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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #150 on: May 18, 2014, 08:02:00 PM »
The article states in several places that the timescale for the collapse of the Amundsen Sea Embayment, ASE, marine glaciers is difficult to determine, and then goes on to state:

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

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

Focusing on the upper bound 200-yr period is like putting lipstick on a PIG (Pine Island Glacier).
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #151 on: May 18, 2014, 08:41:26 PM »
In my last post I pointed out that focusing on the consideration that it could conceivably take as long as 200-yrs for the ASE glaciers to collapse, rather than on the fact that this period to ASE collapse will almost certainly be shorter (and possibly much shorter), is like putting "Lipstick on a PIG (Pine Island Glacier)".  Indeed, the past 40-yr period considered by the NASA was dominated by many temporary climate change "masking factors", that cannot be counted on to continue for an extended period of time as partially pointed out by Michael Mann in his April 2014 SciAm article: "False Hope: The rate of global temperature rise may have hit a plateau, but a climate crisis still looms in the near future":

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

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

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

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



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

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

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

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

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


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


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


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

To repeat, as currently estimates of "climate sensitivity" do not include this vegetation aerosol precursor negative feedback; in order for Global Circulation Models, GCM's including this negative feedback to match historical records they will need to utilize higher effective "climate sensitivity" values; which should resulting in higher projections of global temperature increase, if plant growth/activity does not keep path with the rate of future greenhouse gas, GHC, emissions.
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steve s

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Re: Potential Collapse Scenario for the WAIS
« Reply #152 on: May 18, 2014, 08:47:54 PM »
ASLR, it's all in the phrasing. Or maybe the timing. Having facts is not the issue; using them is.

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

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

Good deal either way for the ASLR problem's recognition. Doesn't matter that the technical report said the same thing in different words. Previously the time frame could be overlooked by pundits -- not so readily now.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #153 on: May 19, 2014, 12:42:21 AM »
steve s,

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

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

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

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

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

Quote: "Our Highest Scenario is an upper limit for SLR by 2100, but the possibility exists that SLR could exceed this limit beyond this timeframe (Pfeffer et al 2008).
…..
Most of the ice loss in Antarctica has come from the West Antarctic ice sheet (WAIS; Rignot et al. 2008).  A significant portion of the WAIS is floating at or grounded below sea level, as are relatively smaller parts of the ice sheets in East Antarctica and Greenland.  Floating ice shelves support land-based ice sheets. Current and future ocean warming below the surface make ice shelves susceptible to catastrophic collapse, which in turn can trigger increased ice discharge to the ocean (Rignot et al. 2004, Scambos et al. 2004, Jacobs et al. 2011, Joughlin and Alley 2011, Yin et al. 2011).  Better understanding of how the polar ice sheets will respond to further changes in climatic conditions over the 21st century requires continued development of physical models (Price et al. 2011)."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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CraigsIsland

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Re: Potential Collapse Scenario for the WAIS
« Reply #155 on: May 19, 2014, 07:33:55 AM »
steve s,

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

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

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

Best,
ASLR

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

Craig

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #156 on: May 19, 2014, 08:21:49 AM »
Here is an amusing semilog plot of my estimate of time to icesheet collapse as it evolved.

sidd

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #157 on: May 19, 2014, 04:12:47 PM »
sidd,

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

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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steve s

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Re: Potential Collapse Scenario for the WAIS
« Reply #158 on: May 19, 2014, 10:33:09 PM »
Talking of growth rates, anyone want to estimate what year the Thwaites Glacier is going to be recognized as contributing more to SLR than the Pine Island Glacier?

