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Author Topic: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios  (Read 80683 times)

sidd

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The second retreat at 11.1 Kyr in Marngerud might be associated with MWP1A ?
I have finally found the time to read the Bassis paper DOI: 10.1038/NGEO1887 which discovers a critical thickness:
"Simulations of floating termini revealed that above a critical ice thickness (∼1,000 m), a fully buoyant calving front becomes unstable."

This is a numerical study which does not include  a great deal, including the "viscous component of ice dynamics," concentrating rather on "the rapid dynamics of fracture and associated calving." I kinda like this approach, focussing on the period close to largescale fracture, sorta like what is done in the study of critical phenomena where one critical exponent swamps the rest. I shall have to reread this treatment very carefully, and see if I can deduce a universality class for such a transition.

sidd



AbruptSLR

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I have referred to this NEEM ice core finding before; but many people who are focused on the risk of ice mass loss from the GIS; forget that such research indicates that the WAIS presents a greater risk for abrupt SLR this century:

http://www.sciencepoles.org/news/news_detail/climate_reconstruction_last_interglacial_greenland_ice_sheet_not_sensitive

"Climate reconstruction of last interglacial shows Greenland Ice Sheet not so sensitive to warming
30.01.2013 - ICE & SNOW, ARCTIC
For the first time, scientists have been able to completely reconstruct the climate during the Eemian period (130,000 – 115,000 years ago), the last interglacial period in Earth's history before today.
Examining the lower part of a 2,540 metre ice core extracted from the ice sheet in northern Greenland, the international team of researchers from 14 countries involved in the North Greenland Eemian Ice Drilling (NEEM) project was able to determine that the Greenland Ice Sheet shrank a lot less during the Eemian, despite the fact that average temperatures in northern Greenland were 5-8°C higher than today's levels.
Published in Nature, researchers determined that during the warmest part of the Eemian some 125,000 years ago, the Greenland Ice Sheet had lost 400 metres in ice height since the ice age before the Eemian. The ice sheet was only 130 metres lower than it is today. Over a period of 6,000 years, the ice sheet lost only about 25% of its mass, according to the study.
The challenge for the team of scientists was to identify individual annual layers of snow deposition in the lower part of the ice core. Unlike the upper layers of the ice core, in which annual layers of snow deposition are stacked like a layer cake, the lower layers which were deposited during the Eemian and the following transition period towards the last ice age had folded into one another. The snow that was on the surface of the ice sheet melted and refroze repeatedly during the Eemian, and meltwater seeped into the layers of ice and snow beneath.
The team was able to decipher the layers in the ice core by looking at the physical properties of the ice core, determining the water and oxygen isotope count the ice contained as well as the amount of methane trapped in the air bubbles, and then compared these values to data taken from ice cores in Antarctica.
While the data show that the Greenland Ice Sheet did not react so much to the rise in temperatures during the Eemian, it also shows that melt from the Greenland Ice Sheet contributed to less than half the total sea level rise at the time. With sea level 4-8 metres higher during the Eemian than they are today, the data indicate that melt form the Antarctic Ice Sheet played a larger role in sea level rise. This means the ice sheet in Antarctica, and in particular the West Antarctica Ice Sheet, might be more vulnerable to melt than previously thought."
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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #52 on: August 05, 2013, 06:59:15 PM »
The following linked article and abstract indicate that the earth may be more sensitive (responsive) to ice mass loss that current GCMs are calibrated to; therefore, it is reasonable to assume that future ice mass loss will be higher that current GCM projections:

http://www.nature.com/ngeo/journal/v6/n7/full/ngeo1859.html

Barbados-based estimate of ice volume at Last Glacial Maximum affected by subducted plate
By: Jacqueline Austermann, Jerry X. Mitrovica, Konstantin Latychev & Glenn A. Milne; Nature Geoscience; 6, pp: 553–557; (2013); doi:10.1038/ngeo1859

Abstract: "The record of sea-level change at Barbados derived from the dating of fossil corals has been used to argue that globally averaged, or eustatic, sea level during the Last Glacial Maximum was approximately 120 m below present. This estimate is roughly 10 m lower than inferences based on sea-level data from other far-field sites and, if correct, would suggest that the Barbados record is a largely uncontaminated measure of eustasy. However, these previous analyses were based on numerical corrections for glacial isostatic adjustment that adopted one-dimensional viscoelastic Earth models. Here we assess the impact of three-dimensional mantle viscoelastic structure on predictions of post-glacial sea-level change at Barbados. Our simulations indicate that the predictions are strongly perturbed by the presence of a high-viscosity slab associated with subduction of the South American Plate beneath the Caribbean Plate. The slab suppresses local deformation and reduces the sea-level rise predicted during the deglaciation phase. To accommodate this reduction while maintaining a fit to the Barbados sea-level record requires an excess ice volume at the Last Glacial Maximum equivalent to about 130 m of eustatic sea-level rise. Given a downward revision in estimates of the Antarctic ice sheet contribution to this excess ice volume, we conclude that a significant amount of Northern Hemisphere ice at the Last Glacial Maximum remains unaccounted for in sea-level-based ice sheet reconstructions."
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #53 on: August 07, 2013, 11:26:37 PM »
The following reference provides paleo-evidence that supports concerns about the risks of ASLR:

Gornitz, V., 2013: Rising Seas: Past, Present, and Future. Columbia University Press.

"Publisher's description: The Earth's climate is already warming due to increased concentrations of human-produced greenhouse gases in the atmosphere, and the specter of rising sea level is one of global warming's most far-reaching threats. Sea level will keep rising long after greenhouse gas emissions have ceased, because of the delay in penetration of surface warming to the ocean depths and because of the slow dissipation of excess atmospheric carbon dioxide. Adopting a long perspective that interprets sea level changes both underway and expected in the near future, Vivien Gornitz completes a highly relevant and necessary study of an unprecedented age in Earth's history.
Gornitz consults past climate archives to help better anticipate future developments and prepare for them more effectively. She focuses on several understudied historical events, including the Paleocene-Eocene Thermal Anomaly, the Messinian salinity crisis, the rapid filling of the Black Sea (which may have inspired the story of Noah's flood), and the Storrega submarine slide, an incident possibly connected to a sea level occurrence roughly 8,000 years old. By examining dramatic variations in past sea level and climate, Gornitz concretizes the potential consequences of rapid, human-induced warming. She builds historical precedent for coastal hazards associated with a higher ocean level, such as increased damage from storm surge flooding, even if storm characteristics remain unchanged. Citing the examples of Rotterdam, London, New York City, and other forward-looking urban centers that are effectively preparing for higher sea level, Gornitz also delineates the difficult economic and political choices of curbing carbon emissions while underscoring, through past geological analysis, the urgent need to do so."
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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #54 on: August 09, 2013, 04:21:19 PM »
To add to the post that I made yesterday about ENSO in the "Southern Ocean Trends" thread about the Antarctic Circumpolar Wave (ACW):

The following 2-yr old Internet article provides paleo-evidence that the ENSO will likely remain strong, and may increase it frequency; as the world warms:

"ScienceDaily (July 15, 2011) — Dramatic climate swings behind both last year's Pakistan flooding and this year's Queensland floods in Australia are likely to continue as the world gets warmer, scientists predict.

Researchers at the Universities of Oxford and Leeds have discovered that the El Niño Southern Oscillation (ENSO), the sloshing of the warmest waters on the planet from the West Pacific towards the East Pacific every 2-7 years, continued during Earth's last great warm period, the Pliocene.
Their results suggest that swings between the two climatic extremes, known as El Niño and La Niña, may even have occurred more frequently in the warmer past and may increase in frequency in the future. Extreme ENSO events cause droughts, forest fires and floods across much of the world as well as affecting fishery production.
Reporting in the journal Paleoceanography, the team of geochemists and climate modellers use the Pliocene as a past analogue and predictor of the workings of Earth's future climate.
The Pliocene (which lasted from 5 to 3 million years ago) had carbon dioxide levels similar to the present day, with global mean temperatures about 2-3ºC higher, so it is a useful test-ground for climate research.
Lead Scientist Nick Scroxton from Oxford University's Department of Earth Sciences said: 'We know from previous studies that the mean state of the Pacific during the warm Pliocene was similar to the climate patterns observed during a typical El Niño event that we see today.
'However, until recently it was believed that a warmer Pacific would reduce the climate swings that cause the dramatic weather extremes throughout the region leading to a permanent state of El Niño. What we didn't expect was that climatic variability would remain strong under these warmer conditions.'
The team combined experiments performed on the Met Office Hadley Centre climate model, HadCM3, with the analysis of the chemical composition of lots of individual shells of small organisms, known as foraminifera.
These were collected from a deep sea sediment core in the East Equatorial Pacific, and provided a record of temperature in the upper layer of the ocean through time. They discovered that the range of temperatures experienced by these organisms during the Pliocene, was higher than what would be expected from just the seasonal cycle.
The extra variation in temperature can be explained by the additional extreme temperature swings provided by the El Niño/La Niña system.
The authors say the agreement in findings from both ocean data and modelling leaves little doubt that ENSO will persist in a warmer world. Earlier this year a team from Japan studying corals from the same period showed climatic variability in the western Pacific on a similar scale to today, questioning the idea of a permanent El Niño during the Pliocene.
This new study goes further, showing that the oscillation is Pacific-wide, and is likely to be caused by the El Niño/La Niña. This suggests that our warmer future will continue to be dogged, maybe even more regularly, by extreme climatic events.


University of Oxford (2011, July 15). Dramatic climate swings likely as world warms: Ancient El Niño clue to future floods. ScienceDaily. Retrieved July 31, 2011, from http://www.sciencedaily.com¬ /releases/2011/07/110714103249.htm

N. Scroxton, S. G. Bonham, R. E. M. Rickaby, S. H. F. Lawrence, M. Hermoso, A. M. Haywood. Persistent El Niño–Southern Oscillation variation during the Pliocene Epoch. Paleoceanography, 2011; 26 (2) DOI: 10.1029/2010PA002097"

But it is certain that even if the ENSO amplitude and/or frequency do not increase: (1) as the atmosphere warms it can hold more water, so the water impact of any ENSO cycle will be stronger (due to the water content); and (2) the ENSO cycle can reinforce various blocking patterns, which when superimposed with the increasing meanderings of the jet-streams (due to the reduction in thermal gradient from the poles to the equator due to global warming), the impact of extreme weather events will be longer.

« Last Edit: August 09, 2013, 04:40:15 PM by AbruptSLR »
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #55 on: August 17, 2013, 10:34:31 PM »
The following website provides a simple overview explaining paleo-cycles of glaciation and de-glaciation; which I provide for those less familar with the details of some of this science:

http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/paleoclimate/
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #56 on: August 22, 2013, 05:37:22 PM »
The following reference, and link, to a pdf of a 2011 PowerPoint presentation (see also the attached figure from the pdf, where delta T is the temperature difference between the upper atmosphere in North Pole and in the Equator) by Prof Bill Langford (who presents both paleo and model evidence) about the possible abrupt climate change from our current three cell atmospheric circulation pattern to a single Hadley Cell (equable climate pattern).  This reference makes it very clear that the Northern Hemisphere (NH) is more likely to make this transition before the Southern Hemisphere; and that any such transition is likely to be abrupt.   I find this Langford 2011 work to be particularly disturbing, considering that the rapid loss of Arctic Sea Ice might be sufficient to adequately warm the Arctic atmosphere sufficiently (probably due to an associated rapid increase in Arctic atmosphere specific humidity) to induce such an abrupt transition in the NH; which could then trigger ASLR this century (among many other abrupt climate changes):

HADLEY CELL EXPANSION IN TODAY’S CLIMATE AND PALEOCLIMATESBill Langford; University Professor Emeritus
Department of Mathematics and Statistics; University of Guelph, Canada; Presented to the BioM&S Symposium on Climate Change and Ecology; University of Guelph; April 28, 2011


http://www.fields.utoronto.ca/programs/scientific/10-11/biomathstat/Langford_W.pdf

As additional background I provide the following link to Brian Farrell's 1990 theory which also considers changes from our current atmospheric circulation pattern to that for an equable climate (with a single Hadley cell):

http://www.seas.harvard.edu/climate/eli/research/equable/hadley.html

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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #57 on: August 22, 2013, 06:00:17 PM »
The following linked reference (with a free pdf) makes it very clear (see the following abstract) that the occurrence of localized topical warming (say due to regional temperature differences due to air pollution in India and China vs the Pacific equator and/or the occurrence of a strong El Nino event); can promote the formation of atmospheric Rossby waves that can then propagate atmospheric heat directly to the polar regions; which in turn could result in the occurrence of an equable climate (whether in the past as support by the paleo evidence discussed in the pdf, or in the near future as indicated by the current patterns of: poleward expanding Hadley cells, reducing atmospheric temperature gradient between the poles and the equator, and increasing formation of Rossby waves particularly in the Northern Hemisphere atmosphere):


Can Planetary Wave Dynamics Explain Equable Climates?By: Sukyoung Lee, Steven Feldstein, David Pollard, and Tim White; May 3, 2010


http://www.meteo.psu.edu/~sbf1/papers/EQUABLE.pdf

Abstract:

"Viable explanations for equable climates of the Cretaceous and early Cenozoic (about
145 to 50 million years ago), especially for the above-freezing temperatures detected for high latitude continental winters, have been a long-standing challenge. In this study, we suggest that enhanced and localized tropical convection may be capable of triggering a high-latitude warming through the excitation of poleward propagating Rossby waves. This warming takes place through the poleward heat flux and overturning circulation that accompany the Rossby waves. This mechanism is tested with an atmosphere-mixed layer ocean general circulation model (GCM). By comparing results from two GCM runs, one with localized tropical heating and the other without, we find that the run with the heating produces substantially warmer high-latitudes. Given a contrast of 200 Wm−2 between the localized tropical heating and compensating cooling elsewhere in the tropics, the high-latitude temperature increase is as large as 16oC in the Northern Hemisphere (NH) winter. This result suggests that through Rossby wave dynamics an enhanced and localized tropical heating may be able to significantly reduce the pole-to-equator temperature difference."
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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #58 on: August 22, 2013, 07:45:51 PM »
The following link leads to an AGU December 2012 poster entitled: "The early Eocene equable climate problem: Can a perturbed physics climate model ensemble identify possible solutions?" by Navjit Sagoo, Paul Valdes and Rachel Flecker.  This post concludes that their case that models modern atmospheric conditions with a reduced temperature gradient and increased mean annual temperature, MAT (similar to modern projected global warming cases) their perturbed physics climate model matched current observations better than other GCM projections.  This supports concerns that the modern climate could abruptly change to an equable climate similar to that of the early Eocene (see the prior two posts and my following post).

http://fallmeeting.agu.org/2012/files/2012/12/Final_poster_AGU.pdf
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #59 on: August 22, 2013, 07:50:22 PM »
I hope/believe that the following linked reference of persistent near-tropical Eocene conditions in Antarctica, is not likely to occur for at least a few hundred years, but considering the perturbed physics involved in any transition from a modern to an equable climate; it is very difficult to say how abruptly such a transition may take:

http://www.nature.com/nature/journal/v488/n7409/abs/nature11300.html


Persistent near-tropical warmth on the Antarctic continent during the early Eocene epochby: Jörg Pross, Lineth Contreras, Peter K. Bijl, David R. Greenwood, Steven M. Bohaty, Stefan Schouten, James A. Bendle, Ursula Röhl, Lisa Tauxe, J. Ian Raine, Claire E. Huck, Tina van de Flierdt, Stewart S. R. Jamieson, Catherine E. Stickley, Bas van de Schootbrugge, Carlota Escutia, Henk Brinkhuis; Nature; 488,73–77 (02 August 2012); doi:10.1038/nature11300

Abstract:

"The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume. Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth’s climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future as a consequence of unabated anthropogenic carbon emissions. Climatic conditions of the early Eocene ‘greenhouse world’, however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10 °C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing."
« Last Edit: November 10, 2013, 04:18:41 AM by AbruptSLR »
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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #60 on: August 23, 2013, 12:57:16 AM »
A draft pdf copy of the following reference is available at the link provided below.  See my comments in my reply #58 in this thread about the significance of this paper:

http://www.paleo.bris.ac.uk/~ggdjl/warm_climates/sagoo_etal.pdf

The Early Eocene equable climate problem: Can perturbations of climate model parameters identify possible solutions?
by: by Navjit Sagoo, Paul Valdes, Rachel Flecker, and Lauren Gregoire;  Royal Society Philosophical Transactions A; 2013

Abstract:
"Geological data for the early Eocene (56 Ma to 47.8 Ma) indicates extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable data–model differences in the prediction of these polar surface temperatures, resulting in the so called “equable climate problem”.

