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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #200 on: January 04, 2015, 03:47:15 PM »
ASLR,
That would be one possibility. Another would be that peak discharge would occur somewhere between 2100-2200. But the potential risk that 1 meter/decade would be reached even before 2100 is indeed what counts most from a risk-management perspective. I wonder when peak discharge is reached in the model of DeConto & Pollard, and under what assumptions.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #201 on: January 04, 2015, 03:58:03 PM »
Lennart,

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

Best,
ASLR
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #202 on: January 04, 2015, 04:41:46 PM »
Good points, ASLR. In the Payne-model referred to earlier they had modelled WAIS with a combination of six different resolutions, with 150m the highest. For a timescale of five centuries we would really need to know how the rest of EAIS behaves to put the maximum 9m contribution in the model of DeConto & Pollard into perspective.

Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #203 on: January 05, 2015, 11:27:24 AM »
Pollard & DeConto 2012 describes a model for Antarctica with 10-40 km grid resolution:
http://www.geosci-model-dev.net/5/1273/2012/gmd-5-1273-2012.pdf

If that's the same model and resolution used in their model mentioned above, then it seems higher resolutions could produce even faster SLR, based on the example of Payne's model.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #204 on: January 06, 2015, 09:16:24 PM »
The linked article provides evidence that geothermal heat flux is probably contributing to relatively high rates of basal ice melting beneath the Thwaites Glacier; which if true (and there are multiple lines of evidence of this) this basal meltwater would almost certainly contribute to the reduced stability of the marine ice sheet above the Byrd Subglacial Basin, and by extension the rest of the WAIS:

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


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


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

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Re: Potential Collapse Scenario for the WAIS
« Reply #205 on: January 06, 2015, 09:26:45 PM »
The following link leads to a very nice Part 1 summary of the recent research history (from about 1968 to about the late 1990's) on the stability of the WAIS, and which includes a very nice video by NASA about Rignot et al's 2014 research on this topic:

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

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

Nice overview!

Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #206 on: January 06, 2015, 10:01:32 PM »
In the two linked internet articles, Will Thomas presents a historical primer on the coming WAIS collapse.  This excellent primer illustrates just how recent our understanding of the risks of the WAIS collapse, and it is very clear that there is so much more to learn about this risk, that I believe that most of the WAIS collapse will be actively occurring before the researchers have a full understanding of that risk.  Note that in the video of Rignot in the second link, Rignot states that if the ASE marine glaciers keep retreating at their present rate of retreat this portion of the WASI will be actively collapsing within two hundred years; however, the rate of the ASE marine glacier retreat is accelerating, which is why I believe that this portion of the WAIS will be actively collapsing sometime after 2040.

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

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

And thanks for posting part 2 as well.

Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #207 on: January 06, 2015, 10:23:41 PM »
While I posted about the findings of Weber et al 2014 in the Paleo-Evidence thread (see Reply #119 in the Paleo-Evidence thread), the following link to a New Zealand Herald article shows that the Antarctic Ice Sheet is capable of contributing at least one meter of sea level rise to the global total by 2100:

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

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

Melt events could occur in just a decade, syas this quote from the article:
Quote
The research revealed that Antarctica's vast ice sheet collapsed at least eight times during a period between 9000 and 20,000 years ago. Sediment preserved in drill cores retrieved from the ice showed that while these mass collapses had happened every couple of hundred years, the melt events could occur in just a decade. "It's like an earthquake - for a long time, nothing happens, but when it does, boom - it happens all at the same time,"

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #208 on: January 07, 2015, 12:08:23 AM »
The linked article focuses on the coming collapse of the WAIS; however, I like the quote from Kevin Trenberth concerning the question of whether we are currently in a climate crisis or not, as I agree that our greatest crisis is a lack of human will power to address climate change in a manner commensurate with the magnitude of the problem.  Until society shows both the wisdom  and the backbone necessary to properly address our current/coming climate situation, I will continue to contend that we are currently experiencing a Climate Crisis (unless one is over 50 years old and does not care what happens to future generations, at least from a collapse of the WAIS):

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

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

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

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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #209 on: January 07, 2015, 12:38:18 AM »
Here's the new paper by Pollard, DeConto & Alley 2015:
http://www.sciencedirect.com/science/article/pii/S0012821X14007961

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

So that could be 3m within a century from WAIS alone, and 5m by 2200 from AIS. So maybe 7-8m  by 2200 including GIS, GIC and thermal expansion?

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #210 on: January 07, 2015, 01:07:43 AM »
Lennart,

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

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

Edit: I note that the values given in the attached image are for a simple Pliocene-like warming scenario, and not for any RCP or SRES pathways.
« Last Edit: January 07, 2015, 10:08:46 AM by AbruptSLR »
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #211 on: January 07, 2015, 04:54:18 PM »
Pollard et al say:
"The equivalent eustatic sea level rise reaches 5 m after ∼200 yr and 17 m after ∼3000 yr (Fig. 4, red curve), similar in magnitude to albeit uncertain proxy estimates of past sea-level variations mentioned above. About 3 mesl comes from West Antarctica, and the remaining ∼14 mesl comes from East Antarctic basins."

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

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

So what does this mean?

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

Any other views?

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #212 on: January 07, 2015, 09:50:48 PM »
Lennart,

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

Best,
ASLR
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #213 on: January 07, 2015, 10:07:50 PM »
Pollard(2014) indicates that the game will be over as soon as we see substantial surface melt on PIG/Thwaites. I am not yet convinced that the absence of surface melt will "stabilize" WAIS for  couple centuries; one weakness in the model is the absence of basal hydrology.

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #214 on: January 07, 2015, 10:24:17 PM »
The attached figure from Nature Geoscience 2012, DOI: 10.1038/NGEO1671, show in good detail the areas of the Antarctic subject to the indicated number of days of surface ice melting in January 2005.  This figure indicates that both the PIG/Thwaite drainage basins and the Ross Sea Embayment areas are subject to a substantial risk of surface ice melting in the future (as per Pollard's concern).
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jai mitchell

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Re: Potential Collapse Scenario for the WAIS
« Reply #215 on: January 07, 2015, 11:21:02 PM »
3 meters in 35 to 45 years

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Re: Potential Collapse Scenario for the WAIS
« Reply #216 on: January 07, 2015, 11:25:58 PM »
Pollard et al say:

Any other views?

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #217 on: January 07, 2015, 11:33:47 PM »
Pollard et al say:

Any other views?

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #218 on: January 07, 2015, 11:48:27 PM »
3 meters in 35 to 45 years

Jai, seems more like 3m in almost 100 years to me.

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Re: Potential Collapse Scenario for the WAIS
« Reply #219 on: January 07, 2015, 11:55:08 PM »
oops you are right, it is 3 meters in 70-90 years, just less than 1/2 way on first tic mark on the x-axis. . .
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Re: Potential Collapse Scenario for the WAIS
« Reply #220 on: January 08, 2015, 04:25:37 AM »
Per Wikipedia:

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

As the only way that Pollard et al 2015 could get adequate SLR contribution from the EAIS was by invoking hydrofracturing, it would seem clear that global warming increase of 2–3 °C can provide sufficient surface ice melting to get the WAIS to at least partially collapse this century.
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Re: Potential Collapse Scenario for the WAIS
« Reply #221 on: January 08, 2015, 11:34:57 AM »
Per Wikipedia:

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

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

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

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

I would like to note that the world could easily blow past the 2 to 3 C global temperature increase (characteristic of the mid-Pliocene) well before the end of this century.  It will be very interesting to see how the ACME program addresses Pollard et al 2015's findings and extends them to a projection of our modern case.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #222 on: January 08, 2015, 10:53:55 PM »
In addition to my earlier comments, the following offers a couple more comments about Pollard et al 2015's collapse progression (for a stepped Pliocene condition imposed on modern conditions with both "cliff failures" and hydrofracturing) shown in the first attached image (see caption below); regarding how these initial conditions and collapse condition differ from my expectations for our modern progression following RCP 8.5 this century.

