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Author Topic: Potential Collapse Scenario for the WAIS  (Read 179251 times)

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #50 on: March 11, 2013, 11:20:39 PM »
Bruce,

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

“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 #51 on: March 12, 2013, 12:08:22 AM »
Bruce,

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

26th International Forum for Research into Ice Shelf Processes - FRISP -
June 12- 14, 2012
Utö Värdshus
Stockholm Archipelago, Sweden
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Bruce Steele

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Re: Potential Collapse Scenario for the WAIS
« Reply #52 on: March 12, 2013, 07:17:42 AM »
ASLR, the Purkey paper gets into more detail on the AABW reduction. Purkey et al 2012 shows an 8 SV drop in the volume of water colder than 0 degrees C. Also " the water-mass freshening of AABW in the Indian and Pacific sectors is equivalent to roughly half the recent mass loss of the WAIS."    A lot to read and absorb but it backs up much of your thread. Warmer and fresher water just doesn't sink the way it used to and warmer CDW being pushed onto the shelf is undercutting the base of the ice . It took me awhile to get a grip on the arctic topography and currents. Learning which areas of the Antarctic have sills that trap saline waters during seasonal sea ice freeze-up will be something I need to better understand. Thanks again for all your work. If I read correctly you have concentrated on the Antarctic for < 5 years, I have been trying to study carbonate chemistry for 9 years . It takes about 100,000 years for terrestrially  supplied alkalinity to rebalance large perturbations in the pH balance of the worlds oceans . I saw a graph of former ice sheet collapse events in deep time, it looks like the time it takes for the ice sheets to rebound after a collapse is also in the 100,000 year range. Just speculating ,there may be a connection.       

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #53 on: March 12, 2013, 02:08:54 PM »
Bruce,

I agree that Purkey et al 2012 is a great reference, and I agree that getting to understand the Antarctic ocean, atmosphere, bathymetry, ice, topology, feedbacks, boundary conditions, and forcing functions is complicated, and non-stationary, and takes time (note that I am a full-time civil engineering and have only been looking at the Antarctic in my spare time for the past year and a half; which has the advantage that I have been focusing on primarily the most recent research available on the internet).  As I feel that I have not provided adequate discussion about the complex ocean/ice interactions/mechanisms for my postulated collapse scenario the FRIS and RIS I plan to open another thread soon to focus on this important matter (which is quite different from the collapse scenario for the Bellingshausen/Amundsen Sea marine ice sheets).
« Last Edit: May 30, 2013, 03:36:51 PM by AbruptSLR »
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #54 on: March 13, 2013, 12:49:54 AM »
As I decided that the information that I provide regarding Antarctic methane hydrates seem inadequate I provide the following abstract from Potential methane reservoirs beneath Antarctica by Wadham et al 2012:
"Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 1015 g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage."

Also an internet article states:

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

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

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

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

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

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

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


“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 #57 on: May 05, 2013, 08:59:04 PM »
I thought that I would post this image from: Reconstructions before rifting and drifting reveal the geological connections between Antarctica and its conjugates in Gondwanaland, by J.J. Veevers, Earth-Science Reviews, Volume 111, Issues 3–4, March 2012, Pages 249–318;
because it indicates how complex the tectonics are for the West Antarctic, which could activate both earthquakes and volcanic action with sufficient ice mass loss from the WAIS.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #58 on: May 14, 2013, 08:05:26 PM »
I thought that I would post the first attached image to should how significant the isostatic rebound would be for the Antarctic if all the ice were to melt, as compared to the second image showing the current bed elevations (per BedMap2).  Note that as most all of this rebound occurs underwater, it contibutes directly to the observed sea level of the future.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #59 on: May 30, 2013, 03:35:22 PM »
I have commented repeatedly about the need to both update and augment the GCM projections about the risks of abrupt SLR primarily from the potential collapse of the WAIS this century, to include both the most recent observations and to include consideration of factors not addressed within the traditional methodology adopted by the IPCC for projecting the risks of SLR (abrupt or otherwise).