In this paper, for the first time an ensemble with a perturbed climate-sensitive model parameters approach has been applied to modelling the early Eocene climate. We performed more than 100 simulations with perturbed physics parameters, and identified two simulations which have an optimal fit with the proxy data. We have simulated the warmth of the early Eocene at 560 ppmv CO2 which is a much lower CO2 level than many other models. We investigate the changes in atmospheric circulation, cloud properties and ocean circulation that are common to these simulations and how they differ from the remaining simulations in order to understand what mechanisms contribute to the polar warming.  The parameter set from one of the optimal early Eocene simulations also produces a favourable fit for the Last Glacial Maximum boundary climate and outperforms the control parameter set for the present day. Although this does not “prove” that this model is correct, it is very encouraging that there is a parameter set that creates a climate model able to simulate well very different paleoclimates and the present day climate.  Interestingly, to achieve the great warmth of the early Eocene this version of the model does not have a strong future climate change Charney climate sensitivity. It produces a Charney climate sensitivity of 2.7 °C whereas the mean value of the 18 models in the AR4 is 3.26 °C ± 0.69 °C.  Thus this value is within the range and below the mean of the models included in the IPCC Fourth Assessment Report (AR4)."
« Last Edit: November 10, 2013, 04:23:51 AM by AbruptSLR »
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #61 on: August 23, 2013, 01:46:28 AM »
Further to the implications of Sagoo et al 2013's paper (see immediate prior post in this thread), the attached image shows that under the RCP 8.5 scenario (that I discussed at length in other threads), the 560ppm CO2 levels at which Sagoo et al 2013 found could sustain an equable climate weather pattern (ie a single Hadley cell), could be reached as early as 2050 to 2055.  For this to happen the specific humidity in the Arctic area would need to increase both due to a reduction in the sea ice and the transport of heat to the Arctic both by water vapor from the Gulf Stream in the North Atlantic, and from atmospheric Rossby waves.  Again such a profound change in weather patterns would significantly increase the risk of ASLR by 2100.

{Edited addition: See Richard's comments in the next post correctly pointing out that Sagoo et al 2013's value of 560ppm CO2 only applies to the early Eocene era, and it does not relate to modern conditions}
« Last Edit: August 23, 2013, 03:33:52 PM by AbruptSLR »
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Richard Rathbone

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #62 on: August 23, 2013, 04:36:20 AM »
Thats not what Sagoo et al says.

To get the equable climate, they not only had CO2 at 560ppm, they rewound 50 million years of continental drift too.

When they ran the same model with modern geography, it didn't get close to being equable at 560pmm.

They have a model which does a decent job of simulating  paleo, ancient and modern climates. It only goes equable at 560ppm in the Eocene. Thats evidence for the Eocene not being relevant to 21st century climate due to continental drift, not that it is relevant due to 560ppm.

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #63 on: August 23, 2013, 05:28:28 AM »
Richard,

Thanks for straightening that matter out about continental drift; it appears that I went through the paper too quickly. 

That said, I guess that we will need to wait until ESMs such as FAMOUS are advanced enough to accurately model all of the other forcing/feedback factors that are going on today that were most likely not as significant, or not present, in the early Eocene (such as: black carbon; hydrofracking, probable rapid permafrost loss, possible rapid marine hydrate loss; an ozone hole over Antarctica, melt ice/ocean interaction; dynamic ocean/atmospheric interactions; and global warming that is occurring at a rate over a hundred times faster that even during the PETM); before, we have any clear idea as to when an equable climate might re-occur.

Best,
ASLR
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #64 on: August 23, 2013, 04:21:36 PM »
To elaborate on my comments in my immediately preceeding post: 

(a) Sagoo et al 2013's finding that the early Eocene's equable climate was stable with a Charney climate sensitivity of 2.7 oC, which is less than the best estimates of the modern Charney climate sensitivity of 3.26 +/- 0.69 oC; which implies that it is likely in the modern condition that if temporary forcing conditions [such as: (i) a strong El Nino decade or two; (ii) a multi-decade surge of CO2 and CH4 from permafrost degradation; or (iii) a decade long surge of CH4 from East Siberian Arctic Shelf, ESAS, methane hydrate release] could push the atmosphere past the tipping point, then the equable climate condition would likely be stable at much lower forcing levels.  Note also that this same point is supported by Langford's (jointly with Greg Lewis's) 2011 Bifucation Analysis.

(b) It is likely that the Sagoo et al 2013's analysis (while state of the art) probably did not fully capture mechansims for introducing both heat and water vapor into the Arctic this century including: (i) early loss of Arctic Sea Ice (seasonally by 2016 +/-3 yrs) resulting in both albedo decreases and increased vapor from the Arctic Ocean; (b) with more warming the Gulf Stream can carry warm water into higher-latitudes of the Altantic Ocean where the heat and vapor can feed directly into the Polar Cell; and (c) increased hurricane and Rossby Wave activity can periodically feed more energy into the Arctic/Polar Cell.

and (c) the Ocean Heat Content, OHC, has increased more rapidly than most GCM's have projected (partially due to increased warming of Antarctic Bottom Water, AABW; as in the Southern Ocean these RCM models would need kilometer scale resolution to capture the influence of eddies, upwelling, and ice mass loss); which could then allow the Gulf Stream to deliver more heat to Arctic than current models (including FAMOUS) project.
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #65 on: August 23, 2013, 04:30:18 PM »
While I am elaborating (see prior series of posts), I would like to point out the in the "Timing" thread opened by JimD (see the following link):

http://forum.arctic-sea-ice.net/index.php/topic,516.0.html

I point out that it is possible that the O'Leary et al 2013 sea level spike might possibly have been cause by a temporary bifurcation to an equable climate condition around 118.1 k years ago, during the Eemian (which essentially has a modern continent configuration); which are least raises the question of what environmental conditions existed at the very end of the Eemian, that might have (or might not have) caused such a postulated unstable atmospheric condition at that time.
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sidd

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #66 on: August 23, 2013, 10:02:53 PM »
Re: Sagoo(2013)

They find atmospheric heat transport predominates over oceanic in equable climates, I find that surprising. Perhaps it is because of the rigid lid ocean.

sidd

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #67 on: August 24, 2013, 06:54:46 AM »
Re: Sagoo(2013)

They find atmospheric heat transport predominates over oceanic in equable climates, I find that surprising. Perhaps it is because of the rigid lid ocean.

sidd

What's surprising about it? Why wouldn't it dominate?

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #68 on: August 24, 2013, 06:19:45 PM »
Richard and Sidd,

First, I would like to point out that while scientific researchers seem to me to be making great efforts, and are making great progress towards, addressing the risks of climate change (and SLR); the very complexity of climate change makes it difficult to make definitive statements like scientific researchers like to make; and that most researchers do not appear to be comfortable with scenario based hazard analysis as I have used to elaborate on my view of the risks of abrupt sea level rise this century.

Second, the hazard scenario that I presented in the "Collapse" thread (and elsewhere, see the "Philosophical" thread for summary Probability Density Function graphs) is not dependent at all on a transition to an equable climate and my hazard analysis indicates that for the RCP 95% CL path that society is currently following (with no signs of slowing down) that eustatic sea level could be 1m higher circa 2055.