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

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

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

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

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

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

Caption for Second Image: "Mean Water Temperature Above Freezing and Salinity Measurements at the Pine Island Glacier from 2004 to 2009"
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #223 on: January 09, 2015, 11:05:43 PM »
While the austral winters have been warming faster in Antarctica than the austral summers, the attached NASA map of surface temperature anomalies on August 29, 2014, illustrates how much of this Antarctic Amplification is occurring in Western Antarctica.  This supports Pollard et al 2015's premise that the WAIS may be subject to hydrofracturing and cliff failures sooner (due to Antarctic Amplification) rather than later as global warming continues:
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Re: Potential Collapse Scenario for the WAIS
« Reply #224 on: January 10, 2015, 12:13:08 AM »
Quote
influence of changing ocean currents as the seaways through the WAIS open circa 2100 (or before).

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

how does this compare to today?  It seems that the cliff collapse mechanism would prevent the pathway from opening up under the ice sheet if we were to see grounding line retreats at the rate that you are talking about here (I think).
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Re: Potential Collapse Scenario for the WAIS
« Reply #225 on: January 10, 2015, 12:47:46 AM »
Quote
influence of changing ocean currents as the seaways through the WAIS open circa 2100 (or before).

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

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

As the distance from the PIG to the Rutford groundings lines is something like 500 km, if one assumed grounding line retreats from both sides that would be 250/85 years or about 3 km of grounding line retreat per year on average.  Regarding the cliff failure mechanism, it maybe slower to develop for the PIG as it is confined within a relatively narrow channel which will help to support some ice shelf for sometime.  Nevertheless, any Pine Island Ice Shelf will continue to calve so any subglacial cavity that may (or may not) exist when the seaway between the ASE and the Weddell Sea is formed, may only be a few tens of kilometers long.
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Re: Potential Collapse Scenario for the WAIS
« Reply #226 on: January 10, 2015, 12:48:18 AM »
Whether obvious to everyone, or not, I thought that I would like a few positive feedback mechanisms that would accelerated/activated on both local and global scales by the hydrofracturing/cliff failure WAIS collapse scenario described in the Pollard et al 2015 paper, which are:

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

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

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

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

5.  However, I realize that I should mention that the cooling of the Southern Ocean by the introduction of a large armada of icebergs would serve as a negative feedback until all of the icebergs had melted.
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Re: Potential Collapse Scenario for the WAIS
« Reply #227 on: January 10, 2015, 01:43:03 AM »
The linked article indicates that the basal roughness beneath the Institute and Moller Ice Streams have been smoothed by past ice flows and are continuing to be smoothed by current ice movement (thus increase the probability of faster future ice mass loss events):

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

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

Abstract: "We present a detailed analysis of bed roughness beneath Institute and Möller Ice Streams, west Antarctica, using radio-echo sounding data (RES) acquired in the austral summer of 2010/11. We assess roughness using a two-parameter approach and also assess the directionality of roughness relative to present-day ice flow. Our work highlights the wealth of additional information that resides in analyses of bed roughness. Employing these multiple approaches we show that spatially variable roughness patterns are partly a consequence of the ability of flowing ice not only to smooth the bed but also to redistribute and remove sediments, and to do this along-flow. Accordingly, we identify some fast-flow tributaries underlain by topography that has been streamlined and other tributaries that are underlain by sediments. We also identify locations that are currently protected from erosion, but where more ancient erosion may once have occurred. We conclude that detailed roughness analysis is a useful tool for landscape interpretation; and we suggest that the roughness of an ice-sheet's bed should be viewed not only as the consequence of ancient marine sedimentation, but also as a product of more contemporary erosion and redistribution of sediments, as well as bedrock-smoothing that is ongoing because of continuing dynamic activity. In this way, basal roughness has the potential to evolve continually with ice sheet form and flow, and should not be viewed simply as a snapshot of either present-day or palaeo-basal conditions."
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Re: Potential Collapse Scenario for the WAIS
« Reply #228 on: January 10, 2015, 01:55:18 AM »
While the following reference has been previously cited in the EAIS thread, I thought that I would post it here as it is so clearly relevant to the recent Pollard et al 2015 work:

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

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

Abstract: "Changes in ice discharge from Antarctica constitute the largest uncertainty in future sea-level projections, mainly because of the unknown response of its marine basins1. Most of West Antarctica’s marine ice sheet lies on an inland-sloping bed and is thereby prone to a marine ice sheet instability. A similar topographic configuration is found in large parts of East Antarctica, which holds marine ice equivalent to 19 m of global sea-level rise, that is, more than five times that of West Antarctica. Within East Antarctica, the Wilkes Basin holds the largest volume of marine ice that is fully connected by subglacial troughs. This ice body was significantly reduced during the Pliocene epoch. Strong melting underneath adjacent ice shelves with similar bathymetry8 indicates the ice sheet’s sensitivity to climatic perturbations. The stability of the Wilkes marine ice sheet has not been the subject of any comprehensive assessment of future sea level. Using recently improved topographic data in combination with ice-dynamic simulations, we show here that the removal of a specific coastal ice volume equivalent to less than 80 mm of global sea-level rise at the margin of the Wilkes Basin destabilizes the regional ice flow and leads to a self-sustained discharge of the entire basin and a global sea-level rise of 3–4 m. Our results are robust with respect to variation in ice parameters, forcing details and model resolution as well as increased surface mass balance, indicating that East Antarctica may become a large contributor to future sea-level rise on timescales beyond a century."
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Re: Potential Collapse Scenario for the WAIS
« Reply #229 on: January 10, 2015, 06:34:17 AM »
Re: which WAIS seaway opens first
Vaughan(2011) doi:10.1029/2011GC003688


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

Bellinghausen to Weddell  1830 yr
Ross to Weddell 85000 yr

I enclose part of fig 1 showing putative seaways

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Re: Potential Collapse Scenario for the WAIS
« Reply #230 on: January 10, 2015, 06:39:40 AM »
Re:

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


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

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Re: Potential Collapse Scenario for the WAIS
« Reply #231 on: January 10, 2015, 07:39:00 AM »
rutford = A-W pathway



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

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

Quote
from 1992 to 2011. Pine Island Glacier retreated 31 km at its center, with most retreat in 2005–2009 when the glacier ungrounded from its ice plain
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Re: Potential Collapse Scenario for the WAIS
« Reply #232 on: January 10, 2015, 08:25:46 AM »
agreed that Vaughan(2011) estimates for seaway opening are optimistic (too long, if i have to spell it out)

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Re: Potential Collapse Scenario for the WAIS
« Reply #233 on: January 10, 2015, 03:36:32 PM »
Re:

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


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

sidd

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

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


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

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

See also:
Hansen, J.E., and M. Sato, 2012: Paleoclimate implications for human-made climate change. In Climate Change: Inferences from Paleoclimate and Regional Aspects. A. Berger, F. Mesinger, and D. Šijački, Eds. Springer, pp. 21-48, doi:10.1007/978-3-7091-0973-1_2.
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Re: Potential Collapse Scenario for the WAIS
« Reply #234 on: January 10, 2015, 04:05:37 PM »
agreed that Vaughan(2011) estimates for seaway opening are optimistic (too long, if i have to spell it out)

sidd

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

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

Finally, I post Pollard et al (2015) figure showing their collapse progression sequence (with time) to illustrate their collapse area around Rutford and PIG (between 2050 and 2100)
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Re: Potential Collapse Scenario for the WAIS
« Reply #235 on: January 10, 2015, 04:16:58 PM »
Further to my last post, and in order to support my position that the bottom topology beneath the WAIS presents a large number of local conditions with different pinning cases, side shear cases, basal friction cases, etc, I re-post the two attached Bedmap 2 images.
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #236 on: January 10, 2015, 04:46:37 PM »
New paper by Dutton et al 2015 on WAIS- and/or EIAS-collapse during the Eemian:
http://www.sciencedirect.com/science/article/pii/S0277379114004120