Steve

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #159 on: May 19, 2014, 10:59:18 PM »
steve s,

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

Best,
ASLR
“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 #160 on: May 30, 2014, 01:56:29 AM »
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

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

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

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #161 on: May 30, 2014, 02:16:35 AM »
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

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

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

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #162 on: May 30, 2014, 02:21:57 AM »
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

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

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

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

Abstract: :Current uncertainties in projections of sea-level rise from ice sheets and glaciers are embarrassingly large because we are lacking large-scale, high-resolution models coupled with the ocean, sea ice and the atmosphere, and constrained by massive data assimilation to minimize the impact of unresolved physics. Progress is being made in those directions, however, under the impetus of new remote-sensing observations that reveal rapid, significant changes affecting the outlet glaciers and that help constrain ice-sheet models in a new, effective way; furthermore, high-resolution, higher-order physics ice-sheet models are being developed and applied to ice-sheet-wide problems with encouraging results; ice–ocean–sea-ice–atmosphere coupled models are also starting to emerge; and efforts are made on the remote-sensing side to alleviate our most significant knowledge gaps such as bed topography and ice thickness, and sea-floor bathymetry beneath ice shelves, along glacial fjords and on continental shelves, to name a few. While one might easily argue that ice sheets and glaciers will remain fundamentally unpredictable, I will discuss current progress and frameworks that are likely to provide significant advances in projecting ice-sheet and glacier evolution. A most fundamental aspect of this new framework, however, is that the problem is of a multidisciplinary nature, beyond glaciology."
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #163 on: June 08, 2014, 08:10:27 PM »
The following link leads to a very nice Part 1 summary of the recent research history (from about 1968 to about the late 1990's) on the stability of the WAIS, and which includes a very nice video by NASA about Rignot et al's 2014 research on this topic:

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #164 on: June 09, 2014, 05:46:20 PM »
SkS has a nice commentary on the new Climate Crocks video on WAIS collapse, which has appearances by Archer, Alley, Rignot, Hansen and others.

https://www.skepticalscience.com/new-video-meltwater-pulse-2b.html
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Re: Potential Collapse Scenario for the WAIS
« Reply #165 on: June 09, 2014, 06:30:11 PM »
Very nice video indeed:

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Anne

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Re: Potential Collapse Scenario for the WAIS
« Reply #166 on: June 10, 2014, 07:31:35 PM »
A search on the forum suggests this hasn't been posted before. This from Science Daily suggests that Thwaites Glacier is also subject to variable geothermal heat from below:
Quote
The UTIG researchers had previously used ice-penetrating airborne radar sounding data to image two vast interacting subglacial water systems under Thwaites Glacier. The results from this earlier work on water systems (also published in the Proceedings of the National Academy of Sciences) formed the foundation for the new work, which used the distribution of water beneath the glacier to determine the levels and locations of heat flow.
In each case, Schroeder, who received his Ph.D. in May, used techniques he had developed to pull information out of data collected by the radar developed at UTIG.
According to his findings, the minimum average geothermal heat flow beneath Thwaites Glacier is about 100 milliwatts per square meter, with hotspots over 200 milliwatts per square meter. For comparison, the average heat flow of the Earth's continents is less than 65 milliwatts per square meter.
The presence of water and heat present researchers with significant challenges.
"The combination of variable subglacial geothermal heat flow and the interacting subglacial water system could threaten the stability of Thwaites Glacier in ways that we never before imagined," Schroeder said.
Science Daily report here: Link

Full paper:
Dustin M. Schroeder, Donald D. Blankenship, Duncan A. Young, and Enrica Quartini. Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet. PNAS, June 9, 2014 DOI: 10.1073/pnas.1405184111
http://www.pnas.org/content/early/2014/06/04/1405184111

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #167 on: June 10, 2014, 08:28:15 PM »
Anne,

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

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

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

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

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

Thanks again,
ASLR
« Last Edit: June 10, 2014, 08:43:22 PM by AbruptSLR »
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wili

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Re: Potential Collapse Scenario for the WAIS
« Reply #168 on: June 10, 2014, 08:59:41 PM »
(Please see my question about this on the other thread.)
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #169 on: July 07, 2014, 07:36:48 PM »
Reply #77 in the "Risks and Changes of RCMs for the Southern Ocean" thread (see link below), references recent model results confirming that projected changes in the Southern Hemisphere Westerly winds will bring warm CDW to the grounding lines of many Antarctic marine glaciers, including those in the ASE:

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

Also see (and the associated extract):

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

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

« Last Edit: July 08, 2014, 01:50:40 AM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #170 on: July 23, 2014, 05:49:51 PM »
The following link leads to a further discussion of the Spence et al 2014 findings discussed in Reply #169 (and in the Trends of the Southern Ocean thread):


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

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Re: Potential Collapse Scenario for the WAIS
« Reply #171 on: August 15, 2014, 11:29:33 AM »
Using methodology that is likely to be accepted by IPCC for AR6 (ie meaning very conservative), the linked reference (with a free access PDF) estimates that Antarctica alone may contribute up to 37 cm (14.5 inches) to global seas by 2100; which is more than triple previous IPCC worst-case estimates for a likely Antarctic SLR contribution by 2100 (see attached image).  However, assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5.  While some may view this as an upper bound; I am of the opinion that it more likely represents a lower bound.

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

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

Abstract: "The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02–0.14 m; 90% range: 0.0–0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04–0.21 m; 90% range: 0.01–0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04–0.17 m; 90% range: 0.02–0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets."
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Re: Potential Collapse Scenario for the WAIS
« Reply #172 on: August 21, 2014, 05:41:58 PM »
According to Dr Nancy Bertler, of Victoria University's Antarctic Research Centre, this month, she and her team finished processing ice cores, taken from a depth of 763m at the bottom of the Roosevelt Island, on the eastern limits of the Ross Ice Shelf, as part of the RICE project.  The record contained in the ice was much longer than Dr Bertler had expected, and appeared to stretch back to the critical time in question, where the Ross Ice Shelf last collapsed abruptly.  Hopefully, we should see published findings in a year, or so.

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

http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11310259
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Re: Potential Collapse Scenario for the WAIS
« Reply #173 on: August 25, 2014, 12:15:14 AM »
In the two linked internet articles, Will Thomas presents a historical primer on the coming WAIS collapse.  This excellent primer illustrates just how recent our understanding of the risks of the WAIS collapse, and it is very clear that there is so much more to learn about this risk, that I believe that most of the WAIS collapse will be actively occurring before the researchers have a full understanding of that risk.  Note that in the video of Rignot in the second link, Rignot states that if the ASE marine glaciers keep retreating at their present rate of retreat this portion of the WASI will be actively collapsing within two hundred years; however, the rate of the ASE marine glacier retreat is accelerating, which is why I believe that this portion of the WAIS will be actively collapsing sometime after 2040.


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


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

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Re: Potential Collapse Scenario for the WAIS
« Reply #174 on: August 25, 2014, 12:22:10 AM »
The following link leads to a March 2014 internet article by Bruce Milton, summarizing the nature and risks of abrupt climate change, including a discussion of the risks of a WAIS collapse:

http://truth-out.org/news/item/22469-abrupt-climate-change-no-bioperturbation
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Re: Potential Collapse Scenario for the WAIS
« Reply #175 on: August 28, 2014, 04:25:09 PM »
While I posted about the findings of Weber et al 2014 in the Paleo-Evidence thread (see Reply #119 in the Paleo-Evidence thread), the following link to a New Zealand Herald article shows that the Antarctic Ice Sheet is capable of contributing at least one meter of sea level rise to the global total by 2100:

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


http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11315512
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Re: Potential Collapse Scenario for the WAIS
« Reply #176 on: September 12, 2014, 10:05:15 PM »
The following reference provides a new reconstruction of Antarctic near-surface temperatures from 1958 – 2012 (see also Reply #3); and this reconstruction indicates that the recent positive trend for the SAM (partially due to both the ozone hole and the recent negative [La Nina dominated] phase of the ENSO), has been recently had a cooling effect on West Antarctica; however, I note that as we enter a positive [El Nino dominated] phase of the ENSO, and as the ozone hole heals itself, we can expect an acceleration of the rate of increase of the West Antarctic near-surface temperatures; which of course will serve to accelerate the rate of collapse of the WAIS:


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


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

Abstract: "A reconstruction of Antarctic monthly mean near-surface temperatures spanning 1958–2012 is presented. Its primary goal is to take advantage of a recently revised key temperature record from West Antarctica (Byrd) to shed further light on multidecadal temperature changes in this region. The spatial interpolation relies on a kriging technique aided by spatio-temporal temperature covariances derived from three global reanalyses (ERA-Interim, MERRA, and CFSR). For the full extent of the reconstruction, we find statistically significant annual warming in the Antarctic Peninsula and virtually all of West Antarctica, but no significant temperature change in East Antarctica. Importantly, the warming is of comparable magnitude both in central West Antarctica and in most of the Peninsula, rather than concentrated either in one or the other region as previous reconstructions have suggested. The Transantarctic Mountains act, for the temperature trends, as a clear dividing line between East and West Antarctica, reflecting the topographic constraint on warm air advection from the Amundsen Sea basin. The reconstruction also serves to highlight spurious changes in the 1979–2009 time series of the three reanalyses that reduces the reliability of their trends, illustrating a long-standing issue in high southern latitudes. The study concludes with an examination of the influence of the Southern Annular Mode (SAM) on Antarctic temperature trends. Our results suggest that the trend of the SAM toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in East Antarctica (as already well documented) and but also (only in fall) in West Antarctica."
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Re: Potential Collapse Scenario for the WAIS
« Reply #177 on: September 13, 2014, 01:13:22 AM »
The linked reference, with an open access pdf, indicates that at the moment the grounding line zone for the  Union Glacier (in the WAIS) is in near-equilibrium, but that if the rate of ice mass loss were to accelerate in the future (say due to climate change) then this glacier has the potential for significant grounding line retreat:

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

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #178 on: September 14, 2014, 06:34:49 AM »
Feldmann and Levermann, Postsdam, with the PISM model
pull a plug on one unstable icesheet and you drain more than one ...

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

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

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

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #179 on: September 14, 2014, 08:04:53 AM »
Feldmann and Levermann, Postsdam, with the PISM model
pull a plug on one unstable icesheet and you drain more than one ...

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

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

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

sidd

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

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

The report is inherently conservative and the authors know this.  There is going to be no other last chance for humanity than this next 2 years.
Haiku of Past Futures
My "burning embers"
are not tri-color bar graphs
+3C today

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Re: Potential Collapse Scenario for the WAIS
« Reply #180 on: September 14, 2014, 09:10:54 AM »
DeConto and Pollard write:
"In the most extreme RCP scenarios, subsequent retreat of the Siple Coast margin results in the near-total collapse of the West Antarctic Ice Sheet (WAIS) within a few centuries, followed by retreat into the deep subglacial basins underlying the East Antarctic Ice Sheet (EAIS). Antarctica is shown to contribute up to 9m of sea level rise within the next five centuries. Under such high greenhouse gas conditions, atmospheric warming alone is sufficient to cause substantial ice retreat, without any influence from ocean warming and sub-ice melt. Conversely, in the absence of increasing atmospheric temperatures, very little ocean warming (<0.5 C) is required to trigger substantial WAIS retreat, even if present-day atmospheric temperatures are held constant. Given current rates of ocean heat uptake, this has serious implications for future commitment to sea level rise regardless of future greenhouse gas emissions."

So what are we talking about here? A risk of about maybe 15m total SLR by 2500, including about a 4m contribution from GIS? That would be more than double the current IPCC-worst case based on physical models, and in line with some estimates based on semi-empirical models.

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Re: Potential Collapse Scenario for the WAIS
« Reply #181 on: September 14, 2014, 08:42:47 PM »
I must agree with jai that "pessimistic" is a relative term, and I view both the Feldmann & Levermann, and the DeConto & Pollard, findings as representing lower-bound solutions to the non-stoppable ASLR risks that the world is facing at the moment.