Third, while I do not find it surprising that Sagoo et al 2013 finds a large amount of heat being transported to the Arctic via the atmosphere via a single Hadley Cell pattern for an equable climate condition; I will note that from a hazard analysis point of view that Sagoo et al 2013 do not evaluate the consequence of a possible 1m sea level rise circa 2055; which if they did with a very advanced ESM (beyond their current FAMOUS model) they would find that with a 1m higher eustatic sea level, due to the finger print effect (note that ice mass loss from the GIS tends to lowers sea level on the Atlantic side of the Arctic Ocean, while ice mass loss from the WAIS tends to increase sea level near the Bering Strait) warm Pacific ocean water would begin to flow through the Bering Strait into the Arctic Ocean (circa 2055).  Therefore, Sagoo et al 2013's modern analysis may be missing the risk of strong ocean transport of heat into the Arctic Ocean from the Pacific Ocean.

Fourth, some would say that following a RCP 8.5 95% CL scenario has such a low probability of occurrence that it is alarmist to talk about such a scenario seriously; but we have been following this scenario for at least 20-yrs, with the most serious consequences masked by ocean heat uptake, air pollution in Asia and the El Nino hiatus period; and I do not see any real measures being put in effect to get off of this BAU path before 2050.
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #69 on: August 25, 2013, 02:43:17 AM »
The pdf at the following link describes the nature, and importance, of the present ocean water flow from the Pacific into the Arctic Ocean, and indicates that the rate of heat flow from the Pacific into the Arctic Ocean is increasing.  Therefore, ESM, GCM and RCM projections that do not correctly model the true risk and influence of SLR on the introduction of heat energy into the Arctic Ocean, will give no-conservative (from the public safety point of view) with regard to such considerations as the rate of Sea Ice loss from the Arctic Ocean, and the risk of a transition to an equable climate (at some point in the future):

http://psc.apl.washington.edu/HLD/ArcticChange12/2012_Lect5_Woodgate_EntrancesandExitsHO.pdf

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #70 on: August 25, 2013, 06:38:25 PM »
The attached image from the linked reference indicates that for SRES A1B the eastern Bering Sea will have an average SST during the summer (JAS) of approximately 2oC warmer than at present by 2045.  This raises the risk that this warm water could be transported into the Arctic Ocean (either by a sea surface slope due to high SLR by 2045, and/or by a dipole condition such as occurred in 2007) to accelerate early season (ie July) Arctic Sea Ice loss when the solar irradiance is high; which could in-turn both warm Arctic Ocean SST and high evaporation rates; which could contribute to accelerated Arctic amplification and increased risk of an equable climate transition:


Expected declines in recruitment of walleye Pollock (Theragra chalcogramma) in the eastern Bering Sea under future climate change; by: Franz J. Mueter, Nicholas A. Bond, James N. Ianelli, and Anne B. Hollowed; ICES Journal of Marine Science (2011), 68(6), 1284–1296. doi:10.1093/icesjms/fsr022

http://www.acoustics.washington.edu/fis437/resources/Week%202/Meuter%20et%20al%20pollock%20recruit%202011.pdf
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #71 on: August 25, 2013, 09:41:36 PM »
Mr. Rathbone: I suppose that I should not be surprised since Kidder and Worseley (doi:10.1016/j.palaeo.2010.05.036) also predict the same. I attach two figures, the first from thei 2010 paper and the second from an earlier 2004 paper.

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #72 on: August 26, 2013, 05:01:06 AM »
While I agree that you cannot direct compare the early Eocene world to the modern world; nevertheless following the BAU scenario the world will be near 1000 ppm CO2; and the early Eocene epoch had a very similar CO₂ level.  The following linked reference indicates that during that period Wilkes Land coast in East Antarctica (at about 70o South) the average winter temperature was warmer than 10oC and totally frost free in the dark of an Austral winter:

http://www.nature.com/nature/journal/v488/n7409/abs/nature11300.html


Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch; by: Jörg Pross, et al, Nature; 488, 73–77; doi:10.1038/nature11300; 01 August 2012


Abstract:

"The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume. Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth’s climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future as a consequence of unabated anthropogenic carbon emissions. Climatic conditions of the early Eocene ‘greenhouse world’, however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10 °C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing."
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #73 on: August 26, 2013, 10:16:59 AM »
The linked reference provides very recent information regarding the transition from the "Greenhouse" early Eocene Climatic Optimum (circa 54 to 52 Ma) to the mid-Miocene (circa 15 to 13 Ma) with "… an abrupt aridification of East Antarctica near the Eocene-Oligocene transition (~34 Ma), which suggests that ice coverage influenced high-latitude atmospheric circulation patterns through albedo effects from the earliest Oligocene onward.":


http://onlinelibrary.wiley.com/doi/10.1002/ggge.20106/abstract

Passchier, S., S. M. Bohaty, F. Jiménez-Espejo, J. Pross, U. Röhl, T. van de Flierdt, C. Escutia, and H. Brinkhuis (2013), Early Eocene to middle Miocene cooling and aridification of East Antarctica, Geochem. Geophys. Geosyst., 14, 1399–1410, doi:10.1002/ggge.20106.

Abstract:

"Few high-latitude terrestrial records document the timing and nature of the Cenozoic “Greenhouse” to “Icehouse” transition. Here we exploit the bulk geochemistry of marine siliciclastic sediments from drill cores on Antarctica's continental margin to extract a unique semiquantitative temperature and precipitation record for Eocene to mid-Miocene (~54–13 Ma). Alkaline elements are strongly enriched in the detrital mineral fraction in fine-grained siliciclastic marine sediments and only occur as trace metals in the biogenic fraction. Hence, terrestrial climofunctions similar to the chemical index of alteration (CIA) can be applied to the alkaline major element geochemistry of marine sediments on continental margins in order to reconstruct changes in precipitation and temperature. We validate this approach by comparison with published paleotemperature and precipitation records derived from fossil wood, leaves, and pollen and find remarkable agreement, despite uncertainties in the calibrations of the different proxies. A long-term cooling on the order of ≥8°C is observed between the Early Eocene Climatic Optimum (~54–52 Ma) and the middle Miocene (~15–13 Ma) with the onset of transient cooling episodes in the middle Eocene at ~46–45 Ma. High-latitude stratigraphic records currently exhibit insufficient temporal resolution to reconstruct continental aridity and inferred ice-sheet development during the middle to late Eocene (~45–37 Ma). However, we find an abrupt aridification of East Antarctica near the Eocene-Oligocene transition (~34 Ma), which suggests that ice coverage influenced high-latitude atmospheric circulation patterns through albedo effects from the earliest Oligocene onward."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #74 on: September 02, 2013, 07:08:20 PM »
The following linked reference (with a free access pdf), raises so many concerns about state-dependent climate sensitivity and its implications for future climate change that I strongly recommend that the reader take the time to download the pdf and read what the authors have to say about this complex and important topic.  Caballero & Huber 2013 (C&H 2013) present a thoughtful and balanced discussion such as that indicated by the first attached figure 1 that compares the changes in Mean Average Temperature, MAT, with atmospheric carbon dioxide concentrations for both the Paleogene (~65 to 35 Mya) the modern boundary conditions, indicating both a consistent ~5oC lower MAT for modern conditions than for Paleogene conditions.
 
http://www.pnas.org/content/110/35/14162.abstract

State-dependent climate sensitivity in past warm climates and its implications for future climate projections; by: Rodrigo Caballero and Matthew Huber; PNAS August 27, 2013 vol. 110 no. 35 pp 14162-14167, doi: 10.1073/pnas.1303365110



"Abstract
Projections of future climate depend critically on refined estimates of climate sensitivity. Recent progress in temperature proxies dramatically increases the magnitude of warming reconstructed from early Paleogene greenhouse climates and demands a close examination of the forcing and feedback mechanisms that maintained this warmth and the broad dynamic range that these paleoclimate records attest to. Here, we show that several complementary resolutions to these questions are possible in the context of model simulations using modern and early Paleogene configurations. We find that (i) changes in boundary conditions representative of slow “Earth system” feedbacks play an important role in maintaining elevated early Paleogene temperatures, (ii) radiative forcing by carbon dioxide deviates significantly from pure logarithmic behavior at concentrations relevant for simulation of the early Paleogene, and (iii) fast or “Charney” climate sensitivity in this model increases sharply as the climate warms. Thus, increased forcing and increased slow and fast sensitivity can all play a substantial role in maintaining early Paleogene warmth. This poses an equifinality problem: The same climate can be maintained by a different mix of these ingredients; however, at present, the mix cannot be constrained directly from climate proxy data. The implications of strongly state-dependent fast sensitivity reach far beyond the early Paleogene. The study of past warm climates may not narrow uncertainty in future climate projections in coming centuries because fast climate sensitivity may itself be state-dependent, but proxies and models are both consistent with significant increases in fast sensitivity with increasing temperature."



