 10.1002/2014EF000239

http://onlinelibrary.wiley.com/doi/10.1002/2014EF000239/full (http://onlinelibrary.wiley.com/doi/10.1002/2014EF000239/full)

Abstract: "Sea-level rise due to both climate change and non-climatic factors threatens coastal settlements, infrastructure, and ecosystems. Projections of mean global sea-level (GSL) rise provide insufficient information to plan adaptive responses; local decisions require local projections that accommodate different risk tolerances and time frames and that can be linked to storm surge projections. Here we present a global set of local sea-level (LSL) projections to inform decisions on timescales ranging from the coming decades through the 22nd century. We provide complete probability distributions, informed by a combination of expert community assessment, expert elicitation, and process modeling. Between the years 2000 and 2100, we project a very likely (90% probability) GSL rise of 0.5–1.2 m under representative concentration pathway (RCP) 8.5, 0.4–0.9 m under RCP 4.5, and 0.3–0.8 m under RCP 2.6. Site-to-site differences in LSL projections are due to varying non-climatic background uplift or subsidence, oceanographic effects, and spatially variable responses of the geoid and the lithosphere to shrinking land ice. The Antarctic ice sheet (AIS) constitutes a growing share of variance in GSL and LSL projections. In the global average and at many locations, it is the dominant source of variance in late 21st century projections, though at some sites oceanographic processes contribute the largest share throughout the century. LSL rise dramatically reshapes flood risk, greatly increasing the expected number of “1-in-10” and “1-in-100” year events."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 11, 2015, 08:29:38 PM
ASLR,
Good points, as usual.

Looking at your attached fig.2 from Kopp et al 2014, we can add up the 99.5-percentile values:
- 0.6m thermal expansion
- 0.3m glaciers & ice caps
- 0.7m GIS
- 0.9m AIS

So that would be a worst-case of 2.5m in total by 2100.

Pollard et al 2015, Applegate et al 2014, Rignot et al 2014, Joughin et al 2014 all seem to make this worst-case less improbable then Kopp et al 2014 still thought. So maybe we should add another potential 0.3m from GIS and 0.7m from AIS to get an updated worst-case of 3.5m by 2100?

Or could AIS contribute even more than 1.6m by 2100? Pollard et al find 3m in 90 yrs, once we get to Pliocene conditions. These could start at about 2050, or even earlier? And warming would then continue, so maybe 3m would be possible in 50 years instead of 90? In that case another 1.5m by 2100 could maybe be possible, for a total of 5m as the 'best-estimate' worst-case.

This would seem reasonable enough from a precautionary perspective, but as you say, it's an impossibly hard sell to policy makers and public, since very few experts, except maybe Hansen, would be willing to defend such an estimate.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on January 11, 2015, 09:44:34 PM
Have you seen this?

Sensitivity of theWeddell Sea sector ice streams to sub-shelf melting
and surface accumulation

A. P. Wright et. al.
doi:10.5194/tc-8-2119-2014
http://www.the-cryosphere.net/8/2119/2014/tc-8-2119-2014.pdf (http://www.the-cryosphere.net/8/2119/2014/tc-8-2119-2014.pdf)

Quote
High-Salinity Shelf Water (HSSW) is currently responsible
for melting at the grounding lines of the ice streams
feeding the Filchner–Ronne Ice Shelf. This water mass is
cooler than the Circumpolar Deep Water but it is still warm
enough to cause melt rates of between 0.1 and 2.5ma near
to the grounding line of Rutford Ice Stream (Jenkins et al.,
2006). Recent predictions of ocean circulation models indicate,
however, that relatively modest future climate warming
might result in changes to circulation patterns in the Southern
Ocean that would allow warmer deep-ocean water to penetrate
across the continental shelf in this area (Hellmer et al.,
2012). If this were to happen then melt rates at the grounding
lines of the Filchner–Ronne tributaries would be expected
to increase by an order of magnitude (Hellmer et al., 2012)


In reading this paper I was surprised to see the analysis of the Rutford ice stream in the models, even though they see a 500M water depth sub-ice stream, they still don't see significant grounding line retreat/float.  Here is why:

Quote
The Rutford Fjord, however, is
the longest, narrowest and deepest of all the Filchner–Ronne
tributaries and the glacier is well constrained within steep
rock walls on both margins. The buttressing this provides
may explain its apparent stability in the model despite the
reverse bed slope throughout much of its length.

In other words, the ice stream is constrained from float due to the steep canyon topography/ice interactions.  But, this makes me wonder. 

Did they consider atmospheric conditional changes under RCP 8.5 with increased precipitation (rain) and melt pond/fracturing events and ice-stream internal heating from Moulin drainage?

It seems to me that sufficient side-slip basal lubrication and increased ductility of warmer contact ice would allow this ice stream to 'POP' out of its channel given a few meters of sea level rise and a few hundreds of meters of ice stream thinning. . .

also, this is an oldie but a goodie, haven't heard much about his lately.  However it seems to be very applicable given the above modelling results.

http://www.sciencedirect.com/science/article/pii/0037073891901362 (http://www.sciencedirect.com/science/article/pii/0037073891901362)

Marine ice-sheet decoupling as a mechanism for rapid, episodic sea-level change: the record of such events and their influence on sedimentation

Abstract: Unlike terrestrial ice sheets, marine ice sheets display more sensitivity to sea level than to climate, and they are capable of rapid mass wasting. This mass wasting involves ice shelf decoupling from the sea floor and rapid collapse, followed by “drawdown” of the ice sheet. Glaciologists argue that the marine ice-sheet decoupling mechanism could cause sea-level rises of a few meters within several hundred years. . .

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 12, 2015, 05:12:34 AM
Lennart,

For what it is worth, the RAND Corps advises against trying to identify a specific upper limit for sea level increase by a given date.  Instead they recommend identifying the rate of SLR at which a given decision maker cannot respond fast enough to prevent unacceptable damage as the definition of abrupt SLR.

In this regard, the NRC 2013 abrupt climate change report makes it clear that these researchers consider ASLR to be at least a 1m of SLR within an approximately 30-year period (or a rate of SLR of 33 mm/yr over such a 30-year period by 2100); while Lempert et al 2012 consider different combinations of rates of SLR, with different initiation dates for the abrupt contribution adding up to 1.4m over various time periods by 2100.  Furthermore, one needs to consider that under either of these two criteria/scenarios, the rate of SLR would likely be accelerating for dates after 2100.  Furthermore, the NRC 2013 report makes it clear that a "Well-Characterized" rate of SLR of 1m by 2100 (11mm/yr) is very likely, this leaves approximately 22mm/yr of SLR to be coming from the WAIS by about 2080, in order to roughly meet the NRC 2013 minimum criteria of ASLR.

Lempert, R., Sriver, R.L. and Keller, K., (2012); "Characterizing Uncertain Sea Level Rise Projections to Support Investment Decisions" Report to POLA.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 12, 2015, 01:52:24 PM
Have you seen this?

Sensitivity of theWeddell Sea sector ice streams to sub-shelf melting
and surface accumulation

A. P. Wright et. al.
doi:10.5194/tc-8-2119-2014

jai,

Thanks for the Wright et al 2014 reference which I had not seen before (for convenience, I provide a more complete reference at the end of this brief post).  Aside from explaining timing and modeling issues, I do not believe that any of Wright et al 2014's finding invalidate my 2013 collapse scenario (which has support references scattered throughout the "Surge", "PIG/Thwaites", and "FRIS/RIS" threads).  As I do not have time to make a detailed response, I will make a few brief comments regarding the possible interconnection between the Weddell and Amundsen Seas (a seaway) before 2100:
1.  My collapse scenario shows the PIG seaway leg extending much more rapidly than the Evans/Rutford seaway leg, largely due to the PDO entering a positive phase; which I believe will advect warm CDW beneath the PIIS, which will lead to accelerated calving and grounding line retreat.
2. While Hellman 2012 does not project a warm CDW current to extend beneath the FRIS before the 2060-2070 timeframe, more recent research shows that vortex shedding can periodically send pulses of warm CDW through the Filchner Trough and beneath the Filchner Ice Shelf well before 2060.
3. The retreat of ice streams as close together as the Evans and Rutford ice streams can work synergistically to accelerate each other's retreats, so as the Evans ice stream is less stable its retreat could promote the subsequent retreat of the Rutford ice steam.
4. The Jakobshavn Glacier has comparable geometry to the Rutford ice steam, and since the Jakobshavn has lost its ice shelf, it has been subject to cliff failures and is postulated to soon be subject to hydrofracturing as well.   Thus if melt pond formation occurs on the FRIS after 2050, hydrofracturing could lead to successive calving of major icebergs from the FRIS over a decade or two that could eventually result in the Rutford and Evans ice streams loosing their ice shelves and thus both could be subject to cliff failures and hydrofracturing before 2090 (note that past collapse events are responsible for the extant geometries of both the Jakobshavn and Rutford bed topologies).
5.  As rates of retreats of the calving faces of both the Rutford/Evans seaway leg and the PIG seaway leg should slow as these calving faces approach the current divide between the two drainage basins; I postulate that advection of warm CDW into these two legs will bore the several kilometer long subglacial cavity that you have noted previously which will allow ocean currents to connect between the Weddell and Amundsen Seas before 2090; which I postulate will accelerate the final collapse of the VAF in this area of the WAIS.

That partial explanation is all that I have time for now about this portion of my 2013 WAIS collapse scenario.

Best,
ASLR


A. P. Wright, A. M. Le Brocq, S. L. Cornford, R. G. Bingham, H. F. J. Corr, F. Ferraccioli, T. A. Jordan, A. J. Payne, D. M. Rippin, N. Ross, and M. J. Siegert, (2014), "Sensitivity of theWeddell Sea sector ice streams to sub-shelf melting and surface accumulation", The Cryosphere, 8, 2119–2134,  www.the-cryosphere.net/8/2119/2014/ (http://www.the-cryosphere.net/8/2119/2014/), doi:10.5194/tc-8-2119-2014

http://www.the-cryosphere.net/8/2119/2014/tc-8-2119-2014.pdf (http://www.the-cryosphere.net/8/2119/2014/tc-8-2119-2014.pdf)

Abstract: "A recent ocean modelling study indicates that possible changes in circulation may bring warm deep-ocean water into direct contact with the grounding lines of the Filchner–Ronne ice streams, suggesting the potential for future ice losses from this sector equivalent to _0.3m of sealevel rise. Significant advancements have been made in our knowledge of both the basal topography and ice velocity in the Weddell Sea sector, and the ability to accurately model marine ice sheet dynamics, thus enabling an assessment to be made of the relative sensitivities of the diverse collection of ice streams feeding the Filchner–Ronne Ice Shelf.  Here we use the BISICLES ice sheet model, which employs adaptive-mesh refinement to resolve grounding line dynamics, to carry out such an assessment. The impact of realistic perturbations to the surface and sub-shelf mass balance forcing fields from our 2000-year “reference” model run indicate that both the Institute and Möller ice streams are highly sensitive to changes in basal melting either near to their respective grounding lines, or in the region of the ice rises within the Filchner–Ronne Ice Shelf. These same perturbations have little impact, however, on the Rutford, Carlson or Foundation ice streams, while the Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by 50% of likely present-day values."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 12, 2015, 04:31:02 PM
In regards to how to interpret Pollard et al 2015's assumption of a step application of Pliocene atmospheric and oceanic conditions on a modern AIS configuration, I provide:

(a) the first image of showing the IPCC AR5 50% CL RCP 8.5 surface temperature increase (from the 1986-2005 mean [so add about 0.7 C to reference to preindustrial]) distribution to circa 2090.
(b) the second image shows the findings of PlioMIP Experiment 2 comparing mid-Pliocene conditions to pre-industrial conditions.

This indicates that unless one assumes: (a) a higher confidence level than 50% for the IPCC RCP 8.5 results; and/or (b) that a state-of-the-art Earth Systems Model analysis (say from ACME) will show that activation of several positive feedback mechanisms will increase Antarctic Amplification in the WAIS region beyond that indicated by the AR5 RCP 8.5 analysis; then the conditions assumed by Pollard et al 2015 are slightly more severe (but comparable) from a surface melt-water point of view than for surface temperature conditions for RCP 8.5 50% CL by 2090.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 12, 2015, 11:58:39 PM
Attached is an old Google image (possibly from 2005) showing melt ponds on the surface of the PIG/PIIS.  As such surface ice melting events become more common in the future (with continued global warming), hydrofracturing of icebergs from the PIG/PIIS will become more common.

Note that this image was taken from the Earthexplorer site at the following link:

http://earthexplorer.usgs.gov/ (http://earthexplorer.usgs.gov/)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 13, 2015, 04:03:23 PM
Lennart,

Don't forget: DeConto R, and Pollard D., (2014), "Antarctica's potential contribution to future sea-level rise", SCAR - COMNAP Symposium, which for modern conditions (not Pliocene) finds that:

"… the same model shows the potential for massive ice and freshwater discharge beginning in the second half of this century.  …
During peak rates of retreat, freshwater discharge exceeds 1 Sv …"

And as previously discussed, since 1 Sv = 86mm of SLR per year, this research indicates that the WAIS might plausibly contribute over 0.86 meters per decade to SLR before the end of this century.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 13, 2015, 08:10:26 PM
While the linked video (from the 2012 "Chasing Ice" documentary) comes from a marine terminating glacier in Greenland, it provides an idea of the cliff failure type of behavior that can be expected in the coming decades for marine glaciers in Antarctica:

https://www.youtube.com/watch?v=hC3VTgIPoGU (https://www.youtube.com/watch?v=hC3VTgIPoGU)

Edit:  Per the description of the video the event happened in 2008 at the: "...  Ilulissat Glacier in Western Greenland. The calving event lasted for 75 minutes and the glacier retreated a full mile across a calving face three miles wide. The height of the ice is about 3,000 feet, 300-400 feet above water and the rest below water."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 13, 2015, 08:12:25 PM
ASLR,

I asked Pollard and DeConto how long this peak discharge lasted in their simulation, but so far they've not replied.

But we can look at Kopp et al 2014 again to see what their maximum estimates are:
http://onlinelibrary.wiley.com/doi/10.1002/2014EF000239/full (http://onlinelibrary.wiley.com/doi/10.1002/2014EF000239/full)

Their table 1 shows these maxima for RCP8.5:
- for 2100 about 2.5m, but the separate maximum contributions from GIS, AIS, etc add up to about 3.5m
- for 2200 about 9.5m, so a 6-7m maximum rise in the century from 2100

For RCP2.6 the maxima are:
- for 2100 about 2m, but separate contributions add up to about 2.75m
- for 2200 about 8m, so a 5.25-6m maximum rise in the century from 2100

Apparently, a risk of 6m SLR from 2100-2200 may already be locked in, no matter what we do, barring great political miracles. And this could still be an under-estimate. So we can only try to reduce the risk and think more about possible adaptation options in the long run.

In the shorter run, it seems we cannot exlcude a risk of about 1 meter/decade for a while from about the last third of this century onwards. So maybe about 4-5m by 2100 can also not be excluded.

This seems to imply we should already think now about adaptation options for such a rise, at least in long term planning processes, and then zooming in on potential local/regional variations from global mean SLR.

If abrupt SLR is defined as 1m in 3 decades, then the risk of such abrupt SLR is not a worst-case, but significantly higher. For this century such a rate of SLR would seem to fit in a total of about 2m by 2100.

Of course, all such numbers are only rough indications/estimates and not very hard/exact. But that's the best we can do for now.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: CraigsIsland on January 13, 2015, 09:42:26 PM
While the linked video (from the 2012 "Chasing Ice" documentary) comes from a marine terminating glacier in Greenland, it provides an idea of the cliff failure type of behavior that can be expected in the coming decades for marine glaciers in Antarctica:

https://www.youtube.com/watch?v=hC3VTgIPoGU (https://www.youtube.com/watch?v=hC3VTgIPoGU)

Edit:  Per the description of the video the event happened in 2008 at the: "...  Ilulissat Glacier in Western Greenland. The calving event lasted for 75 minutes and the glacier retreated a full mile across a calving face three miles wide. The height of the ice is about 3,000 feet, 300-400 feet above water and the rest below water."


That clip still amazes me- thanks for the numbers - I always wondered what the actual sizes were - chasing ice kept comparing it to Manhattan
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 13, 2015, 10:06:00 PM

If abrupt SLR is defined as 1m in 3 decades, then the risk of such abrupt SLR is not a worst-case, but significantly higher. For this century such a rate of SLR would seem to fit in a total of about 2m by 2100.


The point of the US National Research Council, NRC, of defining abrupt SLR as 1m in three decades is not to consider conditions near 2100, but rather to say that what policymakers really want to know is when does the main phase of the collapse start (or said another way: when does the initiation phase leading up to the main collapse phase end). 

You can use any SLR projection curves that you like to determine when this period of ASLR will begin, but as an example using my 2013 Collapse Scenario for SLR curves for RCP 8.5 shown in the attached image, this end of the initiation period would occur in about 2040 for a 95% CL and around 2050 for a 50% CL.  By these times the policymaker would have to have implemented an appropriate defensive plan, or be prepared to deal with the consequences.

Best,
ASLR

Edit: Note that the NRC definition of 1m of SLR per three decades does not mean that the rate of SLR will not increase beyond this rate; only that the policymaker can no longer avoid taking appropriate action after this threshold is past, as appropriate defensive measures take at least 3 decades to implement.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 13, 2015, 10:43:30 PM
The point of the US National Research Council, NRC, of defining abrupt SLR as 1m in three decades is not to consider conditions near 2100, but rather to say that what policymakers really want to know is when does the main phase of the collapse start (or said another way: when does the initiation phase leading up to the main collapse phase end). 

You can use any SLR projection curves that you like to determine when this period of ASLR will begin, but as an example using my 2013 Collapse Scenario for SLR curves for RCP 8.5 shown in the attached image, this end of the initiation period would occur in about 2040 for a 95% CL and around 2050 for a 50% CL.  By these times the policymaker would have to have implemented an appropriate defensive plan, or be prepared to deal with the consequences.

Best,
ASLR

Edit: Note that the NRC definition of 1m of SLR per three decades does not mean that the rate of SLR will not increase beyond this rate; only that the policymaker can no longer avoid taking appropriate action after this threshold is past, as appropriate defensive measures take at least 3 decades to implement.

Thanks for attaching that image again: eye-balling, it shows a potential of around 2 meter/decade SLR for a while in the second part of this century. So if defensive measures need to be ready for implementation by about 2040 at the latest, then contingency planning for such measures needs to start at 2020 at the latest, I would imagine?

Or is 20 years not enough for planning these measures? In that case we would need to start now, and for example the Dutch Delta Committee would need to start thinking an order of magnitude further than they've done so far: from adapting to 20 cm/decade to adapting to 200 cm/decade in the second part of this century. Is that what you're saying?

I corresponded with them just before Christmas, but they say they're monitoring the science and will react to new insights as they think appropriate, but so far IPCC remains leading. They refer me to the government and parliament to voice my concerns there, as they're under direction from the government and cannot change policy on their own.

So now the question is how to best approach government and parliament. I've informed the two most aware parties, and national environmental activists, but without response so far.

I'm also keeping Urgenda and it's laywer informed, who are interested, as they've already sued the government for not mitigating enough. But maybe they should also be sued for not doing enough adaptive planning?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 13, 2015, 11:07:17 PM
ASLR,
I just looked back at your old post in the philosophical thread:
http://forum.arctic-sea-ice.net/index.php/topic,60.msg967.html#msg967 (http://forum.arctic-sea-ice.net/index.php/topic,60.msg967.html#msg967)

I see an estimated 5% chance of 2m by 2070 and of 5.4m by 2100 for global mean SLR, which would be even 20% or so higher for the region of California.

Who commissioned these numbers? And what have they done with them?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 14, 2015, 12:48:23 AM
Lennart,

First, I just re-attached my SLR curves (which are only for RCP 8.5) as an example.  Feel free to use the curves provided by Kopp et al 2014 if that is all that you think that you can sell.  Also, as to when the Dutch Delta Committee would need to revise their guidance documents, I could not say, but it would take at least 30-years to fund, design, permit and build appropriate defensive measures.

Regarding my curves, I developed them in 2012 to try to convince the State of California to adopt this line of thinking (i.e. that a cliff failure & hydrofracture dominated scenario could cause the WAIS to contribute multiple meters of SLR by 2100); however, they declined study this matter at that time as they had just received the findings of the NRC 2012 report (see reference below). So the only thing that has been done with this pre-study work is that I have posted them on this Forum.

NRC, (2012), Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future, Committee on Sea Level Rise in California, Oregon, and Washington; Board on Earth Sciences and Resources and Ocean Studies Board; Division on Earth and Life Studies; The National Academies Press, Washington, D.C.

Best,
ASLR

Edit: Also if you want to find my critiques of the NRC 2012 and other conventional SLR guidance documents you can find them in the "Critique" thread at the following link:

http://forum.arctic-sea-ice.net/index.php/topic,70.0.html (http://forum.arctic-sea-ice.net/index.php/topic,70.0.html)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 14, 2015, 05:25:49 AM
At one foot per decade, retreat is the only plan, for it will not stop there.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: CraigsIsland on January 14, 2015, 06:55:47 AM
Lennart,

First, I just re-attached my SLR curves (which are only for RCP 8.5) as an example.  Feel free to use the curves provided by Kopp et al 2014 if that is all that you think that you can sell.  Also, as to when the Dutch Delta Committee would need to revise their guidance documents, I could not say, but it would take at least 30-day to fund, design, permit and build appropriate defensive measures.

Regarding my curves, I developed them in 2012 to try to convince the State of California to adopt this line of thinking (i.e. that a cliff failure & hydrofracture dominated scenario could cause the WAIS to contribute multiple meters of SLR by 2100); however, they declined study this matter at that time as they had just received the findings of the NRC 2012 report (see reference below). So the only thing that has been done with this pre-study work is that I have posted them on this Forum.

NRC, (2012), Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future, Committee on Sea Level Rise in California, Oregon, and Washington; Board on Earth Sciences and Resources and Ocean Studies Board; Division on Earth and Life Studies; The National Academies Press, Washington, D.C.

Best,
ASLR

Edit: Also if you want to find my critiques of the NRC 2012 and other conventional SLR guidance documents you can find them in the "Critique" thread at the following link:

http://forum.arctic-sea-ice.net/index.php/topic,70.0.html (http://forum.arctic-sea-ice.net/index.php/topic,70.0.html)

Thanks for trying - I appreciate that others are trying when others may not know how. I've written letters to policy makers but I do not know the weight. I hope I can be influential someday to push the science and to be prepared for the impending sea level rise.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 14, 2015, 03:32:28 PM
it would take at least 30-day to fund, design, permit and build appropriate defensive measures.

That seems extremely fast  :)

But 30 years would sound reasonable. So we have to start rethinking now, and most recent science seems to support that conclusion.

But will science be enough to convince policymakers and/or the public, or judges? We're going to find out...
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 14, 2015, 03:42:17 PM
At one foot per decade, retreat is the only plan, for it will not stop there.

Ok, retreat, but how far? What's the best way to respond to a rising ocean and receding shoreline if it's not clear how fast and how far they will keep rising and receding, even when it's clear they will do so for centuries to millennia?

Take the port of Rotterdam, one of the biggest ports in the world. Do we move it back up every 50 years? Or should we move it up to the German border right away, where it could be safe for maybe 100 years or more? What are the options if SLR increases to a foot per decade or more?

Has anyone really thought about such questions yet? Anyone who has any idea of the potential implications (which I hardly have)?

I've heard US Navy Admiral Titley warn against the rising sea for Navy bases such as in Norfolk, Virginia, and maybe also in San Diego, Ca. Maybe we need floating harbours?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on January 14, 2015, 05:10:24 PM
"sea-level rise above the ∼1 m expected by 2100 is possible if ice sheet response begins to exceed present rates"

And is there ANY chance that the ice sheet response will NOT exceed present rates? Isn't it CERTAIN to accelerate?

http://www.icevirtuallibrary.com/content/article/10.1680/feng.14.00014;jsessionid=24wva0tepb9h.x-telford-live-01 (http://www.icevirtuallibrary.com/content/article/10.1680/feng.14.00014;jsessionid=24wva0tepb9h.x-telford-live-01)

More here: https://www.skepticalscience.com/antarctic-ice-sheet-sleeping-giant-beginning-to-stir.html (https://www.skepticalscience.com/antarctic-ice-sheet-sleeping-giant-beginning-to-stir.html)

Title: Re: Potential Collapse Scenario for the WAIS
Post by: Laurent on January 14, 2015, 05:23:04 PM
Off course we have to take account of the reality where even the speed of increase is accelerating exponentially.
There is no way the ports can adapt to what is coming. The only solution I see is making some floating (and moveable) ports able to withstand any increase of SLR.
We have to fix a limit of CO2 eq  that we will maintain and plan accordingly, the target could be around 10 meter (300 ppm).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: jai mitchell on January 14, 2015, 06:31:12 PM
it would take at least 30-day to fund, design, permit and build appropriate defensive measures.

That seems extremely fast  :)

But 30 years would sound reasonable. So we have to start rethinking now, and most recent science seems to support that conclusion.

But will science be enough to convince policymakers and/or the public, or judges? We're going to find out...

We could build seawalls and causeways within 1-2 years that would give us an additional 3-4 decades of planning/implementation time - though, perhaps not at 1 meter per decade with catastrophic storm surges/floods/droughts and global regional instability/market collapses due to famine.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 14, 2015, 06:46:26 PM
The discussion about how to respond to SLR reminds me of JimD's byline: "We do not err because truth is difficult to see. It is visible at a glance. We err because this is more comfortable." Alexander Solzhenitsyn

Under Robust Decision Making, RDM, a decision maker only needs to ask questions that he can reasonably expect answers to; thus if engineers provide answers as to how to practicably respond to SLR then decision makers are prepared to acknowledge more of the actual risks of SLR; otherwise, they just will not ask uncomfortable questions about potential ice sheet collapse probabilities.  Polls show that conservatives will accept climate change science if they believe that geoengineering can be used to respond to the associated risks; otherwise, they will just deny the science.

Unfortunately, necessity is the mother of invention and engineers will not develop practicable responses until society is prepared to acknowledge the risks associated with ASLR.  Therefore, it appears that we will need to wait a few more years to develop appropriate adaptive defense policies for ASLR until either: (a) A state-of-the-art Earth Systems Model, like ACME provides sufficient evidence to support lawsuits to force policy makers to take action; and/or (b) Sufficient inundation damage occurs that the general population (the consensus) forces policy makers to face reality.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 14, 2015, 07:23:17 PM
"Take the port of Rotterdam, one of the biggest ports in the world. Do we move it back up every 50 years? Or should we move it up to the German border right away, where it could be safe for maybe 100 years or more? What are the options if SLR increases to a foot per decade or more?"

To question 1) : yes

to 2) few and ugly. I think half of GRIS and all of WAIS are gone in a couple centuries, so plan on 6m from there alone. With steric and small glaciers/icecaps, say another meter. So around one foot a decade for twenty decades and hope like hell mitigation efforts hold EAIS in check. This is not something you can build seawalls for. Plan migration now, inland infrastructure needs built.

Civil engineering will be the hot profession for a while, first as hopeless battle is joined against rising tides, and then as each skirmish is lost, and full retreat begins.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: bligh8 on January 14, 2015, 08:16:59 PM
As I understand it six Engineering reports were requested by the State of NJ on “How to deal with Sea Level Rise and Beach Erosion”. Of the six the one that made the most sense (to me) was to move the coast line back 19 miles and build a substantial sea wall, in order to by us some time.

So what did the current admin do? 
They ignored all of the engineering reports and then they dumped 122million $ worth of dredged sand on to beach in order to sell beach badges.

We need better forward thinking.

Best,
Bligh
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on January 15, 2015, 01:05:50 AM
I just realized there were 3 questions not two in the quote:

"Take the port of Rotterdam, one of the biggest ports in the world. Do we move it back up every 50 years? Or should we move it up to the German border right away, where it could be safe for maybe 100 years or more? What are the options if SLR increases to a foot per decade or more?"

My answers should have been labelled 2) and 3):

to 2): Move Rotterdam to the border now
to 3): few and ugly. Plan where possible on building twenty feet up at minimum, more as geography allows. Water supply and sewage infrastructure alone will be decades in design and build.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on January 15, 2015, 04:08:36 PM
Apologies if this has been posted before. It also covers GIS, but is mostly on Antarctica. Lots of good graphs and images. P 51 and following really get at the potentials for rapid collapse.

http://www.atmos.washington.edu/~bitz/514_2013/RecentChangesInGreenlandAntarctica_2013.pdf (http://www.atmos.washington.edu/~bitz/514_2013/RecentChangesInGreenlandAntarctica_2013.pdf)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 15, 2015, 06:27:08 PM
I just realized there were 3 questions not two in the quote:

"Take the port of Rotterdam, one of the biggest ports in the world. Do we move it back up every 50 years? Or should we move it up to the German border right away, where it could be safe for maybe 100 years or more? What are the options if SLR increases to a foot per decade or more?"

My answers should have been labelled 2) and 3):

to 2): Move Rotterdam to the border now
to 3): few and ugly. Plan where possible on building twenty feet up at minimum, more as geography allows. Water supply and sewage infrastructure alone will be decades in design and build.

sidd

While such discussions really belong in the "Sea Level Rise" thread in the Consequences folder, I will note that as all choices made by decision makers are made on the margin, it is politically unacceptable for them to take such farsighted actions, and it is far easier for them to label proposals such as sidd is making as either outliers, and/or alarmist; otherwise, they run the risk of being replaced by other representatives that do not ask for so much effort/resources from the public (as future generations cannot vote).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 17, 2015, 12:02:33 AM
The linked reference (with an open access pdf) provides paleo-evidence from the meltwater channels between the Moller & Foundation Ice Streams (see image) in West Antarctica that was a significant amount of surface meltwater transferred to the bed via englacial routing during the Pliocene.  This provides support to the Pollard et al 2015 postulation that the combination of cliff failure and hydrofracturing is critical in accounting for the SLR contribution from the AIS during the Pliocene.  Furthermore, as we are likely headed towards Pliocene conditions after 2050 (when following a BAU pathway); we are likely to experience cliff failures and hydrofracturing once again contributing to a collapse of the WAIS (and nearby marine glaciers in the EAIS) within the next 100 years:

Rose, K., Ross, N., Bingham, R., Corr, H. F. J., Ferraccioli, F., Jordan, T., Le Brocq, A., Rippin, D. & Siegert, M. (2014), "A temperate former West Antarctic ice sheet suggested by an extensive zone of subglacial meltwater channels", Geology(2014),42(11):971-974, doi: 10.1130/G35980.1
http://geology.gsapubs.org/content/42/11/971.abstract (http://geology.gsapubs.org/content/42/11/971.abstract)

Abstract: "Several recent studies predict that the West Antarctic Ice Sheet will become increasingly unstable under warmer conditions. Insights on such change can be assisted through investigations of the subglacial landscape, which contains imprints of former ice-sheet behavior. Here, we present radio-echo sounding data and satellite imagery revealing a series of ancient large sub-parallel subglacial bed channels preserved in the region between the Möller and Foundation Ice Streams, West Antarctica. We suggest that these newly recognized channels were formed by significant meltwater routed along the ice-sheet bed. The volume of water required is likely substantial and can most easily be explained by water generated at the ice surface. The Greenland Ice Sheet today exemplifies how significant seasonal surface melt can be transferred to the bed via englacial routing. For West Antarctica, the Pliocene (2.6–5.3 Ma) represents the most recent sustained period when temperatures could have been high enough to generate surface melt comparable to that of present-day Greenland. We propose, therefore, that a temperate ice sheet covered this location during Pliocene warm periods."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 17, 2015, 12:33:56 AM
The linked reference (with a free pdf) analyzes the bed topography of BEDMAP2 to interpret the glacial geomorphology of the AIS bed, and one of their key findings is that: "The implication is that over successive glacial cycles, the WAIS has become potentially more susceptible to catastrophic retreat." 
See the abstract, extract and associated image of Figure 8 showing the hypothesized erosion domain that indicates extensive erosion beneath the WAIS, which has likely made this ice sheet more susceptible to catastrophic retreat than during prior interglacial periods (such as the Eemian and the Pliocene).

Stewart S.R. Jamieson, Chris R. Stokes, Neil Ross, David M. Rippin, Robert G. Bingham, Douglas S. Wilson, Martin Margold and Michael J. Bentley, (2014), "The glacial geomorphology of the Antarctic ice sheet bed. Antarctic Science", 26, pp 724-741. doi:10.1017/S0954102014000212.

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9404326&fileId=S0954102014000212 (http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9404326&fileId=S0954102014000212)

http://journals.cambridge.org/action/displayFulltext?type=1&fid=9404330&jid=ANS&volumeId=26&issueId=06&aid=9404326&bodyId=&membershipNumber=&societyETOCSession= (http://journals.cambridge.org/action/displayFulltext?type=1&fid=9404330&jid=ANS&volumeId=26&issueId=06&aid=9404326&bodyId=&membershipNumber=&societyETOCSession=)

Abstract: "In 1976, David Sugden and Brian John developed a classification for Antarctic landscapes of glacial erosion based upon exposed and eroded coastal topography, providing insight into the past glacial dynamics of the Antarctic ice sheets. We extend this classification to cover the continental interior of Antarctica by analysing the hypsometry of the subglacial landscape using a recently released dataset of bed topography (BEDMAP2). We used the existing classification as a basis for first developing a low-resolution description of landscape evolution under the ice sheet before building a more detailed classification of patterns of glacial erosion. Our key finding is that a more widespread distribution of ancient, preserved alpine landscapes may survive beneath the Antarctic ice sheets than has been previously recognized. Furthermore, the findings suggest that landscapes of selective erosion exist further inland than might be expected, and may reflect the presence of thinner, less extensive ice in the past. Much of the selective nature of erosion may be controlled by pre-glacial topography, and especially by the large-scale tectonic structure and fluvial valley network. The hypotheses of landscape evolution presented here can be tested by future surveys of the Antarctic ice sheet bed."

Extract: "The erosion of glacier and ice sheet beds to elevations below sea level may have important implications for ice sheet stability. This is because the landscape controls the susceptibility of the overlying ice mass to reaching flotation, becoming influenced by ocean currents, and to a feedback where ice discharge becomes enhanced as it retreats into regions that have become progressively glacially over-deepened (Thomas 1979). Thus, where our map of selective linear erosion (Fig. 8 ) corresponds to beds that would lie near or below sea level under a modern ice load (Fig. 1), the magnitude of that potential destabilizing influence is expected to steadily increase.  Supporting this notion, reconstructions of past Antarctic topography suggest that more of the landscape lay above sea level prior to the onset of glaciation and glacial erosion, particularly in West Antarctica (Wilson et al. 2012). This is confirmed by the volume of offshore sediment and indicates that over the past 14–34 million years the West Antarctic landscape was significantly and progressively lowered below sea level. The implication is that over successive glacial cycles, the WAIS has become potentially more susceptible to catastrophic retreat."

Caption: "Fig. 8. Hypothesized glacial erosion domain classification based upon the earlier framework of glacial landscape evolution developed by Sugden & John (1976)."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 17, 2015, 12:24:27 PM
The supplementary material of Pollard et al 2015 says:
"In the warm-climate model runs, the Earth’s orbit at 1.08 Ma is used (Laskar et al., 2004), which produces exceptionally warm austral summers (Scherer et al., 2008; DeConto et al., 2012)."

So how different would their results be with the current orbit and austral summers?

They also say:
"Past and future changes in regional ocean conditions and basal melting beneath Antarctic ice shelves present a complex and challenging problem. They involve variations in local currents and access to warm Circumpolar Deep Water among other processes that require high-resolution regional ocean models (Hellmer et al., 2012), which would not be feasible for our time scales and varying grounding-line geometry. For the past “warm” runs here, we simply prescribe a uniform 2oC warming of all ocean temperatures above modern climatology to represent either changing ocean currents or actual ocean warming, and continue to use the model’s sub-ice-melt parameterization described above. A regional circum-Antarctic warming of 2oC at intermediate depths is in line with limited reconstructions of warm Pliocene periods (Dowsett et al., 2009), and future atmospheric-oceanic GCM simulations (Overpeck et al., 2006). However, we note that results do not depend strongly on the magnitude of ocean warming; in fact, much the same retreat can be produced by atmospheric warming alone (via melt-driven hydrofracturing and cliff failure), with no oceanic warming at all (section S.7, Fig. S7c)."

So would higher resolution make much difference? And how plausible is it that ocean warming does not produce a much stronger retreat than atmospheric warming alone? Or would that be a consequence of the different orbit and exceptionally warm austral summers?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 17, 2015, 12:42:41 PM
On the resolution of their ice-sheet model Pollard et al 2015 suppl says:
"Dependence on model resolution is a real concern, especially when modeling grounding-line retreat that is sensitive to the bedrock topography in grounding zones. As mentioned above, previous tests in model intercomparison projects and other papers have shown our results to be quite insensitive to grid size, which is mainly attributed to the use of the Schoof (2007) grounding-line flux (Pollard and DeConto, 2009; 2012a). The cliff-failure mechanism is a new challenge, as it requires discerning whether a ~1 km ice face is vertical or not within a horizontal grid of many kilometers. Our numerical treatment is discussed in Appendix A, emphasizing the use of sub-grid parameterizations of grounding-line position and fractional floating-ice cover.

To evaluate the effect of grid size, we repeated the modern and warm-climate simulations (shown above at 10 km resolution) at resolutions of 40 and 20 km for continental Antarctica, and at 5 km for nested domains over the Wilkes, Aurora and Recovery-Slessor-Bailey basins. As shown in Fig. S5a (top row), the modern ice distributions are very close to each other at all resolutions, as expected from previous modern tests (Pollard and DeConto, 2009, 2012a). After warm-climate retreat (bottom row), the results remain close. Some of the innermost regions of East Antarctic basins retreat slightly farther at finer resolution, and Support Force glacier does not retreat at 40 km resolution. But overall the configurations are very much the same, showing that the main results of the paper are independent of model resolution."


The question then is: would resolutions smaller than 5km make much difference? Tony Payne in his simulation linked above earlier showed results of a model with six nested resolutions, with 150m the highest. That made a big difference in their model. And that was without cliff-failure and hydrofracking, I suppose (although those seem less important for the initial WAIS-collapse, but the more so for continued collapse of WAIS and into EAIS).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 17, 2015, 01:17:37 PM
Just to emphasize the conclusions of Pollard et al 2015 suppl on the role of ocean warming, they say:
"All warm-climate simulations above use a uniform oceanic warming of +2 oC above modern climatology. As discussed in section S.3, +2 oC is in line with published estimates of past and future ocean warming, but given the uncertainty in circum-Antarctic ocean response, the most appropriate value is uncertain. However, decreasing oceanic warming even to 0 oC has surprisingly little effect on the results, as seen in Fig. S7c.

This indicates:
i. Nearly all floating ice is removed by enhanced calving due to hydrofracture, with only a minor contribution from oceanic melting, as also seen in Fig. S6. Consequently, widespread cliff failure, drastic basin retreat and ~17 m sea-level rise can be induced by surface warming and enhanced calving alone, without any ocean warming at all.
ii. Conversely, ocean warming on its own, without the new mechanisms, is sufficient to trigger MISI and cause marine West Antarctic Ice Sheet collapse, as shown in Fig. 5."


They also stress the preliminary nature of their results:
"Much of the modeling work here is preliminary, especially involving the new mechanisms of cliff failure and melt-driven hydrofracture. Our parameterizations are exploratory attempts, following steps taken by Bassis and Walker (2012) and Nick et al (2013). The current model contains several uncertain physical choices noted in the relevant sections above (whether cliff failure can occur with unbuttressed ice shelves or only at subaerial cliffs; whether hydrofracturing weakens ice columns at the grounding line; whether high-frequency smaller-scale calving and normal dynamical flow at the grounding line continue or are suppressed in between large sporadic cliff-failure events; whether calving occurs within ice shelves or only at the edges; and whether shelf calving and sub-ice ocean melt are inhibited by narrow seaways).
These choices each have significant effects on the results, although we note that very similar overall results can be obtained by different offsetting combinations. Clearly, these and other aspects should be tested and improved in further work, including:
Higher resolution and better bed topography especially near modern grounding zones of major subglacial basins. 
Testing using ice models with less approximate dynamics (higher order or full Stokes (Pattyn et al., 2013; Seddik et al., 2012; Favier et al., 2014) and higher resolution or adaptive grids in grounding zones (Cornford et al., 2013).
• Detailed viscoelastic modeling of maximum ice cliff size and structural failure (reviewed in Benn et al., 2007).
Ability of ocean melt alone to remove ice shelves all the way back to deep grounding-line faces.
• Surface runoff processes on ice shelves including variable refreezing (van Angelen et al., 2013), hydrofracturing details (Alley et al., 2005), and englacial drainage networks (Parizek et al., 2010).
• Assessment of increased basal lubrication due to greater liquid supply from the surface. However, this effect is considered to be limited by the conversion from distributed to channelized basal hydrology (Schoof, 2010). Warming of internal ice by liquid percolation is already in the model physics (Pollard and DeConto, 2012a), although in a more basic way than some treatments (Phillips et al., 2013).
• Clogging of restricted seaways by mélange of disintegrated ice, partially buttressing and slowing down retreat of grounded ice (Amundson et al., 2010; Cook S. et al., 2013). If WAIS begins to retreat on decadal timescales, it seems possible that export of collapsed ice away from grounding zones could become rate-limiting. This process could also help ice shelves to coalesce and regrow in cooler climates after collapse (Bentley et al., 1960). As discussed above, a crude parameterization was included in earlier model versions, but is not included here to avoid uncertain effects on results.
• Coupling and feedbacks with gravitationally self-consistent Earth-sea level (GIA) models (Gomez et al., 2013; Stocchi et al., 2013).
• Checking that the new mechanisms do not cause unrealistic behavior at other times such as in glacial climates and glacial-to-modern transitions. We have performed some “cold-climate” tests for these periods, where sub-ice melting is small and there is no melt-driven hydrofracturing. The model Antarctic ice shelves are not removed completely and cliff failure does not occur, and results are similar to those in Pollard and DeConto (2009)."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 17, 2015, 06:10:12 PM
Lennart,

Thanks for three great posts in a row.  Pollard et al 2015 do a fine job of fairly indicating that there is more modeling work to be done on this complex topic, and policy makers who make all of their decisions on the margin may likely use this remaining work to justify their inaction (citing that they cannot justify expending public funds/trust without more explicit & detailed projections).  Be that as it may, I reiterate the following selected reasons for using a precautionary approach for interpreting Pollard et al 2015's preliminary findings:

1.  Pollard et al 2015 cite that no earlier models could adequately project SLR conditions from such EAIS marine glaciers as the Wilkes, Aurora and Recovery-Slessor-Bailey basins to reasonably account for at least approximately 17m of sea level rise during the Pliocene.  Thus ignoring cliff failures and hydrofracturing seems highly inadvisable.
2. The telecommunication of energy from the tropical Pacific to the Western Antarctic is well documented and is projected to increase with continued global warming.  Typically this telecommunication of energy is under represented in the AR5 global circulation models, and I fully expect that state of the art ESMs (such as ACME) to verify considerable surface warming of the surface ice of the WAIS after 2050 (following a BAU), which will trigger the critical hydrofracturing mechanism.
3.  The BSB is particularly susceptible to cliff failures and hydrofracturing including reasons beyond those considered by Pollard et al 2015 including: (a) the unusually high basal geothermal warming not only contributes to basal ice melting but also to a reduction of the viscosity of the basal ice (which promotes cliff failures); (b) paleo-collapses of this area in the past have reduced the basal friction and pinning compared to prior collapses thus increasing the instability of our current case; and (c) the projected increase of cyclonic activity in the Amundsen Sea should result in increasing storm surge that should accelerate cliff failures.
4. I cannot believe that this much potential ice mass loss will not trigger increased seismic and volcanic activity.

I could go on but most of my posts in all of the different threads of the Antarctic folder were made to provide supporting evidence for the type of collapse scenario that Pollard et al 2015 are indicating for the future.  I believe that there is more than enough evidence to justify action; however, our biggest climate change crisis is a lack of will-power to take such actions.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 17, 2015, 10:39:11 PM
ASLR,

From a precautionary perspective I'm really interested in getting more insight into the potential effect of higher resolution in the model of Pollard et al. They used 10 km standard resolution and 5 km resolution for a sensitivity analysis. Ice loss was only marginally more with the higher resolution.

But Tony Payne found WAIS to be relatively insensitive in his model with 5 km resolution. Only below 1 km or even below 500m did WAIS lose much more ice more quickly. See from 25m46s in this presentation by Payne that I linked to before:
http://youtu.be/NXjYpilWtQs?t=25m46s (http://youtu.be/NXjYpilWtQs?t=25m46s)

His model may be quite different from that of Pollard et al, I don't know, but still this effect of higher resolution than 5 km may also show up in their model. At least they seem to consider experimenting with higher resolution to be a top priority for their further research, even though their model already seems more sensitive than Payne's. Or maybe the forcing in Payne's was smaller, or more gradual, than in their's?

Wouldn't it be nice if those researchers would drop by here from time to time to answer our questions?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 18, 2015, 03:57:39 PM
His model may be quite different from that of Pollard et al, I don't know, but still this effect of higher resolution than 5 km may also show up in their model. At least they seem to consider experimenting with higher resolution to be a top priority for their further research, even though their model already seems more sensitive than Payne's. Or maybe the forcing in Payne's was smaller, or more gradual, than in their's?