I am deeply concerned that the coming (starting now and accelerating for at least the next 25 to 30-years) synergy between the North Atlantic (due to the AMO), and the North Pacific (due to the PDO/IPO), Oceans (see the "Forcing" thread); will guarantee an acceleration of both mean global warming, and SLR contribution from the WAIS, over the coming decades.
« Last Edit: September 15, 2014, 04:13:26 AM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #182 on: September 14, 2014, 11:51:34 PM »
"The IPCC is self censoring ..."

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

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

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #183 on: September 15, 2014, 04:31:23 AM »
All,

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

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

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

Best,
ASLR
« Last Edit: September 15, 2014, 04:45:39 AM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #184 on: September 21, 2014, 05:33:50 PM »
I felt bad that I requested that jai provide logical evidence that the IPCC was biased, if he was going to state as much in this thread, and then I stated that I believe that the IPCC (and most scientist) err on the side of least drama, without providing any logical supporting evidence.

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

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

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

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

See also:

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

&

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #185 on: October 05, 2014, 03:32:17 PM »
While not new, I thought that I would provide the following link to the National Academy of Sciences, NAS, website on their 2013 report on abrupt climate change, which includes the attached image indicating that a partial collapse of the WAIS is plausible this century and that if it did it could triple the current projections for SLR by 2100 to roughly over 3m.

http://nas-sites.org/americasclimatechoices/other-reports-on-climate-change/2013-2/abrupt-impacts-of-climate-change/
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Re: Potential Collapse Scenario for the WAIS
« Reply #186 on: October 05, 2014, 03:52:10 PM »
While the linked GOCE ice mass loss findings issued by the ESA (see the following link) was discussed in the PIG/Thwaites 2012 - 2040-2060 thread, I think that it is good to post in this thread as this findings are key to the potential collapse of the WAIS.

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

Furthermore, I note that the ESA is now working to extend the GOCE to the entire Antarctic continent, and as indicated by the attached Cryosat plot, it is likely that the extended GOCE study will find significant ice mass loss near the Totten Glacier in the EAIS.
« Last Edit: October 08, 2014, 01:08:31 PM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #187 on: November 02, 2014, 01:56:13 AM »
While I have previously posted about the following reference (when it was published in the Spring of 2014), the following provides a link to an open access pdf, and I provide the four attached images from this reference.  The first image provides a table of ice flux for the years and ASE marine glaciers listed.  This table indicates that the total annual ice flux from the ASE is comparable to the annual ice mass loss from the Greenland Ice Sheet (see the following link and extract to the Arctic Report Card Update for 2013: Greenland Ice Sheet).  The second attached image graphically shows the individual and total ice fluxes from the ASE marine glaciers; indicating that the flux from Thwaites Glacier is continuing accelerate, while the other marine glaciers have temporarily plateaued (possible due to the recent La Nina and ENSO neutral conditions).  The third and fourth attached images show different representations of the ice velocities for these marine glaciers (as noted on the images).  Again, I am concerned that a strong El Nino in 2015 could trigger an acceleration of ice flux from all of the ASE marine glaciers (but particularly from the PIG and the Thwaites Glacier):

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

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

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

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

Extract: "From the end of April 2012 through the end of April 2013, which corresponds reasonably well to the period between the beginning of the 2012 and 2013 melt seasons, the cumulative ice sheet loss was 570 Gt, over twice the average annual loss rate of 260 Gt y-1 during 2003-2012. The 2012-2013 mass loss is the largest annual loss rate for Greenland in the GRACE record, mostly reflecting the large mass loss during the summer of 2012 (Tedesco et al. 2013b). "
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #188 on: January 02, 2015, 02:34:43 AM »
Nice talk and simulation of potential collapse of WAIS by Tony Payne of University of Bristol, starting with the simulation at 30m41s:
http://youtu.be/NXjYpilWtQs?t=30m41s

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

But Payne shows earlier in the talk how much this apparent stability of the glaciers in models depends on the resolution of these models. So I don't know what forcing scenario was used in this particular simulation, but it had a mixed resolution with 150m per grid cell as the highest. What would happen with even higher resolution? And how complete are these models apart from the resolution?
« Last Edit: January 02, 2015, 02:49:03 AM by Lennart van der Linde »

