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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #300 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/

"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"

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #301 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #302 on: January 26, 2015, 09:02:07 PM »
Eric Rignot on scientific conservatism and the inevitable collapse of WAIS:


Timescales, timescales...

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #303 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

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.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #304 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/

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.

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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #305 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

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.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #306 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


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

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."
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #307 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.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #308 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.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #309 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

See also:
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
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LRC1962

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Re: Potential Collapse Scenario for the WAIS
« Reply #310 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.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #311 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
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #312 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).
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S.Pansa

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Re: Potential Collapse Scenario for the WAIS
« Reply #313 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 (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 on Science Daily.

Edit: Thanks AbruptSLR, just recognized my mess ::) Links should work now.
« Last Edit: March 11, 2015, 04:16:12 PM by S.Pansa »

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #314 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

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

Best,
ASLR
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Re: Potential Collapse Scenario for the WAIS
« Reply #315 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

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Re: Potential Collapse Scenario for the WAIS
« Reply #316 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

We need more of these.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #317 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
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #318 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

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."
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Re: Potential Collapse Scenario for the WAIS
« Reply #319 on: March 20, 2015, 03:16:40 PM »
Lennart van der Linde, the video linked in #315 needs a password.

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Re: Potential Collapse Scenario for the WAIS
« Reply #320 on: March 20, 2015, 05:23:02 PM »
Lisa, I don't have it, it was public when I posted it, sorry  :-\

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Re: Potential Collapse Scenario for the WAIS
« Reply #321 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.


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Re: Potential Collapse Scenario for the WAIS
« Reply #322 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

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

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
« Last Edit: March 26, 2015, 10:05:48 PM by AbruptSLR »
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #323 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)


AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #324 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

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
« Last Edit: April 16, 2015, 05:16:26 AM by AbruptSLR »
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #325 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

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Re: Potential Collapse Scenario for the WAIS
« Reply #326 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

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.

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Re: Potential Collapse Scenario for the WAIS
« Reply #327 on: April 16, 2015, 07:50:49 PM »
In that Payne video, you can really see how PIG triggers Thwaites

Iceismylife

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Re: Potential Collapse Scenario for the WAIS
« Reply #328 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.



Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #329 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

We can now also look at Rohling et al 2013:
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.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #330 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

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."

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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #331 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



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Re: Potential Collapse Scenario for the WAIS
« Reply #332 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

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
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Iceismylife

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Re: Potential Collapse Scenario for the WAIS
« Reply #333 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.)
« Last Edit: April 22, 2015, 10:54:20 PM by Iceismylife »

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #334 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?
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Richard Rathbone

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Re: Potential Collapse Scenario for the WAIS
« Reply #335 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.


Jim Hunt

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Re: Potential Collapse Scenario for the WAIS
« Reply #336 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

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.
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #337 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?
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Iceismylife

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Re: Potential Collapse Scenario for the WAIS
« Reply #338 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?

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 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.

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #339 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

Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #340 on: April 23, 2015, 08:45:07 PM »
100 cm/yr

I suppose you mean 10 cm/yr, for 10 meter/century?

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #341 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

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

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
« Last Edit: April 24, 2015, 01:59:15 AM by AbruptSLR »
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #342 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

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #343 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.

solartim27

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Re: Potential Collapse Scenario for the WAIS
« Reply #344 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.
FNORD

oren

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Re: Potential Collapse Scenario for the WAIS
« Reply #345 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.

steve s

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Re: Potential Collapse Scenario for the WAIS
« Reply #346 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.

Richard Rathbone

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Re: Potential Collapse Scenario for the WAIS
« Reply #347 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?

Richard Rathbone

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Re: Potential Collapse Scenario for the WAIS
« Reply #348 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.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #349 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson