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Author Topic: Potential Collapse Scenario for the WAIS  (Read 179250 times)

wili

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Re: Potential Collapse Scenario for the WAIS
« Reply #100 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)?
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #101 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://piecubed.co.uk/2013/05/31/ice-melt/

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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #102 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #103 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #104 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #105 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #106 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

"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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #107 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).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #108 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

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Re: Potential Collapse Scenario for the WAIS
« Reply #109 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

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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #110 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

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Re: Potential Collapse Scenario for the WAIS
« Reply #111 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #112 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

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."
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #113 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


"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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #114 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.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #115 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

nukefix

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Re: Potential Collapse Scenario for the WAIS
« Reply #116 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.
« Last Edit: August 29, 2013, 06:28:57 PM by nukefix »

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #117 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

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #118 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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

JimD

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Re: Potential Collapse Scenario for the WAIS
« Reply #119 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. 
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

How is it conceivable that all our technological progress - our very civilization - is like the axe in the hand of the pathological criminal? Albert Einstein

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #120 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

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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #121 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/

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Andreas T

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Re: Potential Collapse Scenario for the WAIS
« Reply #122 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

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
from what depth are these sediment cores and how do they resolve such a large area?

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #123 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
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Re: Potential Collapse Scenario for the WAIS
« Reply #124 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/

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.

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #125 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]

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Re: Potential Collapse Scenario for the WAIS
« Reply #126 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

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Re: Potential Collapse Scenario for the WAIS
« Reply #127 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://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."
« Last Edit: January 15, 2014, 05:47:23 AM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #128 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
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Re: Potential Collapse Scenario for the WAIS
« Reply #129 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.
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Re: Potential Collapse Scenario for the WAIS
« Reply #130 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/

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."
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #131 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
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #132 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

"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."
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #133 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
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Re: Potential Collapse Scenario for the WAIS
« Reply #134 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

Scientists Warn of Rising Oceans as Antarctic Ice Melts

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?
« Last Edit: May 12, 2014, 08:57:25 PM by wili »
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #135 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

"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

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
« Last Edit: May 13, 2014, 02:02:15 AM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #136 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

"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."

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #137 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

TeaPotty

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Re: Potential Collapse Scenario for the WAIS
« Reply #138 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...

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Re: Potential Collapse Scenario for the WAIS
« Reply #139 on: May 15, 2014, 09:13:24 AM »
Revkin is a shill, and dotearth is a sewer. Excuse me for being frank.

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #140 on: May 15, 2014, 03:21:59 PM »
I tweeted him and told him he deserves imprisonment:
https://twitter.com/Tea_Potty/status/466206140809101312
« Last Edit: May 15, 2014, 04:43:16 PM by TeaPotty »

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Re: Potential Collapse Scenario for the WAIS
« Reply #141 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


(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
« Last Edit: May 15, 2014, 10:32:46 PM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #142 on: May 15, 2014, 10:09:10 PM »
Thanks, ASLR. And yes, all those points do bear repeating.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

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Re: Potential Collapse Scenario for the WAIS
« Reply #143 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.

The ice was here, the ice was there,   
The ice was all around:
It crack'd and growl'd, and roar'd and howl'd,   
Like noises in a swound!
  Rime of the Ancient Mariner by Samuel Taylor Coleridge

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #144 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #145 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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Clare

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Re: Potential Collapse Scenario for the WAIS
« Reply #146 on: May 18, 2014, 03:14:41 AM »
This week:
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

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #147 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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

idunno

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Re: Potential Collapse Scenario for the WAIS
« Reply #148 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

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

steve s

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Re: Potential Collapse Scenario for the WAIS
« Reply #149 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?