Wouldn't it be nice if those researchers would drop by here from time to time to answer our questions?
Lennart,
1. The Pollard et al 2015 model is certainly different from any other such model (besides DeConto & Pollard 2014, which is essentially the same model with modern forcing) as it includes the combination of cliff failures (from Bassis & Jacobs 2013) and hydrofracturing.
2.  I would certainly imagine that refining the model grid resolution to 500m would probably increase the Pollard et al 2015 model's sensitivity to ice mass loss (however to do so Pollard et al would probably need to limit the area being modeled to different portions of the WAIS, as the ACME program has ordered a custom built computer which will have some of the fastest computing speed in the world when finished).  However, as the Pollard et al model includes cliff failures and hydrofracturing (which Payne et al does not include in their model), I would imagine that the increases in sensitivity of the Pollard et al model to increased ice mass loss will be less than for current models such as used by Payne et al.
3.  As Pollard et al used simple-Pliocene forcing it could be argued that their forcing was "greater" than that used by Payne et al; however, RCP 8.5 roughly catches-up with Pliocene conditions sometime between 2050 and 2100; while the Payne et al model results never exhibit the rapid ice mass loss (1m per decade) indicated by the main collapse phase of the Pollard et al model, because the Payne model does not include either cliff failures or hydrofracturing.
4.   The Pollard et al results indicate that the single most important thing to get right in their model is the surface ice melting (and/or rainfall) and its contribution to hydrofracturing.

Hopefully, other researchers (in-particular those in charge of the ACME program) will be sufficiently impressed by the Pollard et al 2015 findings & methodology that they will include the influences of cliff failures, surface ice melting (and/or rainfall) and hydrofracturing into their models.  I single-out the ACME program because of the complex atmospheric and oceanic interplay in the Antarctic area; which almost all current (ie AR5) GCM projection's do not model particularly well.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 18, 2015, 04:45:57 PM
Good points. Fully agree.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 19, 2015, 08:04:38 PM
The linked article indicates that sediment cores taken through an ice borehole at the Whillans Ice Stream grounding line may (or may not) show that interaction with ocean water is melting the glacial ice at the grounding line faster than researchers previously thought.  While this might not be significant, it is also possible that this may imply that the Ross Sea Sector ice streams are less stable (due to ice ocean interaction) than previously thought:

http://www.scientificamerican.com/article/scientists-drill-through-2-400-feet-of-antarctic-ice-for-climate-clues/ (http://www.scientificamerican.com/article/scientists-drill-through-2-400-feet-of-antarctic-ice-for-climate-clues/)

Also see:
http://grist.org/news/climate-change-could-be-happening-2400-feet-under-antarctic-ice/ (http://grist.org/news/climate-change-could-be-happening-2400-feet-under-antarctic-ice/)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: johnm33 on January 19, 2015, 11:55:41 PM
My understanding is that the tides down there are quite small and with those 2 bursts of movement every day i have to wonder just how little SLR it's going to take to release the whole logjam. Looking at their reported position 84deg S https://en.wikipedia.org/wiki/File:Antarctica_Subglacial_Lakes_Map.png means the whole of the ice shelf is slowly working loose? I'm going to be very interested in when that sedimentation change took place.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on January 20, 2015, 12:06:09 AM
Stupid question time:

If the moon has enough gravitational force to pull on the oceans, wouldn't it also have some gravitational effect on the ice sheet itself, since it is, after all, so massive, and not glued to the bedrock? Is the effect really so miniscule as to not be worth considering? But is it too rigid to be so affected?

I see that the Great Lakes do have some tidal behavior. http://oceanservice.noaa.gov/facts/gltides.html (http://oceanservice.noaa.gov/facts/gltides.html)

The total volume of Lake Superior is 12,000 km^3
The total volume of WAIS is 2.2 million km ^3, of the entire Antarctic ice sheet, 25.4.

http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet (http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet)

So it's certainly massive enough to be affected, even figuring in the differences in density between the ice (much of it highly pressurized, so I don't know how to calculate it precisely) and fresh water.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Laurent on January 20, 2015, 01:24:05 AM
Abruptslr posted a link recently saying that the glacier that was drilled move better when the moon is in line.
http://www.scientificamerican.com/article/scientists-drill-through-2-400-feet-of-antarctic-ice-for-climate-clues/ (http://www.scientificamerican.com/article/scientists-drill-through-2-400-feet-of-antarctic-ice-for-climate-clues/)

Quote
Although other glaciers flow continuously, the Whillans stands still most of the time but then lurches forward twice a day, advancing roughly 45 centimeters each time.

Quote
The twice-daily lurches and icequakes are thought to arise from ocean tides lifting the ice so that it can slide over the sticky spot, relieving mechanical strain that has built up on the glacier since the last high tide
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 20, 2015, 02:05:22 AM
Stupid question time:

If the moon has enough gravitational force to pull on the oceans, wouldn't it also have some gravitational effect on the ice sheet itself, since it is, after all, so massive, and not glued to the bedrock? Is the effect really so miniscule as to not be worth considering? But is it too rigid to be so affected?

wili,

Yes, the moon's gravitational force does pull on the ice sheet itself which does cause rigid body movement, but unlike ice, water flows and produces accumulated tidal motion under the combined influence of the moon and the sun.  Thus while the rigid response of the ice to gravitational forcing might be measured in hundredths to tenth of an inch the tidal range in the Ross Embayment can be 1 to 2 to more feet, twice a day. 

As johnm33 is alluding to, the current IPCC process-based thinking is that the tidal motion of the ice shelf has squeezed the soft bed sediment to form ridges at the Ross Sector ice stream grounding lines; which AR5 believes is pinning/buttressing/resisting the flow of the ice streams in this area; thus if the ocean water (say due to periodic vortex shedding of warm CDW to the grounding lines) is melting the ice at the grounding line (causing the grounding line to retreat upstream of the ridges) then these ice stream could become unpinned and the ice shelf could just float over the top of the ridges.  Still to get a really rapid acceleration of the Ross Sector ice streams would require a significant degradation of the Ross Ice Shelf, RIS; which I believe could be accomplished circa 2060 by a combination of periodic basal melting of the ice shelf due to vortex shedding, and possible surface melt pond hydrofracturing mechanisms similar to what happened at the Larsen B ice shelf.

Best,
ASLR

Edit: In case it is not clear how ice shelves bend under tidal cycles, the attached image shows the Pine Island Ice Shelf, PIIS, bending under tidal action (as measured by satellite)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 23, 2015, 11:09:39 PM
Pollard et al. 2015 have presented a good case that once Pliocene-like conditions prevail in Antarctica (particularly in West Antarctica) that a combination of cliff failures & hydrofracturing could contribute to abrupt SLR, ASLR.  Therefore in this, and following, posts I will briefly discuss the case that chaotic resonance associated with the ENSO phenomena (which is a combination of different forcing modes with multiple periods from annual to decadal eg see the first attached image and different sources from around the globe) can both accelerate the periodic occurrence of Pliocene-like conditions. 

In this first post, I discuss evidence that sometime around 1980 (+/-) the combination of anthropogenic radiative forcing and strong El Nino events triggered an acceleration of contributions from mountain glaciers and ice sheets as shown in the second attached image and as in-particularly indicated by the third attached image for the WAIS ice mass loss.  Similarly, Hay et al 2015 found a rate of GMSL rise from 1901 to 1990 of 1.2 ± 0.2 millimetres per year (90% confidence interval) & they also found that GMSL rose at a rate of 3.0 ± 0.7 millimetres per year between 1993 and 2010, see the fourth attached image (note: the change in trends works even better for the Hay et al data using 1980 +/- as a pivot point).

Hay CC, Morrow E, Kopp RE, Mitrovica JX, (2015) "Probabilistic reanalysis of twentieth-century sea-level rise", Nature. 2015 Jan 14. doi: 10.1038/nature14093

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14093.html (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14093.html)

In my next post, I plan to more clearly relate an unknown portion of this acceleration in ice mass loss contribution (beginning around 1980) to the frequency/period of extreme ENSO events.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 23, 2015, 11:34:11 PM
Following-on to my last post, the first attached image (by the BoM) shows not only the relationship of the Walker Cell to ENSO events (La Nina, Neutral and El Nino), but more importantly to this discussion also the time series for the associate Southern Oscillation Index, SOI, which is a rough indication of ENSO events (positive for La Nina, and negative for El Nino) but more importantly is a good index for the teleconnection of Tropical Pacific atmospheric energy to both the North Pacific and West Antarctica; which is also a function of the Southern Annular Mode, SAM as indicated by the second attached image, that shows how atmospheric Rossby Waves transport Tropical Pacific energy through the atmosphere to both poles (depending on the combination of SAM and ENSO phases). 

The third image shows how solar transmission during the El Chichon volcanic eruption in Mexico in 1982 mitigated the influence of the 1982-83 strong El Nino event (see the first image), while the influence of the 1997-98 strong El Nino on the West Antarctic was mitigate by a positive SAM (note that per the second image a positive SAM stops the Tropical Pac to West Antarctic teleconnection associated with an El Nino).  However, first image shows that in January 2005 the SOI was about negative 30 and also the SAM was negative, which per the second image indicates a teleconnection of energy to the West Antarctic which is supported by the fourth attached image that shows significant surface ice melting in the West Antarctic in January 2005 (which is needed for hydrofracturing).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 23, 2015, 11:59:12 PM
As a follow on to my last post, the first image by England et al 2014 [England, M. et al. (2014), "Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus", Nature Clim. Change 4, 222_227.  See also: Nicola Maher, Alexander Sen Gupta and Matthew H. England, (2014), "Drivers of decadal hiatus periods in the 20th and 21st Centuries", Geophysical Research Letters, DOI: 10.1002/2014GL060527] shows that the 20-year period from roughly 1980 to 2000 was a period of positive IPO (which favors strong El Nino events), which was followed by a period of about fifteen years of negative IPO (associated with La Nina events and the faux global warming hiatus period).  The second attached image shows the SAM time series, which confirms my statement that SAM was negative in January 2005.  The third image shows a correlation of the mean global temperature with both the PDO record and the volcanic record (which is provided for ease of reference).  The fourth attached image, from McGregor et al 2014, shows evidence that current GCMs do a poor job of identifying the inter-relation of the various ocean basins on the ENSO phenomena (see the following abstract and extract associated with the fourth image).  I provide the fourth image to support Cai et al 2014's (see below) point that with continued global warming extreme El Nino events will become at least twice as frequent by 2090 as before 1990, and to set-up my discussion in my next post about how El Nino like conditions in the Tropical Pacific may growth rapidly in the coming decades.

McGregor, S., A. Timmermann, M. F. Stuecker, M. H. England, M. Merrifield, F.-F. Jin and Y. Chikamoto, (2014), "Recent Walker circulation strengthening and Pacific cooling amplified by Atlantic warming", Nature Climate Change; doi:10.1038/nclimate2330
http://web.science.unsw.edu.au/~matthew/nclimate2330-appeared.pdf (http://web.science.unsw.edu.au/~matthew/nclimate2330-appeared.pdf)

Abstract: "An unprecedented strengthening of Pacific trade winds since the late 1990s has caused widespread climate perturbations, including rapid sea-level rise in the western tropical Pacific, strengthening of Indo-Pacific ocean currents, and an increased uptake of heat in the equatorial Pacific thermocline. The corresponding intensification of the atmospheric Walker circulation is also associated with sea surface cooling in the eastern Pacific, which has been identified as one of the contributors to the current pause in global surface warming. In spite of recent progress in determining the climatic impacts of the Pacific trade wind acceleration, the cause of this pronounced trend in atmospheric circulation remains unknown. Here we analyse a series of climate model experiments along with observational data to show that the recent warming trend in Atlantic sea surface temperature and the corresponding trans-basin displacements of the main atmospheric pressure centres were key drivers of the observed Walker circulation intensification, eastern Pacific cooling, North American rainfall trends and western Pacific sea-level rise. Our study suggests that global surface warming has been partly offset by the Pacific climate response to enhanced Atlantic warming since the early 1990s."


Extract: "To further characterize the dynamics of this trans-basin variability (TBV), we define a basin-scale TBV SST index (Fig. 3b) as the monthly mean difference time series of Atlantic-Pacific SSTA…



By comparing the recent 20-yr trend (1992_2011) in the TBV SST index with long-term SST observations (Fig. 4a), we find that the former is unprecedented in the context of the 1872-1992 observations (Fig. 4a). For the 1992-2011 trans-basin SLP trend (Fig. 4b) similarly low probabilities are identified, with values below 0.27% (a 3 standard deviation (3sigma) event, NCEP2 (ref. 23) SLP data) and 0.034% (4.5 sigma event, twentieth century reanalysis SLP data). Comparing the former with overlapping 20-year TBV trends in historical runs (1861-1980, including greenhouse gas, aerosol, volcanic and solar forcings) and RCP8.5 Coupled General Circulation Model experiments (1981-2100), conducted as part of the Coupled Model Intercomparison Project phase 5 (CMIP5; ref. 25), it is found that the current trans-basin SST trend exceeds 3.5sigma of the simulated overlapping 20-year model trends. These results and our global SST-forced CAM4 and AMIP5 model analyses are indicative of a systematic underestimation of atmospheric trans-basin connections on decadal timescales in the current generation of climate models. …"

Cai W, S Borlace, M Lengaigne, P van Rensch, M Collins, G Vecchi, A Timmermann, A Santoso, M J McPhaden, L Wu, M H England,  G Wang,  E Guilyardi, and FF Jin (2014), "Increasing frequency of extreme El Niño events due to greenhouse warming", Nature Climate Change, Published online: 19 January 2014 | doi: 10.1038/nclimate2100


http://www.nature.com/nclimate/journal/v4/n2/full/nclimate2100.html (http://www.nature.com/nclimate/journal/v4/n2/full/nclimate2100.html)


Abstract: "El Niño events are a prominent feature of climate variability with global climatic impacts. The 1997/98 episode, often referred to as ‘the climate event of the twentieth century’, and the 1982/83 extreme El Niño, featured a pronounced eastward extension of the west Pacific warm pool and development of atmospheric convection, and hence a huge rainfall increase, in the usually cold and dry equatorial eastern Pacific. Such a massive reorganization of atmospheric convection, which we define as an extreme El Niño, severely disrupted global weather patterns, affecting ecosystems, agriculture, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide. Potential future changes in such extreme El Niño occurrences could have profound socio-economic consequences. Here we present climate modelling evidence for a doubling in the occurrences in the future in response to greenhouse warming. We estimate the change by aggregating results from climate models in the Coupled Model Intercomparison Project phases 3 (CMIP3) and 5 (CMIP5) multi-model databases, and a perturbed physics ensemble. The increased frequency arises from a projected surface warming over the eastern equatorial Pacific that occurs faster than in the surrounding ocean waters, facilitating more occurrences of atmospheric convection in the eastern equatorial region."

Cai states: "The model is simulating an extreme El Niño event 1 per 20 years from 1891-1990 on average, but from 1991 to 2090 the model simulates a doubling of the frequency of extreme El Niño events."

See also:
https://www.climate.gov/news-features/blogs/enso/climate-change-and-enso-take-2 (https://www.climate.gov/news-features/blogs/enso/climate-change-and-enso-take-2)

Extract: "But these SST changes are occurring in a region where there are known and persistent biases in climate models."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 24, 2015, 12:40:12 AM
Both Kim et al 2014 and Praetorius et al 2014 provide evidence that with continued global warming and with a coming synchronization of the North Pacific and the North Atlantic climates (via warming phases of the PDO and the AMO), El Nino-like conditions should become much more common in the Tropical Pacific through at least the end of this century.  Furthermore, Brigham-Grette et al (2013) provide paleo-evidence that the collapse of the WAIS can lead to rapid Arctic Amplification that can promote an increase of the Equilibrium Climate Sensitivity, ECS.

Seon Tae Kim, Wenju Cai, Fei-Fei Jin, Agus Santoso, Lixin Wu, Eric Guilyardi & Soon-Il An, (2014), "Response of El Niño sea surface temperature variability to greenhouse warming", Nature Climate Change, doi:10.1038/nclimate2326

Summer K. Praetorius, Alan C. Mix, (2014), "Synchronization of North Pacific and Greenland climates preceded abrupt deglacial warming", Science 25 July 2014: Vol. 345 no. 6195 pp. 444-448 DOI: 10.1126/science.1252000


Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel, et al., (2013) "Millennial scale change from Lake El’gygytgyn, NE Russia: Did we step or leap out of the Warm Pliocene into the Pleistocene?"
http://instaar.colorado.edu/meetings/AW2013/abstract_details.php?abstract_id=78 (http://instaar.colorado.edu/meetings/AW2013/abstract_details.php?abstract_id=78)


Julie Brigham-Grette, Martin Melles, Pavel Minyuk, Andrei Andreev, Pavel Tarasov, Robert DeConto, Sebastian Koenig, Norbert Nowaczyk, Volker Wennrich, Peter Rosén, Eeva Haltia, Tim Cook, Catalina Gebhardt, Carsten Meyer-Jacob, Jeff Snyder & Ulrike Herzschuh, (2013), "Pliocene Warmth, Polar Amplification, and Stepped Pleistocene Cooling Recorded in NE Arctic Russia", Science, 340, 1421, doi: 10.1126/science.1233137.

https://www.geo.umass.edu/climate/papers2/BrighamGrette_Science2013.pdf (https://www.geo.umass.edu/climate/papers2/BrighamGrette_Science2013.pdf)

Abstract: "Understanding the evolution of Arctic polar climate from the protracted warmth of the middle Pliocene into the earliest glacial cycles in the Northern Hemisphere has been hindered by the lack of continuous, highly resolved Arctic time series. Evidence from Lake El’gygytgyn, in northeast (NE) Arctic Russia, shows that 3.6 to 3.4 million years ago, summer temperatures were ~8°C warmer than today, when the partial pressure of CO2 was ~400 parts per million. Multiproxy evidence suggests extreme warmth and polar amplification during the middle Pliocene, sudden stepped cooling events during the Pliocene-Pleistocene transition, and warmer than present Arctic summers until ~2.2 million years ago, after the onset of Northern Hemispheric glaciation. Our data are consistent with sea-level records and other proxies indicating that Arctic cooling was insufficient to support large-scale ice sheets until the early Pleistocene."

Next per Real Climate post by Michael E. Mann and Gavin Schmidt (see the first attached image and the extract below):

http://www.realclimate.org/index.php?p=16609 (http://www.realclimate.org/index.php?p=16609)

Extract "Sherwood et al focus on a particular process associated with cloud cover which is the degree to which the lower troposphere mixes with the air above. Mixing is associated with reductions in low cloud cover (which give a net cooling effect via their reflectivity), and increases in mid- and high cloud cover (which have net warming effects because of the longwave absorption – like greenhouse gases). Basically, models that have more mixing on average show greater sensitivity to that mixing in warmer conditions, and so are associated with higher cloud feedbacks and larger climate sensitivity."

That this convective mixing can potentially lead to larger climate sensitivity is supported by the second attached image from Sherwood et al 2014.

Sherwood, S.C., Bony, S. and Dufresne, J.-L., (2014) "Spread in model climate sensitivity traced to atmospheric convective mixing", Nature; Volume: 505, pp 37–42, doi:10.1038/nature12829.
The third image shows how a strengthening of Tropical Pacific Deep Circulation/Convective mixing due either from increased global warming (ala Sherwood et al 2014), or due to a strong El Nino event (see also the fourth attached image) results in an Atmospheric Bridge (due to the deep convection) from the Tropical Pacific to the poles (both near Alaska and near the West Antarctic).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on January 24, 2015, 12:43:58 AM
Thanks for all these links, abstracts and images, ASLR!

Here's one grad students reactions to some of the papers she's been reading about this stuff last year:

http://climatesight.org/2015/01/16/the-most-terrifying-papers-i-read-last-year/ (http://climatesight.org/2015/01/16/the-most-terrifying-papers-i-read-last-year/)

The Most Terrifying Papers I Read Last Year
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 24, 2015, 01:01:31 AM
Thanks wili (I will read the student reactions shortly),

Now I refocus on the influence of the ENSO on the WAIS:

(1) The first image shows how El Nino events tend to warm the Amundsen and Ross Seas, while La Nina's tend to cool them; but I note that El Nino's destabilize WAIS marine glaciers more than La Nina's stabilize them.
(2) The second image shows measurements during the Austral Spring (SON) since about 1980 indicating that the West Antarctic surface temperature anom. has been increasing, while the sea ice extent in the Amundsen-Bellingshausen Sea region has been decreasing.
(3)  The third image shows how the location of the Amundsen Sea Low, ASL, varies with the ENSO, and which indicates that during El Nino events the ASL is located so as that the winds direct warm CDW into the Amundsen Sea Embayment, ASE, (promoting ice mass loss by oceanic melting).
(4) The fourth image shows how since the mid-1970s the ice shelves in the ASE have retreated dramatically due both to global warming and El Nino events, and this retreat will likely accelerate as El Nino-like conditions become increasingly more common in the Tropical Pacific with continued global warming.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 24, 2015, 01:24:08 AM
wili,

It looks like your students have not read Pollard et al 2015 yet; which may give them nightmares if/when they do.

But to wrap-up my series of posts about how extreme El Nino events will become more frequent in the coming decades and how the associated teleconnection of tropical energy will periodically warm the West Antarctic surface temps, which when superimposed on the global warming trend of about 0.8 C per decade (from 1987 to 2007) indicated in the first attached image, will likely lead to my hydrofracturing of Antarctic marine glaciers.  Furthermore, the second attached image shows how the Antarctic areas of surface melting are increasing with time (and also if this trend accelerates could lead to extensive hydrofracturing and cliff failures of Antarctic marine glaciers in the coming decades).

The third attached image shows my attempt to illustrate how a chaotic ENSO phenomena can work to progressively ratchet-up the climate state into conditions with successively greater ECSs.

Lastly, the fourth image shows the experimentally determined shape of a Dragon King PDF; which conceptually could represent the type of climate change risks that the world may be facing if the ENSO/Tropical Pacific Deep Convective Mixing/BAU/WAIS chaotic system resonates over the coming decades to result in not only meters of sea level rise but also possibly ECS values between 5 and 10 C, by 2100.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 24, 2015, 09:17:18 AM
It looks like your students have not read Pollard et al 2015 yet; which may give them nightmares if/when they do.

Terrifying papers fall on a spectrum too...
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 26, 2015, 07:39:22 AM
Alley gave some added comments to his paper with Pollard and DeConto:
http://arstechnica.com/science/2015/01/updated-ice-sheet-model-matches-wild-swings-in-past-sea-levels/ (http://arstechnica.com/science/2015/01/updated-ice-sheet-model-matches-wild-swings-in-past-sea-levels/)

"Step-application of the [warming] is too extreme, clearly…  but, it is within the realm of possibility that for the time-scale of collapse, the true worst worst-case scenario could be even a bit faster than modeled here"
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 26, 2015, 04:47:53 PM
Lennart,

Thanks for yet another great catch.  As the mean global world temperature during the Pliocene was 2 to 3 C warmer than pre-industrial, and following a BAU pathway could result in more than 4 or 5 C by 2100 (assuming a constant ECS); it is relatively easy to see why Alley states that Pollard et al 2015 may not be a worst case scenario w.r.t. SLR for the next 100 to 200 years.  Once global warming gets to the point that the Antarctic Sea Ice extent decreases rapidly, we can expect Antarctic Amplification to accelerate even faster than we are already seeing (particularly for West Antarctica with its teleconnection to the Tropical Pacific).

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on January 26, 2015, 09:02:07 PM
Eric Rignot on scientific conservatism and the inevitable collapse of WAIS:
https://www.youtube.com/watch?v=ANBHZfH4l6M (https://www.youtube.com/watch?v=ANBHZfH4l6M)

Timescales, timescales...
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 27, 2015, 06:41:35 PM
Regarding timescales, the questions of:
(A) "When will the main phase of the WAIS collapse begin?" and
(B) "How fast will the main phase WAIS collapse contribute to SLR?"
Are two issues that currently experts (including Alley and Rignot) are not yet able to answer with sufficient precision for policy makers to revise their SLR guidelines in order to address such recent findings about abrupt collapse as those provided by Pollard et al 2015.  While I cannot provide a precise analysis of the WAIS contribution to SLR (any more than more qualified experts); nevertheless, I can provide the following brief points as to why a relatively early and active WAIS collapse scenario cannot be ruled-out.  Indeed, in the "WAIS Collapse Main Period from 2060 to 2100" thread, I have stated:

http://forum.arctic-sea-ice.net/index.php/topic,85.0.html (http://forum.arctic-sea-ice.net/index.php/topic,85.0.html)

Quote: "… my hazard analysis for RCP 8.5 50% CL forcing is quite aggressive, projecting a eustatic SLR of about 0.5m for the period from 2000 to 2060 (and about 1m of SLR by 2060 for the 95% CL scenario); my SLR projections for my "collapse main period" are more aggressive still, estimating about 3m of eustatic SLR by 2100 for the RCP 8.5 50% CL case, and just over 5m of SLR by 2100 for the RCP 8.5 95% CL case."

Regarding question (A): Rignot has publically commented that the main collapse phase for the WAIS could begin as early as 100-years from now, or as late as 200-years from now; while as noted above (and separate from what the GIS does) I believe that following a BAU the main collapse phase for the WAIS will begin by 2060 for reasons including:

(a) I believe that between now and 2060 the GIS will contribute sufficient surface ice melting and sufficient calving from marine terminating glaciers to help destabilize some of the key West Antarctic marine glaciers and key ice shelves.
(b) I believe that El Nino-like behavior will dominate the Tropical Pacific for the next 15 to 30 years; which will teleconnect energy directly to the West Antarctic, which will promote early collapse of key ice shelves and relatively rapid retreat of key grounding lines.
(c)  I believe that the Southwest Tributary glacier to the PIIS will be triggered to accelerate in the next one to several years, due to major calving events of the PIIS; which in turn will likely active the Thwaites eastern shear margin resulting in an acceleration of the main Thwaites ice stream.
(d) Computer models have projected a major reduction in Antarctic sea ice no later than 2060-2070; which in my mind will trigger the Pollard et al 2015 hydrofracturing mechanism that will rapidly accelerate the cliff failures that I believe will begin occurring in portions of the WAIS by 2060.

Regarding question (B): I believe that Pollard et al 2015's main collapse phase SLR contribution from the WAIS of about 1m per decade may be less that the peak SLR contribution during the 2060 to 2100 period, for reasons including:

(a)  Alley has publically stated that climatic conditions by the main WAIS collapse phase may exceed the Pliocene-like conditions that Pollard et al 2015 imposed on their Antarctic model.
(b) The first attached figure from Bassis & Jacobs (2013) in panel "a" shows the maximum water depth for a given ice thickness in order to prevent a cliff failure.  However, during the main collapse phase (but not necessarily before, due to the GIS fingerprint effect and the density of local meltwater) the fingerprint effect will likely reduce local sea level by several meters, and also isostatic rebound will raise the local seafloor by several meters.  This reduction in local water depth will accelerate cliff failure events, probably beyond that assumed by Pollard et al 2015.

Bassis, J.N., and Jacobs,S., (2013), "Diverse calving patterns linked to glacier geometry", Nature Geoscience, 6, 833–836, doi:10.1038/ngeo1887.

(c) Bassis & Jacobs (2013) do not include the basal drag or the basal ice viscosity considerations evaluated by Van der Veen et al (2011) for the Jakobshaven glacier.  The second attached image (and associate extract below), indicates that for increased basal drag (such as local bed roughness) and lower basal ice viscosity (such as due to the known geothermal energy in the bed of the Byrd Subglacial Basin, BSB, that the upstream ice flow rate will accelerate, which will result in more crevasses that will facilitate more hydrofracturing and cliff failures.

C.J. VAN DER VEEN, J.C. PLUMMER, L.A. STEARNS, (2011), "Controls on the recent speed-up of Jakobshavn Isbræ, West Greenland", Journal of Glaciology, Vol. 57, No. 204.

Extract related to the second attached image: "The contour plots in Figure 8 show that an increase in glacier speed can be achieved by increasing basal drag or driving stress or by lowering the viscosity parameter."

(d)  I cannot believe that if the WAIS is contributing 1m/decade, or more, to SLR that there will not be significant regional seismic and volcanic activity that will both promote calving and surface melting (from volcanic ash).  Furthermore, I believe that combined hydrofacturing and cliff failure events in the BSB will be episodically dynamic which will raise local hydrodynamic water pressures that will also contribute to more calving than Pollard et al 2015's model indicate.

Other threads in this Antarctic folder contain discussion on many other factors (such as the crevasses shown in the third attached image from a Bassis analysis of cracking in key Antarctic ice shelves that would then be subject to hydrofracturing) that may contribute to an early and rapid main collapse phase for the WAIS; which would then lead to collapse of key EAIS marine glaciers.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 31, 2015, 01:03:43 AM
Obviously, a significant increase in surface ice melting in the Antarctic in the coming decades could have a significant impact on ice mass loss via the Pollard et al 2015 postulated hydrofracturing and cliff failures.  Unfortunately, I have had difficulty finding specific projections of such surface ice melting for RCP 8.5 so instead I following link to Surface Ice Melting records for the Antarctic from 1979 to 2014, together with the four selected surface melt plots for the four indicated austral melt seasons (see the linked site for other seasons).  These records indicate to me that it is highly believable that surface ice melting in the lower altitudes of the ASE sector is coming more common and will increase significantly with coming decades:


http://lgge.osug.fr/~picard/melting/ (http://lgge.osug.fr/~picard/melting/)

G. Picard, M.Fily, 2006, Surface melting observations in Antarctica by microwave radiometers: correcting 26 year-long timeseries from changes in acquisition hours. Remote Sensing of Environment.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 07, 2015, 02:01:04 AM
While the linked reference (with a free access pdf) address a hydro-thermodynamic feedback from summer surface ice melt resulting in the surge of calving from a marine terminating glacier in Svalbard; the abstract & conclusions (see extract below) indicate that this newly identified feedback mechanism may soon accelerate ice mass loss from both marine terminating glaciers in Greenland and from marine glaciers in Antarctica (potentially both East and West Antarctica).  While the postulated hydro-thermodynamic feedback mechanism (see the attached image and the associated caption) is less dynamic than the hydro-fracturing and cliff failure mechanism discussed by Pollard et al 2015; it is alarming nevertheless because it appears to be effect at destabilizing and successively mobilizing otherwise stagnant ice regions such as those currently plugging the gateways of such critical glacial drainage basins as the Byrd Subglacial Basin (Thwaites) and the Wilkes Subglacial Basin.  With continuing global warming the postulated hydro-thermodynamic feedback followed by the postulated hydro-fracturing / cliff failure mechanism could deliver a deadly one-two punch to marine terminating, and marine, glaciers in both Greenland and Antarctic sooner than any research thought possible only a few month ago:

Dunse, T., Schellenberger, T., Hagen, J. O., Kääb, A., Schuler, T. V., and Reijmer, C. H.: Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt, The Cryosphere, 9, 197-215, doi:10.5194/tc-9-197-2015, 2015.

http://www.the-cryosphere.net/9/197/2015/tc-9-197-2015.html (http://www.the-cryosphere.net/9/197/2015/tc-9-197-2015.html)

Abstract: "Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the polar regions. Here we present continuous GPS measurements and satellite synthetic-aperture-radar-based velocity maps from Basin-3, the largest drainage basin of the Austfonna ice cap, Svalbard. Our observations demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of Basin-3. The resulting iceberg discharge of 4.2±1.6 Gt a−1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. With the seawater displacement by the terminus advance accounted for, the related sea-level rise contribution amounts to 7.2±2.6 Gt a−1. This rate matches the annual ice-mass loss from the entire Svalbard archipelago over the period 2003–2008, highlighting the importance of dynamic mass loss for glacier mass balance and sea-level rise. The active role of surface melt, i.e. external forcing, contrasts with previous views of glacier surges as purely internal dynamic instabilities. Given sustained climatic warming and rising significance of surface melt, we propose a potential impact of the hydro-thermodynamic feedback on the future stability of ice-sheet regions, namely at the presence of a cold-based marginal ice plug that restricts fast drainage of inland ice. The possibility of large-scale dynamic instabilities such as the partial disintegration of ice sheets is acknowledged but not quantified in global projections of sea-level rise."

Extract from the Conclusions: "We propose a hydro-thermodynamic feedback mechanism triggered by surface melt reaching a growing fraction of the glacier bed. Intrusion of surface melt to the glacier bed provides an efficient heat source through CHW, facilitating a thermal switch from cold to temperate basal conditions, permitting for basal motion. Initiation of hydraulic lubrication, along with rising pore-water pressure within subglacial sediments, further enhances basal motion, eventually destabilizing the overlying ice.



Given continued climatic warming and increasing surface melt, we hypothesize that the hydro-thermodynamic feedback may gain significance in other glaciated areas, including the ice sheets. In light of recent record melt and rising ELA of the Greenland Ice Sheet, the proposed mechanism has the potential to lead to a long-term enhancement of outlet glacier discharge and calving loss, as earlier proposed by Phillips et al. (2013). Our expectation contrasts with recent studies that indicate limited effects of surface-melt-induced acceleration on the future net mass balance of the Greenland Ice Sheet (Nick et al., 2013; Shannon et al., 2013). Surface melt in Antarctica is presently mainly constrained to the ice shelves (Comiso, 2000). Given strong continued warming, surface melt will increasingly occur over coastal areas of Antarctica, making the grounded ice-sheet margins vulnerable to the hydro-thermodynamic feedback."

Caption: "Figure 5. Schematic illustration of the proposed hydro-thermodynamic feedback to summer melt, imbedded within the surge cycle of Basin-3, Austfonna. The approximate start of each phase is indicated at the bottom. Phase 1 follows from long-term changes in glacier geometry, i.e. build-up of a reservoir, and associated changes in driving stress and basal thermal regime. The hydro-thermodynamic feedback loop operates over several years during phase 2 and 3, each loop coinciding with consecutive summer melt periods. Successive mobilization and destabilization initiates the surge. Dynamic thinning, reduction in driving stress and basal heat dissipation eventually terminate the surge.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 07, 2015, 04:01:47 AM
The following is a follow-up to my Reply #305, and I also note that this reminds me of the surge of the Thwaites Ice Tongue in September 2012 (see link):

http://forum.arctic-sea-ice.net/index.php/topic,21.0.html (http://forum.arctic-sea-ice.net/index.php/topic,21.0.html)


The rate of surface elevation reduction from the Austfonna glacier in Norway's Svalbard island chain discussing in the linked article is striking:

http://www.washingtonpost.com/news/energy-environment/wp/2015/01/23/an-arctic-ice-caps-shockingly-rapid-slide-into-the-sea/?postshare=6211422039245668 (http://www.washingtonpost.com/news/energy-environment/wp/2015/01/23/an-arctic-ice-caps-shockingly-rapid-slide-into-the-sea/?postshare=6211422039245668)

Extract: "Ice is disappearing at a truly astonishing rate in Austfonna, an expanse of frozen rock far north of the Arctic Circle in Norway’s Svalbard island chain. Just since 2012, a portion of the ice cap covering the island has thinned by a whopping 160 feet, according to an analysis of satellite measurements by a team led by researchers at Britain’s University of Leeds.
Put another way, the ice cap’s vertical expanse dropped in two years by a distance equivalent to the height of a 16-story building. As another comparison, consider that scientists were recently alarmed to discover that one of Western Antarctica’s ice sheets was losing vertical height at a rate of 30 feet a year."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on February 07, 2015, 04:46:50 AM
""We propose a hydro-thermodynamic feedback mechanism triggered by surface melt reaching a growing fraction of the glacier bed. Intrusion of surface melt to the glacier bed provides an efficient heat source through CHW, facilitating a thermal switch from cold to temperate basal conditions, permitting for basal motion. Initiation of hydraulic lubrication, along with rising pore-water pressure within subglacial sediments, further enhances basal motion, eventually destabilizing the overlying ice."

Yes. Basal hydrology is a key, and i fear, too often neglected.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 07, 2015, 03:29:46 PM
Yes. Basal hydrology is a key, and i fear, too often neglected.

In this regards, the first attached image shows the change in elevation in the Thwaites Glacier from January 2012 to January 2013, during which time a "surge" of the Thwaites Ice Tongue occurred from about Sept to Dec 2012.  Thus the over 6m of elevation drop shown in the figure could have occurred in as little as four months (not twelve).

The second image shows main portions of the subglacial hydrological system beneath Thwaites, indicating that no surface meltwater was needed to trigger the Sept to Dec 2012 surge event of the Thwaites Ice Tongue, as the basal water was delivered via the indicated subglacial hydrological system (note this somewhat old images does not show the interconnected system of subglacial lakes and "swamps" that have subsequently been identified.

To emphasize the importance of the hydro-thermodynamic of this basal meltwater I provide both: (a)  the following Aschwanden et al 2012 reference; and (b) the third attached image (from the PISM glacial model write-up) showing the difference in basal ice viscosity between glaciers with cold basal conditions and those with temperate basal conditions.

Andy ASCHWANDEN et al, (2012), "An enthalpy formulation for glaciers and ice sheets", Journal of Glaciology, Vol. 58, No. 209, doi: 10.3189/2012JoG11J088 441

Abstract: "Polythermal glaciers contain both cold ice (temperature below the pressure-melting point) and temperate ice (temperature at the pressure-melting point). This poses a thermal problem similar to that in metals near the melting point and to geophysical phase-transition processes in mantle convection and permafrost thawing. In such problems the part of the domain below the melting point is solid while the remainder is at the melting point and is a solid/liquid mixture.  Generally, the liquid fraction of that mixture may flow through the solid phase. For ice specifically, viscosity depends both on temperature and liquid water fraction, leading to a thermomechanically coupled and polythermal flow problem."

The last image that I attach of the Thwaites surface condition was taken by the Sentinel 1a satellite on Oct 22 2014, and shows a number of crevasses in the glacial ice in the neighborhood of the Thwaites gateway.  This indicates that should a large El Nino event occur in the 2015-2016 austral summer season, associated surface meltwater would have ready-made pathways through the crevasses down the basal ice along much of the entire gateway and not only at the base of the old residual ice tongue.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 24, 2015, 01:08:38 AM
The linked reference show that the US NRC is seriously considering the use of geoengineering in order to regulate the Earth's surface temperature.  While geoengineering may be an act of desperation, but as the extract from the LA Times indicates as we are approaching desperate times, policy makers may, in several decades time, decide that they will need to implement geoengineering.  If so, this would presumably reduce the risk of the hydrofacturing mechanism cited by Pollard et al 2015, which would leave only the cliff failure mechanism; which the attached figure indicates would result in a much lower rate of sea level rise for as long as we can prevent extensive surface ice melt in the WAIS.   

NRC, (2015), "Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration"

http://www.nap.edu/catalog/18805/climate-intervention-carbon-dioxide-removal-and-reliable-sequestration (http://www.nap.edu/catalog/18805/climate-intervention-carbon-dioxide-removal-and-reliable-sequestration)

See also:
http://www.latimes.com/nation/la-na-climate-technology-20150210-story.html (http://www.latimes.com/nation/la-na-climate-technology-20150210-story.html)

Extract: "The lack of progress for more than two decades, however, makes it “increasingly likely that as a society we will need to deploy” some forms of the least-risky technologies to reduce the Earth's temperature, they said."

http://www.slate.com/articles/health_and_science/science/2015/02/nrc_geoengineering_report_climate_hacking_is_dangerous_and_barking_mad.html (http://www.slate.com/articles/health_and_science/science/2015/02/nrc_geoengineering_report_climate_hacking_is_dangerous_and_barking_mad.html)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: LRC1962 on February 25, 2015, 12:00:41 AM
Provided of course that the geoE does not turn out to have even more harmful affects then te melt. Get any group of engineers in a room and they will all have a sure fire cure to any problem. The main problem usually turns out that they tend to ignore any factors that may nullify their wonderful solution..(see WW1 when Germans used gas, works wonders until wind changes direction on you).
The unfortunate thing about geoE the Earth is that it will be another experiment that will take many generations to find out the out come and yet the ones doing the work will be convinced it  is the solution and therefore will not have to do anything about what is causing the crisis in the first place, GHG. Punt that ball down the road again.
Question: where is the real money coming from to do the geoE? If big oil has any input in it I am positive that they also intend the the ball is punted waaay down that road.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 25, 2015, 12:48:59 AM
Provided of course that the geoE does not turn out to have even more harmful affects then te melt. Get any group of engineers in a room and they will all have a sure fire cure to any problem. The main problem usually turns out that they tend to ignore any factors that may nullify their wonderful solution..(see WW1 when Germans used gas, works wonders until wind changes direction on you).
The unfortunate thing about geoE the Earth is that it will be another experiment that will take many generations to find out the out come and yet the ones doing the work will be convinced it  is the solution and therefore will not have to do anything about what is causing the crisis in the first place, GHG. Punt that ball down the road again.
Question: where is the real money coming from to do the geoE? If big oil has any input in it I am positive that they also intend the the ball is punted waaay down that road.

LRC1962,

All good points, but I think that we need to realize that when climate damage reaches a socially unacceptable level (say by 2050) that the desperate citizens will turn to their government(s) and demand aggressive action comparable to military action (note that when President LBJ warned the US Congress 50-years ago of the probable consequences of anthropogenic global warming, that he was also advised that Solar Radiance Management, SRM, could deal with this future risk so he went ahead and gunned the US economy all that he could in the 1960's).  As to who would pay for it, I believe it likely that military budgets would be used from a coalition of willing countries (estimates have been made that an SRM might cost $30 Billion a year to implement using a fleet of heavy-lift military transport planes; which, would probably be less than 1/100th the annual cost of the climate change related damage by 2050, [plus normally policymakers would be implementing a parallel Negative Emission Technology, NET, campaign (like afforestation to try to suck CO2 out of the atmosphere; which could add many tens of billions per year to the cost depending on the plan]).

It is all quite a dice roll, but looking at our situation, it looks like the directions that things are headed.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 25, 2015, 05:23:07 PM
As a follow-on to my Reply #309 that aggressive use of Solar Radiation Management, SRM, could possibly counter-act some (or possibly all) of the influence of Pliocene-type climatic hydrofracturing in Antarctica modeled by Pollard et al 2015; in this post I would like to present some key caveats to any such aggressive SRM type policy with regard to potential abrupt SLR contributions from the AIS:

- The Pliocene-type of climate modeled by Pollard et al 2015 had global mean surface temperature anomalies that were 2 to 3 C above pre-industrial levels, and it is unlikely that any aggressive SRM plan would be implemented until we are well into that surface temperature range, so we can expect some decades of hydrofracturing in the AIS before SRM adequately limits surface ice melting.  Furthermore, we do not know that any SRM program will be implemented uniformly between the Northern, and Southern, Hemispheres.

- Currently, surface ice melting occurs all around the perimeter of Antarctic at low elevations, and once the "ice plugs" are lost in drainage basins for the: ASE, Wilkes, Recovery, and other key marine glacial basins; the perimeter elevations in these key gateways will drop and the width of the gateways will become much wider.

- The width of the gateways of such key Antarctic marine glacial drainage basins will limit the effectiveness of the buttressing action of any ice mélanges associated with the cliff failure mechanism, and will the 3-D response of the cliff failure mechanism as compared to the likely 1-D response modeled by Pollard et al 2015 and Bassis et al (2013); thus the  Pollard et al 2015 curve for the cliff failure mechanism likely errs on the side of least drama.

-  Other reasons to believe that the Pollard et al 2015 estimate of SLR contribution from the AIS without strong hydrofacturing likely errs on the side of least drama include: (a) the grid spacing of the Pollard et al model is too coarse; (b) the model underestimates the influence of the ocean on AIS ice mass loss including from (I) continued warming of the CDW due to ocean thermal inertia after 2060 (which will continue for at least 40-years after an aggressive SRM plan is ramped up); (II) changes in local ocean currents; (III) the possible formation of sub-glacial ocean passageways between the Pine Island trough and the Weddell Sea.

- It is quite probable that by 2060 the FRIS possible the RIS could be subjected to a series of major calving events around their calving faces due to ice melt pond effects (note the low elevation of these ice shelves promotes hydrofracturing); which would reduce ice shelf buttressing on the associated marine glaciers and would likely expose the Recovery drainage basin to cliff failures.

- SRM may not get the ENSO phenomena of increasing frequency of strong El Ninos under control for many decades which could sustain the teleconnection of Pacific Tropical energy directly to the WAIS for many decades after 2060.

-Once the ice plug for the BSB drainage basin is lost say by 2050, the importance of the high geothermal energy in this area could sustain abrupt ice mass loss for decades without hydrofracturing until the ASE marine glaciers have contributed at least 1 m of ASLR by 2100.

- Once the "slow" response positive feedback mechanisms (e.g. permafrost, tundra shrubs & albedo reduction, methane from peat sources, etc) are triggered, it will likely take decades before SRM slows these positive feedback mechanisms.

I am out of time, but the moral of the lesson is that SRM is not a magic wand permitting BAU behavior, and we need to get GHG emissions under control or we run a significant risk of damage from abrupt SLR contribution from the AIS (& outlet glaciers in Greenland) by 2100 (possibly to the extent that total SLR by 2100 might be on the order of 2 to 3m of SLR by 2100 even with an aggressive SRM plan started by 2050 and ramped up by 2060).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: S.Pansa on March 11, 2015, 03:18:59 PM
Interesting new paper just surfaced in the Journal of Glaciology regarding MIS stability, especially WAIS.

Victor C. Tsai, Andrew L. Stewart, Andrew F. Thompson. Marine ice-sheet profiles and stability under Coulomb basal conditions. Journal of Glaciology, 2015; 61 (226): 205 DOI: 10.3189/2015JoG14J221 (http://dx.doi.org/10.3189/2015JoG14J221) (open access)

Quote
ABSTRACT. The behavior of marine-terminating ice sheets, such as the West Antarctic ice sheet, is of interest due to the possibility of rapid grounding-line retreat and consequent catastrophic loss of ice. Critical to modeling this behavior is a choice of basal rheology, where the most popular approach is to relate the ice-sheet velocity to a power-law function of basal stress. Recent experiments, however, suggest that near-grounding line tills exhibit Coulomb friction behavior. Here we address how Coulomb conditions modify ice-sheet profiles and stability criteria. The basal rheology necessarily transitions to Coulomb friction near the grounding line, due to low effective stresses, leading to changes in ice-sheet properties within a narrow boundary layer. Ice-sheet profiles ‘taper off’ towards a flatter upper surface, compared with the power-law case, and basal stresses vanish at the grounding line, consistent with observations. In the Coulomb case, the grounding-line ice flux also depends more strongly on flotation
ice thickness, which implies that ice sheets are more sensitive to climate perturbations. Furthermore, with Coulomb friction, the ice sheet grounds stably in shallower water than with a power-law rheology. This implies that smaller perturbations are required to push the grounding line into regions of negative bed slope, where it would become unstable. These results have important implications for ice-sheet stability in a warming climate.