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

Highlights
• Peak eustatic sea level (ESL) for MIS 5e estimated at ∼7.6 ± 1.7 m above present.
• Polar ice sheets contributed ∼5–8 m of ice-equivalent sea level to this peak.
• Partial collapse of Antarctic ice sheet may have occurred early in MIS 5e.
• Gradual sea-level rise of ∼0.2 m ka−1 recorded between ∼129 and 125 ka.

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Re: Potential Collapse Scenario for the WAIS
« Reply #237 on: January 10, 2015, 05:02:22 PM »
Dutton et al 2015 say:
"We observe a pattern of gradually rising sea level in the Seychelles between ∼129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present... Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand."

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

But 7.6-5.9=1.7m in 128.6-125=3.6 ka, so almost 0.5 m/kyr, or 0.5 mm/yr on average.
« Last Edit: January 10, 2015, 05:07:41 PM by Lennart van der Linde »

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Re: Potential Collapse Scenario for the WAIS
« Reply #238 on: January 10, 2015, 05:25:12 PM »
The following reference must be the second paper that Alley mentioned to Lennart of the two that came out this week.  This paper complements the Pollard et al 2015 paper (which looked at a simple Pliocene case superimposed on current AIS conditions in a stepped manner).  This reference provides all of the appropriate caveats for making an actual projection of our current case, and notes that the initiation phase of the main collapse phase is still the most difficult to determine.  That said I still like my general collapse scenario that I posted in 2013:

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

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

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

Abstract: "Ocean-ice interactions have exerted primary control on the Antarctic Ice Sheet and parts of the Greenland Ice Sheet, and will continue to do so in the near future, especially through melting of ice shelves and calving cliffs. Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed, shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West Antarctica, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state is likely to involve loss of most of the West Antarctic Ice Sheet, causing >3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic Ice Sheets share some of the same vulnerabilities to shrinkage from marine influence."
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Re: Potential Collapse Scenario for the WAIS
« Reply #239 on: January 10, 2015, 06:07:57 PM »
Dutton et al 2015 say:
"We observe a pattern of gradually rising sea level in the Seychelles between ∼129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present... Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand."

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


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

Lennart,

Thanks for the link to:

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

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

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

Again I note that we will probably need to wait until the ACME project issues projections before we get anything like a reasonable projection of a plausible AIS collapse scenario in the next 100 to 200 years, and even that may only be a lower bound approximation of the true SLR contribution risks.
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Re: Potential Collapse Scenario for the WAIS
« Reply #240 on: January 10, 2015, 09:56:19 PM »
The Alley abstract indicates some commonality between GRIS and EAIS. I do not see this clearly, so i await the full paper. Any thoughts ?

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

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

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

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

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #241 on: January 10, 2015, 10:29:32 PM »
sidd,

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

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

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

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

Best,
ASLR
« Last Edit: January 10, 2015, 10:55:41 PM by AbruptSLR »
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Re: Potential Collapse Scenario for the WAIS
« Reply #242 on: January 10, 2015, 11:16:49 PM »
ASLR, sidd,

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

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

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

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Re: Potential Collapse Scenario for the WAIS
« Reply #243 on: January 10, 2015, 11:30:55 PM »
Also see:
http://people.oregonstate.edu/~carlsand/PALSEA2/Past_Meetings_files/rome_meeting_report.pdf

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

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

"Here we present a complete reef-crest sequence for the last interglacial highstand and its U-series chronology from the stable northeast Yucatán peninsula, Mexico. We find that reef development during the highstand was punctuated by reef-crest demise at +3 m and back-stepping to +6 m. The abrupt demise of the lower-reef crest, but continuous accretion between the lower-lagoonal unit and the upper-reef crest, allows us to infer that this back-stepping occurred on an ecological timescale and was triggered by a 2–3-m jump in sea level. Using strictly reliable 230Th ages of corals from the upper-reef crest, and improved stratigraphic screening of coral ages from other stable sites, we constrain this jump to have occurred ~121 kyr ago and conclude that it supports an episode of ice-sheet instability during the terminal phase of the last interglacial period."