The C&H 2013 quote below, indicate that changes in cloud cover associated with a weakening of the atmospheric Hadley Cell (presumably related to a transition from a three cell to a one cell configuration) results in a marked increase in the fast or "Charney" climate sensitivity at a MAT of about 23 oC (which they associate with a modern atmospheric carbon dioxide concentration of about 4,000 ppm, see the attached figure).  Thus the C&H 2013 findings would appear to indicate that the modern Earth has a long way to go before possibly changing to an equable climate atmospheric circulation pattern.  However, I would like to note that from a hazard assessment point of view regarding out modern condition: (a) we do not know how fast the "slow" climate sensitivity factors will change (such as a possible sudden albedo flip; or rapid methane releases from either the permafrost or from methane hydrates); and (b) we do not know whether the current very rapid rate of radiative forcing might temporarily support several years of Madden-Julian oscillation type conditions that could convey large amounts of tropical atmospheric heat directly to the Arctic regions; which could lead to the "periodic strange attractor" type of behavior that I discuss in the first half of this thread that could lead to abrupt climate change.

"Finally, fast-feedback sensitivity in the present model is strongly nonuniform, increasing rapidly at high temperatures due mostly to positive short-wave cloud feedbacks. These changes in cloud cover and cloud radiative forcing (CRF) are coincident with major changes in the model’s general circulation. As shown in previous work (52), the 23 °C threshold marks the transition to a regime in which large-amplitude equatorial waves reminiscent of the Madden–Julian oscillation converge sufficient zonal momentum onto the equator to drive mean superrotating (i.e., westerly) winds along the equatorial upper troposphere. This transition is also observed in a “superparameterized” version of the atmosphere model (53), where the standard convective parameterization is replaced by an embedded cloud-resolving model within each column that is arguably closer to physical reality. The transition coincides with a substantial weakening of the Hadley cell, which is consistent with decreased high- and midlevel cloud cover in the deep tropics and with low-level clouds in the subtropics (Fig. S2). Moreover, as temperature increases, the midlatitude storm tracks become weaker and shift poleward, resulting in decreased low and midlevel clouds, especially in the southern midlatitudes (Fig. S2). There is observational support for the notion that such a shift in storm tracks is associated with positive cloud feedback (54)."

Associated Selected References:
52. Caballero R, Huber M (2010) Spontaneous transition to superrotation in warm climates simulated by CAM3. Geophys Res Lett 37:L11701.
53. Arnold NP, Kuang Z, Tziperman E (2013) Enhanced MJO-like variability at high SST. J Clim 26(3):988–1001.
54. Bender FAM, Ramanathan V, Tselioudis G (2012) Changes in extratropical storm track cloudiness 1983–2008: Observational support for a poleward shift. Climate Dynamics 38(9-10):2037–2053."

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #75 on: September 02, 2013, 07:54:03 PM »
While I have previously made the point raised in the following website, that the WAIS is subject to rapid warming, I thought that I would reiterate that: The current rapid thinning of the Thwaites Glacier coastal areas are resulting in an increased frequency of surface penetrating crevasses; that could fill with surface melt water in the future due to rapid warming of this area (see linked article); that could lead to accelerated calving; that could lead to a "Thwaites Effect"; that could lead to a high RSLR in the Bering Sea; that could force warm Pacific water into the Arctic Ocean; that could result in an Artic albedo flip; that could drive the Earth System Sensitivity, ESS (see Climate Sensitivity in Wikipedia) upward; that could ratchet the Earth's climate equilibrium to a different level.

http://www.washington.edu/news/2013/08/14/earth-orbit-changes-were-key-to-antarctic-warming-that-ended-last-ice-age/
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #76 on: September 05, 2013, 11:55:53 PM »
The linked reference shows that the paleorecord indicates that a reduction in Southern Ocean sea ice can lead to local warming and acceleration of ice mass loss contributing to SLR:

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12376.html



Onset of deglacial warming in West Antarctica driven by local orbital forcing; WAIS Divide Project Members; Nature; (2013); doi:10.1038/nature12376

Abstract:
"The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes."
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sidd

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #77 on: September 12, 2013, 11:10:28 PM »
This reminded me of an older paper, Johanson and Fu (2009),DOI: 10.1175/2008JCLI2620.1
"Hadley Cell Widening: Model Simulations versus Observations"

which pointed out that

"We have demonstrated that the GCMs in the CMIP3 multimodel dataset are unable to reproduce the recent Hadley cell widening but additional work must be completed so as to understand why widening in theGCMs is so much smaller than observed. "

which reinforces my (nebulous, so far) suspicions that current climate models are unable to capture the transition to a one or two cell regime.

sidd

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #78 on: September 13, 2013, 11:24:14 PM »
Sidd,

Since 2009 some progress has been made on the critical question of Hadley Cell, HC, expansion, for both future and past conditions.  The first linked reference (with a pdf) compares model results of the mid-Pliocene and for the modern condition for RCP 4.5; which confirms a high probability of HC expansion in the future:

http://www.clim-past.net/9/1613/2013/cp-9-1613-2013.pdf

A comparative study of large-scale atmospheric circulation in the context of a future scenario (RCP4.5) and past warmth (mid-Pliocene); by: Y. Sun, G. Ramstein, C. Contoux, and T. Zhou; 2013; Clim. Past, 9, 1613–1627, 2013; www.clim-past.net/9/1613/2013/; doi:10.5194/cp-9-1613-2013


"Abstract. The mid-Pliocene warm period (~3.3–3.0 Ma) is often considered as the last sustained warm period with close enough geographic configurations compared to the present one associated with atmospheric CO2 concentration (405±50 ppm) higher than the modern level. For this reason, this period is often considered as a potential analogue for the future climate warming, with the important advantage that for mid-Pliocene many marine and continental data are available. To investigate this issue, we selected the RCP4.5 scenario, one of the current available future projections, to compare the pattern of tropical atmospheric response with the past warm mid-Pliocene climate.  We use three Atmosphere-Ocean General Circulation Model (AOGCM) simulations (RCP4.5 scenario, mid- Pliocene and present-day simulation) carried out with the IPSL-CM5A model and investigate atmospheric tropical dynamics through Hadley and Walker cell responses to warmer conditions, considering that the analysis can provide some assessment of how these circulations will change in the future.  Our results show that there is a damping of the Hadley cell intensity in the northern tropics and an increase in both subtropics. Moreover, northern and southern Hadley cells expand poleward.  The response of the Hadley cells is stronger for the RCP4.5 scenario than for the mid-Pliocene, but in very good agreement with the fact that the atmospheric CO₂ concentration is higher in the future scenario than in the mid-Pliocene (543 versus 405 ppm). Concerning the response of the Walker cell, we show that despite very large similarities, there are also some differences. Common features to both scenarios are: weakening of the ascending branch, leading to a suppression of the precipitation over the western tropical Pacific. The response of the Walker cell is stronger in the RCP4.5 scenario than in the mid-Pliocene but also depicts some major differences, as an eastward shift of its rising branch in the future scenario compared to the mid-Pliocene.  In this paper, we explain the dynamics of the Hadley and Walker cells, and show that despite a minor discrepancy, the mid-Pliocene is certainly an interesting analogue for future climate changes in tropical areas."