Some quotes from the press release:

Quote
... Research by Caltech scientists now suggests that estimates of future rates of melt for the West Antarctic Ice Sheet--and, by extension, of future sea-level rise--have been too conservative. In a new study ... a team led by Victor Tsai ... found that properly accounting for Coulomb friction--a type of friction generated by solid surfaces sliding against one another--in computer models significantly increases estimates of how sensitive the ice sheet is to temperature perturbations driven by climate change. ...

"Our results show that the stability of the whole ice sheet and our ability to predict its future melting is extremely sensitive to what happens in a very small region right at the grounding line. It is crucial to accurately represent the physics here in numerical models," says study coauthor Andrew Thompson, an assistant professor of environmental science and engineering at Caltech.

...

According to Tsai, many earlier models of ice sheet dynamics tried to simplify calculations by assuming that ice loss is controlled solely by viscous stresses, that is, forces that apply to "sticky fluids" such as honey--or in this case, flowing ice. The conventional models thus accounted for the flow of ice around obstacles but ignored friction. "Accounting for frictional stresses at the ice sheet bottom in addition to the viscous stresses changes the physical picture dramatically," Tsai says.

...

In most previous models, the ice sheet sits firmly on the bed and generates a downward stress that helps keep it attached it to the seafloor. Furthermore, the models assumed that this stress remains constant up to the grounding line, where the ice sheet floats, at which point the stress disappears.

Tsai and his team argue that their model provides a more realistic representation--in which the stress on the bottom of the ice sheet gradually weakens as one approaches the coasts and grounding line, because the weight of the ice sheet is increasingly counteracted by water pressure at the glacier base. "Because a strong basal shear stress cannot occur in the Coulomb model, it completely changes how the forces balance at the grounding line," Thompson says.

...

"We predict that the ice sheets are more sensitive to perturbations such as temperature," Tsai says.

Read more  here (http://www.sciencedaily.com/releases/2015/03/150310105228.htm) on Science Daily.

Edit: Thanks AbruptSLR, just recognized my mess ::) Links should work now.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 11, 2015, 04:09:18 PM
S.Pansa,
Thanks for the great reference on the stability of marine and marine-terminating glaciers.  For those who had trouble with the links, I provide the following link to an open access pdf and the attached image showing the difference between the previously assumed Power Law and the more accurate Coulomb analysis.

http://www.igsoc.org/journal/61/226/t14j221.pdf (http://www.igsoc.org/journal/61/226/t14j221.pdf)

Furthermore, the linked web article by Kitware, elaborates on the three key goals [focused on water cycle, biochemistry, and cryosphere systems] for the first three years of the ACME (Accelerated Climate Model – Energy) program, with the cryosphere effort focused on determining the stability of the AIS for the coming 40-years.  Hopefully, Kitware will incorporate a Coulomb analysis in their state of the art ACME model:

http://www.prweb.com/releases/2015/02/prweb12539509.htm (http://www.prweb.com/releases/2015/02/prweb12539509.htm)

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on March 11, 2015, 08:35:45 PM
Thanx for the reference to the Tsai paper. It's actually a rather good review of Schoof(2007) in addition to  the new analysis. I note they raise the exponent in the dependence of mass flux upon grounding line thickness to 5 from 4.75
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on March 14, 2015, 01:40:35 AM
Nice episode of VICE on HBO, featuring Eric Rignot on WAIS-collapse:
https://www.youtube.com/watch?v=_h92Ath_2XA&feature=youtu.be (https://www.youtube.com/watch?v=_h92Ath_2XA&feature=youtu.be)

We need more of these.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 14, 2015, 03:01:42 AM
Lennart,

Thank you.  I hope that Vice President Biden is correct that the belief in climate change will grow rapidly in the USA in the next few years.  But even if he is correct, belief is one thing, and actions are another.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 19, 2015, 07:08:34 PM
The linked reference (with an open access pdf) presents comparative projected ice discharge quantities for the Weddell & Amundsen Seas, as calculated by PRISM (see attached image).  This analysis indicates that for their model & set of assumptions that the Weddell Sea Sector construction to SLR is more sensitive to increases in ocean temperature than is the ASE.  However, as there is a good degree of uncertainty (in my mind at least) that the PRISM projection is appropriate for the ASE, I will wait to see the ACME projections in about 3-years, before I have any confidence that the ASE is not likely to begin making abrupt contributions to SLR within the next 40-years.

Martin, M. A., Levermann, A., and Winkelmann, R. (2015), "Comparing ice discharge through West Antarctic Gateways: Weddell vs. Amundsen Sea warming", The Cryosphere Discuss., 9, 1705-1733, doi:10.5194/tcd-9-1705-2015.

http://www.the-cryosphere-discuss.net/9/1705/2015/tcd-9-1705-2015.html (http://www.the-cryosphere-discuss.net/9/1705/2015/tcd-9-1705-2015.html)

Abstract: "Future changes in Antarctic ice discharge will be largely controlled by the fate of the floating ice shelves, which exert a back-stress onto Antarctica's marine outlet glaciers. Ice loss in response to warming of the Amundsen Sea has been observed and investigated as a potential trigger for the marine ice-sheet instability. Recent observations and simulations suggest that the Amundsen Sea Sector might already be unstable which would have strong implications for global sea-level rise. At the same time, regional ocean projections show much stronger warm-water intrusion into ice-shelf cavities in the Weddell Sea compared to the observed Amundsen warming. Here we present results of numerical ice sheet modelling with the Parallel Ice Sheet Model (PISM) which show that idealized, step-function type ocean warming in the Weddell Sea leads to more immediate ice discharge with a higher sensitivity to small warming levels than the same warming in the Amundsen Sea. This is consistent with the specific combination of bedrock and ice topography in the Weddell Sea Sector which results in an ice sheet close to floatation. In response to even slight ocean warming, ice loss increases rapidly, peaks and declines within one century. While the cumulative ice loss in the Amundsen Sea Sector is of similar magnitude after five centuries of continued warming, ice loss increases at a slower pace and only for significantly higher warming levels. Although there is more marine ice stored above sea level in close vicinity of the grounding line compared to the Weddell Sea Sector, the ice sheet is farther from floatation and the grounding line initially retreats more slowly."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: lisa on March 20, 2015, 03:16:40 PM
Lennart van der Linde, the video linked in #315 needs a password.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on March 20, 2015, 05:23:02 PM
Lisa, I don't have it, it was public when I posted it, sorry  :-\
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on March 22, 2015, 07:13:21 AM
That Martin paper has another scary graphic, fig 10, which i attach. Weddell could be the next,bigger Amundsen.

Sell coastal flood insurance short.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 26, 2015, 08:44:23 PM
The linked reference indicates that the West Antarctic ice sheet volume loss has accelerated by 70% in the last decade; which should resulting in increased SLR contribution from the WAIS (see extract from the LA Times):

Fernando S. Paolo, Helen A. Fricker & Laurie Padman, (2015), "ICE SHEETS - Volume loss from Antarctic ice shelves is accelerating", Science DOI: 10.1126/science.aaa0940

http://www.sciencemag.org/content/early/2015/03/25/science.aaa0940 (http://www.sciencemag.org/content/early/2015/03/25/science.aaa0940)

Abstract: "The floating ice shelves surrounding the Antarctic Ice Sheet restrain the grounded ice-sheet flow. Thinning of an ice shelf reduces this effect, leading to an increase in ice discharge to the ocean. Using eighteen years of continuous satellite radar altimeter observations we have computed decadal-scale changes in ice-shelf thickness around the Antarctic continent. Overall, average ice-shelf volume change accelerated from negligible loss at 25 ± 64 km3 per year for 1994-2003 to rapid loss of 310 ± 74 km3 per year for 2003-2012. West Antarctic losses increased by 70% in the last decade, and earlier volume gain by East Antarctic ice shelves ceased. In the Amundsen and Bellingshausen regions, some ice shelves have lost up to 18% of their thickness in less than two decades."

See also:

http://www.latimes.com/science/sciencenow/la-sci-sn-antarctic-ice-shelves-melting-faster-20150326-story.html (http://www.latimes.com/science/sciencenow/la-sci-sn-antarctic-ice-shelves-melting-faster-20150326-story.html)

Extract: “The frozen fringes of western Antarctica have been melting 70% faster in the last decade, raising concern that an important buttress keeping land-based ice sheets from flowing to the sea could collapse or vanish in coming decades, a new study shows.



They hold back the ice discharge from the ice sheet into the ocean," Paolo said. "In the long term, that is the main concern from losing volume from an ice shelf.”
The study adds to growing concern that climate change has altered the equilibrium of growth and melt on a part of the continent holding an estimated 530,000 cubic miles of ice. That's enough ice to raise the sea level by 11 feet, by some estimates.
“If the rate of change that we have observed remains the same, then we should expect a larger contribution of the ice sheet to sea level rise," Paolo said.
Shelves in the Bellingshausen and Amundsen seas had the most rapid thinning, losing an average of 24 to 63 feet per decade, according to the study, which analyzed satellite-based radar data from 1994-2012.
The most dramatic loss occurred on the Venable ice shelf on the Bellingshausen Sea, which thinned by an average of 118 feet per decade, according to the study. At that rate, it could disappear in 100 years. The same fate could befall the Crosson shelf on the Amundsen Sea, the study found.
Those rates are conservative "lower bound" estimates, said Paolo."

Edit: See the attached plot from the paper
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 16, 2015, 01:16:52 AM
Re:post # 318,
"Martin, M. A., Levermann, A., and Winkelmann, R. (2015), "Comparing ice discharge through West Antarctic Gateways: Weddell vs. Amundsen Sea warming", The Cryosphere Discuss., 9, 1705-1733, doi:10.5194/tcd-9-1705-2015."

They note that Moller and Institute might be closer to rapid retreat (compared to PIG, Thwaites, ASE) than I thought, because a lot of the ice there is closer to flotation. But now i see Cornford(2015) doi:10.5194/tcd-9-1887-2015, also open access, using BISICLES (vertically integrated as opposed to 3D PISM SSA+SIA of Martin, but with higher rez, as you would expect) and they do not see this. They do see retreat, but first in ASE.

Note:

1) Martin(2015) uses step forcing, Cornford(2015) uses models of expected atmos + ocean forcing of various models

2) Thwaites behaves weirdly in Cornford.

3) Cornford confirms that icestream from Thwaites joining PIG as the trigger (as AbruptSLR suspected)

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 16, 2015, 02:11:28 AM
sidd,

Thanks for the reference.  I believe that BISICLES is the base program to be used in the ACME program for ice sheet modeling.  This paper seems to show the fastest rate of retreat for ASE (see attached image) that I have seen BISICLES project to date, so I will be interested in seeing what projection they have by the end of the first phase of the ACME project (as well as in their final projection in about 10-years).  However, I would be even more interested if the ACME WAIS models adopt the cliff failure and hydrofracturing methodology developed by Pollard et al (2015).

Cornford, S. L., Martin, D. F., Payne, A. J., Ng, E. G., Le Brocq, A. M., Gladstone, R. M., Edwards, T. L., Shannon, S. R., Agosta, C., van den Broeke, M. R., Hellmer, H. H., Krinner, G., Ligtenberg, S. R. M., Timmermann, R., and Vaughan, D. G. (2015), "Century-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate", The Cryosphere Discuss., 9, 1887-1942, doi:10.5194/tcd-9-1887-2015.

http://www.the-cryosphere-discuss.net/9/1887/2015/tcd-9-1887-2015.pdf (http://www.the-cryosphere-discuss.net/9/1887/2015/tcd-9-1887-2015.pdf)

Abstract: "We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet.  Each of the simulations begins with a geometry and velocity close to present day observations, and evolves according to variation in meteoric ice accumulation, ice shelf melting, and mesh resolution. Future changes in accumulation and melt rates range from no change, through anomalies computed by atmosphere and ocean models driven by the E1 and A1B emissions scenarios, to spatially uniform melt rates anomalies that remove most of the ice shelves over a few centuries. We find that variation in the resulting ice dynamics is dominated by the choice of initial conditions, ice shelf melt rate and mesh resolution, although ice accumulation affects the net change in volume above flotation to a similar degree. Given sufficient melt rates, we compute grounding line retreat over hundreds of kilometers in every major ice stream, but the ocean models do not predict such melt rates outside of the Amundsen Sea Embayment until after 2100. Sensitivity to mesh resolution is spurious, and we find that sub-kilometer resolution is needed along most regions of the grounding line to avoid systematic under-estimates of the retreat rate, although resolution requirements are more stringent in some regions – for example the Amundsen Sea Embayment – than others – such as the Möller and Institute ice streams."

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 16, 2015, 05:01:01 AM
BISICLES is based on the vertically integrated Schoof and Hindmarsh treatment from 2011, so they can get good x-y rez, since they rely on the reliability of the vertical integral to sum over z. While I have enormous respect for anything Schoof does, i think in a few years we can have efficient codes to do the full 3D stokes at reasonable computational cost.  In that respect i actually think the Martin 3D PISM-PIK might be the right way to go, although it relies on SSA+SIA approximation which expands in the aspect ratio of the sheet which is a small number, so has some chance of converging.

The major problem is the difficulty both approaches (to be fair, there are problems with any approach) have is that they fail spectacularly, for example in places where bedrock slope or till properties change too fast. In this respect I quote Cornford(2015)

" An adjustment in the region of Pine Island Glacier’s grounding line was required, prior
to the relaxation, to prevent sustained thickening of the order of 100 m/a . A similar
tendency is seen in other models of Pine Island Glacier, and is dealt with elsewhere
by imposing a large synthetic mass balance (Joughin et al., 2010), by constraining
the ice viscosity and accepting a worse match to the observed velocity (Favier et al.,
2014), or by modifying the bed to give acceptable thickening rates while matching the
observed velocity (Rignot et al., 2014; Nias et al., 2015). Here, we soften the ice around
the grounding line, by reducing the stiffening factor ..."

"We also adjusted the initial conditions in the region of Thwaites Glacier, but for the
opposite reason. Without any adjustment, Thwaites Glacier thinned and the grounding
line began to retreat given the accumulation and melt rates described above. This was
prevented in some of our simulations by adding a highly localized (10 km radius) region
of 5 m/a extra accumulation to a0 . Recent observations and modelling indicate that
the unstable retreat of Thwaites Glacier may have begun early in the 21st century ..."

So I think, wait for a decade for a real full stokes, with good basal hydrology for detail answers.

Another thing that struck me was an effect that illuminates the vicious nature of the straits we are in. The BAU A1B scenario actually dumps more snow on AIS than the 450ppm E1 scenario, so that mitigating from A1B to E1 increases SLR over the next couple hundred years.  Not that I believe either the models or the scenarios entirely ...

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on April 16, 2015, 08:09:49 AM
Also see the end of this 2013 presentation (posted earlier) by Tony Payne, co-author of Cornford et al. 2015, on BISICLES, meshed resolutions and connection between PIG and Thwaites retreat/collapse:
https://www.youtube.com/watch?v=NXjYpilWtQs&feature=youtu.be&t=25m46s (https://www.youtube.com/watch?v=NXjYpilWtQs&feature=youtu.be&t=25m46s)

The speed up in collapse at higher resolution is remarkable. Add in hydrofracturing and cliff failure, and rates of collapse would probably be much faster still.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 16, 2015, 07:50:49 PM
In that Payne video, you can really see how PIG triggers Thwaites
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Iceismylife on April 18, 2015, 09:36:07 PM
ASLR,

The 1.2 meters/century of Grant et al (2012) is for sea levels below present, the 0.7 m/century for up to 5 m above present. I understand the 0.7 m/century to be the max speed averaged over several centuries, so on shorter time scales the max speed could be higher. I do find their wording not entirely clear, however.

...
That is the easiest way to hedge.


Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on April 19, 2015, 08:56:38 AM
ASLR,

The 1.2 meters/century of Grant et al (2012) is for sea levels below present, the 0.7 m/century for up to 5 m above present. I understand the 0.7 m/century to be the max speed averaged over several centuries, so on shorter time scales the max speed could be higher. I do find their wording not entirely clear, however.

...
That is the easiest way to hedge.

I was referring to Grant et al 2012 then, where it was not so clear to me if they meant at least 0.7 meter/century during interglacials, or at most 0.7 m/cy:
http://www.highstand.org/erohling/Rohling-papers/2012-Grant-et-al-nature11593.pdf (http://www.highstand.org/erohling/Rohling-papers/2012-Grant-et-al-nature11593.pdf)

We can now also look at Rohling et al 2013:
http://www.highstand.org/erohling/Rohling-papers/2013-Rohling-ea-Sci-Repts-srep03461.pdf (http://www.highstand.org/erohling/Rohling-papers/2013-Rohling-ea-Sci-Repts-srep03461.pdf)

They say:
"Initial (Red Sea-based) LIg SLR rate estimates of 1.6 +/- 1.0 m cy-1 lacked direct age control. Subsequent studies proposed 1000-year average LIg rates of ~0.26 m cy-1 and 0.56–0.92 m cy-1, which is consistent with a 1000-year smoothed estimate of 0.7 +/- 0.4 m cy-1 over the -5 to +5 m sea-level range based on improved dating of the Red Sea record. Note that such smoothing masks brief intervals with more rapid rise. Data from western Australia suggest a rapid rise within the LIg at 0.6 m cy-1. We infer that LIg SLR likely occurred at sustained rates of ~1 m cy-1 or less."

So sustained rates of more than 1 meter/century during interglacials seem unlikely, although they can't be excluded, especially on shorter timescales. With current forcings it could be probably be much more.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 20, 2015, 12:14:42 AM
The linked reference (with an open access pdf) focuses on the influence of tides on changes in the subglacial water system that then result in cyclical accelerations in the ice flow velocities of the Rutford Ice Stream.  This research has direct relevance to other Weddell Sea marine glaciers; and indicate that this region is more likely to contribute to accelerating sea level rise rates than previously expected.

Rosier, S. H. R., Gudmundsson, G. H., and Green, J. A. M. (2015), "Temporal variations in the flow of a large Antarctic ice-stream controlled by tidally induced changes in the subglacial water system", The Cryosphere Discuss., 9, 2397-2429, doi:10.5194/tcd-9-2397-2015.

http://www.the-cryosphere-discuss.net/9/2397/2015/tcd-9-2397-2015.html (http://www.the-cryosphere-discuss.net/9/2397/2015/tcd-9-2397-2015.html)

Abstract: "Observations show that the flow of Rutford Ice Stream (RIS) is strongly modulated by the ocean tides, with the strongest tidal response at the 14.77 day tidal period (Msf). This is striking because this period is absent in the tidal forcing. A number of mechanisms have been proposed to account for this effect, yet previous modeling studies have struggled to match the observed large amplitude and decay length scale. We use a nonlinear 3-D viscoelastic full-Stokes model of ice-stream flow to investigate this open issue. We find that the long period Msf modulation of ice-stream velocity observed in data cannot be reproduced quantitatively without including a coupling between basal sliding and tidal subglacial water pressure variations. Furthermore, the subglacial water system must be highly conductive and at low effective pressure, and the relationship between sliding velocity and effective pressure highly nonlinear in order for the model results to match GPS measurements. Hydrological and basal sliding model parameters that produced a best fit to observations were a mean effective pressure N of 105 kPa, subglacial drainage system conductivity K of 7 × 109 m2d-1, with sliding law exponents m = 3 and q =10. Coupled model results show the presence of tides result in a ~ 12% increase in mean surface velocity. Observations of tidally-induced variations in flow of ice-streams provide stronger constraints on basal sliding processes than provided by any other set of measurements."

Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 20, 2015, 06:11:37 AM
So sustained rates of more than 1 meter/century during interglacials seem unlikely, although they can't be excluded, especially on shorter timescales. With current forcings it could be probably be much more.

i would not take comparison to previous interglacials too seriously. We have suppressed the next glacial for millennia. This interglacial is gonna be a loooong one.

But just for for a fun comparison to the last interglacial, let me drag up an oldie but a goodie, John Mercer in full cry from1968 exhibiting hindsight, insight and foresight. Not the now famous paper from 1978, this one is ten years older.

"ANTARCTIC ICE AND SANGAMON SEA LEVEL [1] John H. MERCER, Institute of Polar Studies, Ohio State University, USA"
[1] Contribution No. 139 of the Institute of Polar Studies. Supported by National Science Foundation Grant GA-136

Sangamon can be read as Eemian here, the last interglacial.

"ABSTRACT
Lake sediments and inactive solifluxion flows in central Antarctica indicate that
summer temperatures were 7°C to 10°C higher than they are today sometime during
the Pleistocene. A temperature rise of this amount would have little effect on the
East Antarctic Ice Sheet, which has probably existed since the late Pliocene, but all
ice shelves would be destroyed, because they consist of "cold" ice and cannot exist
where the mean temperature of the warmest month is much above freezing point. The
portion of the West Antarctic Ice Sheet that is grounded below sea level and is in
dynamic equilibrium with the Ross and Filchner ice shelves would disintegrate, raising
sea level by about 4 m to 6 m. That this has happened at least once during the
Pleistocene is suggested by a well-marked sea level stand of about 6 m, dated by
uranium and thorium isotopes at about 120,000 years ago, probably at the end of the
Sangamon Interglacial. The present West Antarctic Ice Sheet has re-formed since then."

The Abstract is, charmingly, reproduced in French as well, which I haven't seen lately except in French publications such as Journal de Physique. Perhaps this was published in a French journal.

He goes on:

"Thus the West Antarctic Ice Sheet is an uniquely vulnerable and unstable body of
ice which cannot exist unless composed of "cold" ice throughout. Although it reaches
2000 m above sea level, the elevated portions would in no way help it to survive if
average summer temperature rose above freezing point at sea level. Furthermore,
compared to the slow melting away of an ice sheet of similar size on land, its dis-
appearance by disintegration into the sea would be rapid, perhaps even catastrophic."

and from the summary and conclusions:

"The evidence given by West and Sparks (1961) that the rise in sea level to above present levels took place during the Sangamon Hypsithermal and was very rapid, suggests possible catastrophic disintegration of the West Antarctic Ice Sheet at that time, but further evidence is needed."

There is a fascinating discussion too at the end, dealing with penguin rookeries ...

I have attached Fig 1, for Mercer's idea of the last interglacial

sidd


Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 21, 2015, 11:24:54 PM
The linked reference cites greater uncertainty about warming trends in West Antarctica; and while denialist will cite this as a reason to continue down a BAU emissions pathway; to me this is greater evidence that as we now come out of the recent faux "hiatus" period, that the likely combination of long-term natural temperature variability (such as the PDO cycle) together with anthropogenic global warming, indicates that we are likely entering a period of unusually high warming in West Antarctica.

Ludescher, J., Bunde, A., Franzke, C., Schellnhuber, H.J. (2015), "Long-term persistence enhances uncertainty about anthropogenic warming of West Antarctica", Climate Dynamics, DOI: 10.1007/s00382-015-2582-5

http://link.springer.com/article/10.1007/s00382-015-2582-5 (http://link.springer.com/article/10.1007/s00382-015-2582-5)

Abstract: "Previous estimates of the strength and the uncertainty of the observed Antarctic temperature trends assumed that the natural annual temperature fluctuations can be represented by an auto-regressive process of first order [AR(1)]. Here we find that this hypothesis is inadequate. We consider the longest observational temperature records in Antarctica and show that their variability is better represented by a long-term persistent process that has a propensity of large and enduring natural excursions from the mean. As a consequence, the statistical significance of the recent (presumably anthropogenic) Antarctic warming trend is lower than hitherto reported, while the uncertainty about its magnitude is enhanced. Indeed, all records except for one (Faraday/Vernadsky) fail to show a significant trend. When increasing the signal-to-noise ratio by considering appropriate averages of the local temperature series, we find that the warming trend is still not significant in East Antarctica and the Antarctic Peninsula. In West Antarctica, however, the significance of the trend is above 97.4%, and its magnitude is between 0.08 and 0.96 °C per decade. We argue that the persistent temperature fluctuations not only have a larger impact on regional warming uncertainties than previously thought but also may provide a potential mechanism for understanding the transient weakening (“hiatus”) of the regional and global temperature trends."

See also:

http://www.reportingclimatescience.com/news-stories/article/natural-variability-plays-bigger-role-in-antarctic-than-thought.html (http://www.reportingclimatescience.com/news-stories/article/natural-variability-plays-bigger-role-in-antarctic-than-thought.html)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Iceismylife on April 22, 2015, 10:35:04 PM
...

So sustained rates of more than 1 meter/century during interglacials seem unlikely, although they can't be excluded, especially on shorter timescales. With current forcings it could be probably be much more.
There are two processes that lead to sea level rise.  Taking an ice pick to ice above sea level, braking it up then floating it out to sea and melting in situ.

Melting at a rate more than 1 meter/century seems unlikely.

How fast can ice be broken up and floated out to sea?

My read on this is very fast. 10 meters/century doesn't look to be imposable, and may even be likely.

(not to discount thermal expansion but ice volume above flotation is the fastest way to get sea level rise.)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 22, 2015, 11:50:34 PM
10 meters/century doesn't look to be imposable, and may even be likely.

While I can imagine scenarios where 10 meters of SLR could possibly occur by 2115, calling such imagined scenarios "likely" would seem to require some support explanation as to how the EAIS and the GrIS could lose multi-meters each in this timeframe.

Therefore, Iceismylife, do you care to enlighten us all as to what scenarios you are imagining?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Richard Rathbone on April 23, 2015, 12:20:01 PM
I'd imagine its scenarios like enough ice breaking up and falling into the sea from the WAIS during March 2065 to raise the sea level by 1 centimeter.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: Jim Hunt on April 23, 2015, 03:12:52 PM
Somewhat belatedly NASA Earth Observatory reports that "Iceberg B-34 Makes Its Debut off Antarctica"

http://earthobservatory.nasa.gov/IOTD/view.php?id=85727 (http://earthobservatory.nasa.gov/IOTD/view.php?id=85727)

Quote
On March 6, 2015, the U.S. National Ice Center (NIC) discovered a new iceberg adrift off the coast of Antarctica. Measuring 27 kilometers (17 miles) long, iceberg B-34 meets the 19-kilometer minimum required for tracking by the NIC.

The berg appears to have fractured from West Antarctica’s Getz Ice Shelf and moved out into in the Amundsen Sea sometime in mid- to late-February 2015.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 23, 2015, 06:09:08 PM
I'd imagine its scenarios like enough ice breaking up and falling into the sea from the WAIS during March 2065 to raise the sea level by 1 centimeter.

Per the attached image the maximum that the WAIS could contribute to SLR would be 4.8 m (more realistically 4.3m as it has high mountain glaciers); so are you imagining splitting the remaining 5.7m between the EAIS & the GrIS equally by 2115?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Iceismylife on April 23, 2015, 06:33:31 PM
10 meters/century doesn't look to be imposable, and may even be likely.

While I can imagine scenarios where 10 meters of SLR could possibly occur by 2115, calling such imagined scenarios "likely" would seem to require some support explanation as to how the EAIS and the GrIS could lose multi-meters each in this timeframe.

Therefore, Iceismylife, do you care to enlighten us all as to what scenarios you are imagining?
https://www.youtube.com/watch?v=ezcgPAptbIk (https://www.youtube.com/watch?v=ezcgPAptbIk)
If you advance the calving face in the Jakobshovn glacier far enough into the ice sheet then you could flow ice out of it like a scaled up version of this ice flow video. A 5 mile wide ice flow at 1,500 feet deep at 8 miles per hour will flow 100,000 cubic miles of ice a year.

If you look at the Bosphorus http://en.wikipedia.org/wiki/Bosphorus (http://en.wikipedia.org/wiki/Bosphorus) you have sea water from the Mediterranean flowing into the black sea under less salty water from the black sea flowing in the opposite direction and they flow at a reasonably high speed.

Antarctica's ice shelfs are going away.  With the buttresses removed the ice sheets flow fast, but the question isn't, "How fast the ice sheets will flow?" it is, how fast they will brake up and float out to sea?

My opinion is very fast.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 23, 2015, 07:47:07 PM
10m/century represents a vary large amount of heat. 100 cm/yr=1000mm/yr=1e23 Joule/yr = 3000 Terawatt

By comparison the total net radiative imbalance (about 1 watt/sq m) corresponds to about 60 mm/yr ice melt. So about 16 times net radiative imbalance going only into the ice sheets.

There is only one heat store that can do that, that's from the ocean. This scale of ice breakup and flow into the ocean would handily reverse the net increase in OHC ...

More seriously, ice flow at 8 miles/hr hasn't been seen yet., and i do not think the models come up with those speeds.  A better way to get heat into the ice is ... rain. Consider what hurricane Sandy would have done to the saddle in GIS at 67 N.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on April 23, 2015, 08:45:07 PM
100 cm/yr

I suppose you mean 10 cm/yr, for 10 meter/century?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 24, 2015, 01:37:57 AM
10m/century represents a vary large amount of heat. 100 cm/yr=1000mm/yr=1e23 Joule/yr = 3000 Terawatt

By comparison the total net radiative imbalance (about 1 watt/sq m) corresponds to about 60 mm/yr ice melt. So about 16 times net radiative imbalance going only into the ice sheets.

There is only one heat store that can do that, that's from the ocean. This scale of ice breakup and flow into the ocean would handily reverse the net increase in OHC ...

More seriously, ice flow at 8 miles/hr hasn't been seen yet., and i do not think the models come up with those speeds.  A better way to get heat into the ice is ... rain. Consider what hurricane Sandy would have done to the saddle in GIS at 67 N.

sidd

sidd,

Besides agreeing with Lennart that your heat calculations per year are 10 times too high (which is somewhat beside the point when considering James Hansen's armada of icebergs circling Antarctic and melting over a century after a collapse of the WAIS) ; I concur that rainfall is a very important issue, not because it might provide heat for surface ice melting, but because it could promote a rapid manifestation of Pollard el al 2015's cliff failure & hydrofracting collapse mechanism for portions (say the ASE portion) of the WAIS, by providing direct surface water for the pre-existing crevasses in say the ASE marine glaciers.

In this regards, the linked January 15, 2015 Science Daily article (& associated image) discusses the concerns of the authors of the Gorodetskaya et al (2014) paper (previously cited in this folder) about the 2009 and 2011 nine atmospheric river, AR, events that dropped hundreds of gigatonnes of snow in Dronning Maud Land.  The following extract indicates that the authors were concern that their results not be misinterpreted to imply that SLR contribution from the AIS will be less than previously assumed (i.e. because future snow accumulation would limit net mass loss); when the authors actual want to convey alarm that multiple atmospheric rivers are even impacting Antarctica, with unknown future consequences.

In the worst case image that by 2040 the current positive PDO phase has teleconnected sufficient energy to the ASE that if a series of AR event were to then strike the ASE that the precipitation fell as rain instead of snow, at least in the lower altitude coastal areas.  This could trigger a series of cliff failure and hydrofracturing events that could conceivable result in major grounding line retreats of multiple ASE marine glaciers; which could form an small version of the iceberg armada like Hansen envisioned in just one or two years.

http://www.sciencedaily.com/releases/2015/01/150120112206.htm (http://www.sciencedaily.com/releases/2015/01/150120112206.htm)

Caption: "L indicates the atmospheric river's low-pressure trough and H indicates the blocking high-pressure ridge further downstream, directing moisture transport (red arrows) into the Dronning Maud Land and the Princess Elisabeth base (white square). The colours show total moisture amounts (in centimetres equivalent of water)."

Extract from Science Daily: "The findings point to atmospheric rivers' impressive snow-producing power. "When we looked at all the extreme weather events that took place during 2009 and 2011, we found that the nine atmospheric rivers that hit East Antarctica in those years accounted for 80 per cent of the exceptional snow accumulation at Princess Elisabeth station," says Irina Gorodetskaya.

And this can have important consequences for Antarctica's diminishing ice sheet. "There is a need to understand how the flow of ice within Antarctica's ice sheet responds to warming and gain insight in atmospheric processes, cloud formation and snowfall," adds Nicole Van Lipzig, co-author of the study and professor of geography at KU Leuven.

A separate study found that the Antarctic ice sheet has lost substantial mass in the last two decades -- at an average rate of about 68 gigatons per year during the period 1992-2011.

"The unusually high snow accumulation in Dronning Maud Land in 2009 that we attributed to atmospheric rivers added around 200 gigatons of mass to Antarctica, which alone offset 15 per cent of the recent 20-year ice sheet mass loss," says Irina Gorodetskaya.

"This study represents a significant advance in our understanding of how the global water cycle is affected by atmospheric rivers. It is the first to look at the effect of atmospheric rivers on Antarctica and to explore their role in cryospheric processes of importance to the global sea level in a changing climate," says Martin Ralph, contributor to the study and Director of the Center for Western Weather and Water Extremes at the University of California, San Diego.

"Moving forward, we aim to explore the impact of atmospheric rivers on precipitation in all Antarctic coastal areas using data records covering the longest possible time period. We want to determine exactly how this phenomenon fits into climate models," says Irina Gorodetskaya.

"Our results should not be misinterpreted as evidence that the impacts of global warming will be small or reversed due to compensating effects. On the contrary, they confirm the potential of Earth's warming climate to manifest itself in anomalous regional responses. Thus, our understanding of climate change and its worldwide impact will strongly depend on climate models' ability to capture extreme weather events, such as atmospheric rivers and the resulting anomalies in precipitation and temperature," she concludes."


Irina V. Gorodetskaya, Maria Tsukernik, Kim Claes, Martin F. Ralph, William D. Neff, Nicole P. M. Van Lipzig. The role of atmospheric rivers in anomalous snow accumulation in East Antarctica. Geophysical Research Letters, 2014; 41 (17): 6199 DOI: 10.1002/2014GL060881

http://onlinelibrary.wiley.com/doi/10.1002/2014GL060881/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014GL060881/abstract)

Abstract: "Recent, heavy snow accumulation events over Dronning Maud Land (DML), East Antarctica, contributed significantly to the Antarctic ice sheet surface mass balance (SMB). Here we combine in situ accumulation measurements and radar-derived snowfall rates from Princess Elisabeth station (PE), located in the DML escarpment zone, along with the European Centre for Medium-range Weather Forecasts Interim reanalysis to investigate moisture transport patterns responsible for these events. In particular, two high-accumulation events in May 2009 and February 2011 showed an atmospheric river (AR) signature with enhanced integrated water vapor (IWV), concentrated in narrow long bands stretching from subtropical latitudes to the East Antarctic coast. Adapting IWV-based AR threshold criteria for Antarctica (by accounting for the much colder and drier environment), we find that it was four and five ARs reaching the coastal DML that contributed 74–80% of the outstanding SMB during 2009 and 2011 at PE. Therefore, accounting for ARs is crucial for understanding East Antarctic SMB."

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 24, 2015, 05:22:07 AM
mea culpa.

but the amount of heat is still around 1e22 J/yr which will also reverse OHC increase, and is still 1.6 annual net radiative imbalance ...

the armada of icebergs thing can only happen if the ice can flow into the ocean faster than models indicate

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 24, 2015, 05:48:42 AM
Also, this armada of icebergs thing is irrelevant to SLR ... once a bit of ice floats, SLR from that bit is done. So all the SLR melt is on _grounded_ice, and the heat has to get to grounded ice.

In short, VAF of grounded ice is the thing to watch. Ocean will invade from below, and rain from above. SLR will come from ice melting in place. And the heat has to get to that place.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: solartim27 on April 24, 2015, 07:59:48 AM
Also, this armada of icebergs thing is irrelevant to SLR ... once a bit of ice floats, SLR from that bit is done. So all the SLR melt is on _grounded_ice, and the heat has to get to grounded ice.

In short, VAF of grounded ice is the thing to watch. Ocean will invade from below, and rain from above. SLR will come from ice melting in place. And the heat has to get to that place.

The heat does not need to melt the ice In Situ.  As the grounded ice fractures and then starts to float away, the SLR is immediate.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: oren on April 24, 2015, 08:54:58 AM
In short, Antarctica or parts thereof could become and armada of icebergs for much less the energy than required to melt all those icebergs later.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on April 24, 2015, 01:44:11 PM
The question that this hypothesis depends upon is the floating ice flow rate prior to becoming oceanic. Perhaps heavy enough rain could keep the bergs separated and provide the needed volume of water for flushing the ice. An Antarctic monsoon hypothesis, more or less.

The continent is fairly dry now, but it seems to me that would require a huge volume of water, given the size of bergs to be carried. Lake Missoula-type releases as formed the Columbia Gorge might be sufficient, moving ice instead of basalt. So, if rainwater could form large ponds under or on the ice, to be followed by periodic releases as ice dams collapse, it seems to me that sufficient flows might be generated, repeatedly clearing channels that refill after each discharge.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Richard Rathbone on April 24, 2015, 01:55:37 PM
I'd imagine its scenarios like enough ice breaking up and falling into the sea from the WAIS during March 2065 to raise the sea level by 1 centimeter.

Per the attached image the maximum that the WAIS could contribute to SLR would be 4.8 m (more realistically 4.3m as it has high mountain glaciers); so are you imagining splitting the remaining 5.7m between the EAIS & the GrIS equally by 2115?

10 meters in the next century is one possible scenario that involves a rate of 10 meters per century, but its not the only one. Do you actually believe that its impossible to get a sea level rise of 1cm in March 2065 without having a sea level rise of 1cm in every month from now until 2065 and in every month from then until 2115 or do you just not understand that rates of 100 meters per millenium and 10 meters per century and 1 meter per decade are the same thing expressed in different units?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Richard Rathbone on April 24, 2015, 02:00:23 PM
In short, Antarctica or parts thereof could become and armada of icebergs for much less the energy than required to melt all those icebergs later.

And in the absence of detailed calculations a factor of 10 seems a reasonable estimate to me. 1 meter per century from in situ melt or 10 times that from falling into the sea to float away and melt later.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 24, 2015, 11:01:13 PM
In short, Antarctica or parts thereof could become and armada of icebergs for much less the energy than required to melt all those icebergs later.

oren,

I am not sure what everyone else is saying on this topic, but I concur with you that given Pollard et al (2015) cliff failure and hydrofracturing response, an armada of icebergs is clearly plausible, even without rainfall (i.e. with only surface meltwater) if we stay on a BAU pathway through at least 2040 to 2050 (which will guarantee that we reach the Pliocene conditions that Pollard et al 2015 assume before the end of this century).  Without forming an armada of icebergs how could one achieve the rates of SLR contribution indicated by the attached plot from Pollard et al 2015?

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on April 24, 2015, 11:29:10 PM
Any mechanism that is not gradual is hard to model. Ice dam formation and release is at its base a catastrophic process capable of moving far greater masses of solids quickly down riverine channels than a gradual process using the same amount of fluids. 

We know the Bretz Floods happened; any such process in Antarctica would increase the centennial slr over the quantity without it given the same rainfall and heat flux. The pressurized ponds under the Thwaites might provide surprises when combined with cliff fracturing. Gradualism is not a safe religion, if mathematically convenient. The highest Pollard estimates would prove low.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 25, 2015, 06:02:00 AM
does anyone have the total VAF (volume above flotation) for AIS handy ? i seem to recall it was estimated to be about 3.5m or so for WAIS, so the 10m/century thing couldn't go on too long, unless EAIS got involved ...

MWP1A was 5m/century for 500 years, a meter every score of years, but there was a lot more ice about then.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 25, 2015, 12:18:05 PM
does anyone have the total VAF (volume above flotation) for AIS handy ? i seem to recall it was estimated to be about 3.5m or so for WAIS, so the 10m/century thing couldn't go on too long, unless EAIS got involved ...

MWP1A was 5m/century for 500 years, a meter every score of years, but there was a lot more ice about then.

sidd,
While I asked & answered the same question in Reply #337; I provide the following extract from Wikipedia for the WAIS potential SLR contribution:

http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet (http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet)

Extract: "It has been hypothesised that this disintegration could raise sea levels by approximately 3.3 metres (11 ft). (If the entire West Antarctic Ice Sheet were to melt, this would contribute 4.8 m (16 ft) to global sea level.)"
Also, I provide the accompanying table (in meters) from Pfeffer 2011 for the potential SLR contributions for both the AIS & the GIS (GrIS); which concur with the figure in Reply #337.

Also, remember that the Pollard et al (2015) SLR projections include contributions from the EAIS (see my Reply #349).

Very Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: oren on April 25, 2015, 02:24:19 PM
When discussing the 10 meter SLR over a century there is also thermal expansion, and some other factors I am not an expert of. So I don't think the whole 10m is supposed to come from GIS WAIS and EAIS. This must have been discussed many times somewhere on the forum.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 25, 2015, 05:35:54 PM
When discussing the 10 meter SLR over a century there is also thermal expansion, and some other factors I am not an expert of. So I don't think the whole 10m is supposed to come from GIS WAIS and EAIS. This must have been discussed many times somewhere on the forum.

oren,

There are many different ways of thinking about the various different levels of plausible SLR contributions from different sources by 2100 or later, and you can find some of those discussions in the linked thread below:

http://forum.arctic-sea-ice.net/index.php/topic,874.300.html (http://forum.arctic-sea-ice.net/index.php/topic,874.300.html)

The accompany four images are taken from that thread with the first image showing the AR5 way of thinking broken-down by source.  The second & third images are from an expert panel by Horton, showing at least one expert giving a chance of 7m of combined SLR by 2100.  The fourth image from O'Leary shows paleo-evidence of about 6m of SLR during the Eemian peak (MIS 5e) and given the over-lapping error bars this SLR could have happened in as much as 2,000 years to as little as 100 years (or less).

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 25, 2015, 05:48:39 PM
oren,

While I was scrolling through old SLR plots, I thought that you might be interested in the attached four plots, just to help calibrate recent SLR contributions, & potential total ice mass loss contributions, from different sources.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on April 25, 2015, 07:41:47 PM
Also see fig.2a in Rohling et al 2013, which shows 10 cm/yr as a sort of probabilistic ultimate speed limit for SLR, based on paleo-records:
http://www.nature.com/srep/2013/131212/srep03461/fig_tab/srep03461_F2.html (http://www.nature.com/srep/2013/131212/srep03461/fig_tab/srep03461_F2.html)

But who knows, these records may have to be rewritten in the not too distant future?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Iceismylife on April 25, 2015, 09:37:07 PM
...

More seriously, ice flow at 8 miles/hr hasn't been seen yet., and i do not think the models come up with those speeds.  A better way to get heat into the ice is ... rain. Consider what hurricane Sandy would have done to the saddle in GIS at 67 N.

sidd
I'm not talking about how fast ice can flow over bedrock.  I'm talking about how fast icebergs floating in water can flow.  And that speed is just as fast as the water is flowing.  If you advance the calving face on the jacobshavn glacier 100 km inland past its current location then you would need an ice flow rate 1/200 of 8 miles/hr.  Or it would only have to double what the glacier is currently doing during its summertime peek.  Over a 200 km long calving face.  Just something to think about.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: oren on April 25, 2015, 11:12:23 PM
Thanks a lot for these very detailed responses. Highly appreciated.
Focusing on the relative contribution of non-IS sources of SLR, looking at the 99.9% of the first table, 1.06m out of 2.45m (over 90 years) comes from glaciers and ice caps, land water storage and thermal expansion, which is over 40% of the total. Getting to 10m SLR / century in some worst case scenario will be proportionately more from IS than from other sources, so "only" about 8 meters need to come from GIS, WAIS and EAIS in such a scenario.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Iceismylife on April 26, 2015, 12:24:50 AM
In very simple terms.  The loss of 50% of Greenland's ice sheet in a 35 year time span would hit 10 meters per century rate of sea level rise.  Jakobshavn could reach that loss rate easily and I think it will. 

Zachariae isstrom calved icebergs all winter.  It has speed up 50% from 2012 until now.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: Shared Humanity on April 26, 2015, 05:21:27 AM
In very simple terms.  The loss of 50% of Greenland's ice sheet in a 35 year time span would hit 10 meters per century rate of sea level rise.  Jakobshavn could reach that loss rate easily and I think it will. 

Zachariae isstrom calved icebergs all winter.  It has speed up 50% from 2012 until now.

Please. I've come to expect more rigorous discussion here. Let's take this kind of wild speculation somewhere else.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: icefest on April 26, 2015, 09:45:03 PM
In very simple terms.  The loss of 50% of Greenland's ice sheet in a 35 year time span would hit 10 meters per century rate of sea level rise.  Jakobshavn could reach that loss rate easily and I think it will. 

Zachariae isstrom calved icebergs all winter.  It has speed up 50% from 2012 until now.



This would mean that zachariae would be losing 2% of the current Greenland ice volume a year.

2.8 million kmm3 as compared to ~17 km3. That's 5 orders of magnitude. Incredibly improbable.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 29, 2015, 11:23:27 PM
The linked reference (see attached image of the large range of various projections of cumulative PIG SLR contributions through 2050), indicates the large range of projected Antarctic ice mass loss by different models and discusses establishing minimum performance benchmarks before model projections should be considered for guidance.  This paper indicates to me that ice sheet modelers need to get their house in order before issuing any more SLR guidance documents that err embarrassingly far on the side of least drama.