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Re: Potential Collapse Scenario for the WAIS
« Reply #244 on: January 10, 2015, 11:50:51 PM »
IPCC AR5 WG1 Ch.5, p.426:
http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter05_FINAL.pdf

"Since AR4, there is evidence for meter-scale variability in local LIG sea level between 126 ka and 120 ka (Thompson and Goldstein, 2005; Hearty et al., 2007; Rohling et al., 2008a; Kopp et al., 2009; Thompson et al., 2011). However, there are considerable differences in the timing and amplitude of the reported fluctuations due to regional sea level variability and uncertainties in sea level proxies and their ages... In summary, there is evidence for two intra-LIG sea level peaks (high confidence) during which sea level varied by up to 4 m (medium confidence). The millennial-scale rate of sea level rise during these periods exceeded 2 m kyr–1 (high confidence)."

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #245 on: January 11, 2015, 12:37:13 AM »
Re; Hansen and Sato on negative feedback from ocean cooling

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

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #246 on: January 11, 2015, 04:59:40 AM »
ASLR, sidd,

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

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

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

Lennart,

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

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

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

Abstract: "The last interglacial stage (LIG; ca. 130–115 ka) provides a relatively recent example of a world with both poles characterized by greater-than-Holocene temperatures similar to those expected later in this century under a range of greenhouse gas emission scenarios. Previous analyses inferred that LIG mean global sea level (GSL) peaked 6–9 m higher than today. Here, we extend our earlier work to perform a probabilistic assessment of sea level variability within the LIG highstand. Using the terminology for probability employed in the Intergovernmental Panel on Climate Change assessment reports, we find it extremely likely (95 per cent probability) that the palaeo-sea level record allows resolution of at least two intra-LIG sea level peaks and likely (67 per cent probability) that the magnitude of low-to-high swings exceeded 4 m. Moreover, it is likely that there was a period during the LIG in which GSL rose at a 1000-yr average rate exceeding 3 m kyr−1, but unlikely (33 per cent probability) that the rate exceeded 7 m kyr−1 and extremely unlikely (5 per cent probability) that it exceeded 11 m kyr−1. These rate estimates can provide insight into rates of Greenland and/or Antarctic melt under climate conditions partially analogous to those expected in the 21st century."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #247 on: January 11, 2015, 09:49:49 AM »
ASLR,
Indeed, up to 11 m/ky during the Eemian is also what Rohling et al 2013 estimate:
http://www.nature.com/srep/2013/131212/srep03461/full/srep03461.html?message-global=remove

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

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

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

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

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

That would be my very rough worst-case risk assessment for now, but maybe this could still be an under-estimate?

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Re: Potential Collapse Scenario for the WAIS
« Reply #248 on: January 11, 2015, 01:26:48 PM »
Lennart,

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

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

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

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

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

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

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: Potential Collapse Scenario for the WAIS
« Reply #249 on: January 11, 2015, 05:56:32 PM »
ASLR,
You may be right that it could be more than 2.5m by 2100. I don't know. I guess I'm trying to find the maximum number that I can communicate to policymakers and public while referring them to the best available papers/scientists that make this number plausible. We can speculate about this still being an under-estimate, but if there's no or hardly any scientist who's willing to defend that number, then it may make our speculation less credible.

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

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

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

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

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

This is my reasoning so far, but again, you may be right, if you think this is still too risky.