The second linked reference (with a pdf), finds that more distributed warm (poleward from the equator) promotes HC expansion; which is the case for modern global warming:

http://math.nyu.edu/~gerber/pages/documents/tandon_gerber_sobel_polvani-JC-2013.pdf

Understanding Hadley Cell Expansion versus Contraction: Insights from Simplified
Models and Implications for Recent Observations
; NEIL F. TANDON, EDWIN P. GERBER, ADAM H. SOBEL AND LORENZO M. POLVANI, 2013, JOURNAL OF CLIMATE; VOLUME 26


Abstract:
"This study seeks a deeper understanding of the causes of Hadley Cell (HC) expansion, as projected under global warming, and HC contraction, as observed under El Nino. Using an idealized general circulation model, the authors show that a thermal forcing applied to a narrow region around the equator produces ‘‘El Nino–like’’ HC contraction, while a forcing with wider meridional extent produces ‘‘global warming–like’’ HC expansion. These circulation responses are sensitive primarily to the thermal forcing’s meridional structure and are less sensitive to its vertical structure. If the thermal forcing is confined to the midlatitudes, the amount of HC expansion is more than three times that of a forcing of comparable amplitude that is spread over the tropics. This finding may be relevant to recently observed trends of rapid tropical widening.  The shift of the HC edge is explained using a very simple model in which the transformed Eulerian mean (TEM) circulation acts to diffuse heat meridionally. In this context, the HC edge is defined as the downward maximum of residual vertical velocity in the upper troposphere vmax * ; this corresponds well with the conventional Eulerian definition of the HC edge. In response to a positive thermal forcing, there is anomalous diabatic cooling, and hence anomalous TEM descent, on the poleward flank of the thermal forcing. This causes the HC edge (vmax * ) to shift toward the descending anomaly, so that a narrow forcing causes HC contraction and a wide forcing causes HC expansion."

These articles support the idea that HC expansion is very likely in the near future as we continue along the RCP 8.5 scenario.

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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #79 on: September 13, 2013, 11:46:37 PM »
For your reference on Hadley Cell expansion in the Southern Hemisphere, I also provide the following linked extract:

http://meetingorganizer.copernicus.org/EGU2013/EGU2013-6657.pdf

Planning for the impacts of Hadley cell expansion on water supply in Victoria, Australia; David Post, Bertrand Timbal, Francis Chiew, Harry Hendon, and Rae Moran; 2013; Geophysical Research Abstracts; Vol. 15, EGU2013-6657; EGU General Assembly 2013

"… Our research has linked the extent, duration and severity of this drought to the ongoing observed expansion of the Southern Hemisphere Hadleycell of 0.5 degrees per decade. This expansion has intensified the sub-tropical ridge over southern Australia, pushing cool season mid-latitude storm tracks further south, leading to a reduction in winter rainfall over the region. Modelling has shown that the expansion of the Hadley cell can only be reproduced if anthropogenic influences (greenhouse gases, aerosols and stratospheric ozone) are included in the models, thus providing evidence that the Millennium drought was at least partly attributable to climate change. Climate model projections also indicate that the expansion of the Hadley Cell is likely to continue. ..."

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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #80 on: September 19, 2013, 10:28:18 PM »
The linked reference indicates that paleo-evidence from the Pliocene indicate that the EAIS is more sensitivity than previously though:


http://www.nature.com/ngeo/journal/v6/n9/full/ngeo1889.html


Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth;
by: Carys P. Cook, Tina van de Flierdt, Trevor Williams, Sidney R. Hemming, Masao Iwai, Munemasa Kobayashi, Francisco J. Jimenez-Espejo, Carlota Escutia, Jhon Jairo González, Boo-Keun Khim Robert M. McKay, Sandra Passchier, Steven M. Bohaty, Christina R. Riesselman, Lisa Tauxe, Saiko Sugisaki, Alberto Lopez Galindo, Molly O. Patterson Francesca Sangiorgi, Elizabeth L. Pierce, Henk Brinkhuis, Adam Klaus, Annick Fehr, James A. P. Bendle Peter K. Bijl et al.; Nature Geoscience; 6, 765–769; doi:10.1038/ngeo1889; 21 July 2013
Abstract:
"Warm intervals within the Pliocene epoch (5.33–2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric CO2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene."
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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #81 on: September 23, 2013, 10:41:21 AM »
The linked 2012 reference provides paleo-evidence support to concept that massive glacial dewatering events can destabilize ice fields around the ASE:

http://www.sciencedirect.com/science/article/pii/S0921818112000628


Did massive glacial dewatering modify sedimentary structures on the Amundsen Sea Embayment shelf, West Antarctica?;
by: Estella Weigelt, Gabriele Uenzelmann-Neben, Karsten Gohl, & Robert D. Larter; 2012 Global and Planetary Change; Volumes 92–93, July 2012, Pages 8–16

Abstract:
"Multichannel seismic reflection lines collected in the western Amundsen Sea Embayment (ASE) provide an insight into the sedimentary cover on the shelf, which documents glacial processes. Numerous columnar, reflection-poor structures penetrating the sedimentary sequences on the middle shelf form the focus of this study. The features range between 50 and 500 m in width, and from a few metres up to 500 m in height. The columns originate and end at different depths, but do not seem to penetrate to the seafloor. They show well-defined vertical boundaries, and reflection signals can be identified below them. Hence, we exclude gas-bearing chimneys. Based on the general seismic reflection characteristics we suggest that the columns originate from dewatering processes which occur close to glaciated areas where fluids are pressed out of rapidly loaded sediments. Likely several mud-diapirs rise from water-rich mud layers within a mixed sedimentary succession and penetrate overlying denser and coarse-grained sediment strata. The presence of fluid-escape veins indicates a glacial origin and overprinting of the older sedimentary sequences on the ASE. The locations of the structures indicate that grounded ice sheets reached at least onto the middle shelf during former glacial periods."
“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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #82 on: September 24, 2013, 06:44:48 AM »
Two older papers

1)Smith(2011) doi:10.1016/j.quascirev.2010.11.020 from which i attach fig 7. Note that the ice shelf retreated a hundred kilometers in a couple hundred years, as quickly as 400m/yr (over a retrograde seabed.) They note that PIG is going over a klick a year.

2)Jenkins(2010)  doi:10.1038/NGEO890 Fig 2c showing PIG bed. PIG will not quit retreat till it sees prograde bed about 250 Km inland. By then it is well into eastern flank of Thwaites and Byrd Subpolar basin (BSB).

So now will have _two_ big gates for CDW into BSB. Thwaites will not tarry, waiting for PIG either, and Thwaites is much wider.

Hello, grounding line at Transantarctic mountains ... in century timescales ...

sidd

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #83 on: September 24, 2013, 06:52:36 AM »
I should mention that the fast retreat at 400m/yr in Fig 7 of Smith(2011) in my last post coincides with MWP1A (think 5m SLR/century for five centuries). That rate of retreat is what PIG is doubling or trebling  now, over a retrograde bed, just like Getz and Dodson in the reference about 11Kyr before present. Thwaites is champing at the bit, too, as PIG eats away at its eastern flank.

Sweet dreams.

sidd


AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #84 on: September 25, 2013, 10:07:40 AM »
Sidd,

Thanks for your greats posts.  Paleo-evidence like this makes it clear that even if the do not sustain multiple meters of SLR this century; then certainly we will experience multiple meters next century.