Durand, G. and Pattyn, F.  (2015), "Reducing uncertainties in projections of Antarctic ice mass loss, The Cryosphere Discuss.", 9, 2625-2654, doi:10.5194/tcd-9-2625-2015.

http://www.the-cryosphere-discuss.net/9/2625/2015/tcd-9-2625-2015.html (http://www.the-cryosphere-discuss.net/9/2625/2015/tcd-9-2625-2015.html)

Abstract: "Climate model projections are often aggregated into multi-model averages of all models participating in an Intercomparison Project, such as the Coupled Model Intercomparison Project (CMIP). A first initiative of the ice-sheet modeling community, SeaRISE, to provide multi-model average projections of polar ice sheets' contribution to sea-level rise recently emerged. SeaRISE Antarctic numerical experiments aggregate results from all models willing to participate without any selection of the models regarding the processes implemented in. Here, using the experimental set-up proposed in SeaRISE we confirm that the representation of grounding line dynamics is essential to infer future Antarctic mass change. We further illustrate the significant impact on the ensemble mean and deviation of adding one model with a known biais in its ability of modeling grounding line dynamics. We show that this biased model can hardly be discriminated from the ensemble only based on its estimation of volume change. However, tools are available to test parts of the response of marine ice sheet models to perturbations of climatic and/or oceanic origin (MISMIP, MISMIP3d). Based on recent projections of the Pine Island Glacier mass loss, we further show that excluding ice sheet models that do not pass the MISMIP benchmarks decreases by an order of magnitude the mean contribution and standard deviation of the multi-model ensemble projection for that particular drainage basin."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 01, 2015, 05:07:25 PM
While I believe that Lennart just alluded this reference in the EAIS thread, I repeat it here in the WAIS thread as very few people seem to remember what is going on in all of the multiple Antarctic threads:

Alley, R.B., S. Anandakrishnan. K. Christianson, H.J. Horgan, A. Muto, B.R. Parizek, D. Pollard and R.T. Walker (2015) "Oceanic forcing of ice-sheet retreat: West Antarctica and more", Ann. Rev. Earth Plan. Sci., 43, 7.1-7.25, doi:10.1146/annurev-earth-060614-105344.

http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344?journalCode=earth (http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344?journalCode=earth)


Abstract: "Ocean-ice interactions have exerted primary control on the Antarctic Ice Sheet and parts of the Greenland Ice Sheet, and will continue to do so in the near future, especially through melting of ice shelves and calving cliffs. Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West Antarctica, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state will likely involve loss of most of the West Antarctic Ice Sheet, causing >3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic Ice Sheets share some of the same vulnerabilities to shrinkage from marine influence."

Expected final online publication date for the Annual Review of Earth and Planetary Sciences Volume 43 is May 30, 2015. Please see http://www.annualreviews.org/catalog/pubdates.aspx (http://www.annualreviews.org/catalog/pubdates.aspx) for revised estimates.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 01, 2015, 06:58:14 PM
The linked reference (using both gravimetry & altimetry, satellite data) indicates that ice mass loss from the AIS, & particularly from the WAIS, is continuing to accelerate (for example the WAIS ice mass loss increased from about 121 billion tons in 2008 to twice that in 2014).  The research partially links this AIS ice mass loss acceleration to the Antarctic Circumpolar Wave (ACW) via changes in precipitation. 

Additionally, as now the Tropical Pacific atmosphere is finally moving into a possibly more permanent El Nino configuration, the attached Earth Surface Wind & Mean Sea Level Pressure Map for May 1, 2015 shows that the ABSL and an un-named low pressure system off of Wilkes are now generating winds that are blowing warm CDW into both the ASE and underneath the Totten Ice Shelf.

A. Mémin , T. Flament, B. Alizier, C. Watson, F. Rémy (2015), "Interannual variation of the Antarctic Ice Sheet from a combined analysis of satellite gravimetry and altimetry data", Earth and Planetary Science Letters, Volume 422, 15 July 2015, Pages 150–156


http://www.sciencedirect.com/science/article/pii/S0012821X15001946 (http://www.sciencedirect.com/science/article/pii/S0012821X15001946)


Abstract: "Assessment of the long term mass balance of the Antarctic Ice Sheet, and thus the determination of its contribution to sea level rise, requires an understanding of interannual variability and associated causal mechanisms. We performed a combined analysis of surface-mass and elevation changes using data from the GRACE and Envisat satellite missions, respectively. Using empirical orthogonal functions and singular value decompositions of each data set, we find a quasi 4.7-yr periodic signal between 08/2002 and 10/2010 that accounts for ∼15–30%∼15–30% of the time variability of the filtered and detrended surface-mass and elevation data. Computation of the density of this variable mass load corresponds to snow or uncompacted firn. Changes reach maximum amplitude within the first 100 km from the coast where it contributes up to 30–35% of the annual rate of accumulation. Extending the analysis to 09/2014 using surface-mass changes only, we have found anomalies with a periodicity of about 4–6 yrs that circle the AIS in about 9–10 yrs. These properties connect the observed anomalies to the Antarctic Circumpolar Wave (ACW) which is known to affect several key climate variables, including precipitation. It suggests that variability in the surface-mass balance of the Antarctic Ice Sheet may also be modulated by the ACW."

See also:
http://www.firstpost.com/world/antarcticas-ice-sheets-melting-twice-faster-92-billion-tonnes-per-year-2222562.html (http://www.firstpost.com/world/antarcticas-ice-sheets-melting-twice-faster-92-billion-tonnes-per-year-2222562.html)

Extract: "Since 2008, ice loss from West Antarctica's unstable glaciers doubled from an average annual loss of 121 billion tons of ice to twice that by 2014, the researchers found."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on May 01, 2015, 08:18:12 PM
There is a paper out by Harig and Simons doi:10.1016/j.epsl.2015.01.029, latest GRACE data

"Ignoring GIA model uncertainty, over the period 2003–2014, West Antarctica has been losing ice mass at a rate of −121 ± 8 Gt/yr and has experienced large acceleration of ice mass losses along the Amundsen Sea coast of −18 ± 5 Gt/yr^2 , doubling the mass loss rate in the past six years. The Antarctic Peninsula shows slightly accelerating ice mass loss, with larger accelerated losses in the southern half of the Peninsula. Ice mass gains due to snowfall in Dronning Maud Land have continued to add about half the amount of West Antarctica’s loss back onto the continent over the last decade. We estimate the overall mass losses from Antarctica since January 2003 at −92 ± 10 Gt/yr."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on May 01, 2015, 09:40:09 PM
A hat tip to Mercer, Strong Language about Thwaites, pessimism about model improvements:

doi:10.1146/annurev-earth-060614-105344

"Oceanic Forcing of Ice-Sheet Retreat: West Antarctica and More" Alley et al.

"Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West Antarctica, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state will likely involve loss of most of the West Antarctic Ice Sheet, causing greater than3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario."

"Mercer (1968) cited the geological evidence of West et al. (1960) (incorrectly cited as West & Sparks 1961) showing that “rise in sea level to above present levels took place during the Sangamon Hypsithermal [MIS 5e] and was very rapid,” which “suggests possible catastrophic disintegration of the West Antarctic Ice Sheet at that time, but further evidence is needed.” Above we summarize some of the more recent data on that rise above present levels, but newer data also provide insight on the rate of rise. Other than adding many better-dated and more widely distributed records to the citation list, a follower of Mercer could write the same sentence today."

"If Thwaites Glacier experiences a sustained Jakobshavn-type ice-shelf loss and retreats into the central basins beneath the West Antarctic Ice Sheet that reach >2,000 m below sea level, the resulting cliff would almost surely be highly unstable. If any m ́ lange produced were sufficiently weak, the resulting cliff failure might cause the glacier to retreat much more rapidly than simulated by models lacking this process. Pollard et al. (2014) found that a parameterization for this process increased the instability and collapse rate of the West Antarctic Ice Sheet and of marine portions of the East Antarctic Ice Sheet, with this parameterization and the forcing adopted causing West Antarctic Ice Sheet collapse to occur on decadal timescales once initiated. No fully physical model now exists that includes this process, and given the dependence on poorly known fracture mechanics of ice, a quantitatively well-constrained model appears unlikely in the near future."


"The geological record, and modeling targeting the modern setting, indicate that Thwaites Glacier will likely exhibit threshold behavior, with retreat off the sill (Figures 2 and 4) triggering much more rapid retreat that likely will be irreversible over human timescales of centuries or less. The stability threshold may already have been crossed, although the few modeling experiments to date do not provide full agreement on that. Whether the threshold has been crossed, and how rapidly the ongoing retreat may leave the stabilizing sill, may depend on processes and conditions that are not yet fully understood and measured, such that future modeling seems likely to leave substantial uncertainty for some time. Notably, retreat into the deep basins could create conditions unlike any seen on Earth today, with processes that generally are not accurately represented in the current generation of models. In particular, the possibility of cliff failure suggests that Thwaites Glacier retreat and West Antarctic Ice Sheet loss could be much faster than generally simulated."

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 01, 2015, 09:43:49 PM
There is a paper out by Harig and Simons doi:10.1016/j.epsl.2015.01.029, latest GRACE data

"Ignoring GIA model uncertainty, over the period 2003–2014, West Antarctica has been losing ice mass at a rate of −121 ± 8 Gt/yr and has experienced large acceleration of ice mass losses along the Amundsen Sea coast of −18 ± 5 Gt/yr^2 , doubling the mass loss rate in the past six years. The Antarctic Peninsula shows slightly accelerating ice mass loss, with larger accelerated losses in the southern half of the Peninsula. Ice mass gains due to snowfall in Dronning Maud Land have continued to add about half the amount of West Antarctica’s loss back onto the continent over the last decade. We estimate the overall mass losses from Antarctica since January 2003 at −92 ± 10 Gt/yr."

The following is an elaboration on sidd's reference, with a link to an open access pdf and the two attachments jointly constitute Fig 3 from the paper, with the first image showing the mass loss from the WAIS and the second attachment showing the mass loss from the Antarctic Peninsula from 2003 to 2014 (ignoring GIA model uncertainty)

Christopher Harig & Frederik J. Simons (2015), "Accelerated West Antarctic ice mass loss continues to outpace East Antarctic gains", Earth Planet. Sc. Lett., 415, 134-141, doi:10.1016/j.epsl.2015.01.029
 

http://www.princeton.edu/geosciences/people/simons/pdf/EPSL-2015a.pdf (http://www.princeton.edu/geosciences/people/simons/pdf/EPSL-2015a.pdf)


Abstract: "While multiple data sources have confirmed that Antarctica is losing ice at an accelerating rate, different measurement techniques estimate the details of its geographically highly variable mass balance with different levels of accuracy, spatio-temporal resolution, and coverage. Some scope remains for methodological improvements using a single data type. In this study we report our progress in increasing the accuracy and spatial resolution of time-variable gravimetry from the Gravity Recovery and Climate Experiment (GRACE). We determine the geographic pattern of ice mass change in Antarctica between January 2003 and June 2014, accounting for glacio-isostatic adjustment (GIA) using the IJ05_R2 model.  Expressing the unknown signal in a sparse Slepian basis constructed by optimization to prevent leakage out of the regions of interest, we use robust signal processing and statistical estimation methods.  Applying those to the latest time series of monthly GRACE solutions we map Antarctica’s mass loss in space and time as well as can be recovered from satellite gravity alone. Ignoring GIA model uncertainty, over the period 2003–2014, West Antarctica has been losing ice mass at a rate of −121 ±8 Gt/yr and has experienced large acceleration of ice mass losses along the Amundsen Sea coast of −18 ±5 Gt/yr2, doubling the mass loss rate in the past six years. The Antarctic Peninsula shows slightly accelerating ice mass loss, with larger accelerated losses in the southern half of the Peninsula. Ice mass gains due to snowfall in Dronning Maud Land have continued to add about half the amount of West Antarctica’s loss back onto the continent over the last decade. We estimate the overall mass losses from Antarctica since January 2003 at −92 ±10 Gt/yr."


Caption for image (the upper panels are for the WAIS & the lower panels are for the Antarctic Peninsula) : "Fig. 3. Time-resolved maps of ice mass change (mass corrected using the GIA model by Ivins et al., 2013) over West Antarctica and the Antarctica Peninsula for odd years from 2003 to 2013. Each panel shows the estimated mass change from January of the labeled year (e.g., 2003) to January of the following year (e.g., 2004).  Changes seen between panels are due to accelerations. The top two rows of panels correspond to the area of box a in Fig. 1 and use the top scale bar. The bottom two rows use the bottom scale bar and correspond to box b in Fig. 1. For West Antarctica, the area of the localization includes grounded ice basins with a 0.5◦ buffer along ocean borders, and is outlined with a dashed line. For the Peninsula the localization includes grounded ice and ice shelves with a 0.5◦ buffer, also shown with a dashed line. The integral values of the mass change per year are shown as “Int”, expressed in gigatons (Gt). When the color bar is saturated, as in 2011, the minimum value of the field is shown in the top right as “Min” with units of centimeters per year water equivalent."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 03, 2015, 04:35:12 AM
A hat tip to Mercer, Strong Language about Thwaites, pessimism about model improvements:

doi:10.1146/annurev-earth-060614-105344

"Oceanic Forcing of Ice-Sheet Retreat: West Antarctica and More" Alley et al.

"If Thwaites Glacier experiences a sustained Jakobshavn-type ice-shelf loss and retreats into the central basins beneath the West Antarctic Ice Sheet that reach >2,000 m below sea level, the resulting cliff would almost surely be highly unstable. If any mélange produced were sufficiently weak, the resulting cliff failure might cause the glacier to retreat much more rapidly than simulated by models lacking this process. Pollard et al. (2014) found that a parameterization for this process increased the instability and collapse rate of the West Antarctic Ice Sheet and of marine portions of the East Antarctic Ice Sheet, with this parameterization and the forcing adopted causing West Antarctic Ice Sheet collapse to occur on decadal timescales once initiated. No fully physical model now exists that includes this process, and given the dependence on poorly known fracture mechanics of ice, a quantitatively well-constrained model appears unlikely in the near future."

sidd

I just thought that I would highlight that per Alley et al 2015 cliff failures & hydrofracturing combined with weak mélange restraint (i.e. a high probability of iceberg armadas) for the Thwaites Glacier could lead to a chain reaction:  "causing West Antarctic Ice Sheet collapse to occur on decadal timescales once initiated."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on May 03, 2015, 06:43:26 AM
I find the authors (Alley 2015, doi:10.1146/annurev-earth-060614-105344)  pessimism about models telling. I see Alley, Parizek, Pollard in there. But I doubt if Rignot shares the sentiment that models cannot improve, or cannot improve quickly enuf.

For the record, i think modelling will prove more powerful than Alley et al. imagine.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 03, 2015, 05:27:23 PM
I find the authors (Alley 2015, doi:10.1146/annurev-earth-060614-105344)  pessimism about models telling. I see Alley, Parizek, Pollard in there. But I doubt if Rignot shares the sentiment that models cannot improve, or cannot improve quickly enuf.

For the record, i think modelling will prove more powerful than Alley et al. imagine.

sidd

sidd,

First there are many different types of models, but I think that the question that Alley et al 2015 raise is whether the IPCC will accept the model findings as being directly traceable to observed/calculated physical input parameters based on deductive logic.  Certainly the cliff failure & hydrofracturing model developed by Pollard & DeConto already project the type of response that Alley et al 2015 say cannot be directly physically modeled for some (long) time to come.  This is apparently because other researchers are not willing to adopt the Bassis fracture equations for the cliff failure nor the hydrofracturing mode as apparently there are too many parameters that are poorly bounded and thus require the modeler to select and/or adjust them to match the poorly understood paleo conditions.

Second, the current WAIS conditions (particularly basal) are poorly understood/constrained, making it difficult to prescribe clear model input data without a wide range of uncertainty and/or sensitivity runs (which are normally run with low resolution).

Finally, the ACME model is committing millions of dollar to try to improve these marine ice sheet model projections; but even they understand that the projections at the end of their first 3-yr phase will be incomplete and that we will all likely need to wait until the end of their full 10-yr effort before having results that are reasonably accurate (& it is this 10-yr lag that Alley et al 2015 are lamenting).

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 13, 2015, 01:49:19 AM
With the cliff failure and hydrofracturing model of Pollard & DeConto projecting the possibility of rapid calving for marine glaciers if the mélange offers sufficiently low buttressing action, the linked modelling paper (with an open access pdf) is very topical:

Krug, J., Durand, G., Gagliardini, O., and Weiss, J.: Modelling the impact of submarine frontal melting and ice mélange on glacier dynamics, The Cryosphere, 9, 989-1003, doi:10.5194/tc-9-989-2015, 2015.

http://www.the-cryosphere.net/9/989/2015/tc-9-989-2015.html (http://www.the-cryosphere.net/9/989/2015/tc-9-989-2015.html)

Abstract: "Submarine melting of the calving face of tidewater glaciers and the mechanical back force applied by the ice mélange layer are two mechanisms generally proposed to explain seasonal variations at the calving front of tidewater glaciers. However, the way these processes affect the calving rate and glacier dynamics remains uncertain. In this study, we used a finite element-based model that solves the full Stokes equations to simulate the impact of these forcings on two-dimensional theoretical flow line glacier configurations. The model, which includes calving processes, suggests that frontal melting affects the position of the terminus only slightly (less than a few hundred metres) and does not affect the multiannual glacier mass balance at all. However, the ice mélange has a greater impact on the advance and retreat cycles of the glacier front (more than several kilometres) and its consequences for the mass balance are not completely negligible, stressing the need for better characterization of forcing properties. We also show that ice mélange forcing against the calving face can mechanically prevent crevasse propagation at sea level and hence prevent calving. Results also reveal different behaviours in grounded and floating glaciers: in the case of a floating extension, the strongest forcings can disrupt the glacier equilibrium by modifying its buttressing and ice flux at the grounding line."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 18, 2015, 12:47:19 PM
In order to gain some perspective I have decided that after today, I will take a break from posting until sometime after the 4th of July.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Anne on May 18, 2015, 02:01:05 PM
ASLR, you will be much missed. Have a good break.  :)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Neven on May 18, 2015, 02:30:12 PM
Yes, have a good time, ASLR. Thanks for all the great links.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on May 18, 2015, 07:39:59 PM
Thank you, ASLR, enjoy your break from posting and your effort to gain some perspective. That we may all benefit when you return :)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: JMP on May 19, 2015, 06:24:56 AM
OMG.  You will be missed. 
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on May 19, 2015, 09:44:45 AM
Enjoy your well-earned break. 
Title: Re: Potential Collapse Scenario for the WAIS
Post by: johnm33 on May 19, 2015, 10:42:59 AM
Phew! at last a chance to catch up. Best  Wishes.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on May 20, 2015, 10:07:22 PM
Recent lecture by Richard Alley, including remarks on Pollard et al 2015 and Applegate et al 2014 on potentially very fast ice loss from WAIS and GIS:
https://www.youtube.com/watch?v=yCunWFmvUfo (https://www.youtube.com/watch?v=yCunWFmvUfo)

Thanks to Colorado Bob for posting this over at the ASIB.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on July 07, 2015, 02:42:13 AM
The linked reference discusses this impact of the collapse of the WAIS on Antarctic surface climate:

Eric J. Steig, Kathleen Huybers, Hansi A. Singh, Nathan J. Steiger, Qinghua Ding, Dargan M. W. Frierson, Trevor Popp & James W. C. White (2015), "Influence of West Antarctic Ice Sheet collapse on Antarctic surface climate", Geophysical Research Letters, DOI: 10.1002/2015GL063861


http://onlinelibrary.wiley.com/doi/10.1002/2015GL063861/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL063861/abstract)


Abstract: "Climate model simulations are used to examine the impact of a collapse of the West Antarctic Ice Sheet (WAIS) on the surface climate of Antarctica. The lowered topography following WAIS collapse produces anomalous cyclonic circulation with increased flow of warm, maritime air toward the South Pole and cold-air advection from the East Antarctic plateau toward the Ross Sea and Marie Byrd Land, West Antarctica. Relative to the background climate, areas in East Antarctica that are adjacent to the WAIS warm, while substantial cooling (several ∘C) occurs over parts of West Antarctica. Anomalously low isotope-paleotemperature values at Mount Moulton, West Antarctica, compared with ice core records in East Antarctica, are consistent with collapse of the WAIS during the last interglacial period, Marine Isotope Stage 5e. More definitive evidence might be recoverable from an ice core record at Hercules Dome, East Antarctica, which would experience significant warming and positive oxygen isotope anomalies if the WAIS collapsed."

Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on July 29, 2015, 10:17:55 AM
Anders Levermann of PIK on WAIS's point of no return:
http://www.project-syndicate.org/commentary/anders-levermann-explains-why-nothing-can-be-done-to-halt-the-collapse-of-the-amundsen-sea-s-ice-shelf (http://www.project-syndicate.org/commentary/anders-levermann-explains-why-nothing-can-be-done-to-halt-the-collapse-of-the-amundsen-sea-s-ice-shelf)

"Rather than reacting to global warming with gradual and predictable patterns of change, the West Antarctic ice sheet has suddenly “tipped” into a new state. A relatively small amount of melting beneath the Amundsen Sea’s ice shelf has pushed its grounding line to the top of a sub-glacial hill, from which it is now “rolling down.” Simply put, one thermal kick was enough to initiate an internal dynamic that will now continue under its own momentum, regardless of any action that humans might take to prevent it."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 01, 2015, 01:43:59 AM
The linked reference (with an open access pdf) provides historical information indicating that continued global warming will increase ENSO activity and will telecommunicate more atmospheric energy to Antarctica (particularly West Antarctica), which will increase surface temperatures, and will increase the propensity for surface ice melting (which could fuel more hydrofracturing).

Turney, C. S. M., Fogwill, C. J., Klekociuk, A., van Ommen, T. D., Curran, M. A. J., Moy, A. D., and Palmer, J. G.  (2015), "Tropical and mid-latitude forcing of continental Antarctic temperatures", The Cryosphere Discuss., 9, 4019-4042, doi:10.5194/tcd-9-4019-2015.

http://www.the-cryosphere-discuss.net/9/4019/2015/tcd-9-4019-2015.html (http://www.the-cryosphere-discuss.net/9/4019/2015/tcd-9-4019-2015.html)
http://www.the-cryosphere-discuss.net/9/4019/2015/tcd-9-4019-2015.pdf (http://www.the-cryosphere-discuss.net/9/4019/2015/tcd-9-4019-2015.pdf)

Abstract. Future changes in atmospheric circulation and associated modes of variability are a major source of uncertainty in climate projections. Nowhere is this issue more acute than across the mid- to high-latitudes of the Southern Hemisphere (SH) which over the last few decades has experienced extreme and regional variable trends in precipitation, ocean circulation, and temperature, with major implications for Antarctic ice melt and surface mass balance. Unfortunately there is a relative dearth of observational data, limiting our understanding of the driving mechanism(s). Here we report a new 130-year annually-resolved record of δ D – a proxy for temperature – from the South Geographic Pole where we find a significant influence from extra-tropical pressure anomalies which act as "gatekeepers" to the meridional exchange of air masses. Reanalysis of global atmospheric circulation suggests these pressure anomalies play a considerably larger influence on mid- to high-latitude SH climate than hitherto believed, modulated by the tropical Pacific Ocean. Our findings suggest that future increasing tropical warmth will strengthen meridional circulation, exaggerating current trends, with potentially significant impacts on Antarctic surface mass balance.

Extract: "By extending historical observations over the South Pole and in combination with reanalysis products we find that meridional circulation changes associated with centres of pressure anomalies are part of a broader change observed over recent decades. Of particular note is the marked decrease in rainfall in southwest Australia since the 1970s. Our results demonstrate this trend is part of a hemispheric pattern of alternating northerly and southerly airflow linked to changes in the southwest Pacific and the tropical Pacific. We explore possible teleconnections via a strengthening of the Ferrel Cell and weakening Polar Cell. Comparison of 30-year running means of isotopic and climate datasets suggest the continuing trend to lower pressure anomalies in the southwest Pacific – with largely stable values in the Indian Ocean – are consistent with increased ENSO variability, implying precipitation will continue to decline in southwest.  Australia if El Niños become more frequent, and lead to greater warming over the
Antarctic, potentially impacting the future surface mass balance."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on August 01, 2015, 05:17:00 AM
I don't like the sound of that "weakening polar cell" in the South. We see what that does to the north already.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 01, 2015, 11:42:00 AM
New information about the Southern Hemisphere mid-to-upper tropospheric planetary wave, helps to explain recent surface warming over West Antarctica and the Antarctic Peninsula:

Damien Irving and Ian Simmonds (2015), "A novel approach to diagnosing Southern Hemisphere planetary wave activity and its influence on regional climate variability", Journal of Climate 2015 ; e-View doi: http://dx.doi.org/10.1175/JCLI-D-15-0287.1 (http://dx.doi.org/10.1175/JCLI-D-15-0287.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0287.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0287.1)

Abstract: "Southern Hemisphere mid-to-upper tropospheric planetary wave activity is characterized by the superposition of two zonally-oriented, quasi-stationary waveforms: zonal wavenumber one (ZW1) and zonal wavenumber three (ZW3). Previous studies have tended to consider these waveforms in isolation and with the exception of those studies relating to sea ice, little is known about their impact on regional climate variability. We take a novel approach to quantifying the combined influence of ZW1 and ZW3, using the strength of the hemispheric meridional flow as a proxy for zonal wave activity. Our methodology adapts the wave envelope construct routinely used in the identification of synoptic-scale Rossby wave packets and improves on existing approaches by allowing for variations in both wave phase and amplitude. While ZW1 and ZW3 are both prominent features of the climatological circulation, the defining feature of highly meridional hemispheric states is an enhancement of the ZW3 component. Composites of the mean surface conditions during these highly meridional, ZW3-like anomalous states (i.e. months of strong planetary wave activity) reveal large sea ice anomalies over the Amundsen and Bellingshausen Seas during autumn and along much of the East Antarctic coastline throughout the year. Large precipitation anomalies in regions of significant topography (e.g. New Zealand, Patagonia, coastal Antarctica) and anomalously warm temperatures over much of the Antarctic continent were also associated with strong planetary wave activity. The latter has potentially important implications for the interpretation of recent warming over West Antarctica and the Antarctic Peninsula."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 03, 2015, 08:35:25 PM
sidd,

Thanks for the reference.  I believe that BISICLES is the base program to be used in the ACME program for ice sheet modeling.  This paper seems to show the fastest rate of retreat for ASE (see attached image) that I have seen BISICLES project to date, so I will be interested in seeing what projection they have by the end of the first phase of the ACME project (as well as in their final projection in about 10-years).  However, I would be even more interested if the ACME WAIS models adopt the cliff failure and hydrofracturing methodology developed by Pollard et al (2015).

Cornford, S. L., Martin, D. F., Payne, A. J., Ng, E. G., Le Brocq, A. M., Gladstone, R. M., Edwards, T. L., Shannon, S. R., Agosta, C., van den Broeke, M. R., Hellmer, H. H., Krinner, G., Ligtenberg, S. R. M., Timmermann, R., and Vaughan, D. G. (2015), "Century-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate", The Cryosphere Discuss., 9, 1887-1942, doi:10.5194/tcd-9-1887-2015.

http://www.the-cryosphere-discuss.net/9/1887/2015/tcd-9-1887-2015.pdf (http://www.the-cryosphere-discuss.net/9/1887/2015/tcd-9-1887-2015.pdf)

Abstract: "We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet.  Each of the simulations begins with a geometry and velocity close to present day observations, and evolves according to variation in meteoric ice accumulation, ice shelf melting, and mesh resolution. Future changes in accumulation and melt rates range from no change, through anomalies computed by atmosphere and ocean models driven by the E1 and A1B emissions scenarios, to spatially uniform melt rates anomalies that remove most of the ice shelves over a few centuries. We find that variation in the resulting ice dynamics is dominated by the choice of initial conditions, ice shelf melt rate and mesh resolution, although ice accumulation affects the net change in volume above flotation to a similar degree. Given sufficient melt rates, we compute grounding line retreat over hundreds of kilometers in every major ice stream, but the ocean models do not predict such melt rates outside of the Amundsen Sea Embayment until after 2100. Sensitivity to mesh resolution is spurious, and we find that sub-kilometer resolution is needed along most regions of the grounding line to avoid systematic under-estimates of the retreat rate, although resolution requirements are more stringent in some regions – for example the Amundsen Sea Embayment – than others – such as the Möller and Institute ice streams."

Best,
ASLR

As a follow-up to this earlier post, I provide the two attached additional images, and the two additional linked information, and I reiterate that I hope that the ACME effort learns from the methodologies currently be used by Pollard, DeConto, Applegate, and others (see the Paleo thread for August 3rd 2015), as I believe that Cornford et al 2015 are too conservative (as in transferring risk from the modeler to the general public):

See also:
http://crd.lbl.gov/departments/applied-mathematics/ANAG/about/staff/dan-martin/ (http://crd.lbl.gov/departments/applied-mathematics/ANAG/about/staff/dan-martin/)
http://crd.lbl.gov/assets/pubs_presos/Martin-LIWG-2015-final.pdf (http://crd.lbl.gov/assets/pubs_presos/Martin-LIWG-2015-final.pdf)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on August 18, 2015, 02:46:37 PM
Cornford et al 2015 final version is now published:
http://www.the-cryosphere.net/9/1579/2015/tc-9-1579-2015.html (http://www.the-cryosphere.net/9/1579/2015/tc-9-1579-2015.html)

Abstract
"We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet, deploying sub-kilometer resolution around the grounding line since coarser resolution results in substantial underestimation of the response. Each of the simulations begins with a geometry and velocity close to present-day observations, and evolves according to variation in meteoric ice accumulation rates and oceanic ice shelf melt rates. Future changes in accumulation and melt rates range from no change, through anomalies computed by atmosphere and ocean models driven by the E1 and A1B emissions scenarios, to spatially uniform melt rate anomalies that remove most of the ice shelves over a few centuries. We find that variation in the resulting ice dynamics is dominated by the choice of initial conditions and ice shelf melt rate and mesh resolution, although ice accumulation affects the net change in volume above flotation to a similar degree. Given sufficient melt rates, we compute grounding line retreat over hundreds of kilometers in every major ice stream, but the ocean models do not predict such melt rates outside of the Amundsen Sea Embayment until after 2100. Within the Amundsen Sea Embayment the largest single source of variability is the onset of sustained retreat in Thwaites Glacier, which can triple the rate of eustatic sea level rise."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 19, 2015, 06:57:15 PM
The linked reference by Hughes et al (2015) presents state-of-the-art analysis about the Jakobshavn Effect (Hughes, 1986), focused on progressive ice-bed uncoupling due to such factors as: basal meltwater, buoyancy friction (particularly with changing surface elevation), boundary constraints of the fjord.  This work has relevance to multiple marine-terminating, and marine, glaciers in both Greenland and Antarctica (see the extract for concerns about the PIG an the Thwaites Glacier, among other Antarctic marine glaciers):

Hughes, T., Sargent, A., Fastook, J., Purdon, K., Li, J., Yan, J.-B., and Gogineni, S.: Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica, and Jakobshavn Isbrae, Greenland, The Cryosphere Discuss., 9, 4271-4354, doi:10.5194/tcd-9-4271-2015, 2015.

http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.pdf (http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.pdf)

Abstract. The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.


Extract: "Equation (24), based only on the force balance, is especially useful here because of its robust simplicity that applies to all flowlines and flowbands (ice streams) that end at a specified ice thickness h0. It gives phi variations along x that are usually somewhat higher than when the mass balance is also included, but with the same general trend. Using Eq. (24), Pingree et al. (2011) showed how Eq. (24) produced ice elevations before and after a former surge lifecycle of Lambert Glacier in East Antarctica, and for impending surge lifecycles of Thwaites Glacier and Pine Island Glacier entering the Pine Island Bay polynya in West Antarctica that continue into East Antarctica. Using Eq. (24), Hughes (2011) has tentatively assigned inception, growth, mature, declining, and terminal lifecycle stages shown in Table 2 to all major Antarctic ice streams at the present time."

Edit: See the two attached associated images related to the Jakobshavn Effect; which elsewhere in this fold I have associated with the more dynamic "Thwaites Effect"
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on August 19, 2015, 08:23:38 PM
The 2015 paper by Hughes et al. is very reminiscent of the 2014 paper doi:10.5194/tcd-8-2043-2014
I like the simple geometric approach.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 03, 2015, 12:14:37 AM
While I believe that the linked reference's use of the PISM ice sheet model is conservative; nevertheless, their findings support the idea the pending destabilization of the ASE marine glaciers will destabilize the remaining portions of the WAIS (however, I suspect that the estimated timeframe is scientifically conservative as PISM does not utilize either cliff failures or hydrofracturing):

Johannes Feldmann and Anders Levermann (November 2, 2015), "Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin", PNAS, doi: 10.1073/pnas.1512482112


http://www.pnas.org/content/early/2015/10/28/1512482112 (http://www.pnas.org/content/early/2015/10/28/1512482112)


Abstract: "The future evolution of the Antarctic Ice Sheet represents the largest uncertainty in sea-level projections of this and upcoming centuries. Recently, satellite observations and high-resolution simulations have suggested the initiation of an ice-sheet instability in the Amundsen Sea sector of West Antarctica, caused by the last decades’ enhanced basal ice-shelf melting. Whether this localized destabilization will yield a full discharge of marine ice from West Antarctica, associated with a global sea-level rise of more than 3 m, or whether the ice loss is limited by ice dynamics and topographic features, is unclear. Here we show that in the Parallel Ice Sheet Model, a local destabilization causes a complete disintegration of the marine ice in West Antarctica. In our simulations, at 5-km horizontal resolution, the region disequilibrates after 60 y of currently observed melt rates. Thereafter, the marine ice-sheet instability fully unfolds and is not halted by topographic features. In fact, the ice loss in Amundsen Sea sector shifts the catchment's ice divide toward the Filchner–Ronne and Ross ice shelves, which initiates grounding-line retreat there. Our simulations suggest that if a destabilization of Amundsen Sea sector has indeed been initiated, Antarctica will irrevocably contribute at least 3 m to global sea-level rise during the coming centuries to millennia."

Extract: "The result of this study is an if–then statement, saying that if the Amundsen Sea Sector is destabilized, then the entire marine part of West Antarctica will be discharged into the ocean.”
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 08, 2015, 11:44:29 AM
The linked open access reference documents a 20th century increase in snowfall in coastal West Antarctica, that evidently is associated with a deepening of the ASL, which in-turn appears to be linked to periods of coupling between the ENSO and SAM (see the attached image).  It should be remembered that such increased coastal snowfall increases the gravitational driving force on the coastal glaciers in the WAIS.  Furthermore, a deepening of the ASL can result in accelerated advection of more warm CDW to accelerate grounding line retreat of key WAIS marine glaciers.

E. R. Thomas, J. S. Hosking, R. R. Tuckwell, R. A. Warren and E. C. Ludlow (2015), "Twentieth century increase in snowfall in coastal West Antarctica", Geophysical Research Letters DOI: 10.1002/2015GL065750

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065750/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL065750/abstract)

Abstract: "The Amundsen Sea sector of the West Antarctic ice sheet has been losing mass in recent decades; however, long records of snow accumulation are needed to place the recent changes in context. Here we present 300 year records of snow accumulation from two ice cores drilled in Ellsworth Land, West Antarctica. The records show a dramatic increase in snow accumulation during the twentieth century, linked to a deepening of the Amundsen Sea Low (ASL), tropical sea surface temperatures, and large-scale atmospheric circulation. The observed increase in snow accumulation and interannual variability during the late twentieth century is unprecedented in the context of the past 300 years and evidence that the recent deepening of the ASL is part of a longer trend."

Extract: "Ice core records from Ellsworth Land, West Antarctica reveal a twentieth century increase in regional snow accumulation and its interannual variability that is considered exceptional in the context of the past 300 years. The annual snow accumulation since 1900 increased by ~ 30%, proving that the dramatic increases observed in the Antarctic Peninsula extend into West Antarctica and that these changes occurred following a 200 year period of relatively stable conditions. Snow accumulation in this region is governed by changes in SLP in the Amundsen Sea region, resulting in enhanced meridional (onshore) winds drawing moist air to the coast of Ellsworth Land, and directly impacting global sea level rise through wind driven upwelling and subsequent thinning of West Antarctic ice shelves [Pritchard et al., 2012]. The close relationship between SLP and snow accumulation at these sites make this a unique proxy for past ASL (and onshore wind) conditions. The recent deepening trend of the ASL is predicted to continue through the 21st century in response to greenhouse gas concentration increases [Raphael et al., 2015]. The dramatic increase in snow accumulation in Ellsworth Land provides evidence that this recent deepening in the ASL region is part of a longer trend, observed as early as the 1920s, with acceleration since the 1990s when the coupling between ENSO and SAM is strongest."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 11, 2015, 12:59:38 AM
While the researchers (of the linked open access reference) are correct to include both the fingerprint effect (of ice mass loss on SLR) and corrected viscosity of the upper mantle in their Antarctic Ice-Sheet model, once the grounding line retreats to the reverse slope portion of the bed that is characteristic of most key Antarctic marine glaciers, the influence of these two considerations become less critical when cliff failures and hydrofracturing are also considered (as David Pollard is very well aware):

Natalya Gomez, David Pollard & David Holland (November 10, 2015), "Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss", Nature Communications 6, Article number: 8798 doi:10.1038/ncomms9798

http://www.nature.com/ncomms/2015/151110/ncomms9798/full/ncomms9798.html (http://www.nature.com/ncomms/2015/151110/ncomms9798/full/ncomms9798.html)

Abstract: "The stability of marine sectors of the Antarctic Ice Sheet (AIS) in a warming climate has been identified as the largest source of uncertainty in projections of future sea-level rise. Sea-level fall near the grounding line of a retreating marine ice sheet has a stabilizing influence on the ice sheets, and previous studies have established the importance of this feedback on ice age AIS evolution. Here we use a coupled ice sheet–sea-level model to investigate the impact of the feedback mechanism on future AIS retreat over centennial and millennial timescales for a range of emission scenarios. We show that the combination of bedrock uplift and sea-surface drop associated with ice-sheet retreat significantly reduces AIS mass loss relative to a simulation without these effects included. Sensitivity analyses show that the stabilization tends to be greatest for lower emission scenarios and Earth models characterized by a thin elastic lithosphere and low-viscosity upper mantle, as is the case for West Antarctica."

Extract: "The ice-sheet model in this paper does not include the new mechanisms of hydrofracturing by surface melt and ice-cliff failure, recently proposed to produce East Antarctic retreat as implied by (albeit uncertain) geologic evidence of high sea-level stands in past warm periods. A future paper exploring these effects with the coupled Earth–ice model is planned, but the mechanisms are somewhat speculative, and their effect is basically to accelerate WAIS retreat and amplify EAIS retreat, and the basic findings of this paper regarding negative-feedback influences of Earth-gravitational interactions are not expected to change."

Edit: I note that the forcing scenarios with names indicating various multiples of the atmospheric CO2 burden, should not be taken as literal concentrations of atmospheric CO2 for a variety of reasons including: (a) one needs to consider CO2 equivalent GHGs and aerosol affects; (b) ECS could be well above 3C; (c) Hansen et al. (2015)'s positive feedback mechanisms associated with ice mass loss was not considered by Gomez et al. (2015); (d) various Earth Systems that are normally considered slow response (permafrost degradation, etc.) could actually be fast response; which might mean that ESS could be between 4.5 and 6C by the end of this century; and (e) Gomez et al. (2015) may not be accounting correctly for vary Earth System initial states, such as the influence of the Antarctic ozone whole and ocean heat content in the Southern Ocean.

Edit2: Furthermore, I note that the amount of glacial rebound indicated by the authors would also be associated with an increase in both seismic and geothermal activity, that were almost certainly not considered within the modeled projections.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on November 18, 2015, 07:33:45 PM
Ritz et al 2015 on potential Antarctic contribution to SLR by 2100 and 2200:
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16147.html (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16147.html)

Abstract
Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions the centennial to millennial contribution could be several metres. Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: crandles on November 19, 2015, 12:09:11 AM
Ritz et al 2015 on potential Antarctic contribution to SLR by 2100 and 2200:
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16147.html (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16147.html)

BBC article on this
http://www.bbc.co.uk/news/science-environment-34859398 (http://www.bbc.co.uk/news/science-environment-34859398)
suggest
Quote
But the prospect of a 30cm-or-more contribution - claimed by some previous research - has just a one-in-20 chance.

and mode of just 10cm by 2100.

Seems like good news if the higher outcomes really are as unlikely as being suggested.

Quote
"We're constraining the model with the observations. Nobody has really done this sort of formal scoring before."
makes me wonder if this effectively disregards possibility of new modes of failure like 100m+ cliff failures.

Two modes at 6cm and 49cm for 2200 sounds a bit weird? Is just 6cm from Antactica by 2200 at all plausible for A1B?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 19, 2015, 12:29:43 AM
Ritz et al 2015 on potential Antarctic contribution to SLR by 2100 and 2200:
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16147.html (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16147.html)

BBC article on this
http://www.bbc.co.uk/news/science-environment-34859398 (http://www.bbc.co.uk/news/science-environment-34859398)
suggest
Quote
But the prospect of a 30cm-or-more contribution - claimed by some previous research - has just a one-in-20 chance.

and mode of just 10cm by 2100.

Seems like good news if the higher outcomes really are as unlikely as being suggested.

Quote
"We're constraining the model with the observations. Nobody has really done this sort of formal scoring before."
makes me wonder if this effectively disregards possibility of new modes of failure like 100m+ cliff failures.

Two modes at 6cm and 49cm for 2200 sounds a bit weird? Is just 6cm from Antactica by 2200 at all plausible for A1B?

Garbage in, garbage out.

Rignot stated that his lower bound for total SLR by 2100 is 1.2 m and he is still working on what he considers the upper bound to be.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on November 19, 2015, 07:35:38 AM
makes me wonder if this effectively disregards possibility of new modes of failure like 100m+ cliff failures.

Two modes at 6cm and 49cm for 2200 sounds a bit weird? Is just 6cm from Antactica by 2200 at all plausible for A1B?

Garbage in, garbage out.

Rignot stated that his lower bound for total SLR by 2100 is 1.2 m and he is still working on what he considers the upper bound to be.

DeConto and Pollard are expected to publish a new paper on Antarctica in the coming months. So let's see what they have to say in addition to this sneak preview of their findings:
http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf (http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf)

"the magnitude and rate of Antarctic ice sheet retreat are highly dependent on which future greenhouse gas scenario is followed, but even the lower emission scenarios produce an Antarctic contribution of several meters within the next several centuries. Once atmospheric CO2 concentrations exceed 2x preindustrial levels, we find that hydrofracturing by surface melt on ice shelves can trigger large-scale ice sheet retreat, regardless of circum-Antarctic ocean warming. Hence, unlike the LIG, atmospheric (not ocean) warming has the potential to become the primary mechanism driving future retreat of the Antarctic ice sheet. In simulations without atmospheric warming, we find small amounts of ocean warming can still produce large-scale retreat of the West
Antarctic Ice Sheet, although the timescale of ocean-driven retreat is slower than atmospherically driven retreat."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 19, 2015, 11:12:37 AM
DeConto and Pollard are expected to publish a new paper on Antarctica in the coming months. So let's see what they have to say ...

Agreed, and great caught on the EGU abstract.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: crandles on November 19, 2015, 04:08:41 PM
Oh well, One man's GIGO is another man's 'sane and well crafted'.
http://scienceblogs.com/stoat/2015/11/18/potential-sea-level-rise-from-antarctic-ice-sheet-instability-constrained-by-observations/ (http://scienceblogs.com/stoat/2015/11/18/potential-sea-level-rise-from-antarctic-ice-sheet-instability-constrained-by-observations/)

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 19, 2015, 04:48:08 PM
Once atmospheric CO2 concentrations exceed 2x preindustrial levels, we find that hydrofracturing by surface melt on ice shelves can trigger large-scale ice sheet retreat, regardless of circum-Antarctic ocean warming. Hence, unlike the LIG, atmospheric (not ocean) warming has the potential to become the primary mechanism driving future retreat of the Antarctic ice sheet. In simulations without atmospheric warming, we find small amounts of ocean warming can still produce large-scale retreat of the West Antarctic Ice Sheet, although the timescale of ocean-driven retreat is slower than atmospherically driven retreat."

Per the following link the pre-industrial CO2eq atmospheric concentration was 280ppm while thru 2014 the CO2 eq atmospheric concentration was about 487ppm, and the rate of CO2 eq increase per year since 1970 is about 3ppm/yr, indicating that we are currently at about 490ppm CO2eq:

http://www.esrl.noaa.gov/gmd/aggi/aggi.html (http://www.esrl.noaa.gov/gmd/aggi/aggi.html)

As 280 times 2 = 560ppm, we need to increase CO2eq by another 70ppm to get to DeConto & Pollard's threshold for hydrofracturing; which could occur by 2038 (assuming 3ppm CO2eq/yr).

Furthermore, this assumes that the effective value of ECS, and the aerosol concentrations, assumed by DeConto & Pollard are correct (while I suspect that they error on the side of least drama).  Thus one mans' "sane & well crafted" projection is another man's "insane and reckless" projection.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Timothy Astin on November 19, 2015, 07:16:23 PM
Garbage in, garbage out.

This is an unfair and unscientific comment. The Ritz et al 2015 paper is a detailed and careful piece of science. It has been peer reviewed for a journal that has excellent reviewing and editing.

This paper forms one of a range of predictions, and is at the lower end of recent estimates for contributions from the Antarctic Peninsula for sea level rise by 2100.

It is an important study to compare and contrast with other predictive approaches.

It is important to read the supplementary information (which is freely available). It includes details on the modelling assumptions, and has further discussion including comparison with other studies.

As Tamsin Edwards says in blog discussion at the link Crandles gives above, their study effectively replicates ice cliff failure in their model by another means, so simply saying that it doesn't take account of that mechanism is not fair either.