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

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

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

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

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

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

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

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

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

The fourth attached image presents the joint probability distributions for these eleven key parameters/mechanisms used in the MAGICC analyses.  Per Bodman et al 2013: "Joint distribution of the eleven key MAGICC parameters used with the MCMH algorithm. The diagonal elements show the histograms for the individual prior (black line) and posterior (shaded region) distributions. The off–diagonal contour plots indicate the joint marginal distributions between any pair of these parameters."
As I have run out of time and space, I will conclude by saying that Bodman et al's 2013 findings should be updated to include the risks associated with such possible forcing functions as: (a) Arctic Sea Ice "albedo flip", (b) recent black carbon findings; (c) the risks of wildfires in the Arctic permafrost regions; (d) natural and hydro-fracking related releases of methane; (d) see other factors discussed in the "Forcing" thread.  Again in subsequent posts I will present discussions using Event Tree (Fault Tree) and MCMC (or MCMH) analyses related to the risks of abrupt SLR (which is a different approach than that used by the RAND Corps and PennState; which I presented/discussed previously).
« Last Edit: May 30, 2013, 03:40:33 PM by AbruptSLR »
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Laurent

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Re: Potential Collapse Scenario for the WAIS
« Reply #60 on: May 30, 2013, 04:14:22 PM »
When you say iso-static rebound, you mean that while the Antarctic will loose some weigh, it will also go up because lighter...if what i understand is correct then, that should be added to the volume of ice that will sent away to increase the sea level rise. Have you an estimate of that volume of sea water added ? should be around 63 meter + something ?

Thanks AbruptSLR

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #61 on: May 30, 2013, 04:39:45 PM »
Laurent,

The iso-static rebound will vary across the WAIS area depending on the local conditions, varying from a few 10's of meters to several hundreds of meters (eventually).  The images that I posted on page 1 of this 2 page thread from Vaughan et al 2011 provides a dotted line along several different cross-sections through the WAIS area that show the various potential iso-static rebounds.  Also, to the degree that the magma causing the rebound flows out from under adjoining landmasses (such as the EAIS) rather than the adjoining seafloor, then yes this rebound will clearly add (eventually) to SLR.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #62 on: May 30, 2013, 04:41:33 PM »
Before I leave the topic of updating forcing input for ice mass loss, I would like to note here that all of the GCM's have been calibrated to match the scientific community's prior understanding of paleo-responses during previous interglacial period; however, recent new paleo-evidence (eg see the "WAIS Divide" borehole thread and the Arctic Sea Ice Blog discussion of the Lake El'gygytgyn boreholes) indicates that the earth system responses in the past exhibited short periods of abrupt climate change; to which the GCMs (ESMs) need to be recalibrated.  Furthermore, the WAIS Divide core demonstrates that the WAIS was absent during the Eemian (MIS 5e) period, and the following 2013 summary about the Lake El'gygytgyn ice cores indicates multiple times when the WAIS was absent during "super interglacials"; and the GCMs (ESMs) need to be re-calibrated to match these finding of periods when the WAIS was absent in the past.

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #63 on: May 30, 2013, 05:33:50 PM »
If the west Antarctic Ice shelve wasn't were in the Eemian (-130.000 year), it wasn't were with a CO2 level of 300 ppm (or not far) !? Do you confirm ?
« Last Edit: May 30, 2013, 07:33:30 PM by Laurent »

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #64 on: May 31, 2013, 01:57:02 AM »
Laurent,

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

Best,
ASLR
“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 #65 on: May 31, 2013, 02:48:04 AM »
Laurent,

To expand slightly on my last post, attached please find two attached images from a 2011 article by Steve Brown comparing the Eemian to the Holocene>
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sg_smith

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Re: Potential Collapse Scenario for the WAIS
« Reply #66 on: May 31, 2013, 07:35:45 AM »
Hi,

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

Cheers

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #67 on: May 31, 2013, 04:55:52 PM »
sg_smith,