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #189 on: January 02, 2015, 03:48:45 AM »
Lennart,

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

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

Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #190 on: January 02, 2015, 11:07:10 AM »
ASLR,
Yes, as a matter of fact I asked Rignot what he thinks of this simulation and he thinks it's still quite limited. He said this model is no better than the others. It is intrinsically very difficult for such models to collapse an ice sheet quickly: no calving, no melt at the grounding line, no 3D treatment of the grounding line, and bed with erroneous mountain peaks that should not be there.

I'll also ask Richard Alley what he thinks of it. He said earlier he has two papers on Thwaites coming out soon, in the coming week, together with Pollard and DeConto.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #191 on: January 03, 2015, 05:05:45 PM »
Lennart,

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

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

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

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

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

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

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

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

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

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

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

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


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

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

Abstract: "A hybrid ice sheet-shelf model with freely migrating grounding lines is improved by accounting for 1) surface meltwater enhancement of ice shelf calving; and 2) the structural stability of thick (>800 m), marine-terminating (tidewater) grounding lines. When coupled to a high-resolution atmospheric model with imposed or simulated ocean temperatures, the new model is demonstrated to do a good job simulating past geologic intervals with high (albeit uncertain) sea levels including the Pliocene (3Ma; +20 ±10m) and the Last Interglacial (130-115ka; +4-9m).  When applied to future IPCC CMIP5 RCP greenhouse gas forcing scenarios with ocean temperatures provided by the NCAR CCSM4, the same model shows the potential for massive ice and freshwater discharge beginning in the second half of this century. In both RCP2.6 and 8.5 scenarios considerable retreat begins in the Pine Island Bay region of West Antarctica. In the more aggressive (and arguably more likely) RCP8.5 scenario, Pine Island Bay retreat is followed by more massive retreat of the entire WAIS, and eventual ice retreat into deep East Antarctic basins. During peak rates of retreat, freshwater discharge exceeds 1 Sv and exceeds 0.2 Sv for several centuries with potential to disrupt ocean circulation in addition to contributing between 2m and 9m sea level rise within the next 500 years. Here, we demonstrate that large portions of the Antarctic Ice Sheet (in West and East Antarctica) can retreat on relatively short (decadal to centennial) timescales, posing a serious threat to global populations."
« Last Edit: January 28, 2015, 08:49:07 PM by AbruptSLR »
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #193 on: January 03, 2015, 11:36:14 PM »
ASLR,

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

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

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

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

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

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

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

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

But maybe thery're all just more cautious or reticent or conservative than Hansen and Wanless?

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Re: Potential Collapse Scenario for the WAIS
« Reply #194 on: January 04, 2015, 12:00:26 AM »
Lennart,

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

Best,
ASLR
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Re: Potential Collapse Scenario for the WAIS
« Reply #195 on: January 04, 2015, 12:38:20 AM »
ASLR,

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

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

Interesting times, with plenty of reason for concern.

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Re: Potential Collapse Scenario for the WAIS
« Reply #196 on: January 04, 2015, 02:09:28 AM »
ASLR,

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

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

Interesting times, with plenty of reason for concern.

Lennart,

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

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

Best,
ASLR

Edit: I fixed a math error
« Last Edit: January 04, 2015, 02:26:04 AM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #197 on: January 04, 2015, 07:43:39 AM »
ooo, tanx, bassis was the paper i could not recall in the other thread

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #198 on: January 04, 2015, 10:07:57 AM »
as sea level rise due to melting glaciers is about ~ 0.01 Sv, and as glaciers currently contribute about 0.71mm/year to SLR; thus the peak 1.0 Sv discharge that DeConto & Pollard 2014 cite is equal to a rate of SLR of about 0.071meters per year, or about 1/30th the rate that Jackson cited.

ALSR,

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #199 on: January 04, 2015, 11:19:39 AM »
Lennart,

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

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

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

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

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