There are weaknesses in all predictive methods, especially modelling methods, the further they get away from the boundary conditions. In this case, perhaps a weakness of the predictions is in the extrapolation of statistical relationships derived from a relatively narrow time window of observations.

The other modelling approaches have weaknesses too, and other ice models which attempt to replicate complex physics can turn out to be based on poor assumptions.

That is why it is important that a variety of predictive approaches are tried. 


 



Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 19, 2015, 07:39:42 PM
Garbage in, garbage out.

This is an unfair and unscientific comment. The Ritz et al 2015 paper is a detailed and careful piece of science. It has been peer reviewed for a journal that has excellent reviewing and editing.

"All models are wrong but some models are useful", but the key issue is useful for what?  If one is happy to let science plod along very slowly then perhaps the comment is "unscientific"; but as scientists take no responsibility for the catastrophic impact on society if the probabilities from such studies of abrupt ice sheet collapse are wrong, then the comment is not in my opinion "unfair".  The Ritz et al. 2015 paper does not consider hydrofracturing, which DeConto & Pollard show may be the greatest risk of abrupt marine ice sheet collapse, possibly starting as soon as circa 2038.  I think that if a researcher ignores the most important input for abrupt ice sheet mass loss, then it is fair for me to say GIGO.

Edit: The attached image [for Pliocene conditions] from Pollard et al. (2015) shows the importance of including both cliff failures and hydrofracturing within a model whose results are to be relied upon for policy making.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: oren on November 21, 2015, 12:17:06 AM
While the researchers (of the linked open access reference) are correct to include both the fingerprint effect (of ice mass loss on SLR) and corrected viscosity of the upper mantle in their Antarctic Ice-Sheet model, once the grounding line retreats to the reverse slope portion of the bed that is characteristic of most key Antarctic marine glaciers, the influence of these two considerations become less critical when cliff failures and hydrofracturing are also considered (as David Pollard is very well aware):

Natalya Gomez, David Pollard & David Holland (November 10, 2015), "Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss", Nature Communications 6, Article number: 8798 doi:10.1038/ncomms9798

http://www.nature.com/ncomms/2015/151110/ncomms9798/full/ncomms9798.html (http://www.nature.com/ncomms/2015/151110/ncomms9798/full/ncomms9798.html)

Abstract: "The stability of marine sectors of the Antarctic Ice Sheet (AIS) in a warming climate has been identified as the largest source of uncertainty in projections of future sea-level rise. Sea-level fall near the grounding line of a retreating marine ice sheet has a stabilizing influence on the ice sheets, and previous studies have established the importance of this feedback on ice age AIS evolution. Here we use a coupled ice sheet–sea-level model to investigate the impact of the feedback mechanism on future AIS retreat over centennial and millennial timescales for a range of emission scenarios. We show that the combination of bedrock uplift and sea-surface drop associated with ice-sheet retreat significantly reduces AIS mass loss relative to a simulation without these effects included. Sensitivity analyses show that the stabilization tends to be greatest for lower emission scenarios and Earth models characterized by a thin elastic lithosphere and low-viscosity upper mantle, as is the case for West Antarctica."

Extract: "The ice-sheet model in this paper does not include the new mechanisms of hydrofracturing by surface melt and ice-cliff failure, recently proposed to produce East Antarctic retreat as implied by (albeit uncertain) geologic evidence of high sea-level stands in past warm periods. A future paper exploring these effects with the coupled Earth–ice model is planned, but the mechanisms are somewhat speculative, and their effect is basically to accelerate WAIS retreat and amplify EAIS retreat, and the basic findings of this paper regarding negative-feedback influences of Earth-gravitational interactions are not expected to change."

Edit: I note that the forcing scenarios with names indicating various multiples of the atmospheric CO2 burden, should not be taken as literal concentrations of atmospheric CO2 for a variety of reasons including: (a) one needs to consider CO2 equivalent GHGs and aerosol affects; (b) ECS could be well above 3C; (c) Hansen et al. (2015)'s positive feedback mechanisms associated with ice mass loss was not considered by Gomez et al. (2015); (d) various Earth Systems that are normally considered slow response (permafrost degradation, etc.) could actually be fast response; which might mean that ESS could be between 4.5 and 6C by the end of this century; and (e) Gomez et al. (2015) may not be accounting correctly for vary Earth System initial states, such as the influence of the Antarctic ozone whole and ocean heat content in the Southern Ocean.

Edit2: Furthermore, I note that the amount of glacial rebound indicated by the authors would also be associated with an increase in both seismic and geothermal activity, that were almost certainly not considered within the modeled projections.

I have long wondered on the negative feedback associated with gravitational effects and marine terminating glaciers. The effects of gravity changes following loss of ice mass are immediate and relatively easy to model, as opposed to mantle rebound which is a slower process with many more unknowns.
However, I have some issues with this paper's assumptions and model results.
First, it mixes gravitation and rebound together and I find it hard to understand each effect separately. An error in the rebound model could undermine the results which arise from gravitation effects. In Figure 3 where these effects are separated, it seems that when sea level rate of change is stable adding gravitational effects lowers sea level in the first 50-100 years. I find this result implausible (should be no mass change ==> no gravitational effects compared to present) and therefore the whole analysis of the separate contributions of these factors problematic.
In addition, some of the scenarios (2x, 4x and 8x pre-industrial CO2, immediate or over 1000 years) are unrealistic. 2x of pre-industrial CO2 is expected in about 60 years (or less when counting all GHGs). The most probable scenarios are 2x "immediate", and 4x to 8x over 1000 years.
In addition, a 2 deg C rise in ocean temperatures is assumed (immediate or over 1000 years). There is no sensitivity analysis of this important number, and no correlation between it and the CO2 level. So running worst-case 8x CO2 but limiting ocean warming to 2 deg limits the worst-case in an unknown way.
Finally, in the 1000 year scenarios with fully coupled model (blue lines in Fig.1), for the first 500 years Antarctica will cause 0.3m of sea level drop. I believe this result is wrong and this undermines the whole paper. Even if Zwally is right about present AIS negative contribution to SLR, this is not expected to continue for 500 years or even 100 years at this rate under warming scenarios.

Bottom line, I find it hard to take this paper's summary as is. Indeed it seems gravitational effects form a significant negative feedback, and so do rebound effects under slower scenarios. But how strong are these feedbacks? I'm still not sure.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 21, 2015, 12:44:12 AM
Bottom line, I find it hard to take this paper's summary as is. Indeed it seems gravitational effects form a significant negative feedback, and so do rebound effects under slower scenarios. But how strong are these feedbacks? I'm still not sure.

It is even harder to understand the references finding of a significant negative feedback when one considers that even with all of the ice mass loss to date in Antarctica the local sea level has not dropped at all (see attached image of satellite measurements of local sea level changes), due to such factors contributing an increase in local sea level of: (a) increasing ocean heat content; (b) decreasing average seawater salinity; and (c) the fingerprint effect of ice mass loss from North Hemisphere ice sheets (Greenland) and other glaciers.

Caption for attached image: "Sea Level Anomalies on 2012/01/01 exploiting 4 altimeters: Jason-2, Jason-1, Envisat and Cryosat-2. Credits Cnes-Ssalto/Duacs-Esa"

Edit: I do not expect the local Antarctic sea levels to drop until well after cliff failures and hydrofracturing have been well initiated (circa 2035 to 2040).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Csnavywx on November 21, 2015, 02:40:31 AM
Wait, what? A1B assumes a mean CO2 concentration of 700 ppm by 2100. And the statistical mode for their low end scenario is 6cm of Antarctic contribution by 2200?

What?

Okay, let's start with the most generous assumptions. What's the current rate of estimated Antarctic contribution to sea level rise?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 21, 2015, 03:34:07 AM
What's the current rate of estimated Antarctic contribution to sea level rise?

Different sources give slightly different values, but the attached image provides the official AR5 values:

Caption for the image: "Caption for Figure 2: Contribution of global glaciers (red), Greendland (green) and Antarctica (blue) to sea level rise between 1992-2012. Positive correlation between cumulative ice mass loss and sea level equivalent, shaded areas indicate uncertainty"
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Richard Rathbone on November 21, 2015, 03:43:57 AM
Wait, what? A1B assumes a mean CO2 concentration of 700 ppm by 2100. And the statistical mode for their low end scenario is 6cm of Antarctic contribution by 2200?

What?

Okay, let's start with the most generous assumptions. What's the current rate of estimated Antarctic contribution to sea level rise?

They haven't got failure modes in their model. They assume the ice just flows like it is at the moment. And as long as ice flows like it is at the moment, their analysis looks good to me. However thats only reasonably certain for another couple of decades. The moment cliff failure might set in, their analysis is irrelevant as an upper bound, but would still serve as a lower bound. So beyond 2040, treat everything they say as being the likely bound, as being a lower bound, not an upper one.

Title: Re: Potential Collapse Scenario for the WAIS
Post by: Csnavywx on November 21, 2015, 04:30:09 AM
Thanks ASLR and Richard.

That really bothered me. Even a generously low extrap puts 7cm in the ocean by 2200 using 1998-2012 average melt rates.

With no failure modes, the entire paper makes more sense as a lower bound.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on November 21, 2015, 08:18:50 AM
The Pollard(2015) paper is apt as a comparison from the dark side.  A first reading of Ritz(2015) led me to it also after meandering through some calculation, Schoof, Bassis, the Jacobshawn thread and eventually Pollard. In the following, i refer to

Ritz(2015) doi:10.1038/nature16147
Mouginot(2014) doi:10.1002/2013GL059069
Shepherd(2012) doi:10.1126/science.1228102
Schoof(2007) doi:10.1029/2006JF000664
Bassis(2012) doi:10.1098/rspa.2011.0422
Bassis(2013) doi:10.1038/NGEO1887
Pollard(2015) doi:10.1016/j.epsl.2014.12.035


My thoughts on Ritz were:

1)Ritz only looks at MISI instability, but marine fronted ice on flatland topo will also retreat under forcing

2)Ritz Suppl. 1.7 mass waste calibration from Shepherd(2012) uses only laser and i/o method, but not the larger mass waste from GRACE which is also in Shepherd. Ritz reference Mouginot(2014) but do not use the (much larger) mass waste estimate in Mouginot for calibrationI have asked one of the authors about this on Dr. Connolley's blog.

3)Ritz have no calving law but claim a horizontal mass waste term which is similar to Bassis mechanism for cliff failure. But Bassis treats granular flow which to me is uncompliant with Ritz "no suction" check on max tensile stress (which Ritz set equal to the free water opposing buttress) to get a max strain rate. (Bassis(2012) explicitly does the case of no cohesive strength.) If Ritz turn the "no suction" check off, they get much larger result, see Ritz extended data fig 10

4)Ritz has no explicit ice shelf collapse or basal melt, these are also parametrised with the low end calibration in 2)

5)Ritz treats heat balance such as melt thru parametrisation. This one gets me. The Schoof treatment assumes that water is at pressure melting point, but in reality is hotter. So the Schoof condition they apply is optimistic. Pollard does a quadratic melt dependence in temperature in excess
of pressure melting point, which may not be exact, but at least begins to address this issue.

6)Pollard does a step Pliocene level forcing,  and a step change of 2C in ocean temperature but i am sure they can do A1B or other scenario as well. I do like the incorporation scheme for Bassis cliff failure in Pollard. So I prefer the Pollard treatment and look forward to a treatment of A1B, perhaps they will say something in the coming paper.

7)There is no simulation in Ritz or Pollard about binge purge cycles.

If you look at Schoof, say Fig 5a), 8, or 9a),b) you see the hysteresis loop. Schoof refers to this:

"A possible interpretation of Heinrich events is that the discharge of sediment-laden icebergs occurred as a result of an abrupt and irreversible retreat of the grounding across this overdeepening ..."

i attach fig 5 and 9 at the end.

What i have in mind is a an ice sheet with two stable states on each side of an overdeepened topo as in Schoof. The thing collapses back across the hole thru cliff failure, and the hole is emptied thru iceberg transport.

As Bassis(2013) puts it:
"Our simulations indicate that calving is a two-part process that requires both ice fracture and the subsequent transport of detached icebergs away  from the calving front."

Then if there is enuf ice left, the thing jumps back across the hole to the seaward stable point and jumps back for another cycle. The longer time constant in this sawtooth is, i think, the berg transport away, but in the large like a relaxation oscillator. In the Thwaites basin the hole goes to the Transantarctic mountains, and one cycle would drain a great deal of WAIS.

Which reminded me of the recent Jacobshawn calving and that Pollard has this to say:

"Huge calving events observed at the fronts of Jakobshavn Isbrae and  Helheim glaciers ... in water depths of ∼700 m to 1000 m with no contiguous  ice shelves, may be the closest example, but may still not be a good analog  as discussed in Appendix A."

In Appendix A.

"The closest analog today might be the separation and overturning of km-scale bergs as observed currently at Jakobshavn and Helheim glaciers  ...  For subaerial cliffs with no ice shelves, it might involve fracturing and violent seaward expelling of ice near the water line (the rough location of maximum unbalanced hydrostatic stress for tidewater cliffs, Bassis and Walker (2012) in a process not seen today."

Eggzackly. We are seeing the beginning at Jacobshawn. Thwaites is at least ten times wider than Jacobshawn. I dont want to see what will happen when it lets go like Jacobshawn is doing, but I fear I shall.

On the whole I am quite thankful to Ritz et al. for making me reread all these nice papers and think. Now I am still confused, but at a higher level.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 21, 2015, 09:49:55 AM
On the whole I am quite thankful to Ritz et al. for making me reread all these nice papers and think. Now I am still confused, but at a higher level.

Nice analysis.  I only wish that Ritz et al (2015) had also taken the time to review all these nice papers, so that policy makers would be less confused (because Ritz et al would have reached the same conclusion that you have).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: S.Pansa on November 23, 2015, 07:33:11 AM
Richard Alley, one of the co-authors of the Ritz paper, has now added some comments about the strength of the paper - and about what is missing in the model. Found at Gred Laden's blog here (http://scienceblogs.com/gregladen/2015/11/22/antarctic-ice-sheet-deterioration-study-left-out-important-factors/):

Quote
Alley lauds the Ritz, Edwards, et al paper as representing “a great amount of careful work, and provid[ing] a particularly broad exploration of some of the poorly known parameters that control the ice sheet.” However, he finds that the study did not address some important mechanisms.

   " …the model does not allow loss of any ice shelves, does not allow grounding-line retreat from calving of icebergs following ice-shelf loss, and does not allow faster retreat from breakage of cliffs higher than those observed today, especially if aided by meltwater wedging in crevasses. The model restricts grounding-line retreat to the rate given by thinning of ice during viscous flow of an unbuttressed but still-present ice shelf, with a specified upper limit enforced on the rate of that retreat. The model also does not allow retreat up a sloping bed under forcing, something that is widely observed. The Supplementary Information includes discussion of checks that the authors did to assess the importance of these assumptions, which the authors argue justify omitting the mechanisms. However, it remains that with the model not allowing very rapid retreat, not allowing ice-cliff crumbling after ice-shelf loss, and not allowing retreat up sloping beds, the model cannot exhibit some possible behaviors that could cause rapid ice-sheet shrinkage.

    So, I view this as an important step forward for the scientific community, but the qualification in the last sentence of the paper leads to additional information showing that we cannot yet confidently place quantitatively reliable limits on the possible sea-level rise from the Antarctic ice sheet. I personally hope that the new paper is right, but I will continue research on this topic in the hope of providing improved estimates. Until such work is successful, I do not believe we can exclude the possibility of faster sea-level rise than suggested in the new paper."

Seems to confirm what others have said here.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on November 23, 2015, 09:38:33 AM
Thanks, S.Pansa, for pointing to those comments by Alley (who btw is co-author of a review-paper, but not the Ritz-paper).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on December 03, 2015, 11:35:11 PM
Watch out for the coming AGU Fall Meeting, starting December 13th.

Big lecture by Rignot:
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/60094

And presentation by Pollard:
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/60833

And by Hansen on scientific reticence and sea level rise:
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/86614

It seems the Pollard presenation will not be shown on AGU on Demand, unfortunately.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 03, 2015, 11:58:23 PM
Lennart,

Thank you very much for the links.

Further, just because I like it so much, I provide the abstract for the Pollard, DeConto, Chang, Applegate and Haran (2015) AGU paper that Lennart linked.  While I cannot attend the presentation, it should be a good one, and I note that it would be nice if the authors applied their same approach on Jakobshavn Glacier, for which there are excellent records for the past 30,000 years to compare any model runs that they might make:

David Pollard, Robert DeConto, Won Chang, Patrick Applegate and Murali Haran (Dec 18, 2015), "Modeling of past and future variations of the Antarctic Ice Sheet with Large Ensembles" AGU Fall Meeting, Paper 60833.

https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/60833

Abstract: "Recent observations of thinning and retreat of the Pine Island and Thwaites Glaciers identify the Amundsen Sea Embayment (ASE) sector of West Antarctica as particularly vulnerable to future climate change. To date, most future modeling of these glaciers has been calibrated using recent and modern observations. As an alternate approach, we apply a hybrid 3-D ice sheet-shelf model to the last deglacial retreat of Antarctica, making use of geologic data from ~20,000 years BP to present, focusing on the ASE but including other sectors of Antarctica.
Following several recent ice-sheet studies, we use Large Ensemble statistical methods, performing sets of ~600 runs over the last 30,000 years with systematically varying model parameters. Objective scores for each run are calculated using modern data and past reconstructed grounding lines, relative sea level records, cosmogenic elevation-age data and uplift rates. Two types of statistical methods are used to analyze the Large-Ensemble
results: simple averaging weighted by the aggregate score, and more advanced Bayesian emulation and calibration methods that rigorously account for some of the uncertainties in the model and observations.

Results for best-fit parameter ranges and envelopes of equivalent sea-level rise with the simple averaging method agree quite well with the more advanced techniques, but only for a Large Ensemble with dense (Full Factorial) parameter sampling. Runs are extended into the future using RCP scenarios, with drastic retreat mechanisms of hydrofracturing and structural ice-cliff failure. In most runs this produces grounding-line retreat into the West Antarctic interior, and into East Antarctic basins for RCP8.5, and the Large Ensemble analysis provides sea-level-rise envelopes with well defined parametric uncertainty bounds."

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 04, 2015, 08:51:04 PM
The linked draft reference provides some insight on what we can expect from the Pollard et al (2015) AGU presentation:

Won Chang, Murali Haran, Patrick Applegate, David Pollard (October 7, 2015), "Improving Ice Sheet Model Calibration Using Paleoclimate and Modern Data"

http://arxiv.org/pdf/1510.01676.pdf (http://arxiv.org/pdf/1510.01676.pdf)

Abstract: "Human-induced climate change may cause significant ice volume loss from the West Antarctic Ice Sheet (WAIS). Projections of ice volume change from ice-sheet models and corresponding future sea-level rise have large uncertainties due to poorly constrained input parameters. In most future applications to date, model calibration has utilized only modern or recent (decadal) observations, leaving input parameters that control the long-term behavior of WAIS largely unconstrained. Many paleo-observations are in the form of localized time series, while modern observations are non-Gaussian spatial data; combining information across these types poses nontrivial statistical challenges. Here we introduce a computationally efficient calibration approach that utilizes both modern and paleo-observations to generate better-constrained ice volume projections.

Using fast emulators built upon principal component analysis and a reduced dimension calibration model, we can efficiently handle high-dimensional and non-Gaussian data. We apply our calibration approach to the PSU3D-ICE model which can realistically simulate long-term behavior of WAIS. Our results show that using paleo observations in calibration significantly reduces parametric uncertainty, resulting in sharper projections about the future state of WAIS. One benefit of using paleo observations is found to be that unrealistic simulations with overshoots in past ice retreat and projected future regrowth are eliminated."

Captions: " Figure 7: Predictive distribution for the ice volume change projection based on the real observations described in Section 4.2. The solid red line shows the predictive distribution based on our approach using both the past grounding line positions the modern binary patterns and the dashed and dotted blue line represents the result based on only the modern binary patterns. The dashed green line shows the projection without calibration. The results show that using the past grounding line leads to a significantly sharper projection by removing the unrealistic ice volume increase in the results solely based on the modern observations."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 05, 2015, 06:37:50 PM
As a short follow-up to my last post about Won Chang, Murali Haran, Patrick Applegate, David Pollard (2015), while I greatly respect their approach and findings, I note that the dynamic ice mass loss for Pine Island Bay in the last 30,000 years (which likely includes ice mass loss input from Pine Island Bay to Meltwater Pulse 1A) may not be as dynamic as what may occur in the Byrd Subglacial Basin area once the grounding line for the Thwaites Glacier reaches the negative bottom slope (possibly as soon as in the next couple of decade with the mean global surface temperature anom. possibly near 2C).  Therefore, the calibration of the cliff failures and hydrofracturing parameters may currently err somewhat on the side of least drama (while still performing much better than most other comparable marine ice sheet models).

Therefore, I reiterate that if Chang et al. or other researchers have the budget that it would be helpful if they were to create a cliff failure and hydrofacturing model of the Jakobshavn Glacier and to calibrate it against the observed behavior during the past 11,000 years (including the Holocene Optimum) as discussed in Reply #171 of the "Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe" thread; because the grounding line for that glacier appears to have retreated down a bottom slope with a markedly negative slope in that timeframe, and because the surface temperatures during the Holocene Optimum are closer to today's conditions (which might help hydrofracturing).
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 22, 2015, 10:47:39 PM
The projected future behavior of the ASL per the linked reference will likely force more warm CDW into the ASE thus promoting more than previously projected ice mass loss from marine glaciers in this key area:

J. Scott Hosking, Andrew Orr, Thomas J. Bracegirdle and John Turner (2015), "Future circulation changes off West Antarctica: Sensitivity of the Amundsen Sea Low to projected anthropogenic forcing", Geophysical Research Letters, DOI: 10.1002/2015GL067143

http://onlinelibrary.wiley.com/doi/10.1002/2015GL067143/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL067143/abstract)

Abstract: "The Amundsen Sea Low (ASL) is a major driver of West Antarctic climate variability, with the potential to accelerate the loss of glacial ice. Using the eleven global climate models which most reliably simulate the seasonality in ASL location, we assess the ASL sensitivity to projected future changes using the CMIP5 historical (1951-2000) and representative concentration pathway experiment RCP8.5 (2051-2100). For the first time, we show that the future ASL will likely migrate polewards in summer (DJF) and autumn (MAM), and eastward in autumn and winter (JJA). The autumn-winter changes drive colder southerly winds over the Ross Sea and warmer northerly winds towards the Antarctic Peninsula. This is consistent with recent trends in ERA-Interim reanalysis meridional winds (1979-2014) and reconstructed temperature (1957-2006), suggesting that the impact of anthropogenic forcing on the ASL is likely to play an important role on both past and future patterns of West Antarctic climate variability."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 01, 2016, 01:08:14 AM
The linked (open access) reference (and attached associated image) uses both proxy, and climate model, evidence to show that as the Eastern Tropical Pacific continues to warm (both due to climate change and also due to a possible multi-decadal positive phase(s) of the PDO/IPO) the coastal areas of the WAIS and in particular the ASE will sustain anomalously high increases in surface temperature.  This increases the risk of possible hydrofracture and cliff failures in the affected areas, possibly as soon as the 2035 to 2040 timeframe:


Turney, C. S. M., Fogwill, C. J., Klekociuk, A. R., van Ommen, T. D., Curran, M. A. J., Moy, A. D., and Palmer, J. G. (2015), "Tropical and mid-latitude forcing of continental Antarctic temperatures", The Cryosphere, 9, 2405-2415, doi:10.5194/tc-9-2405-2015.

http://www.the-cryosphere.net/9/2405/2015/tc-9-2405-2015.html (http://www.the-cryosphere.net/9/2405/2015/tc-9-2405-2015.html)
http://www.the-cryosphere.net/9/2405/2015/tc-9-2405-2015.pdf (http://www.the-cryosphere.net/9/2405/2015/tc-9-2405-2015.pdf)

Abstract: "Future changes in atmospheric circulation and associated modes of variability are a major source of uncertainty in climate projections. Nowhere is this issue more acute than across the mid-latitudes to high latitudes of the Southern Hemisphere (SH), which over the last few decades have experienced extreme and regionally variable trends in precipitation, ocean circulation and temperature, with major implications for Antarctic ice melt and surface mass balance. Unfortunately there is a relative dearth of observational data, limiting our understanding of the driving mechanism(s). Here we report a new 130-year annually resolved record of δD – a proxy for temperature – from the geographic South Pole where we find a significant influence from extratropical pressure anomalies which act as "gatekeepers" to the meridional exchange of air masses. Reanalysis of global atmospheric circulation suggests these pressure anomalies play a significant influence on mid- to high-latitude SH climate, modulated by the tropical Pacific Ocean. This work adds to a growing body of literature confirming the important roles of tropical and mid-latitude atmospheric circulation variability on Antarctic temperatures. Our findings suggest that future increasing tropical warmth will strengthen meridional circulation, exaggerating current trends, with potentially significant impacts on Antarctic surface mass balance."

Extract: "With projected weakening of the trade winds (England et al., 2014), the observed links to Antarctic temperatures suggest the tropics may in fact play an increasingly significant role in driving high-latitude warming (Figs. 4 and 10), with potentially important implications for understanding past climate states (McGlone et al., 2010; Pedro et al., 2011; Visser et al., 2003) and future Antarctic surface mass balance."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 01, 2016, 01:59:55 AM
The linked (open access) reference finds that there are already large committed ice mass losses for the Smith, Pope and Kohler Glaciers in the ASE over the next 30-years, even without any new oceanic or atmospheric forcings:


Goldberg, D. N., Heimbach, P., Joughin, I., and Smith, B.  (2015), "Committed retreat of Smith, Pope, and Kohler Glaciers over the next 30 years inferred by transient model calibration", The Cryosphere, 9, 2429-2446, doi:10.5194/tc-9-2429-2015.


http://www.the-cryosphere.net/9/2429/2015/tc-9-2429-2015.html (http://www.the-cryosphere.net/9/2429/2015/tc-9-2429-2015.html)


Abstract. A glacial flow model of Smith, Pope and Kohler Glaciers is calibrated by means of control methods against time varying, annually resolved observations of ice height and velocities, covering the period 2002 to 2011. The inversion – termed "transient calibration" – produces an optimal set of time-mean, spatially varying parameters together with a time-evolving state that accounts for the transient nature of observations and the model dynamics. Serving as an optimal initial condition, the estimated state for 2011 is used, with no additional forcing, for predicting grounded ice volume loss and grounding line retreat over the ensuing 30 years. The transiently calibrated model predicts a near-steady loss of grounded ice volume of approximately 21 km3 a−1 over this period, as well as loss of 33 km2 a−1 grounded area. We contrast this prediction with one obtained following a commonly used "snapshot" or steady-state inversion, which does not consider time dependence and assumes all observations to be contemporaneous. Transient calibration is shown to achieve a better fit with observations of thinning and grounding line retreat histories, and yields a quantitatively different projection with respect to ice volume loss and ungrounding. Sensitivity studies suggest large near-future levels of unforced, i.e., committed sea level contribution from these ice streams under reasonable assumptions regarding uncertainties of the unknown parameters.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 11, 2016, 09:31:49 PM
I believe that the behavior of marine glaciers adjoining the Filchner-Ronne ice shelf in the following linked reference should be considered as a lower bound, as it ignores/discounts numerous considerations, including:
- Cliff failures and hydrofracturing.
- Possible interconnection of ocean currents between the Weddell and Amundsen Seas, through submarine channels currently filled with marine ice.
- Possible impacts on ice loss associated with possible/probable changes in the adjoining sea ice.
- Positive feedbacks not considered by the authors.

M. Mengel, J. Feldmann & A. Levermann (2016), "Linear sea-level response to abrupt ocean warming of major West Antarctic ice basin", Nature Climate Change, Volume: 6, Pages: 71–74, doi:10.1038/nclimate2808


http://www.nature.com/nclimate/journal/v6/n1/full/nclimate2808.html (http://www.nature.com/nclimate/journal/v6/n1/full/nclimate2808.html)

Abstract: "Antarctica’s contribution to global sea-level rise has recently been increasing. Whether its ice discharge will become unstable and decouple from anthropogenic forcing or increase linearly with the warming of the surrounding ocean is of fundamental importance. Under unabated greenhouse-gas emissions, ocean models indicate an abrupt intrusion of warm circumpolar deep water into the cavity below West Antarctica’s Filchner–Ronne ice shelf within the next two centuries. The ice basin’s retrograde bed slope would allow for an unstable ice-sheet retreat, but the buttressing of the large ice shelf and the narrow glacier troughs tend to inhibit such instability. It is unclear whether future ice loss will be dominated by ice instability or anthropogenic forcing. Here we show in regional and continental-scale ice-sheet simulations, which are capable of resolving unstable grounding-line retreat, that the sea-level response of the Filchner–Ronne ice basin is not dominated by ice instability and follows the strength of the forcing quasi-linearly. We find that the ice loss reduces after each pulse of projected warm water intrusion. The long-term sea-level contribution is approximately proportional to the total shelf-ice melt. Although the local instabilities might dominate the ice loss for weak oceanic warming, we find that the upper limit of ice discharge from the region is determined by the forcing and not by the marine ice-sheet instability."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 15, 2016, 05:01:55 PM
The linked April 2015 video of Richard Alley's talk about the risk that mainstream science may not have yet fully recognized the risk of abrupt sea level rise contribution from the WAIS (say due to cliff failures & hydrofracturing), has been posted before.  Nevertheless, I repost it here because Alley concludes his talk by calling for more oceanic-ice interaction investigation; which is precisely what the following linked research to be conducted at Scripps from Dec 2016 to Dec 2017 as part of the ACME program:

https://www.youtube.com/watch?v=yCunWFmvUfo (https://www.youtube.com/watch?v=yCunWFmvUfo)

The linked website indicates that from Dec 2016 until Dec 2017, Scripps (lead by Julie McClean) will investigate Ocean and Sea-Ice Processes for the ACME program.  Therefore, I believe that it is reasonable to assume that preliminary findings from Phase 1 of the ACME program will not be publically available before 2018.

https://scripps.ucsd.edu/research/proposals/accelerated-climate-modeling-energy-acme-ocean-and-sea-ice-processes (https://scripps.ucsd.edu/research/proposals/accelerated-climate-modeling-energy-acme-ocean-and-sea-ice-processes)

Extract: "For cryosphere, the team will examine the near-term risks of initiating the dynamic instability and onset of the collapse of the Antarctic Ice Sheet due to rapid melting by warming waters adjacent to the ice sheet grounding lines.
 
The experiment would be the first fully coupled global simulation to include dynamic ice shelf–ocean interactions for addressing the potential instability associated with grounding line dynamics in marine ice sheets around Antarctica."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 22, 2016, 03:52:44 PM
The linked reference discusses 300-years of ice core data demonstrating that the Amundsen Sea Low, ASL, is deepening as part of a long-term anthropogenically driven trend.  This trend is accelerating the timeline for the collapse of the WAIS by:

(a) Increasing the advection of warm CDW to key marine glaciers,
(b) Working together with the SAM & El Ninos to advect warm Tropical Pacific atmospheric energy to Western Antarctica, and
(c) Increasing the recent snowfall that has been, and still is, increasing the driving gravitational head on key marine glaciers in this area.

E. R. Thomas, J. S. Hosking, R. R. Tuckwell, R. A. Warren & E. C. Ludlow (2015), "Twentieth century increase in snowfall in coastal West Antarctica", Geophysical Research Letters, doi:10.1002/2015GL065750

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065750/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL065750/abstract)

Abstract: "The Amundsen Sea sector of the West Antarctic ice sheet has been losing mass in recent decades; however, long records of snow accumulation are needed to place the recent changes in context. Here we present 300 year records of snow accumulation from two ice cores drilled in Ellsworth Land, West Antarctica. The records show a dramatic increase in snow accumulation during the twentieth century, linked to a deepening of the Amundsen Sea Low (ASL), tropical sea surface temperatures, and large-scale atmospheric circulation. The observed increase in snow accumulation and interannual variability during the late twentieth century is unprecedented in the context of the past 300 years and evidence that the recent deepening of the ASL is part of a longer trend."

See also:
Strelich, L. (2016), Climate change drives increasing snowfall in western Antarctica, Eos, 97, doi:10.1029/2016EO044021. Published on 21 January 2016

Extract: "Scientists predict that one symptom of a changing climate will be a deepening of the Amundsen Sea Low, a climatological low-pressure center that plays a big role in the regional climate. Here Thomas et al. provide new evidence that this change—and, ultimately, the melting of West Antarctic ice sheets—is already under way.

These phenomena influence regional sea surface temperature, atmospheric circulation, and sea level pressure. Changes in sea level pressure generate changes in snowfall and drive meridional winds that bring moist air up onto the Ellsworth coast, causing ocean upwelling and melting of the West Antarctic ice shelves."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 01, 2016, 05:03:01 PM
The linked reference indicates that current atmospheric & ocean conditions are not sufficient to cause a collapse of the WAIS comparable to that which occurred in the LIG (Eemian); however, it cites a Southern Ocean temperature increase threshold of 2 to 3C (based on paleo-data) for a likely collapse of the WAIS (which most current CMIP models indicate will not happen before 2100).  However, I note that scientists do not put their work into perspective for the reader, as that assume that the reader will provide their own context.  In this case, I note that the authors ignore the risk of cliff failures and hydrofracturing and thus can only be considered a lower-bound approximation.  Furthermore, I note that as the Southern Ocean freshens (with continued warming and ice melt) there should be more local evaporation (as freshwater evaporates more easily than saltwater), which in the short-term will result in more snowfall (particularly in West Antarctica), but in a few decades time could result in more rainfall which would greatly accelerated both surface ice mass loss & hydrofracturing (which would need to be included into any upper bound forecast of the future risk of WAIS collapse before 2100):

Paul Gierz, Klaus Grosfeld, Malte Thoma & Gerrit Lohmann (2016), "Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse", Geophysical Research Letters, DOI: 10.1002/2016GL067818


http://onlinelibrary.wiley.com/doi/10.1002/2016GL067818/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL067818/abstract)

Abstract: "The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 meters in the last warm era, of which probably not much more than 2 meters are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3D thermomechanical ice sheet model forced by an atmosphere ocean general circulation model (AOGCM). Our results show that high LIG sea levels, cannot be reproduced with the atmosphere-ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2-3∘C, accounting for a sea level rise of 3-4 meters during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 09, 2016, 02:08:32 AM
The linked reference quantifies the zone of "passive" ice shelf that can be lost without accelerating the contribution of the buttressed grounded marine glacial to sea level rise.  The Amundsen and Bellingshausen ice shelves were found to have the least area of passive ice shelf in Antarctica (see image):

Johannes Jakob Fürst, Gaël Durand, Fabien Gillet-Chaulet, Laure Tavard, Melanie Rankl, Matthias Braun & Olivier Gagliardini  (2016), "The safety band of Antarctic ice shelves", Nature Climate Change, doi:10.1038/nclimate2912

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2912.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2912.html)

Abstract: "The floating ice shelves along the seaboard of the Antarctic ice sheet restrain the outflow of upstream grounded ice. Removal of these ice shelves, as shown by past ice-shelf recession and break-up, accelerates the outflow, which adds to sea-level rise. A key question in predicting future outflow is to quantify the extent of calving that might precondition other dynamic consequences and lead to loss of ice-shelf restraint. Here we delineate frontal areas that we label as ‘passive shelf ice’ and that can be removed without major dynamic implications, with contrasting results across the continent. The ice shelves in the Amundsen and Bellingshausen seas have limited or almost no ‘passive’ portion, which implies that further retreat of current ice-shelf fronts will yield important dynamic consequences. This region is particularly vulnerable as ice shelves have been thinning at high rates for two decades and as upstream grounded ice rests on a backward sloping bed, a precondition to marine ice-sheet instability. In contrast to these ice shelves, Larsen C Ice Shelf, in the Weddell Sea, exhibits a large ‘passive’ frontal area, suggesting that the imminent calving of a vast tabular iceberg will be unlikely to instantly produce much dynamic change."

Caption: "Map showing the percentage area of "passive" ice in all of Antarctica's ice shelves. Passive ice can be lost without dramatically changing glacier and ice sheet dynamics"

See also:
http://www.climatecentral.org/news/weakening-ice-shelves-sea-level-rise-20003 (http://www.climatecentral.org/news/weakening-ice-shelves-sea-level-rise-20003)

Extract: "The Amundsen and Bellingshausen sea sectors in West Antarctica are home to the most at-risk ice on the continent. Both regions’ ice shelves average less than 10 percent of their ice being “safe” to lose (in a relative sense anyways) before major ice sheet dynamics start to change."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 09, 2016, 07:47:26 PM
The linked reference indicates that the current generation of AOGCM projections are incapable of hindcasting the sea level contribution from the WAIS during the Last Interglacial (LIG or Eemian).  Hopefully, future generations of climate models will include cliff failure and hydrofractuing mechanisms (ala Pollard et al 2015).  Also, while the reference cites a "… Southern Ocean temperature anomaly threshold for total WAIS collapse of 2-3∘C …", it does not acknowledge that the current ozone hole over Antarctica has no parallel during the LIG, and that the current ozone how can/is creating westerly wind that is advecting warm CDW to the grounding lines of key WAIS marine glaciers much more quickly than likely occurred during the LIG/Eemian:

Johannes Sutter, Paul Gierz, Klaus Grosfeld, Malte Thoma & Gerrit Lohmann (2016), "Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse", Geophysical Research Letters, DOI: 10.1002/2016GL067818


http://onlinelibrary.wiley.com/doi/10.1002/2016GL067818/abstract?systemMessage=Wiley+Online+Library+will+be+unavailable+on+Saturday+27th+February+from+09:00-14:00+GMT+/+04:00-09:00+EST+/+17:00-22:00+SGT+for+essential+maintenance.++Apologies+for+the+inconvenience. (http://onlinelibrary.wiley.com/doi/10.1002/2016GL067818/abstract?systemMessage=Wiley+Online+Library+will+be+unavailable+on+Saturday+27th+February+from+09:00-14:00+GMT+/+04:00-09:00+EST+/+17:00-22:00+SGT+for+essential+maintenance.++Apologies+for+the+inconvenience.)

Abstract: "The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 meters in the last warm era, of which probably not much more than 2 meters are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3D thermomechanical ice sheet model forced by an atmosphere ocean general circulation model (AOGCM). Our results show that high LIG sea levels, cannot be reproduced with the atmosphere-ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2-3∘C, accounting for a sea level rise of 3-4 meters during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 18, 2016, 10:00:18 PM
The linked reference discusses field research documenting the manner in which the Ross Ice Sheet/Shelf retreated during the Holocene in a series of relatively abrupt stair-steps that periodically sent armadas of icebergs across the continental shelf, gouging furrows as they moved into the open ocean.  While this information has some relevance to projecting the potential future break-up of the existing Ross Ice Shelf; it also has a good degree of relevance to projecting the armadas of icebergs that are likely to exit out of the Amundsen Sea Embayment if/when the adjoining marine glaciers break-up (see associated image)

Yusuke Yokoyama, John B. Anderson, Masako Yamane, Lauren M. Simkins, Yosuke Miyairi, Takahiro Yamazaki, Mamito Koizumi, Hisami Suga, Kazuya Kusahara, Lindsay Prothro, Hiroyasu Hasumi, John R. Southon, and Naohiko Ohkouchi (2016), "Widespread collapse of the Ross Ice Shelf during the late Holocene", Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1516908113


http://www.pnas.org/content/early/2016/02/09/1516908113.abstract (http://www.pnas.org/content/early/2016/02/09/1516908113.abstract)

Abstract: "The stability of modern ice shelves is threatened by atmospheric and oceanic warming. The geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate. Fields of deep (−560 m), linear iceberg furrows on the outer, western Ross Sea continental shelf record an early post-Last Glacial Maximum episode of ice-shelf collapse that was followed by continuous retreat of the grounding line for ∼200 km. Runaway grounding line conditions culminated once the ice became pinned on shallow banks in the western Ross Sea. This early episode of ice-shelf collapse is not observed in the eastern Ross Sea, where more episodic grounding line retreat took place. More widespread (∼280,000 km2) retreat of the ancestral Ross Ice Shelf occurred during the late Holocene. This event is recorded in sediment cores by a shift from terrigenous glacimarine mud to diatomaceous open-marine sediment as well as an increase in radiogenic beryllium (10Be) concentrations. The timing of ice-shelf breakup is constrained by compound specific radiocarbon ages, the first application of this technique systematically applied to Antarctic marine sediments. Breakup initiated around 5 ka, with the ice shelf reaching its current configuration ∼1.5 ka. In the eastern Ross Sea, the ice shelf retreated up to 100 km in about a thousand years. Three-dimensional thermodynamic ice-shelf/ocean modeling results and comparison with ice-core records indicate that ice-shelf breakup resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf."

See also:
http://phys.org/news/2016-02-colossal-antarctic-ice-shelf-collapse-ice.html (http://phys.org/news/2016-02-colossal-antarctic-ice-shelf-collapse-ice.html)

Extract: ""We found that about 10,000 years ago, this thick, grounded ice sheet broke apart in dramatic fashion," Anderson said. "The evidence shows that an armada of icebergs—each at least twice as tall as the Empire State Building—was pushed out en masse. We know this because this part of the Ross Sea is about 550 meters (1,804 feet) deep, and the icebergs were so large and so tightly packed that they gouged huge furrows into the seafloor as they moved north."


The really big breakup began around 3000 B.C.," Anderson said. "We believe it was similar, in many respects, to the breakup of the Larsen B Ice Shelf in 2002. The Larsen is far smaller than the Ross Ice Shelf, but satellite imagery that year showed the Larsen dramatically breaking apart in just a few weeks. We believe the large breakup of the Ross Ice Shelf occurred at roughly this same pace, but the area involved was so much larger—about the size of the state of Colorado—that it took several centuries to complete."

By 1500 B.C. the breakup had exposed about 100,000 square miles of the Ross Sea that had been either wholly or largely ice-covered for many millennia, Anderson said."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 21, 2016, 07:43:52 PM
The linked (open access) Fogwill et. al. (2015) reference first notes that in order to achieve the observed sea levels during recent past interglacial periods (particularly the Eemian) as yet unidentified mechanisms must have contributed to the accelerated collapse of major portions of the WAIS.  The reference then assumes various collapse scenarios for the WAIS and uses a regional climate model to study the sensitivity of the Southern Ocean to the assumed scenarios in order to study one of several likely feedback mechanisms that could contribute to accelerated WAIS collapse.  The attached image shows the projected decrease in AABW formation and the increase in CDW (400 to 700m deep) temperature associated with these scenarios.  Of particular, concern is that the projections indicate that the scenarios result in the advection of the warmer CDW to key marine glaciers (notable those in the ASE), which results in a positive feedback for sustained WAIS collapse.  The authors acknowledge that their findings are likely conservative (ESLD) as they do not consider continued GHG emissions nor possible high values for ECS/ESS, nor the positive feedbacks cited by Hansen et. al. (2015).  The reference concludes by calling for the development of more advanced climate models (such as ACME [both initial and final]) to further investigate the many and complex issues associated with this matter:

C. J. Fogwill, S. J. Phipps, C. S. M. Turney & N. R. Golledge (2015), "Sensitivity of the Southern Ocean to enhanced regional Antarctic ice sheet meltwater input", Earth's Future, Volume 3, Issue 10, Pages 317–329, DOI: 10.1002/2015EF000306

http://onlinelibrary.wiley.com/doi/10.1002/2015EF000306/full (http://onlinelibrary.wiley.com/doi/10.1002/2015EF000306/full)

Abstract: "Despite advances in our understanding of the processes driving contemporary sea level rise, the stability of the Antarctic ice sheets and their contribution to sea level under projected future warming remains uncertain due to the influence of strong ice-climate feedbacks. Disentangling these feedbacks is key to reducing uncertainty. Here we present a series of climate system model simulations that explore the potential effects of increased West Antarctic Ice Sheet (WAIS) meltwater flux on Southern Ocean dynamics. We project future changes driven by sectors of the WAIS, delivering spatially and temporally variable meltwater flux into the Amundsen, Ross, and Weddell embayments over future centuries. Focusing on the Amundsen Sea sector of the WAIS over the next 200 years, we demonstrate that the enhanced meltwater flux rapidly stratifies surface waters, resulting in a significant decrease in the rate of Antarctic Bottom Water (AABW) formation. This triggers rapid pervasive ocean warming (>1°C) at depth due to advection from the original site(s) of meltwater input. The greatest warming is predicted along sectors of the ice sheet that are highly sensitized to ocean forcing, creating a feedback loop that could enhance basal ice shelf melting and grounding line retreat. Given that we do not include the effects of rising CO2—predicted to further reduce AABW formation—our experiments highlight the urgent need to develop a new generation of fully coupled ice sheet climate models, which include feedback mechanisms such as this, to reduce uncertainty in climate and sea level projections."

Extract: "One major uncertainty, however, is how the marine-based West Antarctic Ice Sheet (WAIS) will respond to future climate change, and particularly how it may contribute to future global mean sea level (GMSL) [Lenton et al., 2008; Pritchard et al., 2012; Vaughan et al., 2013; Golledge et al., 2015]. In part, this question arises from analogy with past interglacial periods when, despite only small apparent increases in mean atmospheric and ocean temperatures, GMSL is predicted to have been far higher than present [Dutton et al., 2015; Dutton and Lambeck, 2012; Kopp et al., 2009]. To achieve these levels, undefined mechanisms must have been at work that substantially increased the net contribution of the Earth's ice sheets to global sea level [Fogwill et al., 2014].
One such mechanism could have been through ice-ocean feedbacks that arose as a consequence of enhanced meltwater discharge to the Southern Ocean. This has been highlighted in recent studies investigating the apparent coupling between Antarctic ice sheet change and atmospheric temperatures during past interglacials [Holden et al., 2010]. In conclusion, this detailed study of the Last Interglacial demonstrated that feedbacks from WAIS retreat were required to simulate the magnitude of the observed warming within Antarctic ice core records.