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

Best,
ASLR
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #68 on: May 31, 2013, 04:57:50 PM »
Before I redirect my posts to ice mass loss accounting, I would like to make another post about the risk of climate change forcing from wildfires in the newly defrosting permafrost regions, or Tundra.  As I previously posted, James Hansen has reported that recent biomass growth (largely in the Tundra, see the first attached figure) has temporarily slowed some of the recently observed vs. the GCM projected increases in mean global temperature.  I (and many others) have also reported that this biomass growth is decreasing the local (northern land areas) albedo resulting in earlier snow melts in the Tundra.  But James Hansen has called this temporary increase in CO2 sequestration in biomass a Faustian Bargain; as this CO2 will likely be released as global temperatures continue to increase as indicated by the last three attached images  (related to the risks of wildfires releasing this temporarily biomass sequestered CO2) from:

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

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

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

The fourth attached image show the risk of actual biomass loss to wildfires; which highlights the risk from the Tundra in the future, not only from increased CO2 emissions but also from future enhanced degradation of the permafrost and the future enhanced emissions of black carbon into the particularly sensitive northern areas.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #69 on: June 01, 2013, 07:41:47 PM »
In a prior post in this thread, I suggested that it would be good for researchers to re-calibrate their GCM ice mass loss projections to reconsider recent new paleo-evidence that the WAIS is less stable than was generally thought even one or two years ago.  While I am unaware that such an exercise has performed focused on the WAIS; I am aware of such an exercise that was recently performed focused on the GIS (or GrIS, for Greenland Ice Sheet) findings of which were published in:
Quantification of the Greenland ice sheet contribution to Last Interglacial sea level rise, E. J. Stone, D. J. Lunt, J. D. Annan, and J. C. Hargreaves; Clim. Past, 9, 621–639, 2013 www.clim-past.net/9/621/2013/; doi:10.5194/cp-9-621-2013

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


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

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

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

As a side note: while I have recently stated that the Eemian (or MIS 5e, or Last Interglacial [LIG]) is not the best interglacial to calibrate to (in the paleo-evidence thread I suggest that calibrating to the Holsteinian may be more appropriate), still there is a lot more paleo-evidence available for the Eemian period (such as from the NEEM ice core project) and calibrating GCM projections to the Eemian is very instructive; as is indicated by the conclusions that the AIS contribution to eustatic SLR during the Eemian (LIG) was substantial; which implies that the current risk of abrupt SLR contribution for the WAIS is more significant that was appreciated as recently as two years ago.
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Re: Potential Collapse Scenario for the WAIS
« Reply #70 on: June 01, 2013, 08:47:35 PM »
While perhaps I should have posted the information in the "Antarctic Peninsula" thread; I am posting it here because I believe that this evaluation of potential Antarctic Peninsula Ice Sheet, APIS, contribution to SLR is very relevant to methodology for updating the risk of abrupt SLR contribution from the WAIS this century:

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

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

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

In subsequent posts I expect to eventually provide meaningful discussion of how decision makers can use related methodology to evaluate the risks of abrupt SLR contributions from the WAIS by 2100 in order to correct for obvious short-coming in current GCM SLR projections.
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Re: Potential Collapse Scenario for the WAIS
« Reply #71 on: June 02, 2013, 05:31:00 AM »
Again, before proceeding to posts about methodology for clarifying the risk of abrupt sea level rise, I would like to point out regarding the following research that: (a) as the new research indicates that the SLR contribution from mountain glaciers and ice caps is lower than previously feared; this implies that more of the observed SLR from 2003 to 2009 came from ice sheets than some researchers previously thought; and (b) the ice mass loss mechanism from relative small mountain glaciers and ice caps is different from that for ice sheets, so the fact that ice mass loss from mountain glaciers and ice caps is less than some researchers previously feared, is not evidence that future ice mass loss from ice sheets will not increase non-linearly from current levels.

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

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

Also, the following related summary is from:

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

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

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

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

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

The study was published Thursday in the journal Science.