To summarize, the changes in the properties of AABW triggered by increasing freshwater input in the Southern Ocean surrounding Antarctica have critical implications for the dynamics of the Antarctic ice sheet. Intriguingly, several recent studies provide growing evidence of rapid contemporary changes in the properties of AABW [Jacobs et al., 2002; Rhein et al., 2013; van Wijk and Rintoul, 2014]. Observations suggest that the AABW layer is warming, freshening, and contracting in volume [Jacobs et al., 2002], although the drivers of these changes are not yet clear. Our simulations and the mechanism described above suggests that contemporary Southern Ocean freshening may already be occurring as a result of increasing delivery of meltwater from Antarctic ice, with the possibility that a marked reduction in the rate of AABW production may be imminent [Purkey and Johnson, 2013; Rhein et al., 2013], triggering further warming at depth in the Southern Ocean. When combined with uncertainties regarding potential increases in ocean temperatures due to shifting winds and/or changing ocean circulation patterns, the potential for marked changes in ocean ice sheet dynamics over the next century is high [Fogwill et al., 2014; Hellmer et al., 2012; Miles et al., 2013; Spence et al., 2014]. Our experiments provide a unique insight into potential future changes in the Southern Ocean that have important implications for the stability of the Antarctic ice sheets. This study examines just one of a number of strong feedback mechanisms operating at the ocean ice sheet interface that question current sea level rise projections; clearly, modeling studies will need to integrate these feedbacks to gain a more realistic picture of future change."


See also:
Sullivan, C. (2016), Antarctic meltwater makes the ocean warmer and fresher, Eos, 97, doi:10.1029/2016EO044811. Published on 1 February 2016.

https://eos.org/research-spotlights/antarctic-meltwater-makes-the-ocean-warmer-and-fresher (https://eos.org/research-spotlights/antarctic-meltwater-makes-the-ocean-warmer-and-fresher)
Extract: "It’s well known that anthropogenic warming will affect global climate and sea levels far into the future. At the edges of ice sheets and glaciers, water, air, and ice all come together in a complex union that carries implications for predicting climate in the future. As global temperatures rise, ice sheets and glaciers melt, dumping their meltwater into the ocean. The future of some areas, such as the West Antarctic Ice Sheet (WAIS), remains a wildcard when it comes to predicting how the oceans might change.
The WAIS spans much of West Antarctica and holds 2.2 million square kilometers of ice. To try and piece together how the ice sheet might change in the future, Fogwill et al. used climate models to examine the meltwater’s potential effects, focusing on three specific Antarctic regions: the Amundsen, Ross, and Weddell embayments. The scientists’ experiments considered numerous scenarios, ranging from only portions of the ice sheet disappearing to complete melting.
Fresh water flowing off the ice sheet reduces the salinity and density of the ocean’s surface water. With lower-density water sitting on top, the ocean’s vertical layers become more distinct and don’t mix as much. The researchers also found that the formation rate of Antarctic Bottom Water—a layer of dense cool water that pools near the ocean floor—decreased by 25%–50% within decades when compared to a preindustrial control. In all scenarios, the results show that waters ranging from 400 to 700 meters in depth will warm rapidly within the first 200 years, with warming at depth fluctuating between 0.5°C and >1°C, depending on the scenario.
The scientists demonstrated that an increase in fresh meltwater from the WAIS decreases ocean salinity and increases water temperatures in critical locations around the edge of the Antarctic ice sheet, including areas of the East Antarctic Ice Sheet (EAIS). In addition, by investigating specific sites along the ice sheet’s edges, the researchers showed that the location of melting is just as critical to ocean dynamics as the volume of meltwater flowing into the ocean, with sites such as the Amundsen Sea, an area of rapid contemporary WAIS change, being critical.
These effects extend beyond the Southern Ocean. Although the impact is strongest there, all across the Southern Hemisphere, salinity and water temperature are changing. In these models, however, the scientists didn’t include rising atmospheric carbon dioxide levels, which could accelerate the rate of ice sheet melting. Given that, the estimations provided could be conservative."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on February 21, 2016, 10:32:34 PM
There is another paper wil Fogwill in 2014 DOI:10.1002/jqs.2683   which was also disturbing. I believe i have commented before on Fig 7 therein and the following discussion of concave basin profiles and fast drawdown.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 22, 2016, 07:00:51 PM
The linked reference compares paleo ice core data with a coupled climate model projections to that Southern Ocean deep convection can drive Antarctic multidecadal warming events.  The projections indicate that such convection driven warming events must be preconditioned by: (1) heat accumulation in the depth Southern Ocean (which is occurring now); (2) changes in wind and/or sea ice patterns (which have been projected in the near future); and (3) fast sea-ice-albedo feedback.
While Hansen et al (2015) projects this type of deep convective ocean behavior most other AR5 model projections do not; thus it is possible that in the future that: (a) initially the forecast increase in snow will fall more on sea ice than on land, where it will contribute to SLR; and (b) after a few decades of the warming event the sea ice extent will be reduced and the increased precipitation will fall more frequently as rain (rather than snow) that contributing the hydrofracturing and abrupt SLR.

J.B. Pedro, T. Martin, E. J. Steig, M. Jochum, W. Park & S.O. Rasmussen (20 February 2016), "Southern Ocean deep convection as a driver of Antarctic warming events", Geophysical Research Letters, DOI: 10.1002/2016GL067861

http://onlinelibrary.wiley.com/doi/10.1002/2016GL067861/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL067861/abstract)

Abstract: "Simulations with a free-running coupled climate model show that heat release associated with Southern Ocean deep convection variability can drive centennial-scale Antarctic temperature variations of up to 2.0 °C. The mechanism involves three steps: Preconditioning: heat accumulates at depth in the Southern Ocean; Convection onset: wind and/or sea-ice changes tip the buoyantly unstable system into the convective state; Antarctic warming: fast sea-ice–albedo feedbacks (on annual–decadal timescales) and slow Southern Ocean frontal and sea-surface temperature adjustments to convective heat release (on multidecadal–century timescales) drive an increase in atmospheric heat and moisture transport toward Antarctica. We discuss the potential of this mechanism to help drive and amplify climate variability as observed in Antarctic ice-core records."

Caption for second image: "Figure S2. Map showing the surface-air-temperature (SAT) anomaly during stage 2 (cf. Figure 3d). Circles mark locations of ice-core records. Color-coding of the circles depicts the maximum lagged correlation coefficient of modeled local SAT with SAT over the convection area (black cross in Weddell Sea). Lower panels show time series of modeled SAT anomalies at selected ice-core sites (red) together with the SAT anomaly over the convection region (black). Note different y-axis scaling for red lines."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on February 23, 2016, 07:09:58 AM
Here are the long awaited Pollard/DeConto/... papers from ANDRILL 2 in PNAS

unfortunately the dois printed on the pdf for papers are the same ?! but they are available from pnas early content, altho the abstract for one leads to the other ? oddities abound

doi:10.1073/pnas.1516030113
doi:10.1073/pnas.1516130113

nyhoo i enclose a heartstopping graf from the Gasson paper, with many meters of sea level rise in much less than a millennium after including cliff failure and hydrofracture.


Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 23, 2016, 08:58:56 AM
Tnx for catching these, sidd.
So they concentrated on the Miocene first and left the RCP-scenarios for later.
In their scenario A they seem to find about 6m of SLR in the first century after collapse, and another 4-5m in the second century, as their fig3 that sidd provides, shows. Also see their fig2 attached below for the different ice sheeets under scenarios A (modern bedrock topography) and B (assumed Miocene bedrock topography).

In their methods section they say:
"an instantaneous warming experiment is performed. This experiment uses the equilibrated ice sheets from the colder climate simulations as boundary and initial conditions. Atmospheric CO2 is increased to either 500 or 840 ppm, and a warm austral summer astronomical configuration is specified (January insolation at 70° S, 539 W m−2). Because of the significant computational expense of the asynchronous GCM–RCM climate forcing, it is not currently feasible to perform simulations with a transient astronomical forcing."

In this situation the extra 340 ppm apparently does not cause faster SLR in the first centuries.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 23, 2016, 11:34:26 AM
Stefan Rahmstorf connects the dots at RealClimate between these papers and two other new SLR-papers in PNAS (and discussed in the Consequences folder under the SLR and social cost of carbon thread:
http://www.realclimate.org/index.php/archives/2016/02/millennia-of-sea-level-change/ (http://www.realclimate.org/index.php/archives/2016/02/millennia-of-sea-level-change/)

He points to:
"two further new papers, also appearing in PNAS this week, by Gasson et al. and by Levy et al.. These papers look at the stability of the Antarctic Ice Sheet during the early to mid Miocene, between 23 and 14 million years ago. What is most relevant here is the advances in modelling the Antarctic ice sheet by including new mechanisms describing the fracturing of ice shelves and the breakup of large ice cliffs. The improved ice sheet model is able to capture the highly variable Antarctic ice volume during the Miocene; the bad news is that it suggests the Antarctic Ice Sheet can decay more rapidly than previously thought."

As noted above, Gasson et al seem to find that about 10m of SLR in two centuries may be likely once WAIS collapse gets going, so maybe from around 2050 or so?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 23, 2016, 12:11:34 PM
Correction, I didn't read carefully enough: Gasson et al don't find 10m in two centuries, but in four, with about 6m in the first two and about 4m in the next two.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 23, 2016, 12:45:17 PM
Also see:
https://www.sciencedaily.com/releases/2016/02/160222155615.htm (https://www.sciencedaily.com/releases/2016/02/160222155615.htm)

Gasson says:
"The ice sheets will take hundreds of years to respond, so although CO2 may be at the same level as during the Miocene in the next 30 years, it doesn't mean that they will melt in 30 years,"

But how many centuries are we talking about? Two, three, more? And how certain are we of that? We're at about two centuries now. According to fig2b (attached below) in Rohling et al 2013 we may not need more time for the ice sheets to start fully responding:
http://www.nature.com/articles/srep03461 (http://www.nature.com/articles/srep03461)

Hopefully it will take a few more centuries, but we're in risky territory.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: GeoffBeacon on February 23, 2016, 01:16:28 PM

Lennart van der Linde

Quote
Correction, I didn't read carefully enough: Gasson et al don't find 10m in two centuries, but in four, with about 6m in the first two and about 4m in the next two.

Is that from WAIS alone? Or does it include other sources?

And thanks.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2016, 05:12:48 PM

Lennart van der Linde

Quote
Correction, I didn't read carefully enough: Gasson et al don't find 10m in two centuries, but in four, with about 6m in the first two and about 4m in the next two.

Is that from WAIS alone? Or does it include other sources?

And thanks.

Geoff,

As the linked Robert Scribbler article indicates that during the Middle Miocene Climate Optimum sea level was 36.5 to 58m meters higher than today, it is safe to say that the Gasson et al (2016) values only include contribution from Antarctica and not from other sources.

Best
ASLR

http://robertscribbler.com/2015/03/11/entering-the-middle-miocene-co2-likely-to-hit-404-parts-per-million-by-may/ (http://robertscribbler.com/2015/03/11/entering-the-middle-miocene-co2-likely-to-hit-404-parts-per-million-by-may/)

Extract: "The Middle Miocene Climate Optimum occurred between about 15 and 17 million years ago. It hosted an atmosphere in which carbon dioxide levels varied wildly from 300 parts per million to 500 parts per million. Temperatures were between 3 to 5 degrees Celsius hotter than the 19th Century. And sea levels were about 120 to 190 feet higher."

See also:
https://www.washingtonpost.com/news/energy-environment/wp/2016/02/22/antarctica-could-be-more-vulnerable-to-major-melting-than-we-thought/ (https://www.washingtonpost.com/news/energy-environment/wp/2016/02/22/antarctica-could-be-more-vulnerable-to-major-melting-than-we-thought/)

Also I provide the following reference information about the Levy et al (2016) paper:

R. Levy, D. Harwood, F. Florindo, F. Sangiorgi, R. Tripati, H. von Eynatten, E. Gasson, G. Kuhn, A. Tripati, R. DeConto, C. Fielding, B. Field, N. Golledge, R. McKay, T. Naish, M. Olney, D. Pollard, S. Schouten, F. Talarico, S. Warny, V. Willmott, G. Acton, K. Panter, T. Paulsen, and M. Taviani (2016), "Antarctic ice sheet sensitivity to atmospheric CO2variations in the early to mid-Miocene", Proceedings of the National Academy of Sciences, pp. 201516030, doi: 10.1073/pnas.1516030113


http://www.pnas.org/content/early/2016/02/17/1516030113.abstract?sid=054ec02a-cd04-4970-9a0b-91d9ea9d0fb7 (http://www.pnas.org/content/early/2016/02/17/1516030113.abstract?sid=054ec02a-cd04-4970-9a0b-91d9ea9d0fb7)

Significance: "New information from the ANDRILL-2A drill core and a complementary ice sheet modeling study show that polar climate and Antarctic ice sheet (AIS) margins were highly dynamic during the early to mid-Miocene. Changes in extent of the AIS inferred by these studies suggest that high southern latitudes were sensitive to relatively small changes in atmospheric CO2 (between 280 and 500 ppm). Importantly, reconstructions through intervals of peak warmth indicate that the AIS retreated beyond its terrestrial margin under atmospheric CO2 conditions that were similar to those projected for the coming centuries."

Abstract: " Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23–14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3–4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on February 23, 2016, 05:55:27 PM
Hi Geoff,

In addition to ASLR: yes, Gasson et al are talking only about Antarctica, so this implies that we have to add SLR from thermal expansion and from melting GIS and smaller ice caps and glaciers to the SLR from WAIS and parts of EAIS in the coming centuries.

This could then add maybe another 2-3m until say 2250-2300 to the potential 6m from WAIS and EAIS.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on February 23, 2016, 10:06:14 PM
Fig S4 in Gasson shows the dramatic effect of hydrofracture and cliff failure
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2016, 10:33:35 PM
I thought that for ease of reference, I might as well provide the following for the Gasson et al (2016) paper (and the attached image with two figures).  Further, I thought that I would note that (a) our current CO₂-e is already near 490 ppm (less aerosol negative forcing) so if we clean-up our aerosols quickly we could be at mid-Miocene atmospheric conditions soon than many people are thinking; and (b) the attached images shows that our current WAIS bathymetry makes our current West Antarctic marine glaciers more sensitive to abrupt collapse than was the case during the mid-Miocene period:

E. Gasson, R.M. DeConto, D. Pollard, and R.H. Levy (2016), "Dynamic Antarctic ice sheet during the early to mid-Miocene", Proceedings of the National Academy of Sciences, pp. 201516130, doi: 10.1073/pnas.1516130113

http://www.pnas.org/content/early/2016/02/17/1516130113 (http://www.pnas.org/content/early/2016/02/17/1516130113)

Significance: "Atmospheric concentrations of carbon dioxide are projected to exceed 500 ppm in the coming decades. It is likely that the last time such levels of atmospheric CO2 were reached was during the Miocene, for which there is geologic data for large-scale advance and retreat of the Antarctic ice sheet. Simulating Antarctic ice sheet retreat is something that ice sheet models have struggled to achieve because of a strong hysteresis effect. Here, a number of developments in our modeling approach mean that we are able to simulate large-scale variability of the Antarctic ice sheet for the first time. Our results are also consistent with a recently recovered sedimentological record from the Ross Sea presented in a companion article."

Abstract: "Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate–ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet–climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52–0.66‰, or a sea level equivalent change of 30–36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability."

Caption for second part of the attached image: "Fig. S3. Sensitivity of model to bedrock topography for instantaneous warming experiments (warmer climate forcing, 500-ppm CO2, no climate feedbacks).  Note the increased initial ice volume for the older topographies, which are more similar to the Eocene/Oligocene topography of ref. 40 and have a greater area of land above sea level, particularly in the West Antarctic. Despite the large difference in response, the change in sea level is similar for all topographies. “max” and “min” are scaled between either the Eocene–Oligocene maximum or minimum reconstructions of ref. 40."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 30, 2016, 12:32:47 AM
While all of the linked IGSOC 2015 abstracts are of interest, I picked four that I thought had particular relevance to the discussion of the stability/timing of the potential partial collapse of the WAIS, this century:

http://www.igsoc.org/symposia/2015/cambridge/proceedings/procsfiles/procabstracts_68.html (http://www.igsoc.org/symposia/2015/cambridge/proceedings/procsfiles/procabstracts_68.html)

Extract: "73A1780
Large-ensemble modeling of last deglacial and future variations of the Antarctic ice sheet
David Pollard, Robert DeConto, Won Chang, Patrick Applegate, Murali Haran
Corresponding author: David Pollard
Corresponding author e-mail: pollard@essc.psu.edu
Recent observations of thinning and retreat of Pine Island and Thwaites Glaciers identify the Amundsen Sea Embayment (ASE) sector of West Antarctica as particularly vulnerable to future climate change. To date, most future modeling of these glaciers has been calibrated using recent and modern observations. As an alternate approach, we apply a hybrid 3-D ice-sheet–shelf model to the last deglacial retreat of Antarctica, making use of geologic data from ~20 000 years BP to present, focusing on the ASE but including other sectors of Antarctica. Following several recent ice-sheet studies, we use large-ensemble statistical techniques, performing sets of ~600 runs with varying model parameters. The model is run for the last 40 ka, both on continental domains and on nested domains over West Antarctica. Various types of objective RMS scores for each run are calculated using reconstructed past grounding lines, relative sea-level records, measured uplift rates, cosmogenic elevation-age data, and modern ice distribution. Runs are extended into the future few millennia using simple warming scenarios. The goal is to produce calibrated probabilistic ranges of model parameter values and quantified envelopes of future ice retreat. Two types of results are described and compared, using (1) statistical techniques with emulation, likelihood functions and MCMC, and (2) a much simpler technique of taking ensemble-mean averages weighted by aggregate RMS scores. One robust conclusion is that for future warming scenarios, most reasonable parameter combinations produce retreat deep into the West Antarctic interior.

&
73A1817
Strong effects of thermodynamic interactions of the Antarctic ice shelves with the ocean circulation on the Southern Ocean and sea-ice formation in a global coupled ocean circulation model
Olga Sergienko, Mathew Harrison
Corresponding author: Olga Sergienko
Corresponding author e-mail: osergien@princeton.edu
Melting/refreezing of ice shelves have strong impacts both on ice shelves (through modification of their shape) and on the ocean circulation (through modification of their water masses). Representation of ice-shelf/ocean interaction in the global ocean circulation models continues to be challenging. Using a high-resolution (1/8 deg) global isopycnal ocean model, MOM6, and a sea-ice model, SIS, we investigate the effects of thermodynamic coupling of the Antarctic ice shelves on the various aspects of ocean circulation. Such high (3–8 km) horizontal spatial resolution allows for detailed resolution of the sub-ice-shelf cavity circulations. The computed ice-shelf melt rates are in very good agreement with observationally derived melt rate estimates. The spatial distributions of simulated melting/freezing rates indicate enhanced melting in the vicinity of the grounding line and very strong melting at the ice-shelf front. Results of our simulations show strong effects of sub-ice-shelf meltwater on circulation of the Southern Ocean. We also find that simulations accounting for the thermodynamic coupling of the Antarctic ice shelves produce consistently thicker sea ice compared with the uncoupled simulations.

&
73A1887
1000 year adaptive mesh simulations of Antarctic ice dynamics
Stephen Cornford, Daniel Martin, Antony Payne, Esmond Ng
Corresponding author: Stephen Cornford
Corresponding author e-mail: ggslc@bristol.ac.uk
Numerical modelling of Antarctic ice dynamics becomes more demanding as the simulation time increases, partly because drainage basins evolve and even merge over long timescales, and to a great extent because fine-scale features – such as the grounding line – can migrate over continental length scales. Century long calculations – for example, the simulations of Pine Island Glacier described by Joughin (2010), Favier (2014) and Seroussi (2014) – need only consider single ice streams, and can take advantage of the relatively little grounding line migration likely to occur to limit fine resolution to a region close to the present-day grounding line. As integration times grow the grounding line tends to sweep out a larger area – meaning that the region of fine resolution must either cover that growing area or evolve with it. At the same time, neighbouring ice streams may merge, so that they can no longer be treated separately. Ultimately, it becomes necessary to carry out simulations of the whole of Antarctica, potentially applying fine resolution everywhere. We present 1000 year simulations of the whole Antarctic response to simplified ocean forcing using the BISICLES ice-sheet model. Some of the simulations feature the complete collapse of the West Antarctic ice sheet, and we are able to use time-evolving adaptive mesh refinement to track the grounding line and reduce the computational complexity by orders of magnitude. We compare the size of pure numerical errors, caused by spatial and temporal under-resolution, with the differences due to approximation made in the model physics, and estimate an upper bound on the speed of West Antarctic collapse.

&
73A1935
Committed near-future retreat of Smith, Pope and Kohler Glaciers inferred from transient model calibration
Daniel Goldberg, Patrick Heimbach
Corresponding author: Daniel Goldberg
Corresponding author e-mail: dngoldberg@gmail.com
A glacial flow model is used to investigate near-future thinning and and grounding line retreat of Pope, Smith, and Kohler Glaciers, West Antarctica. The model is calibrated against observations to infer unknown parameters. We investigate two methods of calibration: the more commonly used ‘snapshot calibration’, which does not consider time dependence and assumes all observations are contemporaneous; and ‘transient calibration’, which accounts for the transient nature of observations. The transiently calibrated model achieves good agreement with time-dependent observations of surface elevation and velocity from 2001 to 2011, while snapshot calibration is unable to reproduce transient observed behaviour – although the poor fit of the snapshot-calibrated model is not apparent when examining an areally integrated metric such as total 2001–2011 sea-level contribution from the region. The models are then run from 2011 to 2041 with no additional forcings. The transiently calibrated model predicts near-steady grounded ice loss of 22.5 km3 a–1 over this period, while the snapshot-calibrated figure, while still large, is nearly 50% less. Moreover the transiently calibrated model reproduces past grounding line retreat and predicts further retreat, while the snapshot-calibrated model does neither. This demonstrates the need for ice models to be able to reproduce time-dependent observational histories in order to make more accurate predictions of near-future ice-stream behavior. Still, these results – along with additional sensitivity studies – suggest that this region will continue to have significant sea-level contributions over the next several decades, regardless of external forcings or uncertainties in unknown parameters.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on March 30, 2016, 05:32:52 AM
yes, i was waiting for someone to come up with the approach in the Cornford Igsoc abstract.

" ... we are able to use time-evolving adaptive mesh refinement to track the grounding line and reduce the computational complexity by orders of magnitude ... "

that may be good enough without comoving mesh.

And i note the sentence in the Sergienko abstract
 
"We also find that simulations accounting for the thermodynamic coupling of the Antarctic ice shelves produce consistently thicker sea ice compared with the uncoupled simulations"

Another piece falls into place.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 30, 2016, 08:50:43 PM
Per the linked (open access) reference Antarctica could contribute 1.05 +/-0.3 m of SLR by 2100 (see attached image):

Robert M. DeConto & David Pollard (31 March 2016), "Contribution of Antarctica to past and future sea-level rise", Nature, Volume: 531, Pages: 591–597, doi:10.1038/nature17145

http://www.nature.com/articles/nature17145.epdf?referrer_access_token=px-zRubs4M6aBBPl42_1GdRgN0jAjWel9jnR3ZoTv0M-pvJMg7VLINRa2mnTNsvXfjbAFNU4M9sSVFBNmnefzinIWT5DIW6fVmmjzqPkWPG0EWAexculA_Dh1H0gVAzIYAUjdsj8uznmBvFk8_blNOM5-opyiSaKMyaJis4af48A0kgec2kZ8QcJLEQ0CKHzo1BxzQZ7aHlC6ggm5qLKPX8C4yz0OZ4SKpsmFZlbgUA%3D&tracking_referrer=www.nature.com (http://www.nature.com/articles/nature17145.epdf?referrer_access_token=px-zRubs4M6aBBPl42_1GdRgN0jAjWel9jnR3ZoTv0M-pvJMg7VLINRa2mnTNsvXfjbAFNU4M9sSVFBNmnefzinIWT5DIW6fVmmjzqPkWPG0EWAexculA_Dh1H0gVAzIYAUjdsj8uznmBvFk8_blNOM5-opyiSaKMyaJis4af48A0kgec2kZ8QcJLEQ0CKHzo1BxzQZ7aHlC6ggm5qLKPX8C4yz0OZ4SKpsmFZlbgUA%3D&tracking_referrer=www.nature.com)

Abstract: "Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6–9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics—including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs—that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years."


See also:
Jeff Tollefson (31 March 2016), "Antarctic model raises prospect of unstoppable ice collapse", Nature, Volume: 531, Pages: 562, doi:10.1038/531562a


http://www.nature.com/news/antarctic-model-raises-prospect-of-unstoppable-ice-collapse-1.19638 (http://www.nature.com/news/antarctic-model-raises-prospect-of-unstoppable-ice-collapse-1.19638)


Extract: "Sea levels could rise by more than 15 metres by 2500 if greenhouse-gas emissions continue to grow."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on March 30, 2016, 10:33:58 PM
Nice, thorough analysis by DeConto and Pollard, among other things, vindicating Mercer's insistence on the importance of the 0C midsummer isotherm. Unfortunately they did not cover the effect of the melt and berg effux freshening the upper waters of the southern ocean, which would have been a nice contact point to the latest Hansen.

But they sound as though they might do that soon.

"In particular, the model lacks two-way coupling between the ice sheet and the ocean. This is especially relevant for RCP8.5, in which >1 Sv of freshwater and icebergs would be supplied to the Southern Ocean during peak retreat (Extended Data Fig. 8 ). Rapid calving and ice-margin collapse also implies ice mélange in restricted embayments that could provide buttressing and a negative feedback on retreat. The loss of ice mass would also have a strong effect on relative sea level at the margin owing to gravitational and solid-earth deformation effects [48], which could affect MISI and MICI dynamics because of their strong dependency on bathymetry. Future simulations should include coupling with Earth models that account for these processes."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 30, 2016, 11:10:27 PM
Nice, thorough analysis by DeConto and Pollard, among other things, vindicating Mercer's insistence on the importance of the 0C midsummer isotherm. Unfortunately they did not cover the effect of the melt and berg effux freshening the upper waters of the southern ocean, which would have been a nice contact point to the latest Hansen.

But they sound as though they might do that soon.

"In particular, the model lacks two-way coupling between the ice sheet and the ocean. This is especially relevant for RCP8.5, in which >1 Sv of freshwater and icebergs would be supplied to the Southern Ocean during peak retreat (Extended Data Fig. 8 ). Rapid calving and ice-margin collapse also implies ice mélange in restricted embayments that could provide buttressing and a negative feedback on retreat. The loss of ice mass would also have a strong effect on relative sea level at the margin owing to gravitational and solid-earth deformation effects [48], which could affect MISI and MICI dynamics because of their strong dependency on bathymetry. Future simulations should include coupling with Earth models that account for these processes."

I do not know whether the doted line in the attached Figure 8 from the extended data gives a hint about the impact of including ice-climate feedback.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on March 31, 2016, 08:06:52 AM
DeConto has 1Sverdrup peak in 2100 from your attachment, 60mm/yr SLR for a hundred years from fig 4c. Hansen has 1 Sverdrup in 2040 (fig S14) in the north atlantic, and the caption sez " Freshwater injection onto the Southern Ocean is double the North Atlantic rate" with a 10 year double time. So he probably has 1Sverdrup from Antarctica right now,  and an ocean model exhibiting melt layer feedback, which deConto lacks.

So say doubling time in Hansen ought to be 40 yr to give a rough match in magnitude of 1Sv in 2100, then deConto and hansen are not so far apart for the 2050-2100 period. Or say, when deConto puts in the melt layer feedback, he will get the same doomsday projections as Hansen.

They are both working on the next iteration, we shall see.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 31, 2016, 04:03:22 PM
DeConto has 1Sverdrup peak in 2100 from your attachment, 60mm/yr SLR for a hundred years from fig 4c. Hansen has 1 Sverdrup in 2040 (fig S14) in the north atlantic, and the caption sez " Freshwater injection onto the Southern Ocean is double the North Atlantic rate" with a 10 year double time. So he probably has 1Sverdrup from Antarctica right now,  and an ocean model exhibiting melt layer feedback, which deConto lacks.

So say doubling time in Hansen ought to be 40 yr to give a rough match in magnitude of 1Sv in 2100, then deConto and hansen are not so far apart for the 2050-2100 period. Or say, when deConto puts in the melt layer feedback, he will get the same doomsday projections as Hansen.

They are both working on the next iteration, we shall see.

sidd,

Thanks for your comments & observations, and I concur that all of this good work is still just a work in progress and as you correctly point-out that DeConto & Pollard (2016) appear to be converging towards Hansen et al (2016), I will make more pointed comments in the Hansen et al thread.  Nevertheless, I point-out here that very few people make any effort to understand the numerous complexities of abrupt sea level rise, as they assume that leading scientists on the IPCC AR5 (like Richard Alley) had their backs to protect them from unexpected surprises.  Unfortunately, as the attached image from the AR5 Ch 13 (sea level) Supplement shows that the new preliminary findings of DeConto & Pollard (2016) much more than double the RCP 8.5 GMSL projections for 2100, without accounting for the risk that the GIS contributions will likely exceed the AR5 projections.

It is my opinion that AR5 WG1 authors (like Richard Alley) should be held accountable for their "happy talk" and should be replaced by people like Eric Rignot for AR6.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 01, 2016, 01:27:05 AM
I should read more carefully. Hansen has 720 GT/yr (2mm/yr SLR equivalent) meltwater injection from Antarctica in 2011,

"We take freshwater injection to be 720 Gt/year from Antarctica and 360 Gt/year in the North Atlantic in 2011, with injection rates at earlier and later times defined by assumption of a 10-year doubling time."

Not so unreasonable when one recalls this is total melt, not mass waste. 1Sv is about 3e4 GT/yr, which a doubling time of 10 yr attains shortly after 2060. Hansen quits injection in 2060.

"Cumulative North Atlantic freshwater forcing in sverdrup years (Sv years) is 0.2 Sv years in 2014, 2.4 Sv years in 2050, and 3.4 Sv years (its maximum) prior to 2060 (Fig. S14)."

Looking at the fearsome fig 4c and extended data fig 8 in DeConto gives 1Sv/yr for fifty years past 2100, accompanied by 50mm/yr SLR for a hundred. So even worse than Hansen, just delayed 50 yr later. So I feel that when they put the meltwater feedback in, their estimates will approach Hansen.

I keep coming back to Blanchon (2009) doi:10.1038/nature07933 supplementary fig 3. If you take the the integral of the SLR curve from 4c in DeConto and integrate it to find the cumulative sea level change, you will get a sharp rise in the beginning in the cumulative graph, which comes from the inital peak in fig 4c, and then a slowing  rate _exactly as in one of the fast jumps in Blanchon record_

I fear more and more that we are in the exponential blowout phase at Thwaites, that we have decades at best to retreat from the ocean. It is much easier to relocate when SLR is 3 mm/yr than when it is 10, 30 or 60.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on April 03, 2016, 08:33:02 AM
Ted Scambos interviewed by Peter Sinclair on DeConto & Pollard:
http://climatecrocks.com/2016/04/02/the-weekend-wonk-what-this-weeks-antarctic-study-means/ (http://climatecrocks.com/2016/04/02/the-weekend-wonk-what-this-weeks-antarctic-study-means/)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 04, 2016, 02:01:41 AM
The linked Phys Org website has a nice video of the man of the moment, David Pollard:

http://phys.org/news/2016-03-sea-level-earlier-years.html (http://phys.org/news/2016-03-sea-level-earlier-years.html)

Extract: ""So, at a time in the past when global average temperatures were only slightly warmer than today," says DeConto, "sea levels were much higher. Melting of the smaller Greenland Ice Sheet can only explain a fraction of this sea-level rise, most which must have been caused by retreat on Antarctica."

To investigate this, DeConto and Pollard developed a new ice sheet-climate model that includes "previously under-appreciated processes" that emphasize the importance of future atmospheric warming around Antarctica."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on April 04, 2016, 07:24:33 PM
Nice to hear/see Pollard talking, as he and DeConto aren't exactly all over youtube...
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on April 04, 2016, 07:27:49 PM
Here's one with DeConto, from Jan 13th this year:
https://www.youtube.com/watch?v=jK_8Pfo6wRk (https://www.youtube.com/watch?v=jK_8Pfo6wRk)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 04, 2016, 08:11:19 PM
Here's one with DeConto, from Jan 13th this year:
https://www.youtube.com/watch?v=jK_8Pfo6wRk (https://www.youtube.com/watch?v=jK_8Pfo6wRk)

Thanks, and I re-posted this link to the Sea Level Rise thread.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 06, 2016, 11:41:57 PM
The linked reference recommends erring on the side of precaution because the correlation of the observed record (per the WAIS Divide ice core) of temperature and snowfall for West Antarctica is more variable than indicated by current climate models (as normally it is assumed that as GMST increases so will the snowfall in West Antarctica, but the observed record indicates that that assumption may not be correct):

T. J. Fudge, Bradley R. Markle, Kurt Cuffey, Christo Buizert, Kendrick Taylor, Eric J. Steig, Edwin Waddington, Howard Conway & Michelle Koutnik (4 April 2016), "Variable relationship between accumulation and temperature in West Antarctica for the past 31,000 years", Geophysical Research Letters, DOI: 10.1002/2016GL068356


http://onlinelibrary.wiley.com/doi/10.1002/2016GL068356/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL068356/abstract)

Abstract: "The Antarctic contribution to sea level is a balance between ice loss along the margin and accumulation in the interior. Accumulation records for the past few decades are noisy, and show inconsistent relationships with temperature. We investigate the relationship between accumulation and temperature for the past 31 ka using high-resolution records from the WAIS Divide ice core in West Antarctica. Although the glacial-interglacial increases result in high correlation and moderate sensitivity for the full record, the relationship shows considerable variability through time with high correlation and high sensitivity for the 0-8 ka period but no correlation for the 8-15 ka period. This contrasts with a general circulation model simulation which shows homogeneous sensitivities between temperature and accumulation across the entire time period. These results suggest that variations in atmospheric circulation are an important driver of Antarctic accumulation but they are not adequately captured in model simulations. Model-based projections of future Antarctic accumulation, and its impact on sea level, should be treated with caution."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 14, 2016, 01:37:14 AM
With a hat-tip to Greenbelt's post in the "Sea Level Rise" thread, the linked article discusses how NOAA has new information indicating that sea level could rise by 3m in the 2050-2060 timeframe due to instabilities in the WAIS:

http://www.insurancejournal.com/news/national/2016/04/12/405089.htm (http://www.insurancejournal.com/news/national/2016/04/12/405089.htm)

Extract: "Think sea level rise will be moderate and something we can all plan for? Think again.
Sea levels could rise by much more than originally anticipated, and much faster, according to new data being collected by scientists studying the melting West Antarctic ice sheet – a massive sheet the size of Mexico.
That revelation was made by an official with the National Oceanic and Atmospheric Administration on Tuesday at the annual RIMS conference for risk management and insurance professionals in San Diego, Calif.
The conference is being attended by more than 10,000 people, according to organizers. It was day No. 3 of the conference, which ends Wednesday.
Margaret Davidson, NOAA’s senior advisor for coastal inundation and resilience science and services, and Michael Angelina, executive director of the Academy of Risk Management and Insurance, offered their take on climate change data in a conference session titled “Environmental Intelligence: Quantifying the Risks of Climate Change.”
Davidson said recent data that has been collected but has yet to be made official indicates sea levels could rise by roughly 3 meters or 9 feet by 2050-2060, far higher and quicker than current projections. Until now most projections have warned of sea level rise of up to 4 feet by 2100.
These new findings will likely be released in the latest sets of reports on climate change due out in the next few years.
“The latest field data out of West Antarctic is kind of an OMG thing,” she said.
Davidson’s purpose was to talk about how NOAA is sharing information with the insurance community and the public, and to explain how data on climate change is being collected.
She explained that reports like those from the Intergovernmental Panel on Climate Change and the National Climate Assessment, which come out roughly every five years, are going on old data.
By the time the scientists compiling those reports get the data it’s roughly two years old, because it took those gathering the data that long to collect it. It takes authors of the reports a few years to compile them.
“By the time we get out the report, it’s actually synthesizing data from about a decade ago,” she said.
Angelina’s focus was also on the data. He spoke about the ongoing development of the Actuaries Climate Index and the Actuaries Climate Risk Index.
The goals of the projects are to create climate change indices that reflect an actuarial perspective, to create an index that measures changes in climate extremes, use indices to inform the insurance industry and the public, and promote the actuarial profession by contributing statistically to the climate change debate.
So far their findings show the climate is definitely changing – though neither Davidson nor Angelina addressed the cause of this change, which they said was not the purpose of their talk.
Angelina said a new way of looking at weather is required when dealing with climate change, and that just looking at averages isn’t enough to give an accurate picture of climate change and the risk it presents.
The projects he’s involved with have instead looked at weather extremes.
“By looking at extremes I can actually acknowledge that I have a problem,” he said."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 09, 2016, 09:30:01 PM
Technische Universitaet Dresden provides the following very useful website that documents Antarctic Ice Sheet mass change per the GRACE satellite, as updated every month.  The first image shows the spatial distribution of ice mass loss (from 2002-2008 thru Jan 2016) across Antarctica.  The second image provides a key to the GRACE mass change basins, from which it can be seen that for the WAIS ice mass loss comes primarily from basins 20, 21, 22 and 23 (which will be detailed in my next post).

Technische Universitaet Dresden,
Gravimetric mass balance: Antarctic Ice Sheet project ESA Climate Change Initiative

https://data1.geo.tu-dresden.de/ais_gmb/ (https://data1.geo.tu-dresden.de/ais_gmb/)

See also:
https://www.sciencedaily.com/releases/2016/05/160509085744.htm (https://www.sciencedaily.com/releases/2016/05/160509085744.htm)

Extract: "The Antarctic ice sheet, with a thickness of up to 4800 meter, has lost mass in the recent years. This was confirmed by a variety of scientific studies. Scientists now visualize the ice-mass loss: The interested public and scientific community can follow the Antarctic ice-mass changes month by month and divided by regions."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 09, 2016, 09:31:49 PM
The four attached plots from Dresden detail the cumulative (from August 16 2002 to Jan 16 2016) ice mass loss from the AIS basins 20, 21, 22 and 23.  These are all basins to watch to see whether ice mass loss from these areas increase non-linearly as/when GMST departures exceed 2C above pre-industrial:
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 02, 2016, 06:00:11 PM
The linked reference provides new field observations about changes in ocean circulation patterns from the continental shelf break to the coast in the Bellingshausen Sea, and they emphasize the importance of better understanding such recent changes in ocean circulation patterns in order to better understand the stability of the WAIS:

Xiyue Zhang, Andrew F. Thompson, Mar M. Flexas, Fabien Roquet & Horst Bornemann (1 June 2016), "Circulation and meltwater distribution in the Bellingshausen Sea: from shelf break to coast", Geophysical Research Letters, DOI: 10.1002/2016GL068998


http://onlinelibrary.wiley.com/doi/10.1002/2016GL068998/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL068998/abstract)

Abstract: "West Antarctic ice shelves have thinned dramatically over recent decades. Oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry towards ice shelves are needed to constrain future changes in melt rates. Six years of seal-acquired observations provide extensive hydrographic coverage in the Bellingshausen Sea, where ship-based measurements are scarce. Warm but modified Circumpolar Deep Water floods the shelf and establishes a cyclonic circulation within the Belgica Trough with flow extending towards the coast along the eastern boundaries and returning to the shelf break along western boundaries. These boundary currents are the primary water mass pathways that carry heat towards the coast and advect ice shelf meltwater offshore. The modified Circumpolar Deep Water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break, suggesting the presence of the Antarctic Slope Current. Constraining meltwater pathways is a key step in monitoring the stability of the West Antarctic Ice Sheet."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 03, 2016, 05:20:31 PM
The linked (open access) reference cites research on four decades of marine glacier grounding line retreat in the Bellingshausen margin (see attached image).  This region contributes significantly to the instability of the WAIS:

Frazer D.W. Christie, Robert G. Bingham, Noel Gourmelen, Simon F.B. Tett & Atsuhiro Muto (22 May 2016), "Four-decade record of pervasive grounding line retreat along the Bellingshausen margin of West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL068972


http://onlinelibrary.wiley.com/doi/10.1002/2016GL068972/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL068972/abstract)

Abstract: "Changes to the grounding line, where grounded ice starts to float, can be used as a remotely-sensed measure of ice-sheet susceptibility to ocean-forced dynamic thinning. Constraining this susceptibility is vital for predicting Antarctica's contribution to rising sea levels. We use Landsat imagery to monitor grounding line movement over four decades along the Bellingshausen margin of West Antarctica, an area little monitored despite potential for future ice losses. We show that ~65% of the grounding line retreated from 1990-2015, with pervasive and accelerating retreat in regions of fast ice flow and/or thinning ice shelves. Venable Ice Shelf confounds expectations in that despite extensive thinning, its grounding line has undergone negligible retreat. We present evidence that the ice shelf is currently pinned to a sub-ice topographic high which, if breached, could facilitate ice retreat into a significant inland basin, analogous to nearby Pine Island Glacier."

See also:
http://www.climatecentral.org/news/overlooked-area-antarctica-major-ice-loss-20408 (http://www.climatecentral.org/news/overlooked-area-antarctica-major-ice-loss-20408)
Extract: "During a 2009-2010 field mission, Bingham looked to shed more light on the region by scanning the ground below one of the fastest-moving Bellingshausen glaciers, the Ferrigno Ice Stream. He found a huge canyon underneath that is likely funneling warm ocean water under the ice.
“This only served to highlight to me that there is so much about the Bellingshausen Sea sector of West Antarctica that has gone unmonitored while most of the world's eyes (glaciologically speaking) were looking beyond to Pine Island Glacier,” Bingham said.
To get a better picture of the overall ice loss in the area, Bingham and his Ph.D. student Frazer Christie, analyzed hundreds of satellite images of the area going back to 1975 and tracked the position of the grounding line along 1,240 miles of coast.
They found that 65 percent of the coastline had seen grounding line retreat since 1990, while only 7 percent had seen an advance. The total amount of ice lost over the last 40 years is about 390 square miles, an area about the size of Dallas.
The results “show that this whole coastline has been in a state of retreat since records began in the early 1970s,” Bingham said. That contrasts with previous thinking that only certain glaciers, like the Ferrigno Ice Stream, were seeing significant ice loss while the rest were fairly stable.
“The study illustrates that Antarctica is not immune to changes and that some of what we are seeing today started decades ago,” Eric Rignot, a NASA glaciologist who was not involved with the work, said in an email.
One notable oddity was the Venable Ice Shelf, which has thinned, but hasn’t retreated much. The researchers think it is pinned to a ridge on the seafloor that is keeping it stable for now. Scientists think the same was true of Pine Island Glacier — for a while.
Exactly what the pervasive ice loss in the Bellingshausen Sea area means for future global sea level rise isn’t entirely clear, in part because of the paucity of data from the area. Bingham says that researchers need a better idea of the topography underlying the ice so they can better model how it will change in the future."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 29, 2016, 12:30:39 AM
The linked document describes a plan for the next decade of research in the WAIS to try to better quantify the rate and volume of change of ice mass loss now & in the future.  While the document has many stellar authors, to me it is conspicuous that Eric Rignot is missing:

Ted Scambos and Robin Bell, Richard Alley, Sridhar Anandakrishnan, David Bromwich, Kelly Brunt, Knut Christianson, Timothy Creyts, Sarah Das, Robert DeConto, Pierre Dutrieux, Helen Amanda Fricker, David Holland, Joseph MacGregor, Brooke Medley, David Pollard, Matthew Siegfried, Andrew Smith, Eric Steig, David Vaughan, Patricia Yaeger (April 2016), "How Much, How Fast? A Decadal Science Plan Quantifying the Rate of Change of the West Antarctic Ice Sheet Now and in the Future"

http://nsidc.org/sites/nsidc.org/files/files/WAIS_SciPlanHMHF_final.pdf (http://nsidc.org/sites/nsidc.org/files/files/WAIS_SciPlanHMHF_final.pdf)

Extract: "This document is the outcome of a community science meeting held September 16-19, 2015 in Loveland Colorado, and a dedicated workshop on January 13-15, 2016 at the University of Colorado in Boulder.


The primary geographic focus of the How Much, How Fast? effort will be the Thwaites Glacier and the adjacent areas of the Amundsen Sea."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 29, 2016, 06:47:32 PM
I was unable to find a link to the following reference (in press), but as the title sounds interesting, I provide the following partial information:

Little, Christopher M., and Urban Nathan M. , (2016) "CMIP5 Temperature biases and 21st Century Warming around the Antarctic Coast"
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on September 02, 2016, 10:18:12 AM
Interview with Rob DeConto by Nature-editor Michael White:
http://forecastpod.org/index.php/2016/08/25/rob-deconto-and-antarctica-in-the-climate-system/ (http://forecastpod.org/index.php/2016/08/25/rob-deconto-and-antarctica-in-the-climate-system/)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on September 02, 2016, 01:25:01 PM
DeConto on Russia Today, at beginning of April:
https://www.youtube.com/watch?v=i9DRolVl1DA (https://www.youtube.com/watch?v=i9DRolVl1DA)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 09, 2017, 01:49:41 AM
The linked article is entitled: "Collapse of West Antarctic Ice Sheet Reveals Inadequacy of Current Climate Strategies", and provides a nice summary of key issues about a possible WAIS collapse this century.

http://www.truth-out.org/news/item/38794-collapse-of-west-antarctic-ice-sheet-reveals-inadequacy-of-current-climate-strategies (http://www.truth-out.org/news/item/38794-collapse-of-west-antarctic-ice-sheet-reveals-inadequacy-of-current-climate-strategies)

Title: Re: Potential Collapse Scenario for the WAIS
Post by: kiwichick16 on January 09, 2017, 11:17:53 AM
thanks for that  aslr.........30 mm sea level rise per year would certainly get my attention

but have I missed it, or has the increase in sea level rise from 3mm / year to 5 mm/year not been verified yet????
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 09, 2017, 05:15:26 PM
thanks for that  aslr.........30 mm sea level rise per year would certainly get my attention

but have I missed it, or has the increase in sea level rise from 3mm / year to 5 mm/year not been verified yet????

It has been verified, but may partially be due to the recent major El Nino event.

Edit: See the attached Jason-2 record thru Sept 17 2016
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 09, 2017, 05:16:34 PM
The linked article is entitled: "Antarctica Past Points to Sea Level Threat", & the reference research clearly increases the recognized probability that the WAIS might collapse this century (with continued warming).

http://climatenewsnetwork.net/antarctic-past-sea-level-threat/?utm_source=Climate+News+Network&utm_campaign=d3139ab809-EMAIL_CAMPAIGN_2017_01_09&utm_medium=email&utm_term=0_1198ea8936-d3139ab809-38798465 (http://climatenewsnetwork.net/antarctic-past-sea-level-threat/?utm_source=Climate+News+Network&utm_campaign=d3139ab809-EMAIL_CAMPAIGN_2017_01_09&utm_medium=email&utm_term=0_1198ea8936-d3139ab809-38798465)

Extract: "Evidence of Antarctic ice sheet melting and sea level rise almost 15,000 years ago raises alarm over current climate change dangers."

See the associated linked (open access) reference at:
Fogwill et. al. (2017) , "Antarctic Ice Sheet Discharge Driven by Atmospheric-Ocean Feedbacks at the Last Glacial Termination", Scientific Reports, 7, Article No. 39979, doi: 10.1038/srep39979.

http://www.nature.com/articles/srep39979 (http://www.nature.com/articles/srep39979)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Lennart van der Linde on March 26, 2017, 10:30:05 PM
Documentary on Andrill with Rob DeConto and David Pollard on potential future sea level rise (from 45m34s onwards):
https://www.youtube.com/watch?v=i-_EECtAoRQ (https://www.youtube.com/watch?v=i-_EECtAoRQ)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Hyperion on April 12, 2017, 11:34:50 AM
Documentary on Andrill with Rob DeConto and David Pollard on potential future sea level rise (from 45m34s onwards):
https://www.youtube.com/watch?v=i-_EECtAoRQ (https://www.youtube.com/watch?v=i-_EECtAoRQ)

Interesting. You can see how this process drives tectonics. The ice mass loss at the periphery causes depressurisation of the puddle of fluid water and carbonate rich magma that the continental fringes float on due to seafloor sediment subductions. This causes trench blockwise subsidence for example as per the 700km / 800km long stretches some 50 km wide that dropped ~30 metres in the Valdivia May 22, 1960 9.5 and Offshore Maule/Biobío February 27, 2010 8.8 events off Chile.
Simultaneously the increase in central Ice mass balance presurisses the ~500+ km deep superheated fluid basalt conduits that connect the continental keels to the midocean spreading zones. When you look at the repeat blockwise pattern of repeated ~50km wide food basalt sheets that spread out from the mid ocean trenches, and take note that the chemical composition of basalt formed is the same for thousands of km along the rifting zone, its clear that this is how it works. The seafloor is extruded in flood basalt pulses caused by the hydraulic pump of the ice sheet pistons, and blocks are simultaneously stacked under the continental fringes. Which is why the layers get younger as you go down. The heat, and tectonic mayhem released by these periodic isostatic overdrive episodes of course can cause large effect on sea levels and ice sheet stability ::)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 05, 2017, 09:35:18 AM
The linked reference has recent data on ice mass loss from Antarctica & it indicates significant losses from the WAIS:

Gardner, A. S., Moholdt, G., Scambos, T., Fahnstock, M., Ligtenberg, S., van den Broeke, M., and Nilsson, J.: Increased West Antarctic ice discharge and East Antarctic stability over the last seven years, The Cryosphere Discuss., doi:10.5194/tc-2017-75, in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2017-75/ (http://www.the-cryosphere-discuss.net/tc-2017-75/)

Abstract. Ice discharge from large ice sheets plays a direct role in determining rates of sea level rise. We map present-day Antarctic-wide surface velocities using Landsat 7 & 8 imagery spanning 2013–2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ~ 2008. The new mapping provides complete coastal and inland coverage of ice velocity with a mean error of < 10 m yr-1, resulting from multiple overlapping image pairs acquired during the daylit period. Using an optimized flux gate, ice discharge from Antarctica is 1932 ± 38 Gigatons per year (Gt yr-1) in 2015, an increase of 35 ± 15 Gt yr-1 from the time of the radar mapping. Flow accelerations across the grounding lines of West Antarctica's Amundsen Sea Embayment, Getz Ice Shelf and Marguerite Bay on the western Antarctic Peninsula, account for 89 % of this increase. In contrast, glaciers draining the East Antarctic Ice Sheet have been remarkably stable over the period of observation. Including modeled rates of snow accumulation and basal melt, the Antarctic ice sheet lost ice at an average rate of 186 ± 93 Gt yr-1 between 2008 and 2015. The modest increase in ice discharge over the past 7 years is contrasted by high rates of ice sheet mass loss and distinct spatial patters of elevation lowering. This suggests that the recent pattern of mass loss in Antarctica, dominated by the Amundsen Sea sector, is likely part of a longer-term phase of enhanced glacier flow initiated in the decades leading up to the first continent wide radar mapping of ice flow.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 20, 2017, 05:38:38 AM
The linked article is entitled: “Decoding Antarctica's response to a warming world”.  Hold your breath.

http://www.bbc.com/news/science-environment-39975709 (http://www.bbc.com/news/science-environment-39975709)

Extract: “In the iceberg-infested waters of the Amundsen Sea Embayment (ASE), it obtained the very first cores to be drilled from just in front of some of the mightiest glaciers on Earth. 

Chief among these are Pine Island Glacier and Thwaites Glacier, colossal streams of ice that drain the White Continent and which are now spilling mass into the ocean at an alarming rate. 

There's concern that deep, warm water is undercutting the glaciers, possibly tipping them into an unstoppable retreat. And that has global implications for significant sea-level rise. 
...
The goal was to retrieve seafloor sediments that would reveal the behaviour of the West Antarctic Ice Sheet (WAIS) in previous warm phases. To read the future in the past. 

"If you find ice-rafted debris (stones dropped by icebergs), for example, you can be sure there was ice on land and that the ice had advanced to the coast," explained Claus-Dieter Hillenbrand from the British Antarctic Survey (BAS). 

"But also new developments - especially what's known as geochemical provenance - have emerged in the last 10 years that mean it's even possible now to compare this material with rocks on land to pin down the actual sources in the hinterland." 
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 02, 2017, 12:47:49 AM
The linked article indicates that the collapse of the WAIS is almost inevitable:
"Guest post: Is the collapse of the West Antarctic Ice Sheet inevitable?"

https://www.carbonbrief.org/guest-post-collapse-west-antarctic-ice-sheet-inevitable (https://www.carbonbrief.org/guest-post-collapse-west-antarctic-ice-sheet-inevitable)

Extract: "So, is the eventual collapse of the West Antarctic Ice Sheet already inevitable? Model projections under low emissions scenarios suggest that ice sheet retreat could stabilise, but under medium and high scenarios, collapse is unstoppable.

The motto for early 21st Century cryospheric science should be “that happened faster than I thought it would.” Wherever we look, either in the past or in the present, we are challenged to keep up – in the ways we measure, theorise, project, and prepare for the future."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 15, 2017, 07:07:16 PM
Get ready for a lot of future hydrofracture events in the WAIS:

"Scientists stunned by Antarctic rainfall and a melt area bigger than Texas"

https://www.washingtonpost.com/news/energy-environment/wp/2017/06/15/scientists-just-documented-a-massive-melt-event-on-the-surface-of-antarctica/?utm_term=.526054dc4fdf (https://www.washingtonpost.com/news/energy-environment/wp/2017/06/15/scientists-just-documented-a-massive-melt-event-on-the-surface-of-antarctica/?utm_term=.526054dc4fdf)

Extract: "Scientists have documented a recent, massive melt event on the surface of highly vulnerable West Antarctica that, they fear, could be a harbinger of future events as the planet continues to warm.

In the Antarctic summer of 2016, the surface of the Ross Ice Shelf, the largest floating ice platform on Earth, developed a sheet of meltwater that lasted for as long as 15 days in some places. The total area affected by melt was 300,000 square miles, or larger than the state of Texas, the scientists report."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on June 15, 2017, 11:56:09 PM
rs is on this now, too:

https://robertscribbler.com/2017/06/15/the-rains-of-antarctica-are-coming-warm-summer-storms-melted-texas-sized-section-of-ross-ice-shelf-surface-during-2016/

The Rains of Antarctica are Coming — Warm Summer Storms Melted Texas-Sized Section of Ross Ice Shelf Surface During 2016
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 16, 2017, 04:38:15 PM
rs is on this now, too:

https://robertscribbler.com/2017/06/15/the-rains-of-antarctica-are-coming-warm-summer-storms-melted-texas-sized-section-of-ross-ice-shelf-surface-during-2016/

The Rains of Antarctica are Coming — Warm Summer Storms Melted Texas-Sized Section of Ross Ice Shelf Surface During 2016

What concerns me is that in a few decades time, austral summertime atmospheric river events may likely fall as rainfall instead of as snowfall.  Such an atmospheric river event could devastate a local Antarctic ice shelf within a single week.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 13, 2017, 07:36:18 PM
The linked article cites a study that finds that the West Antarctic Rift System is the largest volcanic region on Earth, and that some of these volcanic may very well become more active should the WAIS thin sufficiently, which would be a positive feedback mechanism for a more complete collapse of the WAIS:

Title: "Scientists find what they think is largest volcanic region on Earth hidden in Antarctica after student's idea"

http://www.independent.co.uk/environment/antarctica-west-antarctic-rift-system-volcanoes-university-of-edinburgh-max-van-wyk-de-vries-a7891206.html (http://www.independent.co.uk/environment/antarctica-west-antarctic-rift-system-volcanoes-university-of-edinburgh-max-van-wyk-de-vries-a7891206.html)

Extract: "A remote survey discovered 91 volcanoes ranging in height from 100m to 3,850m in a massive region known as the West Antarctic Rift System.

Geologists and ice experts say the range has similarities to east Africa's volcanic ridge, currently acknowledged to be the densest concentration of volcanoes in the world.

Researchers from the University of Edinburgh remotely surveyed the underside of the ice sheet for hidden peaks of basalt rock, like those of other volcanoes in the region whose tips push above the ice.

Previous studies have suggested that volcanic activity may have occurred in the region during warmer periods and could increase if Antarctica's ice thins in a warming climate.

Dr Robert Bingham, of the University of Edinburgh's School of GeoSciences, said: "It is fascinating to uncover an extensive range of volcanoes in this relatively unexplored continent.

"Better understanding of volcanic activity could shed light on their impact on Antarctica's ice in the past, present and future, and on other rift systems around the world.""
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on August 14, 2017, 07:14:44 AM
That Nicolas paper(DOI: 10.1038/ncomms15799 )  has a figure in it that tells me Mercer's indicator to watch midsummer 0C isotherm is flashing, it's  in the deep interior of  Ross shelf in 2016.
I attach fig 1c

for the locations of the weather stations, see the (open access) article.

sidd


Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 14, 2017, 11:02:04 AM
That Nicolas paper(DOI: 10.1038/ncomms15799 )

For those who would like a link to the Nicolas et. al. (2017) paper, I provide the following:

Julien P. Nicolas et. al. (2017), "January 2016 extensive summer melt in West Antarctica favoured by strong El Nino", Nature Communications, DOI: 10.1038/ncomms15799

http://www.ccpo.odu.edu/~klinck/Reprints/PDF/nicolasNatComm17.pdf (http://www.ccpo.odu.edu/~klinck/Reprints/PDF/nicolasNatComm17.pdf)

Abstract: "Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Nino event. The increase in the number of extreme El Nino events projected for the twenty-first century could expose the WAIS to more frequent major melt events."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: solartim27 on October 11, 2017, 05:54:46 PM
Nice article and short video on warm water melting a channel under the Dotson glacier.  The average melt is 6 - 7 m/yr, while video says the localized channel melt is 14 m/yr.
http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/Secrets_of_hidden_ice_canyons_revealed (http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/Secrets_of_hidden_ice_canyons_revealed)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 08, 2017, 05:37:59 PM
The authors of the linked reference present evidence of a mantle plume beneath Marie Byrd Land; which could facility ice mass loss from the WAIS if global warming continues:

Helene Seroussi et al. Influence of a West Antarctic mantle plume on ice sheet basal conditions, Journal of Geophysical Research: Solid Earth (2017). DOI: 10.1002/2017JB014423

http://onlinelibrary.wiley.com/doi/10.1002/2017JB014423/abstract;jsessionid=31E26D20F642A5CB414568D1288E7116.f02t04

Abstract: "The possibility that a deep mantle plume manifests Pliocene and Quaternary volcanism and potential elevated heat flux in West Antarctica has been studied for more than 30 years. Recent seismic images support the plume hypothesis as the cause of Marie Byrd Land (MBL) volcanism and geophysical structure. Mantle plumes may more than double the geothermal heat flux above nominal continental values. A dearth of in situ ice sheet basal data exists that samples the heat flux. Consequently, we examine a realistic distribution of heat flux associated with a possible late Cenozoic mantle plume in West Antarctica and explore its impact on thermal and melt conditions at the ice sheet base. We use a simple analytical mantle plume parameterization to produce geothermal heat flux at the base of the ice sheet. The three-dimensional ice flow model includes an enthalpy framework and full-Stokes stress balance. As both the putative plume location and extent are uncertain, we perform broadly scoped experiments to characterize the impact of the plume on geothermal heat flux and ice sheet basal conditions. The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot. In order to be consistent with observations of basal hydrology in MBL, the upper bound on the plume-derived geothermal heat flux is 150 mW/m2. In contrast, the active lake system of the lower part of Whillans Ice Stream suggests a widespread anomalous mantle heat flux, linked to a rift source."

See also the linked associated article entitle: "Study bolsters theory of heat source under Antarctica"

https://phys.org/news/2017-11-bolsters-theory-source-antarctica.html

Extract: "A new NASA study adds evidence that a geothermal heat source called a mantle plume lies deep below Antarctica's Marie Byrd Land, explaining some of the melting that creates lakes and rivers under the ice sheet. Although the heat source isn't a new or increasing threat to the West Antarctic ice sheet, it may help explain why the ice sheet collapsed rapidly in an earlier era of rapid climate change, and why it is so unstable today.

The Marie Byrd Land mantle plume formed 50 to 110 million years ago, long before the West Antarctic ice sheet came into existence. At the end of the last ice age around 11,000 years ago, the ice sheet went through a period of rapid, sustained ice loss when changes in global weather patterns and rising sea levels pushed warm water closer to the ice sheet—just as is happening today. Seroussi and Ivins suggest the mantle plume could facilitate this kind of rapid loss."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on November 30, 2017, 11:15:57 PM
Based on my interpretation of the two linked references, I suspect that local ice cliff failures near the base of the Thwaites Ice Tongue (see the four images) will begin sometime 2025 and 2033, and will be initiated due to influences from Super El Nino events in that timeframe:

Yu, H., Rignot, E., Morlighem, M., & Seroussi, H. (2017). Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics. The Cryosphere, 11(3), 1283, doi:10.5194/tc-11-1283-2017

https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017.pdf
https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017-assets.html

Abstract. "Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades.  Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing.  We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA’s Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations.  We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and iceberg calving."

Extract: "In our simulations, we find that crevasses propagate significantly faster near the ice front when the ice shelf is shortened.

The reason for the propagation of crevasses is the existence of a nonhydrostatic condition of ice immediately downstream of the grounding line, which is not accounted for in simplified models that assume hydrostatic equilibrium everywhere on the ice shelf.  We also find that calving is enhanced in the presence of pre-existing surface crevasses or shorter ice shelves or when the ice front is undercut.  We conclude that it is important to consider the full stress regime of ice in the grounding line region to replicate the conditions conducive to calving events, especially the nonhydrostatic condition that is critical to propagate the crevasses."

&

The second linked reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of extreme El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on December 01, 2017, 12:44:06 AM
If one accepts that a rough glacial bed on a marine-terminating glacier reflects a lack of sliding erosion, the roughness also marks a region where during previous retreats ice cliff collapse was the dominant mechanism - not sliding nor creep.

I'm no specialist in this area, but the descriptions I've read of the models don't seem to take such bed changes into account as the local singularities they likely are.

Apropos the third diagram above, further retreat by the Thwaites Glacier can be expected to be through ICI starting almost immediately.

So why, ASLR, do you expect a delay to 2025+ and the action of "Super El Nino events"? Are you expecting a collapse of the Thwaites eastern ice shelf first?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 01, 2017, 03:18:19 AM
steve s,

I was thinking the same thoughts about the bottom roughness being an indicator of past cliff failures in this area; however, the residual ice shelf in this area needs to retreat to where the red line meets the bed before the ice geometry is adequate to support cliff failures and also the mélange needs to clear out of the way.  I picked 2025 as the earliest date for the next super el nino as at a ECS of 4.5C I estimate that we will reach a GMSTA of 1.5C circa 2024, and per the second reference in my last link that will drive the period for super el ninos from 20-years to 10-years (for from 2015/16 to 2025/26).  The extra warm water from such a Super El Nino is needed to melt back the grounding line to meet the red line.  Also, I do not think that the Thwaites Eastern Ice Shelf will become unpinned until around 2035 as the ice velocities are slower over there.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 01, 2017, 08:26:08 PM
steve s,

As a follow-on to my last post, I note that per the two attached versions of the same plot from Pollard, DeConto & Alley (2015), the impact of cliff failures without hydrofracturing is limited (beyond normal glacial sliding/flowing behavior).  Thus as I do not believe that we will be approaching the GMSTA value of about 2.7C before about 2040 (assuming ECS =4.5C), I do not expect significant ice cliff failures along line A-B before about 2040.

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: steve s on December 01, 2017, 10:30:54 PM
ASLR,

The graph you show uses sea level rise on the y axis. Sea level rise seems irrelevant for this part of the discussion..

Your earlier image of the Thwaites profile indicates that by roughly the time the calving face retreats 20 km from the grounding line the cliff faces are high enough to spontaneously fail by their own weight -- no free water needed. So I do not see the need for hydrofracturing for a high speed of collapse, just a means of moving ice cubes out to sea. 

Keep up the good work,
Steve
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 02, 2017, 12:12:24 AM
ASLR,

The graph you show uses sea level rise on the y axis. Sea level rise seems irrelevant for this part of the discussion..

Your earlier image of the Thwaites profile indicates that by roughly the time the calving face retreats 20 km from the grounding line the cliff faces are high enough to spontaneously fail by their own weight -- no free water needed. So I do not see the need for hydrofracturing for a high speed of collapse, just a means of moving ice cubes out to sea. 

Keep up the good work,
Steve

The vertical axis of WAIS contribution to sea level rise, slr, is just a convenient unit for measuring net ice mass loss (ice discharge less snowfall).  Nevertheless, it is an aggregate of all ice mass contributions to slr for the WAIS and does not necessarily apply to the case we are considering along line A-B; so the point that you make is valid.  Still the hydrofracturing would clearly help to get the grounding line to retreat the almost 20km necessary for the cliff failures to occur; which was my main issue with citing the 2040 date.

Edit: Also, the graph/plot was for a recent interglacial (I think the Eemian, but I do not remember specifically), with less radiative forcing than where we are headed.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: wili on December 02, 2017, 01:42:50 AM
Apologies if this has been posted:

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076129/abstract

Acceleration in the global mean sea level rise: 2005-2015
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 04, 2017, 12:15:37 AM
The first image shows the trough that transects a portion of the Thwaites ice plug, which has a downstream 'mouth' centered on about W107.1 by S75.5; that is ignored by Yu et al. (2017) 2D analysis along line A-B (See Reply #478).  Also, note that the first image shows that the ice flow feeding both the Thwaites Eastern Ice Shelf and the Thwaites Ice Tongue are inclined from the axis of these two features and that a compression field in the ice near mouth of this trough, redirects this ice flow to align with those ice features.  Also, the second image shows that the subglacial drainage system beneath Thwaites exists through this trough.

Now the linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014 that drained four subglacial lakes (see the third and fourth images), and increased the velocity of the ice flow for Thwaites by about 10% during this drainage event, and in this velocity increase was probably higher along the alignment of the trough due to the basal water flowing through the trough.  Now higher ice velocities mean lower ice surface elevation (due to the conservation of ice discharge), which likely is pre-cracking the ice in this area; which, in my opinion makes it more likely to develop future ice cliffs, particularly as Yu et al. (2017) indicates that these subglacial lake drainage events can happen as frequently as every 20-years, which might means that the next such event might occur around 2033 to 2034, which might coincide with a Super El Nino event (see Reply #480)

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf

Abstract. We present conventional and swath altimetry data from CryoSat-2, revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica (TWG). Much of the drainage happened in less than 6 months, with an apparent connection between three lakes spanning more than 130 km. Hydro-potential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed largescale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events. This shows that there are important limitations in the ability of hydro-potential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."

See also the article entitled: "Hidden lakes drain below West Antarctica’s Thwaites Glacier".

http://www.washington.edu/news/2017/02/08/hidden-lakes-drained-under-west-antarcticas-thwaites-glacier/

Extract: "Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.

Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, Smith said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain."

For reference:

Yu, H., Rignot, E., Morlighem, M., & Seroussi, H. (2017). Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics. The Cryosphere, 11(3), 1283, doi:10.5194/tc-11-1283-2017
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 04, 2017, 12:38:58 AM
Also related to my last post, I provide the following related images:

The first image shows the bed topology near the rough in more detail.

The second image show the consequences of an abrupt ice surface drop event that happened near the 'mouth' of the trough sometime between Jan 2012 and Jan 2013.

The third image shows the nature of the cracking/crevasse pattern in ice near the 'mouth' of the trough in January 2013 (after the event shown in the second image), together with the locations of the grounding line (green) and the calving front (orange).

The fourth image shows a Sentinel-1 image from Nov 27 2017, that should that cracks/crevasses are now occurring over the trough upstream of the 'mouth'.

These images indicate a trend that supports the idea that more cracking/crevasses will form in this region at the base of the Thwaites Ice Tongue; which may facilitate the formation of ice cliff failure mechanisms in this area beginning sometime from 2033 to 2040, when I suspect that hydrofracturing may be frequent in this area.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 04, 2017, 12:56:21 AM
As a follow-on to my last two posts, I provide the following background/related images:

The first image from Stearns et al. (2008) shows a similar subglacial lake drainage event for the Byrd Glacier from Dec 2005 to Feb 2007, that also temporarily accelerated ice flow velocities (due to basal lubrication).

The second image how the relocation of the Amundsen Sea Low, ASL, during El Nino events can cause winds to direct more than typical amounts of warm CDW into the ASE.

The third image from Bakker et al. (2017) shows how a glacial cross-section very similar to the one along line A-B that Yu et al (2017) analyzed at the base of the Thwaites Ice Tongue, is believed to have behaved during the Eemian (MIS 5 peak) event; which shows the importance of the role of the warm CDW in triggering subsequent cliff failures.

The fourth image of cliff failures for the Jakobshavn Glacier (in Greenland) typically roll after calving so as to reduce the drafts of the calved icebergs, thus reducing the likelihood that the mélange will provide significant buttressing to any subsequent cliff failures.

Taken together, these images support the idea that cliff failures could progressively radiate out from the base of the Thwaites Ice Tongue after 2035 to 2040, particularly if the Thwaites Eastern Ice Shelf becomes unpinned circa 2035 as I suspect that it might.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 04, 2017, 01:16:33 AM
As a follow-on to my last few posts, I provide the following related images:

The first image shows that during the combination of an El Nino event and negative SAM conditions, Rossby Waves form in the atmosphere that telecommunicate heat directly from the Tropical Pacific directly to the WAIS, where it promotes surface ice melt events (which promotes hydrofracture events).

The second image shows my marks in green (in 2013, in this thread) showing my guesses of zones of grounding line retreats in the WAIS circa 2040 where the green zone near the base of the Thwaites Ice Tongue have ice cliff faces, while all the other green zones indicate estimated grounding line retreats beneath ice shelves.

The third image shows Hansen et al. (2016) estimates of changes in both GMSTA and Earth Energy Imbalance, EEI, due to assumed major freshwater hosing events (such as the potential collapse of the WAIS), and where the orange curves roughly correspond to the timing indicated in the second image.

The fourth image shows DeConto et al (2016) projected sequence of ice mass loss from the WAIS using conservative assumptions; which might happen roughly 100-years earlier if the scenario shown in second image actually occurs.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 04, 2017, 10:02:23 PM
The linked reference discusses how gas hydrates in the bed sediment beneath marine glaciers can cause 'sticky spots' that can regulate ice stream flow rates.  Also, during a potential abrupt collapse of the WAIS such methane hydrates in the seafloor could result in significant methane emissions into the atmosphere (acting as a positive feedback mechanism):

Winsborrow, M., K. Andreassen, A. Hubbard, A. Plaza-Faverola, E. Gudlaugsson and H. Patton (2016). "Regulation of ice stream flow through subglacial formation of gas hydrates." Nature Geosci 9(5): 370-374, DOI: 10.1038/NGEO2696

https://www.nature.com/articles/ngeo2696
&
http://www.nature.com/articles/ngeo2696.epdf?referrer_access_token=IHHHsNRUI3lD2eFpTMWvl9RgN0jAjWel9jnR3ZoTv0N6H6twa9eus1zouX_OVF0HHps81v4XTc0_11DCSpeGLDxz98tw1yul2mr16lbVJL4uOjHYggNVEvnorXQDpPb-4F8Dx03N10vp8xTpF1OSQUCQuGQbrx_agiKHwJMiE0Vb3p9RlZE1kgUDa_7CPZDbIHfa0-zC2RtwAc1-HEOzfwPw5ovCnEJWlCwr6K4nmQjxYGctlb4MLBBjUrGaOUBg&tracking_referrer=austhrutime.com

 Abstract: "Variations in the flow of ice streams and outlet glaciers are a primary control on ice sheet stability, yet comprehensive understanding of the key processes operating at the ice–bed interface remains elusive. Basal resistance is critical, especially sticky spots—localized zones of high basal traction—for maintaining force balance in an otherwise well-lubricated/high-slip subglacial environment. Here we consider the influence of subglacial gas-hydrate formation on ice stream dynamics, and its potential to initiate and maintain sticky spots. Geophysical data document the geologic footprint of a major palaeo-ice-stream that drained the Barents Sea–Fennoscandian ice sheet approximately 20,000 years ago. Our results reveal a ∼250 km sticky spot that coincided with subsurface shallow gas accumulations, seafloor fluid expulsion and a fault complex associated with deep hydrocarbon reservoirs. We propose that gas migrating from these reservoirs formed hydrates under high-pressure, low-temperature subglacial conditions. The gas hydrate desiccated, stiffened and thereby strengthened the subglacial sediments, promoting high traction—a sticky spot— that regulated ice stream flow. Deep hydrocarbon reservoirs are common beneath past and contemporary glaciated areas, implying that gas-hydrate regulation of subglacial dynamics could be a widespread phenomenon."

Also see:

Title: "Regulation of Ice Stream Flow Through Subglacial Formation of Gas Hydrates"

http://austhrutime.com/ice_stram_flow_regulation_subglacial_gas_hydrates.htm

Extract: "Based on the presence of extensive sedimentary basins and modelling studies (Wadham et al., 2012; Wallmann et al., 2012) it is proposed that abundant gas hydrate accumulations are present beneath the ice sheets of Greenland and Antarctica. Also, gas hydrates have been identified in ice core samples obtained from above the subglacial Lake Vostok in East Antarctica (Uchida et al., 1994). The role of potentially widespread gas hydrate reservoirs in the modification of the thermomechanical regime at the base of contemporary ice sheets, which makes them critically sensitive, as well as their impact on ice steam force balance and dynamics has, so far, not been recognised. This control that was previously unforeseen, given the current lack of knowledge with regard to the distribution of gas hydrate, represents a significant unknown in attempts to model the current and future discharge and evolution of contemporary ice sheets, as well as their contribution to rising global sea levels."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 12, 2017, 06:46:02 PM
The linked reference shows that ice mass loss from the WAIS is a nonlinear function of ocean forcing period.  While many consensus scientists consider ocean forcing a slow response mechanism, reasons to suspect that such nonlinear behavior could be trigger in the next few decades include:
1. The Southern Ocean has been warming since 1750, which is a long period of ocean forcing.
2. The Antarctic Ozone Hole has been advecting warm CDW to the grounding line of key WAIS marine glaciers since the 1970's (which is a somewhat long period).
3. Due to both the Antarctic Ozone Hole and Greenland Ice Sheet, GIS, ice mass loss, Agulhas Leakage has been documented to be occurring for years; which is increasing Arctic Amplification.
4. The Beaufort Gyre has been increasingly accumulating freshwater for longer periods since the mid-20th century and has not generated a pulsed release of freshwater since 2004 (apparently due to ice mass loss from the GIS and associated changes in ocean currents).  Furthermore, a sharp increase in ice mass loss from Jakobshaven Glacier between 2018 and 2028 could cause the Beaufort Gyre to accumulate several times its typical quantity of freshwater; which might then be released in a large pulse in to the North Atlantic thus slow the AMOC and warming Antarctic (including advecting more warm CDW to key marine glacier grounding lines and ice shelves) via the bipolar seesaw mechanism.

K. Snow et al. (11 December 2017), "The Response of Ice Sheets to Climate Variability", Geophysical Research Letters, DOI: 10.1002/2017GL075745

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075745/abstract?utm_content=buffer74be2&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "West Antarctic Ice Sheet loss is a significant contributor to sea level rise. While the ice loss is thought to be triggered by fluctuations in oceanic heat at the ice shelf bases, ice sheet response to ocean variability remains poorly understood. Using a synchronously coupled ice-ocean model permitting grounding line migration, this study evaluates the response of an ice sheet to periodic variations in ocean forcing. Resulting oscillations in grounded ice volume amplitude is shown to grow as a nonlinear function of ocean forcing period. This implies that slower oscillations in climatic forcing are disproportionately important to ice sheets. The ice shelf residence time offers a critical time scale, above which the ice response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic ice streams to perturbations in heat fluxes occurring at decadal time scales."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 18, 2017, 02:20:53 AM
The linked reference adds new information about the telecommunication of tropical energy from the Equatorial Pacific to West Antarctica (the image shows a pattern of atmospheric Rossby wave train from the Nino 3 area to West Antarctica), where this energy can contribute to ice mass loss from the WAIS:

Chris S. M. Turney et al. (2017), "Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperature reconstruction", Clim. Past, 13, 231-248, https://doi.org/10.5194/cp-13-231-2017

https://www.clim-past.net/13/231/2017/cp-13-231-2017-discussion.html

Abstract: "Occupying about 14% of the world’s surface, the Southern Ocean plays a fundamental role in ocean and atmosphere circulation, carbon cycling and Antarctic ice-sheet dynamics. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine–atmosphere–ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54 degrees S). Our annually resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the 1940s, a phenomenon predating the observational record. Climate reanalysis and modelling show a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer. Our results suggest that modern observed high interannual variability was established across the mid-twentieth century, and that the influence of contemporary equatorial Pacific temperatures may now be a permanent feature across the mid- to high latitudes."

Caption for the image: "Figure 6. Rossby wave propagation from the tropical Pacific during the austral spring–summer. Low-to-high-latitude atmospheric teleconnections during the austral spring and summer (October–March). Schematic showing extratropical Pacific–South America (PSA) Rossby wave train (red arrows) associated with low- and high-pressure systems generated by anomalous equatorial upper-level divergence flow (Trenberth et al., 1998); enhanced southerly airflow across the West Antarctic coastline extends into the South Atlantic during anomalously high temperatures in the Nino 3 region (a). Spatial correlations between detrended and deseasonalised Nino 3 sea surface temperature (Rayner et al., 2003) (October–March) and 850 hPa height (b) and zonal wind stress (c) using ERA-Interim (Dee et al., 2011) for the period 1979–2015. Location of key sites are shown. Significance pfield < 0:05."

Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 18, 2017, 10:26:22 PM
I am too cheap to access the linked references, but I cite them as their summaries indicate that two of the factors (the rate of ocean warming at depth & the rate of loss of buttressing from ice shelves) driving ice mass loss from Antarctic marine glaciers have been previously underestimated:

The following reference discusses how strengthening westerly winds over the Southern Ocean is increasing the volume of warm water at a depth near 500m.

Katsuro Katsumata (2017), "Could wind warms Southern Ocean", Nature Climate Change, doi:10.1038/s41558-017-0046-0

http://www.nature.com/articles/s41558-017-0046-0

&

The following reference indicates that thinning Antarctic ice shelves are causing upstream ice flows to accelerate for a greater distance than previously assumed:

Olivier Gagliardini (2017), "The Health of Antarctic Ice Shelves", Nature Climate Change, doi:10.1038/s41558-017-0037-1

http://www.nature.com/articles/s41558-017-0037-1
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on December 20, 2017, 08:32:59 PM
Here are some selected abstract from the IGSOC 2017 conference, that are relevant to the potential collapse of the WAIS:

https://www.igsoc.org/symposia/2017/boulder/proceedings/proceedings.html

76A2543
The potential for positive feedback between deglaciation of the West Antarctic Ice Sheet, decompression-melt-induced subglacial volcanism and resultant sea-level rise
John Behrendt, Wesley LeMasurier
Corresponding author: John Behrendt
Corresponding author e-mail: john.behrendt@colorado.edu
Melting of the West Antarctic Ice Sheet (WAIS) would raise global sea level ~3 m. WAIS flows through the volcanically active West Antarctic rift system (WARS); heat flow is high beneath WAIS. Satellite altimetry shows rapid retreat of ice shelves bordering WAIS resulting from climate change. GRACE satellite data indicate accelerating mass loss from WAIS, reducing basal pressure. Aeromagnetic surveys over WAIS revealed >1000 high-amplitude magnetic anomalies, indicative of the late Cenozoic–recent age subglacial volcanic rocks at its base. Increased volcanic activity resulting from decompression mantle melting beneath a thinning WAIS may serve as a positive feedback mechanism that could further destabilize WAIS. In both Iceland and on midocean ridges, dated volcanism suggests decompression mantle melting associated with reductions in either ice or water loads drives significant volcanism. Acceleration of volcanic activity as the WAIS thins could enhance the rate of ice loss and accelerate global sea level rise.

76A2568
Ice sheets and sea level: to rise, or not to rise, that is no longer the question
Sophie Nowicki
Corresponding author: Sophie Nowicki
Corresponding author e-mail: sophie.nowicki@nasa.gov
On 18 April 2017, the New York Times published an article entitled ‘When Rising Seas Transform Risk into Certainty’, illustrating that rising sea level is now in the public eye. When thinking about sea level, the question is no longer whether levels are rising, but how to increase confidence in projections of ice-sheet evolution and reduce the uncertainty in projection of sea level. These questions lie at the heart of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the first time that an effort dedicated to ice sheets is part of the climate model endeavor (CMIP) that forms the foundation of the IPCC reports. This presentation will introduce ISMIP6, review progress made in both the ice sheet and climate modeling communities in order to improve our understanding of how ice sheets contribute to the climate system, before exploring the challenges ahead and how anyone with an interest in the polar regions can contribute to this new venture.

76A2573
Coupled ice shelf–ocean modelling and complex grounding line retreat for Pine Island Glacier
Jan de Rydt, Hilmar Gudmundsson
Corresponding author: Jan De Rydt
Corresponding author e-mail: janryd69@bas.ac.uk
Recent observations and modelling work have shown a complex mechanical coupling between Antarctica’s floating ice shelves and the adjacent grounded ice sheet. A prime example is Pine Island Glacier, West Antarctica, which has a strong negative mass balance caused by a recent increase in ocean-induced melting of its ice shelf. The mass loss coincided with the retreat of its grounding line from a seabed ridge on which it was at least partly grounded until the 1970s. At present, it is unclear what caused the onset of this retreat, and how feedback mechanisms between the ocean and ice-shelf geometry have influenced the ice dynamics. To address these questions, we present results from an offline coupling between a state-of-the-art shallow-ice flow model with grounding-line resolving capabilities, and a three-dimensional ocean general-circulation model with a static implementation of the ice shelf. We simulate the retreat from an idealized seabed ridge in response to changes in the ocean forcing, and show that the retreat becomes irreversible after 20 years of warm ocean conditions. A comparison with experiments with a simple depth-dependent meltrate parameterization demonstrates that such parameterizations are unable to capture the details of the retreat process, and they overestimate mass loss by more than 40% over a 50-year timescale. In a second set of experiments, we used the coupled model to simulate the evolution of all Amundsen Sea glaciers under a range of warm and cold ocean scenarios.

76A2592
West Antarctic surface elevation change from CryoSat-2 radar altimetry and multi-mission lidar mapping
Tyler Sutterley, Isabella Velicogna, Eric Rignot, Jeremie Mouginot, Thorsten Markus, Tom Neumann
Corresponding author: Tyler Sutterley
Corresponding author e-mail: tyler.c.sutterley@nasa.gov
We present estimates of surface elevation change at the Bellinghausen Sea, Amundsen Sea and Getz regions of the West Antarctic Ice Sheet (WAIS) from CryoSat-2 radar altimetry measurements and a combination of satellite and airborne laser altimetry measurements. These regions are currently some of the most responsible for sea-level rise from the Antarctic continent. Our radar altimetry method combines Level-2 elevation measurements from the low-resolution mode (LRM) and the interferometric synthetic aperture mode (SARin) of the synthetic aperture interferometric radar altimeter (SIRAL) ranging instrument. Our laser altimetry method combines measurements from the Airborne Topographic Mapper (ATM), the Land, Vegetation and Ice Sensor (LVIS) and the Ice Cloud and land Elevation Satellite (ICESat-1). The laser altimetry method allows us to extend the records of each instrument, increases the overall spatial coverage compared to a single instrument, and produces high-quality, coherent maps of surface-elevation change. We compare elevation-change measurements for major outlet glaciers in West Antarctica to assess the regional stability. We find CryoSat-2 and laser altimetry estimates produce comparable rates of elevation change in regions with lower surface slopes. The agreement is lower in regions with mountainous terrain and small outlet glaciers.

76A2595
Land ice in version 2.0 of the Community Earth System Model
William Lipscomb, Jeremy Fyke, Gunter Leguy, Jan Lenaerts, William Sacks, Leo van Kampenhout, Miren Vizcaino
Corresponding author: William Lipscomb
Corresponding author e-mail: lipscomb@ucar.edu
The summer 2017 release of the Community Earth System Model version 2 (CESM2) includes major advances, compared to CESM1, in the treatment of ice sheets and their interactions with the climate. The dynamic ice sheet model is version 2.1 of the Community Ice Sheet Model (CISM2.1), which has a higher-order velocity solver (suitable for simulating fast flow in ice streams and ice shelves) and improved treatments of basal and calving physics. In long spin-ups for the initMIP-Greenland project, the modeled Greenland ice extent, volume and surface velocity agree well with observations. In coupled runs, the Community Land Model (CLM) computes the ice-sheet surface mass balance (SMB) in multiple elevation classes, and the coupler downscales the SMB to the fine-scale CISM grid. Recent CLM snow physics improvements give a more realistic SMB for both Greenland and Antarctica. CESM2 supports two-way coupling of ice sheets, with ice-sheet evolution feeding back conservatively on land-surface types and elevation. A developmental version of CISM, which includes a grounding-line parameterization and an ocean plume model, has been verified for marine ice-sheet benchmark experiments and has the potential to be used for dynamic Antarctic simulations in future versions of CESM.

76A2598
Characterizing uncertainty in projected changes of Antarctic surface temperature, precipitation and sea ice extent
David Schneider
Corresponding author: David Schneider
Corresponding author e-mail: dschneid@ucar.edu
Some of the largest uncertainties in projected anthropogenic climate change impacts occur in or are linked to Antarctica and the Southern Ocean. Projected changes in Antarctic surface mass balance, sea-ce extent and surface temperature differ widely among current-generation climate models, and this uncertainty likely has roots in the mean states (climatologies) of the models. In this presentation, we will highlight projected changes in surface air temperature and precipitation over the Antarctic Ice Sheet and relate the magnitude of these changes to the initial climatology of the model. To characterize the roles of natural variability and model (structural) uncertainty in the spread of these projections, we will use output from the Community Earth System Model Large Ensemble as well as the CMIP5 archive.

76A2599
Observations of recent climate change in East Antarctica outpace future model simulations
Brooke Medley, Joseph McConnell, Thomas Neumann, Carleen H. Reijmer, Sepp Kipfstuhl, Michael Sigl
Corresponding author: Brooke Medley
Corresponding author e-mail: brooke.c.medley@nasa.gov
The West Antarctic Ice Sheet (WAIS) is experiencing rapid warming and substantial ice-mass loss, designating it as one of the regions most vulnerable to change in Antarctica, especially in comparison to the more massive East Antarctic Ice Sheet (EAIS), which is thought to be undergoing little or no mass change. Thus, researchers consider the high, dry EAIS stable with little warming and no significant change in snowfall since 1957. Here, we present new observations of snow accumulation and air temperature near Kohnen station in Queen Maud Land that suggest that this region can experience climate change at a pace similar to or potentially more rapid than observations from WAIS. Over the past 75 years, snow accumulation has increased 5.2 ± 3.7% per decade, a rate that is 1.5 times more rapid than any 75-year interval in the previous nearly 2000 years (1–1850 CE). The recent 20-year mean annual accumulation is 16.5 mm w.e. larger than the preindustrial mean of 66.2 mm w.e. Similarly, annual air temperature has been increasing by 1.1 ± 0.7 °C per decade since 1998, with significant seasonal increases in autumn and spring. By comparing our observed changes with output from the Community Earth System Model, we find that the observed rates of accumulation and temperature change outpace the model simulations by several decades even under the high-emission RCP8.5 scenario.

76A2619
Effects of climate variability on marine ice-sheet stability
Matthew Hoffman, Jeremy Fyke, Stephen Price
Corresponding author: Matthew Hoffman
Corresponding author e-mail: mhoffman@lanl.gov
Theory, modeling, and observations indicate that marine ice sheets on a retrograde bed are only conditionally stable. Previous modeling studies have shown that rapid, unstable retreat can occur when steady ice-shelf basal melting causes the grounding line to retreat past restraining bedrock bumps. Here we explore the initiation and evolution of unstable retreat when the ice-shelf basal melt forcing includes temporal variability mimicking realistic climate variability. We use the three-dimensional, higher-order Model for Prediction Across Scales-Land Ice (MPASLI) model in an idealized model configuration similar to Pine Island Glacier. We find that climate variability has a complex relationship to marine ice-sheet stability and can delay or accelerate unstable retreat.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 09, 2018, 05:01:01 PM
The linked article discusses how the ENSO cycle impacts on Antarctic Pacific Sector ice shelves.  Thus with the frequency of extreme El Nino events predicted to increase with global warming, we can expect the Antarctic Pacific Sector ice shelves to degrade more rapidly in the coming decades:

Title: "El Niño causes West Antarctica’s ice shelves to gain height yet lose mass"

https://www.carbonbrief.org/el-nino-causes-west-antarcticas-ice-shelves-gain-height-yet-lose-mass

Extract: "El Niño events are known for bringing floods to South America and contributing to wildfires in Indonesia, but new research reveals they also affect the height and mass of ice shelves in Antarctica.