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

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

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

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

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

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

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

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

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

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

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

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

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

Furthermore, my scenario based engineering hazard assessments, SBEHAs, will focus on the physical credibility/probability of the hazard scenarios considered; and well as in presenting the findings in a format useful to the engineers who need to deal with the SLR hazards identified.  In this regard, it is valuable to note that currently scientist (including IPCC researchers) discretely cite disclaimers for factors not considered in their analysis; and currently policy makers frequently pass along these uncertainties to engineers, without clarifying how to address these hazardous uncertainties.
As an indication of need/appropriateness of this type of SBEHA I present the fourth attached image from:
Expert judgement assessment: Quantifying uncertainty on thin ice;
R. M. Cooke; 2013, Nature Climate Change; 3,311–312; doi:10.1038/nclimate1860
In this fourth image, experts and combined experts present 5th, 50th and 95th CL percentiles for the contribution of the West Antarctic Ice Sheet (WAIS) to SLR in 2100 (in mm/yr), elicited in 2010 (blue) and 2012 (red). M indicates that the expert is a modeler, and O denotes observationalist. Triangles represent individual expert estimates, rectangles indicate self and equal weights (filled and open rectangles, respectively) and circles show performance-based weighting.  This figure indicates that in only 2-years almost all of the experts increased their assessments of SLR contributions from the WAIS, with one modeler increasing his 95% CL from under 7 mm/yr to about 30 mm/yr.  I can assure the readers that this incremental upward creep in expert assessment of WAIS SLR contribution will continue for two to three more decades, as more evidence becomes available.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Potential Collapse Scenario for the WAIS
« Reply #73 on: June 03, 2013, 02:36:17 AM »
NOAA's advice to decision makers from the website linked below is: "So do you want a conservative or liberal sea level rise scenario?  Choose wisely.  Unfortunately you will have to wait until 2100 to see if you were right."

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

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

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

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

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #74 on: June 03, 2013, 05:14:44 AM »
Gardner(2013) at 549 GT/yr total ice mass loss for 2003-2009 is outstripped by reality. Mass waste from GIS _alone_ was 574GT in 2012.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #75 on: June 09, 2013, 06:17:19 PM »
Sidd,

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

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

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

Best, ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Potential Collapse Scenario for the WAIS
« Reply #76 on: June 09, 2013, 06:28:06 PM »
In the way of food for thought, I present the attached image from:

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

This report/image finds that the Filchner Ronne Ice Shelf, FRIS, is particularly at risk of collapse circa 2150 (due to high rates of base ice melting by that time).  However, the user of such information should make allowances for considerations such as: (a) the ice2sea model assumed a constant ice shelf area (which is non-conservative from a safety point of view); (b) the ice2sea model does not include the possible effects of the Larsen C ice shelf collapsing soon and changing the local weather patterns; (c) the influence of the warm spur of CDW entering the Weddell Gyre which currently being directed beneath the FRIS via the Filchner Trough; and (d) the model that ice2sea is using cannot accommodate abrupt changes and thus is incapable of providing any guidance on the risk that the FRIS might collapse prior to 2100.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Potential Collapse Scenario for the WAIS
« Reply #77 on: June 10, 2013, 04:25:10 PM »
In my June 3rd, 2:36am, post I state that:

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

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

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

Nevertheless, in my over 500 posts I have identified numerous forcing mechanisms for future ice mass loss that could (for at least the next one years) result in such non-linear ice mass loss, that it could well dominate the ice mass gain from snowfall over that time period.  Therefore, I will try to quantify the non-linear ice mass loss mechanisms that I am most concerned about, and possible scenarios (for timing and feed-back mechanisms with other trends); which could be useful (in a Bayesian Learning sense) to help decision makers to include these abrupt forcing mechanism within their threshold of recognized risk.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Potential Collapse Scenario for the WAIS
« Reply #78 on: June 12, 2013, 03:23:46 PM »
Of the potential sources of non-linear contributions to SLR, certainly that potentially coming from the Thwaities Glacier is perhaps the source that concerns knowledgeable researchers the most.  Therefore, I present the following abstract on this topic, from:

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

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

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

1.  As discussed in the "Surge" thread it appears that the possible subglacial cavity in the Thwaites trough identified by Tinto & Bell 2011 was at least infilled by glacial ice when the fall of 2012 surge of the local ice stream occurred, which formed a new section of the Thwaites Ice Tongue.
2.  The first attached image re-posted from MacGregor et al 2012, summarizes the evolution of the recent history of the ASE coastline; and indicates that the Thwaites Ice Tongue has historically sustained a number of surges of the local ice stream out through the Thwaites trough.  This image indicates that the last surge (prior to 2012) possibly occurred in 2002 (when iceberg B-22 broke away from the Thwaites Ice Tongue).  If so this implies that the advective process in the Thwaites trough may be so active as to form a sufficiently large subglacial cavity to trigger a surge (due to the local reduction in basal friction) within a nominally 10-year period (from 2002 to 2012 during the El Nino hiatus period).
3.  With continued warming and expansion of the warm CDW in the ACC, and the likely end of the El Nino hiatus period, shortly, the advective process within the Thwaites trough may accelerate, that could lead to another local ice stream surge in less than ten years.
4.  Each new local ice stream surge (through the Thwaites trough) thins the local ice thickness, which could lead to accelerated: (a) local calving of the ice face; (b) ice flow velocity, resulting in more thinning; and (b) grounding line retreat down the trough due to the ease of local floatation.
5.  As discussed in the "PIG-Thwaites 2012-2060" thread, once the groundling line retreats sufficiently southward along the Thwaite trough it should intercept a sub-glacial lake on the northside of a submerged mount in the Thwaites gateway, that could then facilate the un-pinning of the Thwaites Glacier.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Potential Collapse Scenario for the WAIS
« Reply #80 on: June 14, 2013, 01:22:34 AM »
In my previous post I mentioned that ocean water advection could effective un-pin the Thwaites Glacier in the next ten or more years.  Once it is un-pinned, I believe that it could initially behave somewhat like what has been observed for the Jakobshavn Glacier in Greenland for the past ten to fifteen years.  In this regard the following abstract about the Jakobshavn Effect (or mechanism for glacial grounding line retreat acceleration), the authors find that softening of the basal ice near the leading face of the Jakobshavn Glacier, and both due to ocean warming, increased basal friction heat, and the measured high basal melt rate for the Thwaites Glacier, I believe that the Thwaites Glacier could also accelerate due to basal ice softening, once it is un-pinned:

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

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


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

(a) as the ice thins in the gateway due to both: (i) spreading from ice flow and ice surges; and (ii) advective re-formation of a subglacial cavity (particularly in the trough); the leading edge can become subject to floatation on high tides, which can circulate warm CDW beneath the ice stream form some distance (a kilometer or more); which can progressively soften the basal ice in the leading edge area, which can promote a Jakobshavn Effect.
(b) the mechanism cited in item (a) could become much more significant if the advectively re-formed subglacial cavity in the trough extends (in 5 to 10 years) to intercept the subglacial lake at the northern side of the submerged mount in the middle of the Thwaites gateway (which divides the western and eastern ice streams in the Thwaites gateway, see the "Surge" thread.
(c) once the Jakobshavn Effect is established I have speculated that it could progress into what I have called the Thwaites Effect (see the PIG-Thwaites 2012-2060" thread); where the ice stream velocities in the Thwaites gateway could become several times that that has been recorded for the Jakobshavn Glacier (see the first attached image from Van der Veen et al 2011, and the second image comparing Thwaites to Jakobshavn Glacier).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Potential Collapse Scenario for the WAIS
« Reply #83 on: June 15, 2013, 01:56:38 AM »
Other non-linear interactions not accounted for in NRC 2012 that should be considered with regards to ice mass loss from the Thwaites Glacier include:

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

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

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

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

(5) For the period from 2050 to 2070, the TG groundling line retreats are assumed to accelerate by an additional factor of 3.0 (above the 2050 rate) as follows: 1.7 (Jakobshavn Effect)x1.1 (CDW temp rise effect)x1.1(Zwally Effect)x1.1(basal meltwater increase effect)x1.1(storm activity effect)x 1.1 (albedo effect) x 1.1(methane hydrate emission effect) = 3.0.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Potential Collapse Scenario for the WAIS
« Reply #84 on: June 16, 2013, 05:44:33 PM »
The following 2013 abstract helps to frame the risks that as we exist the current El Nino hiatus period, with regard to the risk that a series of strong El Nino events could accelerate the introduction of warm CDW into the ASE, thereby accelerating ice mass loss from this area, and inparticular from the Thwaites Glacier Basin.  I have underlined key sentences/phrase for emphasis:

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

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #86 on: June 17, 2013, 03:07:09 AM »
Sidd,

Thanks for keeping people thinking about the risk of SLR contributions from the EAIS, and I agree that these EAIS areas appear to currently be very active as indicated by the attached image from Purkey and Johnson 2013 which shows a large amount of "Water Mass" largely due to ice shelf meltwater; which when combined with the local AABW warming results in a relatively high rate of local (Southern Ocean) SLR which further helps to promote grounding line retreat for grounded glaciers in these areas (particularly in the EAIS).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Potential Collapse Scenario for the WAIS
« Reply #87 on: June 18, 2013, 01:58:24 AM »
In order to emphasize my point that coming El Nino events present at rise for future accelerated ice mass loss from glaciers around the the ASE I present the attached image from:  CentralWest Antarctica among most rapidly warming regions on Earth - Supplementary Information, in: Nature Geoscience; DOI: 10.1038/NGEO1671

In this image the black star represents the location of the Byrd Station temperature reading that indicate that the surface temperatures during the indicated DJF 1997-1998 El Nino event were highest measured readings since recordings began in 1957.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Potential Collapse Scenario for the WAIS
« Reply #88 on: June 25, 2013, 05:17:24 PM »
The following abstract from SCAR 2012 Session 7, supports the position that the Thwaites Glacier could retreat at least one hundred kilometers this century:

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

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

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

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

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #92 on: July 07, 2013, 06:36:50 AM »
Lots here after about minute 32 on Arctic dynamics from Alley:

climatestate.com/2013/07/06/state-of-the-climate-system-2013-by-richard-alley/
"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 #93 on: July 07, 2013, 06:00:04 PM »
Sidd,

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

Wili,

Thanks for the link to the Alley lecture, his thinking seem to fall right in line with everything that I am posting on risks of ASLR from the WAIS; as noted by the fact that Alley is a co-author in both the papers that I cite in my replies #78 and 88 in this thread regarding papers by Parizek et al 2013 and Christianson et al 2013; both of which cite some of the latest research on the significant risk of the Thwaites Glacier ice mass loss accelerating rapidly once the warm ocean water un-pins the current choke point in the Thwaites Gateway area (particularly for for scenarios equal to, or above RCP 8.5 50%CL, which we are currently exceeding).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

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Re: Potential Collapse Scenario for the WAIS
« Reply #94 on: July 07, 2013, 06:02:51 PM »
I've seen him on other video's more specifically directed toward this issue that are also quite good. I'll see if I can track down the links.

(Ah, I see I've just become a 'Full Member"! Yeah me!? ;D )
"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 #95 on: July 07, 2013, 06:44:34 PM »
Wili,

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

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

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

From: Feedbacks and mechanisms affecting the global sensitivity of glaciers to climate change
By: B. Marzeion, A. H. Jarosch, and J. M. Gregory; The Cryosphere Discuss., 7, 2761–2800, 2013; doi:10.5194/tcd-7-2761-2013
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

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Re: Potential Collapse Scenario for the WAIS
« Reply #96 on: July 07, 2013, 07:21:07 PM »
Thanks for that reference. Feedbacks related to climate are a particular interest/obsession of mine.

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

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

(Apologies ahead of time if you have already addressed this. I'm afraid I have not yet had time to read through all of every one of your well-sourced posts above.)
"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 #97 on: July 08, 2013, 12:09:01 AM »
Wili,

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

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

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

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

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

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


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

http://forum.arctic-sea-ice.net/index.php/topic,72.0.html
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

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Re: Potential Collapse Scenario for the WAIS
« Reply #98 on: July 08, 2013, 06:52:01 AM »
Thanks, ASLR. Those were some of the things I was thinking, too. But you have the background to say them more confidently. I must say that I don't quite understand how Antarctic melting/calving could lower local sea level. But perhaps I am being dense (wouldn't be the first time  :-\ ).

Thanks again for all your thoughts on this important-to-consider possibility.
"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 #99 on: July 08, 2013, 04:37:12 PM »
Wili,

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

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