During an El Niño event, many of the ice shelves around West Antarctica receive more snow on their surface, but also lose more ice from underneath because of warm ocean water.
Overall, the ice shelves actually lose mass during an El Niño, the research finds, making such events an important factor in the year-to-year fluctuations of ice shelf size.
With more “extreme” El Niño events expected as global temperatures rise, West Antarctica’s ice shelves could see larger fluctuations in height and mass, …"

See also:

Paolo et al (2018), "Response of the Pacific-sector Antarctic ice shelves to the El Nino/Southern Oscillation", Nature Geoscience, doi:1038/s41561-017-0033-0

http://www.nature.com/articles/s41561-017-0033-0
&
http://www.nature.com/articles/s41561-017-0033-0.epdf?referrer_access_token=q9RDK3fDMFVTf8SOvsqtDtRgN0jAjWel9jnR3ZoTv0NkbfdogOpJdXh63nd-byA7uSU-nq2NafOwTW6ZvjE8jHg7PHoxQZIwAlcr2Is7Csb5bVcTu9jaWsBXhjsk1URR_BKmbokI_486RX5YhjTwOkunxnod-j-Y8fE1iTOQyxBl7PNIru2LAxGi4Jn2Pll4yazPQeva6laVort7VIHha26oHO8jIC-NxfMr-wUj9zg%3D&tracking_referrer=www.bbc.com

And see:

http://www.bbc.com/news/science-environment-42614412
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on January 29, 2018, 07:09:49 PM
The linked reference helps to quantify inter-decadal trends of ice mass loss in Marie Byrd Land.  Maybe as El Nino's intensify with continued warming, these climateocean trends will become more significant:

Christie, F. D. W., Bingham, R. G., Gourmelen, N., Steig, E. J., Bisset, R. R., Pritchard, H. D., Snow, K., and Tett, S. F. B.: Marie Byrd Land glacier change driven by inter-decadal climateocean variability, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-263, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2017-263/

Abstract. Over the past 20 years satellite remote sensing has captured significant downwasting of glaciers that drain the West Antarctic Ice Sheet into the ocean, particularly across the Amundsen Sea Sector. Along the neighbouring Marie Byrd Land Sector, situated west of Thwaites Glacier to Ross Ice Shelf, glaciological change has been only sparsely monitored. Here, we use optical satellite imagery to track grounding-line migration along the Marie Byrd Land Sector between 2003 and 2015, and compare observed changes with ICESat and CryoSat- 2-derived surface elevation and thickness change records. During the observational period, 33 % of the grounding line underwent retreat. The greatest retreat rates were observed along the 650-km-long Getz Ice Shelf, further west of which only minor retreat occurred. The relative glaciological stability west of Getz Ice Shelf can be attributed to a divergence of the Antarctic Circumpolar Current from the continental-shelf break at 135° W, coincident with a transition in the morphology of the continental shelf. Along Getz Ice Shelf, grounding-line retreat reduced by 68 % during the CryoSat-2 era relative to earlier observations. This slowdown is a likely response to reduced oceanic forcing, as inferred from climate reanalysis data. Collectively, our findings underscore the importance of spatial and inter-decadal variability in climate and ocean interactions in moderating glaciological change around Antarctica.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on February 23, 2018, 05:57:53 PM
We should all remember that if the WAIS collapses, both during and after the collapse, the associated local tidal elevation ranges and currents will be significantly different than those assessed in the linked reference:

Laurie Padman et al (14 February 2018), "Ocean Tide Influences on the Antarctic and Greenland Ice Sheets", Review of Geophysics, DOI: 10.1002/2016RG000546 

http://onlinelibrary.wiley.com/doi/10.1002/2016RG000546/abstract;jsessionid=A52E6F7A6D5FAFC396565F4009CF45FA.f03t03

Abstract: "Ocean tides are the main source of high-frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice-ocean models and analytical glacier models that quantify the effect of ocean tides on lower-frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice-ocean interface, and higher-resolution models with improved representation of tidal energy sinks."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: salbers on March 04, 2018, 08:00:09 PM
Recent GRACE measurements show accelerating ice loss over Antarctica in general with a concentration over the WAIS:

https://svs.gsfc.nasa.gov/30880
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Stephan on March 23, 2018, 09:11:57 PM
As I am quite new here I wonder whether a table exists, which shows the retreat of the grounding lines of Thwaites, Kohler, Smith, Pope and Pine Island Glacier in the last 20 years or so in km or miles as a function of time. In addition it would be intersting to know whether a change in grounding line retreat velocity is due to local effects (e.g. bumps in the glacier's way) or general conditions (e.g. warming of the deeper ocean water) and how / whether there is a correlation between the speeding-up of each glacier's flow downstream and the grounding line position. Maybe someone of you has an idea where to find this information - Thanks
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on March 23, 2018, 10:00:38 PM
For the first question, a paper on Amundsen glaciers is doi: 10.1002/2014GL060140 I have referred to it before. This thread contains answers to most of the other questions.

" a change in grounding line retreat velocity is due to local effects (e.g. bumps in the glacier's way) or general conditions (e.g. warming of the deeper ocean water) "

Yes. The shelves are pinned on high points and the grounding line on peaks in the beds.

" whether there is a correlation between the speeding-up of each glacier's flow downstream and the grounding line position. "

This is more interesting. While grounding line retreat is more sensitive to warm water intrusion and bed slopes, the overall flow velocity is more complex, controlled by SMB, bed and surface slope, beg properties and basal hydrology. For example there is a presentation by alley that shows that PIG has a traffic jam upstream where several tributaries come together. When grounding line reaches that point ...

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Stephan on March 25, 2018, 08:43:49 PM
Thank you sidd for this information.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: oren on March 26, 2018, 07:48:15 AM
Stephan, bear in mind the retreat is not monotonous. It goes forward and back. It's also not uniform, due to bed topography and other factors. I think I saw a map somewhere up-thread that showed the grounding line of one or more of the glaciers for different years.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on March 30, 2018, 10:22:55 PM
It is good idea to keep an eye on Recovery/Slessor/Baily for their possible ice mass loss later this century:

Anja Diez et al. (30 March 2018), "Basal Settings Control Fast Ice Flow in the Recovery/Slessor/Bailey Region, East Antarctica', Geophysical Research Letters, https://doi.org/10.1002/2017GL076601

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076601

Abstract: "The region of Recovery Glacier, Slessor Glacier, and Bailey Ice Stream, East Antarctica, has remained poorly explored, despite representing the largest potential contributor to future global sea level rise on a centennial to millennial time scale. Here we use new airborne radar data to improve knowledge about the bed topography and investigate controls of fast ice flow. Recovery Glacier is underlain by an 800 km long trough. Its fast flow is controlled by subglacial water in its upstream and topography in its downstream region. Fast flow of Slessor Glacier is controlled by the presence of subglacial water on a rough crystalline bed. Past ice flow of adjacent Recovery and Slessor Glaciers was likely connected via the newly discovered Recovery‐Slessor Gate. Changes in direction and speed of past fast flow likely occurred for upstream parts of Recovery Glacier and between Slessor Glacier and Bailey Ice Stream. Similar changes could also reoccur here in the future."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 02, 2018, 10:38:21 PM
I and others have posted links to this paper which discusses PIG, Thwaites in some detail. PIG retreat seems to have slowed, attributed to less available warm CDW, but Thwaites has retreated faster. In the supplementary thay have a picture of the grounding lines which i attach. My earlier comment on this paper is at:

https://forum.arctic-sea-ice.net/index.php/topic,622.msg148216.html

doi: 10.1038/s41561-018-0082-z

I attach fig s3. The "further retreat" grounding line is arrived at as follows:

"We also consider a ‘further retreat’ scenario, which is designed to account for potential inland migration of the grounding line since 2011 and thus to provide an upper bound on retreat rates since 2011. However, it should be noted that a recent survey confirmed that substantial further retreat has not occurred [38]. The ‘further retreat’ scenario is designed as follows: the coordinates of the 2011 grounding-line observation are advected upstream over the time from its acquisition (2011) to the end of our observational period (2016); the direction is chosen to be opposite to the flow direction according to the MEaSUREs velocity observations; the magnitude of advection speed is chosen to be 1,500 m/yr as this roughly equals the maximum rates obtained from the InSAR analysis in the Amundsen Sea Embayment 11,12 . Finally, the average rate of grounding-line retreat in the ‘further retreat’ scenario was determined using all Bedmap2 grid cells that lie in the area between the 2011 and the inland advected grounding lines, as well as in the respective cross sections on Pine Island and Thwaites glaciers. Here, it was necessary to choose option 1 for the assumed direction of grounding-line motion (that is, the direction of the flow velocity; see above). The ‘further retreat’ scenario allows us to assess the maximum impact that an inaccurate groundingline position (for example, due to considerable but unmapped retreat since 2011) has on our results."

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 02, 2018, 11:37:45 PM
In the Konrad paper there is discussion of the complexities of glacier flow and grounding line movement:

"Retreat at Pine Island Glacier appears to have stagnated at 40 m/yr ±​ 30 m/yr  during the CryoSat-2 period, after it migrated inland at a rate of around 1,000 m/yr between 1992 and 2011 as documented by the previous studies [11] (Fig. 2b). The recent stagnation coincides with a deceleration of thinning from 5 m/yr around 2009 to less than 1 m/yr across a 20 km section inland of the 2011 grounding line [35] , which in principle explains the reduced retreat rate. However, the slowdown in surface lowering could also be due to further ungrounding, and so we first examine this possibility. To maintain contact with the upstream parts of the ~120-km-long central trunk, which are in our data thinning at a maximum rate of 2 m/yr (Supplementary Fig. 3), the grounding line would have had to retreat by at least 15 km since 2011 (more than double that of the previous two decades [11,12] ), at a time when thinning has abated across the lower reaches of the glacier. This leads us to conclude that the main trunk’s grounding line has stabilized, potentially due to the absence of warm sub-shelf water [36] that drove retreat until 2011. This finding is supported by two recent studies [37,38] , which also report a substantial reduction in the pace of retreat since 2011"

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: Shared Humanity on April 03, 2018, 12:38:35 AM
Good news
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 03, 2018, 01:03:17 AM
Good news

Just to be clear, it has been widely known for many years that the rate of retreat of the PIG grounding line has stagnated since about 2011; and that PIG grounding line behavior has already been factored in to advanced ice mass loss projections from the WAIS, including those from DeConto & Pollard.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on April 03, 2018, 06:43:24 AM
Thwaites worries me more than PIG.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 03, 2018, 05:34:08 PM
Thwaites worries me more than PIG.

sidd

Of course I agree; however, the attached Sentinel 1 image from April 2 2018, showing a major calving event for the Southwest Tributary Glacier's Ice Shell, illustrates how the rapid degradation of the Pine Island Ice Shell, PIIS, can reduce the ice shelf buttressing on the SW Tributary Glacier.  This in turn should accelerate the ice flow velocity of the SW Tributary Glacier, thus reducing the associate marginal shear on the northeast margin of the Thwaites Glacier.  Thus I would say that we are currently witnessing the destabilization of the Thwaites Glacier in real time.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: FrostKing70 on April 03, 2018, 06:24:06 PM
What is defined as a "major calving event"?   

Is it area, volume or other?

How big is this calving event?
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on April 03, 2018, 06:38:31 PM
What is defined as a "major calving event"?   

Is it area, volume or other?

How big is this calving event?

I believe that what qualifies as a major calving event is subjective, based on the size of the ice shelf in consideration.  I consider this event major because it extends across the entire calving front of the SW Tributary Glacier.  The area of the calved iceberg is roughly 30 sq km.

Furthermore, this calving event should markedly reduce the buttressing action of the ice shelf on the SW Tributary Glacier, so that should also qualify it as a major event w.r.t. the behavior of the associated marine glacier.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: solartim27 on April 03, 2018, 11:41:02 PM
Not to mention the rift in PIG expanding.  Here's a higher res image from today
https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20180403T084646_B9CD_S_1.final.jpg
Title: Re: Potential Collapse Scenario for the WAIS
Post by: solartim27 on April 03, 2018, 11:43:07 PM
Thwaites worries me more than PIG.
sidd
Me too, bottom part of the same image from above
https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20180403T084646_B9CD_S_1.final.jpg
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 10, 2018, 05:55:47 PM
The linked article indicates that the ocean has been the main driver of Antarctic ice sheet retreat throughout the Holocene which has had an atypically warm plateau as compare to earlier interglacial periods (see also the Early Anthropocene thread, in the Science folder).  This implies that the WAIS is more susceptible to abrupt collapse than consensus climate science likes to admit:

Xavier Crosta et al. (2018), "Ocean as the main driver of Antarctic ice sheet retreat during the Holocene", Global and Planetary Change, https://doi.org/10.1016/j.gloplacha.2018.04.007

https://www.sciencedirect.com/science/article/pii/S0921818118300249

Abstract: "Ocean-driven basal melting has been shown to be the main ablation process responsible for the recession of many Antarctic ice shelves and marine-terminating glaciers over the last decades. However, much less is known about the drivers of ice shelf melt prior to the short instrumental era. Based on diatom oxygen isotope (δ18Odiatom; a proxy for glacial ice discharge in solid or liquid form) records from western Antarctic Peninsula (West Antarctica) and Adélie Land (East Antarctica), higher ocean temperatures were suggested to have been the main driver of enhanced ice melt during the Early-to-Mid Holocene while atmosphere temperatures were proposed to have been the main driver during the Late Holocene. Here, we present a new Holocene δ18Odiatom record from Prydz Bay, East Antarctica, also suggesting an increase in glacial ice discharge since ~4500 years before present (~4.5 kyr BP) as previously observed in Antarctic Peninsula and Adélie Land. Similar results from three different regions around Antarctica thus suggest common driving mechanisms. Combining marine and ice core records along with new transient accelerated simulations from the IPSL-CM5A-LR climate model, we rule out changes in air temperatures during the last ~4.5 kyr as the main driver of enhanced glacial ice discharge. Conversely, our simulations evidence the potential for significant warmer subsurface waters in the Southern Ocean during the last 6 kyr in response to enhanced summer insolation south of 60°S and enhanced upwelling of Circumpolar Deep Water towards the Antarctic shelf. We conclude that ice front and basal melting may have played a dominant role in glacial discharge during the Late Holocene."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on May 24, 2018, 09:29:01 PM
While the reported implications of the three newly identified bed troughs at the bottleneck between East & West Antarctica (i.e. a projection of greater ice mass loss from the interior of Antarctica with continued global warming) are bad enough; I note that the fact that these troughs exist is a clear indication that such higher ice mass loss from the interior of Antarctica has occurred in the past.  This consideration increases the likelihood of such events occurring later this century:

Kate Winter et al. (2018), "Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica", Geophysical Research Letters, doi:10.1029/2018GL077504

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018GL077504

Abstract: "Hypothesized drawdown of the East Antarctic Ice Sheet through the “bottleneck” zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could however drive ice divide migration and increase mass discharge from interior West Antarctica to the Southern Ocean."

Plain Language Summary: "The East and West Antarctic Ice Sheets meet at the inland termination of the Transantarctic Mountains. The ice sheets coalesce at a major ice divide, which could migrate and impact ice flow across large parts of Antarctica. A lack of satellite observations of ice flow and ice thickness has previously restricted characterization of this region, its glaciology, and its subglacial landscape. Our ice-penetrating radar surveys reveal three deep subglacial valleys and mountainous subglacial topography beneath the ice divide. New measurements of ice flow evidence faster ice flow within these troughs than in the surrounding thinner ice. Were the ice sheet to shrink in size, an increase in the speed at which ice flows through these troughs could lead to the ice divide moving and increase the rate at which ice flows out from the center of Antarctica to its edges."

See also:

Title: "Giant canyons discovered in Antarctica"

http://www.bbc.com/news/science-environment-44245893

Extract: "Scientists have discovered three vast canyons in one of the last places to be explored on Earth - under the ice at the South Pole.

And if Antarctica thins in a warming climate, as scientists suspect it will, then these channels could accelerate mass towards the ocean, further raising sea-levels.

"These troughs channelise ice from the centre of the continent, taking it towards the coast," explained Dr Winter.

"Therefore, if climate conditions change in Antarctica, we might expect the ice in these troughs to flow a lot faster towards the sea. That makes them really important, and we simply didn't know they existed before now," she told BBC News.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 04, 2018, 06:22:57 PM
Hopefully, governments will provide sufficient funding to support the recommended drilling program to test for past WAIS collapse. This could help to improve our understanding of the risks that we face in the coming decades:

Spector, P., Stone, J., Pollard, D., Hillebrand, T., Lewis, C., and Gombiner, J.: West Antarctic sites for subglacial drilling to test for past ice-sheet collapse, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-88, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-88/

Abstract. Mass loss from the West Antarctic Ice Sheet (WAIS) is increasing, and there is concern that an incipient large-scale deglaciation of the marine basins may already be underway. Measurements of cosmogenic nuclides in subglacial bedrock surfaces have the potential to establish whether and when the marine-based portions of the WAIS deglaciated in the past. However, because most of the bedrock revealed by ice-sheet collapse would remain below sea level, shielded from the cosmic-ray flux, drill sites for subglacial sampling must be located in areas where thinning of the residual ice sheet would expose presently subglacial bedrock surfaces. In this paper we discuss the criteria and considerations for choosing drill sites where subglacial samples will provide maximum information about WAIS extent during past interglacial periods. We evaluate candidate sites in West Antarctica and find that sites located adjacent to the large marine basins of West Antarctica will be most diagnostic of past ice-sheet collapse. There are important considerations for drill-site selection on the kilometer scale that can only be assessed by field reconnaissance. As a case study of these considerations, we describe reconnaissance at sites in West Antarctica, focusing on the Pirrit Hills, where in the summer of 2016–2017, an 8 m bedrock core was retrieved from below 150 m of ice.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on June 14, 2018, 12:33:25 AM
Ice sheet models will need to more sophisticated fast, if we are going understand the risks of the WAIS collapsing this century:

Title: "New study suggests surprising wrinkle in history of West Antarctic Ice Sheet"

https://phys.org/news/2018-06-wrinkle-history-west-antarctic-ice.html

Extract: "Scientists generally have believed that since the end of the last Ice Age, about 15,000 years ago, the West Antarctic Ice Sheet (WAIS) has been getting smaller and smaller, with its retreat triggered by a warming world and sea-level rise from collapse of Northern Hemisphere ice sheets.

A study published online June 13, 2018 in the journal Nature shows a more complicated history.
Surprising new data and ice-sheet modeling suggest that between roughly 14,500 and 9,000 years ago, the ice sheet below sea level partially melted and shrunk to a size even smaller than today—but it did not collapse. Over the subsequent millennia, the loss of the massive amount of ice that was previously weighing down the seabed spurred uplift in the sea floor—a process known as isostatic rebound. Then the ice sheet began to regrow toward today's configuration.
"The WAIS today is again retreating, but there was a time since the last Ice Age when the ice sheet was even smaller than it is now, yet it didn't collapse," said Northern Illinois University geology professor Reed Scherer, a lead author on the study. "That's important information to have as we try to figure out how the ice sheet will behave in the future."

Don't count on isostatic rebound, however, to be a panacea for modern-day rising sea level, he added.

"What happened roughly 10,000 years ago might not dictate where we're going in our carbon dioxide-enhanced world, where the oceans are rapidly warming in the polar regions. If the ice sheet were to dramatically retreat now, triggered by anthropogenic warming, the uplift process won't help regrow the ice sheet until long after coastal cities have felt the effects of the sea level rise."

Finally, Albrecht and a colleague conducted sophisticated numerical ice-sheet modeling driven by the warming climate and rising sea levels after the last glacial maximum. Those simulations show ice sheet retreat before reaching a turning point, with the grounding line up to 200 kilometers inland of its present day location in the Weddell Sea region and up to 400 kilometers in the Ross Sea region.

"The warming after the last Ice Age made the ice masses of West Antarctica dwindle rather rapidly," Albrecht said. "It retreated inland by more than 1,000 kilometers in a period of 1,000 years in this region—on geological time-scales, this is really high-speed. But now we detected that this process at some point got partially reversed. Instead of total collapse, the ice-sheet grew again by up to 400 kilometers. This is an amazing self-induced stabilization. However, it took a whopping 10,000 years, up until now. Given the speed of current climate-change from burning fossil fuels, the mechanism we detected unfortunately does not work fast enough to save today's ice sheets from melting and causing seas to rise."

Curiously, the ice modeling did not find grounding-line retreat and rebound-driven re-advance in the Amundsen Sea region, where present-day grounding-line retreat is causing concern about future runaway collapse.

"The model of the past doesn't show retreat of Amundsen Sea glaciers much beyond the present-day grounding line," Scherer said. "So what's happening today in that sector is troublesome and could be a wildcard in all this.""

See also:

J. Kingslake et al, Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene, Nature (2018). DOI: 10.1038/s41586-018-0208-x
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 10, 2018, 12:24:38 AM
We should remember that each new generation of conventional model of Thwaites Glacier retreat projections this century indicates more and more retreat; and such conventional glacial models do not include the influence of cliff-hydrofracturing mechanisms:

Hongju Yu et al. (2018), "Retreat of Thwaites Glacier, West Antarctica, over the next 100 years using various ice flow models, ice shelf melt scenarios and basal friction laws", The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-104

https://www.the-cryosphere-discuss.net/tc-2018-104/

Abstract. Thwaites Glacier (TG), West Antarctica, experiences rapid, potentially irreversible grounding line retreat and mass loss in response to enhanced ice shelf melting. Several numerical models of TG have been developed recently, showing a large spread in the evolution of the glacier in the coming decades to a century. It is, however, not clear how different parameterizations of basal friction and ice shelf melt or different approximations in ice stress balance affect projections. Here, we simulate the evolution of TG using different ice shelf melt, basal friction laws and ice sheet models of varying levels of complexity to quantify the effect of these model configurations on the results. We find that the grounding line retreat and its sensitivity to ocean forcing is enhanced when a full-Stokes model is used, ice shelf melt is applied on partially floating elements, and a Budd friction is used. Initial conditions also impact the model results. Yet, all simulations suggest a rapid, sustained retreat along the same preferred pathway. The highest retreat rate occurs on the eastern side of the glacier and the lowest rate on a subglacial ridge on the western side. All the simulations indicate that TG will undergo an accelerated retreat once it retreats past the western ridge. Combining the results, we find the uncertainty is small in the first 30 years, with a cumulative contribution to sea level rise of 5mm, similar to the current rate. After 30 years, the mass loss depends on the model configurations, with a 300% difference over the next 100 years, ranging from 14 to 42mm.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 13, 2018, 11:02:59 PM
The ENSO cycle has repeatedly been demonstrated to generate decadal oceanic pulses of relatively warm CDW (circumpolar deep water) and relative cooler surface water into the Amundsen Sea Embayment, ASE.  The linked reference provides both field and model results that help to better delineate the influence of these ENSO driven oceanic pulses on ice mass loss from key marine glaciers in the ASE.  Furthermore, research indicates that as climate change increases the frequency of strong El Nino events, the frequency of warm CDW pulses into the ASE should increase, resulting in increased ice mass loss from this key region:

Jenkins et al. (2018), "West Antarctic Ice Sheet retreat in the Amundsen Sea driven by decadal oceanic variability", Nature Geoscience, https://doi.org/10.1038/s41561-018-0207-4

http://www.nature.com/articles/s41561-018-0207-4.epdf?referrer_access_token=Bc93rPzj5mAIgFxIj7ONaNRgN0jAjWel9jnR3ZoTv0PHtUgk_ZOT39EqrANp0b8eqygnJyFYtkZtZrrvzpzzWFxFRxOjGyBuySjpDsnaRQh7XJnWxZ3ao5NgE_FXw2TbspGSBS1Ou39d7UURpwlPi_Pto2nRLEma6yWSJG3jZtjtHknyJEJlg9BIxSQMv28PGhskTGPjzqBOEvvM0U4N9vO_qHWkDtkY-E5jhH1DvWdJkNePrE5W2mXS98uEvX9LRJGTRyR_k2N9kxRVb0DlMnr7Jn6NgoQ-PnofJG67wP8%3D&tracking_referrer=www.carbonbrief.org

Abstract: "Mass loss from the Amundsen Sea sector of the West Antarctic Ice Sheet has increased in recent decades, suggestive of sustained ocean forcing or an ongoing, possibly unstable, response to a past climate anomaly. Lengthening satellite records appear to be incompatible with either process, however, revealing both periodic hiatuses in acceleration and intermittent episodes of thinning. Here we use ocean temperature, salinity, dissolved-oxygen and current measurements taken from 2000 to 2016 near the Dotson Ice Shelf to determine temporal changes in net basal melting. A decadal cycle dominates the ocean record, with melt changing by a factor of about four between cool and warm extremes via a nonlinear relationship with ocean temperature. A warm phase that peaked around 2009 coincided with ice-shelf thinning and retreat of the grounding line, which re-advanced during a post-2011 cool phase. These observations demonstrate how discontinuous ice retreat is linked with ocean variability, and that the strength and timing of decadal extremes is more influential than changes in the longer-term mean state. The non-linear response of melting to temperature change heightens the sensitivity of Amundsen Sea ice shelves to such variability, possibly explaining the vulnerability of the ice sheet in that sector, where subsurface ocean temperatures are relatively high."

See also:

Title: "Scientists find ‘natural pulses’ in recent melting of West Antarctic ice sheet"

https://www.carbonbrief.org/scientists-find-natural-pulses-in-recent-melting-of-west-antarctic-ice-sheet

Extract: "Natural ocean variability is heightening the rate of retreat of the West Antarctic ice sheet, a new study finds.

A 16-year study of ocean conditions in Antarctica suggests that the periodic arrival of warm currents as a result of natural variability is worsening the rate of ice mass loss from key glaciers in the region.

The natural pulses of warm water could be key to driving short-term changes in glacier ice mass loss, the lead author tells Carbon Brief. In the long term, this periodic ocean warming is likely to be exacerbated by climate change, he adds.

The new findings serve as a “smoking gun” by helping scientists to understand the mechanisms behind the ice sheet’s retreat, another scientist tells Carbon Brief.

The researchers believe that El Niño is altering the strength of these ocean currents, periodically pulling or pushing the CDW towards or away from the glaciers on Antarctica’s coast, driving the “warm” and “cool” ocean phases, respectively."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on August 14, 2018, 06:39:26 AM
Thanx for that reference. I notice that Dutrieux is an author. Nice work, they used soundings from cruise ships among a lot of other things. I attach a section of fig 4 showing 80Gton melt coming off the thing when section mean potential temperature rises to 1.5-2 C above surface freezing point.

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 15, 2018, 06:19:39 PM
The linked reference indicates that the projected increase (with continued global warming) of more frequent strong El Nino events combined with the projected increase in positive SAM, will significantly increase ice mass loss from the ASE, which will increase the risk of a collapse of the WAIS:

Deb, P., A. Orr, D. H. Bromwich, J. P. Nicolas, J. Turner, and J. S. Hosking, 2018: Summer drivers of atmospheric variability affecting ice shelf thinning in the Amundsen Sea Embayment, West Antarctica. Geophy. Res. Lett., 45. doi: 10.1029/2018GL077092.

http://polarmet.osu.edu/PMG_publications/deb_bromwich_grl_2018.pdf

Abstract:  "Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves."

Extract: "Our study suggests that ASE ice shelves could experience an intensification of melt in the future from both above and below as a result of both regional and large-scale atmospheric changes, potentially increasing the risk of their disintegration, which in turn could potentially trigger a collapse of the West Antarctic ice sheet (DeConto & Pollard, 2016). To better understand this threat will require further detailed investigation of the impacts of ENSO, the polarity of the SAM, and the depth/location of the ASL on ASE ice shelves. Also necessary is improving the reliability of future projections, such as ENSO and its teleconnections, as well as the response of the SAM to recovery of the Antarctic ozone hole and increased greenhouse gas emissions (Polvani, Waugh, et al., 2011)."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: bluesky on August 20, 2018, 05:37:39 PM
Dear AbruptSLR

All these links are very interesting and somewhat very worrying considering the complacency of our policymakers...
Would it be possible to get a physical explanation of how the teleconnection between a strong El Nino and a stronger pulse of relatively warm water in CDW ? Maybe it is already explained somewhere in the forum, but I, unfortunately, have not been able to find it
Is there any paper quantifying the increase of warm water pulse based on modelled projection of higher frequency and stronger El Nino event? And, sorry maybe it is a very basic question,  from which process global warming will increase the frequenwy of El Nino and SAM?

Is there any potential link between the slow down of AMOC and the Antarctica, or is it too far fetched as deep water takes quite some time to go back to the South hemisphere?

Thanks
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 20, 2018, 08:18:27 PM
Dear AbruptSLR

All these links are very interesting and somewhat very worrying considering the complacency of our policymakers...
Would it be possible to get a physical explanation of how the teleconnection between a strong El Nino and a stronger pulse of relatively warm water in CDW ? Maybe it is already explained somewhere in the forum, but I, unfortunately, have not been able to find it
Is there any paper quantifying the increase of warm water pulse based on modelled projection of higher frequency and stronger El Nino event? And, sorry maybe it is a very basic question,  from which process global warming will increase the frequenwy of El Nino and SAM?

Is there any potential link between the slow down of AMOC and the Antarctica, or is it too far fetched as deep water takes quite some time to go back to the South hemisphere?

Thanks

bluesky,

Basically, the top elevation of the circumpolar deep water, CDW, is typically just below deep troughs in the continental shelf of the Amundsen Sea Embayment, ASE.  Further the Amundsen Bellingshausen Sea Low, ABSL (or ASL) & see the first image), is a frequent low pressure atmospheric system that moves east-west along the Amundsen – Bellingshausen Seas coastline, depending on numerous atmospheric conditions, but predominately by the combination of the ENSO & SAM (see the second & third images), due to the teleconnection of atmospheric energy by Rossby Waves from the Tropical Pacific Ocean.  When in the correct position, the ABSL blows wind into the ASE which drags the surface ocean water with it; which in turn causes upwelling of the CDW into the deep troughs which, all lead to the grounding lines of the various ASE marine glaciers.

The AMOC slowdown can impact the ENSO via atmospheric telecommunication from the Atlantic to the Pacific basins, depending on the season and other metocean conditions.

Also see:
The thread entitled: "Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Time Frame":
From Reply #75:
The following linked article supports the point that in a big El Nino year both PIIS and PIG will lose ice more rapidly than normal:

http://www.science20.com/news_articles/antarcticas_pine_island_glacier_melt_blame_el_nino-127129
From Reply #76:
To those who would like access to the source material for the information cited in my immediate past post, please see the following links, abstract, and related references:

http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract

http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf

Pierre Dutrieux, Jan De Rydt, Adrian Jenkins, Paul R. Holland, Ho Kyung Ha, Sang Hoon Lee, Eric J. Steig, Qinghua Ding, E. Povl Abrahamsen, and Michael Schröder, 2014, "Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability", Science; Published online 2 January 2014 [DOI:10.1126/science.1244341]

Abstract:
"Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate."

Supplemental references:

1. S. S. Jacobs, A. Jenkins, H. Hellmer, C. Giulivi, F. Nitsche, B. Huber, R. Guerrero, The
Amundsen Sea and the Antarctic Ice Sheet. Oceanography 25, 154–163 (2012).
doi:10.5670/oceanog.2012.90
2. S. S. Jacobs, A. Jenkins, C. F. Giulivi, P. Dutrieux, Stronger ocean circulation and increased
melting under Pine Island Glacier ice shelf. Nat. Geosci. 4, 519–523 (2011).
doi:10.1038/ngeo1188
3. S. S. Jacobs, H. H. Hellmer, A. Jenkins, Antarctic Ice Sheet melting in the southeast Pacific.
Geophys. Res. Lett. 23, 957–960 (1996). doi:10.1029/96GL00723
4. A. Jenkins, P. Dutrieux, S. S. Jacobs, S. D. McPhail, J. R. Perrett, A. T. Webb, D. White,
Observations beneath Pine Island Glacier in West Antarctica and implications for its
retreat. Nat. Geosci. 3, 468–472 (2010). doi:10.1038/ngeo890
5. D. J. Wingham, D. W. Wallis, A. Shepherd, Spatial and temporal evolution of Pine Island
Glacier thinning, 1995–2006. Geophys. Res. Lett. 36, L17501 (2009).
doi:10.1029/2009GL039126
6. A. Shepherd, E. R. Ivins, G. A, V. R. Barletta, M. J. Bentley, S. Bettadpur, K. H. Briggs, D. H.
Bromwich, R. Forsberg, N. Galin, M. Horwath, S. Jacobs, I. Joughin, M. A. King, J. T.
Lenaerts, J. Li, S. R. Ligtenberg, A. Luckman, S. B. Luthcke, M. McMillan, R. Meister,
G. Milne, J. Mouginot, A. Muir, J. P. Nicolas, J. Paden, A. J. Payne, H. Pritchard, E.
Rignot, H. Rott, L. S. Sørensen, T. A. Scambos, B. Scheuchl, E. J. Schrama, B. Smith, A.
V. Sundal, J. H. van Angelen, W. J. van de Berg, M. R. van den Broeke, D. G. Vaughan,
I. Velicogna, J. Wahr, P. L. Whitehouse, D. J. Wingham, D. Yi, D. Young, H. J. Zwally,
A reconciled estimate of ice-sheet mass balance. Science 338, 1183–1189 (2012).
Medline doi:10.1126/science.1228102
7. E. Rignot, Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR
data. Geophys. Res. Lett. 35, L12505 (2008). doi:10.1029/2008GL033365
8. I. Joughin, E. Rignot, C. E. Rosanova, B. K. Lucchitta, J. Bolhander, Timing of Recent
Accelerations of Pine Island Glacier, Antarctica. Geophys. Res. Lett. 30, 1706 (2003).
doi:10.1029/2003GL017609
9. I. Joughin, B. E. Smith, D. M. Holland, Sensitivity of 21st century sea level to ocean-induced
thinning of Pine Island Glacier, Antarctica. Geophys. Res. Lett. 37, L20502 (2010).
doi:10.1029/2010GL044819
10. H. D. Pritchard, S. R. Ligtenberg, H. A. Fricker, D. G. Vaughan, M. R. van den Broeke, L.
Padman, Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature 484, 502–
505 (2012). Medline doi:10.1038/nature10968
11. A. Shepherd, D. Wingham, D. Wallis, K. Giles, S. Laxon, A. V. Sundal, Recent loss of
floating ice and the consequent sea level contribution. Geophys. Res. Lett. 37, L13503
(2010). doi:10.1029/2010GL042496
12. A. Shepherd, D. Wingham, E. Rignot, Warm ocean is eroding West Antarctic Ice Sheet.; Geophys. Res. Lett. 31, L23402 (2004). doi:10.1029/2004GL021106
From Reply #131:
The linked reference (the second link has a free pdf) ties the warming of the Tropical Atlantic SST to a strengthening of both the Antarctic Circumpolar Winds and the Amundsen Bellingshausen Sea Low (ABSL/ASL) via atmospheric Rossby waves in all seasons except the austral summer.  The conclusions of this paper (see the extract below) recommends that efforts be made to inter-relate this Atlantic tropical-Antarctic teleconnection with other tropical teleconnections (such as those identified by Fogt et al 2011, see the first attached image relating El Nino events & negative Southern Annular Mode, SAM, conditions that promote teleconnection of Tropical Pacific energy towards the Amundsen Sea Embayment, via atmospheric Rossby wave-trains).  As we are now likely approaching very strong El Nino conditions by October 2015, it will be very interesting to see whether both the Tropical Atlantic and the Tropical Pacific soon teleconnect large amounts of atmospheric energy into Western Antarctica.

Additionally, the second attached image today from the Earth nullschool shows that the ABSL is relatively strong (i.e. has a relatively low central pressure) and is currently directing energy directly into the Amundsen Sea Embayment, ASE.

XICHEN LI, EDWIN P. GERBER, DAVID M. HOLLAND, AND CHANGHYUN YOO, (2015), "A Rossby Wave Bridge from the Tropical Atlantic to West Antarctica", J. Climate, 28, 2256–2273, doi: http://dx.doi.org/10.1175/JCLI-D-14-00450.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00450.1

http://polarmet.osu.edu/ACCIMA/li_gerber_jc_2015.pdf

Abstract: "Tropical Atlantic sea surface temperature changes have recently been linked to circulation anomalies around Antarctica during austral winter. Warming in the tropical Atlantic associated with the Atlantic multidecadal oscillation forces a positive response in the southern annular mode, strengthening the Amundsen–Bellingshausen Sea low in particular. In this study, observational and reanalysis datasets and a hierarchy of atmospheric models are used to assess the seasonality and dynamical mechanism of this teleconnection.  Both the reanalyses and models reveal a robust link between tropical Atlantic SSTs and the Amundsen–Bellingshausen Sea low in all seasons except austral summer. A Rossby wave mechanism is then shown to both explain the teleconnection and its seasonality. The mechanism involves both changes in the excitation of Rossby wave activity with season and the formation of a Rossby waveguide across the Pacific, which depends critically on the strength and extension of the subtropical jet over the west Pacific. Strong anticyclonic curvature on the poleward flank of the jet creates a reflecting surface, channeling quasi-stationary Rossby waves from the subtropical Atlantic to the Amundsen–Bellingshausen Sea region. In summer, however, the jet is weaker than in other seasons and no longer able to keep Rossby wave activity trapped in the Southern Hemisphere. The mechanism is supported by integrations with a comprehensive atmospheric model, initial-value calculations with a primitive equation model on the sphere, and Rossby wave ray tracing analysis."

Extract: "Antarctic climate is also influenced by other tropical–polar teleconnections (Fogt et al. 2011; Ding et al. 2012), and key questions remain concerning the relative importance of these effects. The time scales of tropical SST variability differs significantly from one region to another (e.g., ENSO and the east Pacific dominate on interannual time scales, while the AMO and Pacific decadal oscillation are more significant on longer time scales). Moreover, SSTs in different tropical ocean basins may interact with each other through tropical ocean interbasin teleconnections. It is thus important to further investigate the relative importance and the relationship between the teleconnections from different tropical ocean sectors as a function of time scale."

Also see the thread entitled: "Risks and Challenges for Regional Circulation Models of the Southern Ocean"

From Reply #51:
It has been a while since I posted the attached figure from Bertler et al 2006 (see reference at bottom of this post), which shows pictorially the relationship between the location of the Amundsen Sea Low (or Amundsen Bellingshausen Sea Low), ASL (or ABSL) and either a La Nina or an El Nino event.  Taken together with the information in my immediately preceding post (which stated that sea surface warming related to the Atlantic Multidecadal Oscillation, AMO, reduces the surface pressure in the Amundsen Sea), this implies that when the next El Nino event occurs (which may be the austral summer of 2014 to 2015) and shifts the location of the ASL to blow wind directly into the ASE, the winds will likely be stronger due to the lower Amundsen sea pressure associated with AMO effect; which will drive more warm CDW into the ASE resulting in higher than previously expected ice mass loss from the glaciers in this area.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: solartim27 on August 21, 2018, 01:04:32 AM
Here's a nice shot of PIG from todays Sentinel.  I am amazed at the continued degradation of the ice sheet between PIG and the Trib.  Some say a picture is worth a thousand words.  Zoom in, guaranteed to be an interesting summer.
https://www.polarview.aq/images/105_S1jpgfull/S1B_IW_GRDH_1SSH_20180820T043510_80AB_S_1.final.jpg (50 MB image)
Title: Re: Potential Collapse Scenario for the WAIS
Post by: bluesky on August 21, 2018, 12:41:38 PM
Thank you AbruptSLR for taking the time to reexplain the relationship between ENSO and CDW and all the links, this is so useful, I am very grateful
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 27, 2018, 05:50:24 PM
Thank you AbruptSLR for taking the time to reexplain the relationship between ENSO and CDW and all the links, this is so useful, I am very grateful

bluesky,

As a follow-on to my Reply #522:

The first  image shows the deepwater changes across the Amundsen Sea continental shelf through which the warm CDW flows towards the grounding lines of key marine glaciers.

The second image shows a computer simulation of the pattern of warm CDW flow in the Amundsen Sea continental shelf area; which indicates how warm CDW can flow from the PIG to the Thwaites grounding line.

The third image shows that the submerged ridge seaward of Thwaites can help direct the warm CDW come from the PIG towards the 'trough' that crosses the Thwaites ice plug.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.

Next, the second linked reference indicates that from January to June the ASL typically moves from about 110 degrees W (where it is in position to help direct warm CDW into the ASE) to about 150 degrees W (where it does not help to direct warm CDW into the ASE).  I note also that:

(a) As the SAM has become more positive, due to global warming, the ASL has become more intensity and has tended to drift more to the west than previously; and

(b) El Nino events do not typically occur in the January to June timeframe but rather in the October to Dec timeframe, which helps to explain way more warm CDW flows into the ASE during El Nino events

Turner, J., Phillips, T., Hosking, J. S., Marshall, G. J. and Orr, A. (2013), The Amundsen Sea low. Int. J. Climatol., 33: 1818–1829. doi: 10.1002/joc.3558

http://onlinelibrary.wiley.com/doi/10.1002/joc.3558/abstract

Abstract: "We develop a climatology of the Amundsen Sea low (ASL) covering the period 1979–2008 using ECMWF operational and reanalysis fields. The depth of the ASL is strongly influenced by the phase of the Southern annular mode (SAM) with positive (negative) mean sea level pressure anomalies when the SAM is negative (positive). The zonal location of the ASL is linked to the phase of the mid-tropospheric planetary waves and the low moves west from close to 110°W in January to near 150°W in June as planetary waves 1 to 3 amplify and their phases shift westwards. The ASL is deeper by a small, but significant amount, during the La Niña phase of El Niño-Southern Oscillation (ENSO) compared to El Niño. The difference in depth of the low between the two states of ENSO is greatest in winter. There is no statistically significant difference in the zonal location of the ASL between the different phases of ENSO. Over 1979–2008 the low has deepened in January by 1.7 hPa dec−1 as the SAM has become more positive. It has also deepened in spring and autumn as the semi-annual oscillation has increase in amplitude over the last 30 years. An increase in central pressure and eastward shift in March has occurred as a result of a cooling of tropical Pacific SSTs that altered the strength of the polar front jet."


Finally, the third linked 2017 reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of Super El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent."

Best,
ASLR
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on August 27, 2018, 08:13:25 PM
The linked reference provides paleo evidence from about 11,500 year ago, that indicates that portions of the WAIS are very sensitivity to collapse, even under conditions that were cooler than today:

J. Kingslake et al. (2018), "Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene", Nature, https://doi.org/10.1038/s41586-018-0208-x

http://www.nature.com/articles/s41586-018-0208-x.epdf?referrer_access_token=lOkN7hgTt7KBVbuYuXMwc9RgN0jAjWel9jnR3ZoTv0PagDqQuHClF_KBoNEwt0qCDswVby5xisTUuro2GVqEdVyNRmUsMYB32-gwCy-WQGiOJuRHvpbmk3l6OEkAKwxOiPNDPRAKMIlDGFP4EHQgKD_G1qFJE2DhzFl3IkCeDuHh2Xln7I7LeJAB1tog4tIasE0yBRLzYo4hLBA3XhRCpg%3D%3D&tracking_referrer=news.nationalgeographic.com

Abstract: "To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters. Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so). Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today’s grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance. Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss on millennial timescales will depend on bedrock topography and mantle viscosity—parameters that are difficult to measure and to incorporate into ice-sheet models."

See also:

Title: "The West Antarctic Ice Sheet Seems to Be Good at Collapsing"

https://news.nationalgeographic.com/2018/06/west-antarctic-ice-sheet-collapse-climate-change/

Extract: "SCIENTISTS HAVE DISCOVERED that the West Antarctic Ice Sheet underwent a major retreat between 10,000 and 12,000 years ago, at a time when the world was actually cooler than it is today. The collapse happened at the close of the last Ice Age, and it left the ice sheet 135,000 square miles smaller than it is today – a difference nearly as large as the state of Montana.

“That the ice sheet could retreat beyond where it is today, in a climate that was likely quite a bit colder than today, points to extraordinary sensitivity,” says Robert DeConto, a glaciologist at the University of Massachusetts Amherst, who was not involved in the research."
Title: Re: Potential Collapse Scenario for the WAIS
Post by: AbruptSLR on September 19, 2018, 06:14:19 PM
The findings of the linked reference imply that current ice shelf models err on the side of least drama with regard to ice mass loss associated with relatively warm ocean water beneath such ice shelves, as illustrated by measurements from the Getz Ice Shelf in West Antarctica:

Rippin, D. M.: Significant submarine ice loss from the Getz Ice Shelf, Antarctica, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-163, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-163/

Abstract. We present the first direct measurements of changes taking place at the base of the Getz Ice Shelf (GzIS) in West Antarctica. Our analysis is based on repeated airborne radio-echo sounding (RES) survey lines gathered in 2010 and 2014. We reveal that while there is significant variability in ice shelf behaviour, the vast majority of the ice shelf (where data is available) is undergoing basal thinning at a mean rate of nearly 13ma−1, which is several times greater than recent modelling estimates. In regions of faster flowing ice close to where ice streams and outlet glaciers join the ice shelf, significantly greater rates of mass loss occurred. Since thinning is more pronounced close to faster-flowing ice, we propose that dynamic thinning processes may also contribute to mass loss here. Intricate sub-ice circulation patterns exist beneath the GzIS because of its complex sub-ice topography and the fact that it is fed by numerous ice streams and outlet glaciers. It is this complexity which we suggest is also responsible for the spatially variable patterns of ice-shelf change that we observe. The large changes observed here are also important when considering the likelihood and timing of any potential future collapse of the ice shelf, and the impact this would have on the flow rates of feeder ice streams and glaciers, that transmit ice from inland Antarctica to the coast. We propose that as the ice shelf continues to thin in response to warming ocean waters and climate, the response of the ice shelf will be spatially diverse. Given that these measurements represent changes that are significantly greater than modelling outputs, it is also clear that we still do not fully understand how ice shelves respond to warming ocean waters. As a result, ongoing direct measurements of ice shelf change are vital for understanding the future response of ice shelves under a warming climate.
Title: Re: Potential Collapse Scenario for the WAIS
Post by: sidd on December 24, 2018, 09:44:51 AM
I see that Yu(2018) about Thwaites was published in final form on cryosphere. Rignot, Seroussi and Morlinghem are the other authors. Nice paper. Significant caveats:

"There is a subglacial trough between the second and third ridge that connects PIG and TG. If the grounding line of TG retreats into this region (SEM experiments with high melt), the grounding line of TG will connect with the grounding line of PIG, and the two drainage basins will merge into one. The flow of ice could be significantly impacted if this merge takes place. In this study, we did not account for this scenario ..."

...

"Another limitation is that the ice shelf front migration is not included in our simulations. We assume that the ice shelf front position of TG remains fixed; i.e., all ice passing the ice shelf front calves immediately. Densely distributed crevasses along the ice shelf of TG, however, make the ice shelf conducive to rapid calving (Yu et al., 2017). Once the ice shelf is removed, the grounding line will retreat into deeper regions, and the probability of calving increases according to the marine ice-cliff instability theory (Pollard et al., 2015; Wise et al., 2017). Crevassing and calving will therefore reduce ice shelf buttressing and accelerate ice speed; i.e., our simulations underestimate the potential mass loss of TG ..."

But a very nice paper. Open access, read all about it:

doi: 10.5194/tc-12-3861-2018

sidd
Title: Re: Potential Collapse Scenario for the WAIS
Post by: solartim27 on October 18, 2019, 08:01:06 AM
The findings of the linked reference imply that current ice shelf models err on the side of least drama with regard to ice mass loss associated with relatively warm ocean water beneath such ice shelves, as illustrated by measurements from the Getz Ice Shelf in West Antarctica:

Rippin, D. M.: Significant submarine ice loss from the Getz Ice Shelf, Antarctica, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-163, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-163/
New calving at Getz, short gif at link
http://www.esa.int/spaceinimages/Images/2019/10/B47_breaks_off_Getz_Ice_Shelf