Best,
ASLR
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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #85 on: October 31, 2013, 03:26:02 PM »
At the beginning of this thread I made several posts about how chaos theory could be used to project ASLR probabilities, and the following link discusses progress made about how to use chaos theory to predict Dragon King events (like ASLR):

http://www.wired.com/wiredscience/2013/10/chaos-theory-dragon-kings/
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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #86 on: December 12, 2013, 04:57:04 PM »
While this is somewhat old news, it is very important regarding the risk of abrupt climate change that we are facing before 2100 that I am posting the news release from October below.  Obviously, if global temperatures jumped 5 degree C in 13 years, due to a doubling of atmospheric CO2 concentration; triggering a collapse of the WAIS would be only one of the many climate challenges facing society at that point:

http://news.rutgers.edu/research-news/new-finding-shows-climate-change-can-happen-geological-instant/20131003#.UqjiXRZD3tU

James D. Wright and Morgan F. Schaller (2013), "Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum", PNAS 2013 110 (40) 15908-15913:

“Rapid” and “instantaneous” are words geologists don’t use very often. But Rutgers geologists use these exact terms to describe a climate shift that occurred 55 million years ago.
In a new paper in the Proceedings of the National Academy of Sciences, Morgan Schaller and James Wright contend that following a doubling in carbon dioxide levels, the surface of the ocean turned acidic over a period of weeks or months and global temperatures rose by 5 degrees centigrade – all in the space of about 13 years.
Scientists previously thought this process happened over 10,000 years.
Wright, a professor of earth and planetary sciences in the School of Arts and Sciences and Schaller, a research associate, say the finding is significant in considering modern-day climate change.
“We’ve shown unequivocally what happens when CO2 increases dramatically – as it is now, and as it did 55 million years ago,” Wright said. “The oceans become acidic and the world warms up dramatically. Our current carbon release has been going on for about 150 years, and because the rate is relatively slow, about half the CO2 has been absorbed by the oceans and forests, causing some popular confusion about the warming effects of CO2. But 55 million years ago, a much larger amount of carbon was all released nearly instantaneously, so the effects are much clearer.”
The window to this important decade in the very distant past opened when Wright helped a colleague, Kenneth Miller, and his graduate students split core samples they extracted from a part of southern New Jersey once covered by the ocean.
A close-up of the core at the heart of Wright's and Schaller's work. Note the regular dark bands – "like a tree ring," Schaller said.
The patterns found in the long cylinder of sediment told a story. There were distinct clay bands about 2 centimeters thick occurring rhythmically throughout the cores.
“They called me over and said, ‘Look at this,” said Schaller.  “What jumped out at me were these rhythmic clay layers, very cyclic. I thought, ‘Wow, these have got to mean something.”
Wright and Schaller surmised that only climate could account for the rhythmic pattern they saw. “When we see cycles in cores, we see a process,” Schaller said. “In this case, it’s like a tree ring. It’s giving us a yearly account through the sediments.“
This discovery provided the necessary data to finally solve the huge conundrum surrounding this event – the significant error in how fast the carbon was released.
Whatever the cause of the carbon release, -- some scientists theorize that a comet struck the earth -- Wright and Schaller’s contention that it happened so rapidly is radically different from conventional thinking, and bound to be a source of controversy, Schaller believes.
“Scientists have been using this event from 55 million years ago to build models about what’s going on now,” Schaller said. “But they’ve been assuming it took something like 10,000 years to release that carbon, which we’ve shown is not the case.  We now have a very precise record through the carbon release that can be used to fix those models.”
“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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #87 on: December 15, 2013, 05:02:04 PM »
I strongly recommend reading the linked free access article (citation and abstract) which provides a geological perspective on potential future sea-level rise.  This paper provides SLR values and confidence levels that in my opinion provide a firm basis for a Bayesian prior for projecting SLR.  To this geological prior I believe that one needs to apply Bayesian learning in order to develop posterior probability density functions, PDFs, for SLR in order to account for the fact that anthropogenic radiative forcing is at least ten times faster than at any time in the geological record:

Eelco J. Rohling, Ivan D. Haigh, Gavin L. Foster, Andrew P. Roberts & Katharine M. Grant, (2013), "A geological perspective on potential future sea-level rise", Scientific Reports, 3, 3461, doi:10.1038/srep03461

http://www.nature.com/srep/2013/131212/srep03461/pdf/srep03461.pdf

Abstract"
"During ice-age cycles, continental ice volume kept pace with slow, multi-millennial scale, changes in climate forcing. Today, rapid greenhouse gas (GHG) increases have outpaced ice-volume responses, likely committing us to > 9 m of long-term sea-level rise (SLR). We portray a context of naturally precedented SLR from geological evidence, for comparison with historical observations and future projections. This context supports SLR of up to 0.9 ( 1.8 ) m by 2100 and 2.7 (5.0) m by 2200, relative to 2000, at 68% (95%) probability. Historical SLR observations and glaciological assessments track the upper 68% limit. Hence, modern change is rapid by past interglacial standards but within the range of ‘normal’ processes. The upper 95% limit offers a useful low probability/high risk value. Exceedance would require conditions without natural interglacial precedents, such as catastrophic ice-sheet collapse, or activation of major East Antarctic mass loss at sustained CO2 levels above 1000 ppmv."
« Last Edit: December 16, 2013, 05:54:40 PM by AbruptSLR »
“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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #88 on: December 16, 2013, 05:40:35 PM »
ASLR,

Many thanks for this reference.

Rohling et al write (p.3):
"LIg SLR likely occurred at sustained rates of ~1 m cy-1 or less... Given the need for long-term planning in coastal defence, we consider a ‘worst case’ outlook from our natural perspective. The upper bound of our 95% probability envelope (i.e., the 97.5th percentile) implies a 2.5% chance of > 1.8 m SLR by 2100 and > 5.0 m by 2200, relative to 2000 (Figure 3). This 2100 value closely approaches the (unlikely) maximum value suggested by Pfeffer et al."

This is from a 'natural perspective'. However, as you point out: "anthropogenic radiative forcing is at least ten times faster than at any time in the geological record".

Rohling et al conclude (p.5):
"the most important point from our assessment is that SLR since 1700 has been consistent (within uncertainties) with expectations from geologically documented responses to climate-system disequilibria. Thus, no matter how special anthropogenic climate forcing may be in terms of magnitude and rate of increase, the observed sea-level response to anthropogenic forcing has so far remained close to the range of expectations based on well-known natural precedents.
Continued monitoring of SLR, and comparison with the natural context outlined here, may be used to identify if and when sea-level response becomes ‘special’ (i.e., unprecedented during geological interglacials). For example, the higher emissions projections of Vermeer and Rahmstorf imply a shift toward such ‘special’ responses from ~2050. Until such time, however, comparison of SLR observations with our results indicates that future SLR projections can rely with confidence on testing and validation of physical models against well-known examples from the recent geological past. However, this trajectory requires that SLR rates develop toward an eventual value of 4.3 m cy-1, roughly similar to mwp-1a (ref. 36) (Figure 3a), even though today’s global ice volume is only about a third of that at the onset of the last deglaciation. Most of the extra ice during glacial times existed in North America and northwestern Eurasia, where it extended to relatively low latitudes (40–50uN). These ice sheets were highly sensitive to climate change, as witnessed by the fact that they existed during ice ages and were almost entirely absent during interglacials. Both the size and sensitivity of these glacial ice masses would have been conducive to high deglacial rates of SLR. Starting from present-day conditions, rates such as those of mwp-1a would require unprecedented ice-loss mechanisms, such as collapse of a major ice sheet (e.g., the largely marine-based West Antarctic Ice Sheet). Alternatively, such rates might develop with a large increase in the amount of ‘vulnerable’ ice, by activation of major EAIS retreat. From the natural perspective, however, the latter only seems to become relevant under extreme GHG forcing, with long-term CO2 above ~1000 ppmv or so (see Figure 1, and discussion above). Without invoking such exceptional conditions or catastrophic events, our assessment supports the notion that ~2 m of SLR by 2100 represents a useful upper limit."

However, they also say (p.6):
"Where detailed records exist, rates of SLR tracked rates of polar temperature change within a few centuries, while sea-levels tracked a new temperature stasis within 2 to 7 centuries."

Since the forcing now is so much stronger than any known natural forcing, I'm wondering if they don't understate their 'most important point'. To me it seems their analysis points to the possibility, if not the likelihood, of much faster than natural SLR. A rate of several meters per century, maybe up to about 7 meters/century, seems quite possible, once the melting and ice sheet disintegration gets up to speed.

What do you think?

AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #89 on: December 16, 2013, 06:08:57 PM »
Lennart,

While I do not disagree with any of Rohling et al (2013)'s evidence, Rohling has stated publically that if CO2 content in the atmosphere reaches 1,000 ppm then "all bets are off" regarding the use of his (their) analysis; while RCP 8.5 95% CL leads to just such a world.  Furthermore, Rohling et al does not make allowance for such factors as: (a) the Antarctic ozone hole (which is currently accelerating Antarctic ice mass loss); (b) black carbon (which is not in the paleo record); or (c) the rapid rate of collapse of the ASI.  Therefore, I agree that Rohling et al are understating the risks and that sometime between 2200 and 2300 it might be possible to get up to rates of SLR as high as 7 m per century (assuming that BAU continues).

I got to go,
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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #90 on: December 17, 2013, 12:29:22 AM »
Lennart,

First, in my previous post I said that the RCP 8.5 95% probability scenario  lead to a 1,000 ppm CO2 atmosphere concentration by 2100, when actually RCP 8.5 50%CL does.

Next, I did not have time to point out paleo-evidence indicates that such positive feedback mechanisms as: ASI extent reduction, permafrost thawing (and associated methane emissions), and reduction of the duration of snow coverage in the tundra; are slow response feedbacks; while our current experience is that they are changing rapidly due to anthropogenic forcing.

Finally, the majority of our satellite measurements of SLR and Antarctic ice mass loss has occurred during the current El Nino hiatus.  As soon as this hiatus period ends, we are likely to see a significant increase in the rate of SLR that researcher like Pfeffer et al 2008 (whom Rohling et al 2013 reference) are not fully considering.

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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #91 on: December 17, 2013, 11:24:10 AM »
ASLR,

I'm trying to better understand the magnitude of the difference between the natural radiative forcings of the past and the (potential) anthropogenic forcing today and in the coming centuries.

Rohling et al say (p.1):
"we implicitly consider a natural range of forcing types (orbital, major feedbacks) and rates (up to 1.5 Wm-2 ky-1 of annual mean global forcing, or about 3 Wm-2 ky-1 of annual mean forcing at high northern latitudes, where ky stands for thousand years). Anthropogenic rates of climate forcing, close to a global mean of 1 W m-2 cy-1, are much faster than the natural rates considered."

They also say (p.5):
"We infer that the present disequilibrium is already sufficient to cause build-up toward major ice-sheet responses, and that further warming will occur over similar timescales as the developing ice-sheet responses, so that increased forcing would cause (rapid) shifts toward extremes of the parameter ranges considered here (high ultimate SLR rates and rapid adjustment timescales). The median global radiative forcing projections for high-emission RCPs is ~12 W m-2 (ref. 15). For deglaciations, this was 8–10 W m-2 (refs. 17, 28). We infer that the long-term consequences of high-emission RCPs may be suitably gauged from the SLR adjustment rates and timescales of deglaciations, if we assume that such consequences would develop via naturally precedented processes (e.g., because the response becomes rate limited). Similar to a previous study, we consider that the long-term consequences of low- to middle-emission RCPs may be gauged using LIg responses."

So what are they saying, explicitly and/or implicitly?

Natural (global mean) forcings of the past ranged up to 1.5 W/m2 per millennium and up to 10 W/m2 per deglaciation (which lasted at least 10 millennia). This seem to imply a maximum forcing rate of about 0.15 W/m2 per century, sustained for at least several centuries. Since most of this forcing would have been concentrated on the Northern Hemisphere, where most of the ice was, the maximum forcing rate there may have been about double the global mean rate, or 0.3 W/m2 per century.

The current anthropogenic forcing rate is almost 1 W/m2 per century. With strong mitigation we could maybe limit the total forcing to about 3 W/m2 this century. Averaged over two centuries this seems to imply an average forcing rate of (very roughly) 1.5 W/m2 per century, so about 10 times stronger than the maximum natural rate during past deglaciations, as you already pointed out.

Without strong mitigation the total forcing could grow to maybe 8-9 W/m2 in 2100 and to 12 W/m2 over the coming two/three centuries. Averaged over several centuries this seems to imply an average forcing rate of about 3-4 W/m2 per century, so at least 20 times stronger than the maximum natural forcing rate in the past.

Then the question is: will SLR speed up in proportion to the forcing rate? Or is there maybe a physical limit to the rate of ice sheet melting/disintegration, as Rohling et al also ask themselves, and as Pfeffer et al have asked before? And how relevant is the observation that during natural melting episodes the forcing was maybe mainly concentrated on the Northern Hemisphere?

Natural rates of SLR have apparently ranged from up to 1 meter/century during interglacials and up to 5 meter/century during deglaciation. If SLR speeds up in proportion to the forcing, this would seem to imply the possibility of SLR speeding up to maybe 10 meter/century, even with strong mitigation. Without strong mitigation SLR could maybe speed up even more.

But perhaps physical (kinematic?) constraints or negative (iceberg cooling) feedbacks would limit this speeding up to a rate of SLR somewhere between 1 and 10 meter/century? Maybe, but in any case enough (vulnerable) ice seems to be available in Antarctica to sustain, under such strong forcings, (even with strong mitigation) a large rate of SLR of several (3-7?) meters/century for at least several centuries.

The less we invest in mitigation, the more slow positive feedbacks will re-inforce the antropogenic forcing, the more SLR will likely speed up, and the harder it will be to slow this rise down as well as to adapt to it. Rohling et al seem to make a plausible case that at least about 10 meter of SLR is unavoidable by now, but we can probably still slow the maximum rate of this rise down significantly (to maybe about 3 meter/century, or less?).

Under BAU a total SLR of 65-70 meters in the long term seems unavoidable (with maximum rates speeding up to maybe about 7 meter/century?).

I would be happy to hear why all this would be alarmistic rather than alarming.

Laurent

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #92 on: December 17, 2013, 01:18:33 PM »
If there was 300 meters of sea level rise in the past then we should expect something around, may be not exactly because the continents have changed since then but what do we really know about the volume of the earth since then !?
I am not saying that the futur generations will see that much but we should talk about it a little bit more... I think !

AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #93 on: December 17, 2013, 04:19:10 PM »
Laurent,

The world has previously experienced 300m of SLR because during glacial periods there was a lot more ice/snow in the world because the oceans were much lower that they are today (we are currently in an interglacial period).  Furthermore, Lennart is correct that there is currently only a sufficient amount of ice/snow (combined with steric SLR) to cause another 65 to 70m of future SLR (over centuries to millenia depending on the scenario that occurs).

Lennart,

As the NRC 2013 on abrupt climate change has stated that abrupt SLR (with at least 1m of SLR within three decades) is plausible this century, and I have just made over 1,000 posts explaining how the WAIS and coastal areas of the EAIS could plauisably contribute ice mass loss (with some also from the GIS) to contribute 1m of SLR within three decades some time this century; I do not find your analysis alarmist at all (but of course it is alarming).  As you pointed out Rohling et al 2013 also state that: "We infer that the present disequilibrium is already sufficient to cause build-up toward major ice-sheet responses ..." and I believe that there is plenty of evidence in the literature (and in this Antarctic folder) to support that marine ice sheets and marine-terminating glaciers can retreat abruptly.

I recently read the findings of a pole that said that only 8% of American are interested in talking about climate change, as they are distracted by other matters.  Thus I personnally find it difficult to imagine that society will make the effort to get off of a high radiative forcing scenario before the consequences of climate change are significant (relative to the world GDP), particularly as I see that much of the world is primed to implement hydrofracking to access large amounts of fossil fuels over the next several decades (see the attached image of shale gas resources relative to conventional gas resources).
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TeaPotty

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #94 on: December 17, 2013, 05:26:33 PM »
Paper states about current strong anthropogenic forcing (my emphasis):

Our assessment is guided by two questions.
First: is today’s climate system in equilibrium with forcing?
Second: what are the natural timescales and rates of change in ice-volume adjustment to a disequilibrium state, relative to a forcing increase?

...The answer to the first question, whether today’s climate system is in equilibrium with forcing, is negative. Anthropogenic climate forcing is more than an order of magnitude faster than climate forcing or major feedbacks at any known time in the Cenozoic. Key climate-system components,such as deep ocean temperature and ice volume, respond slowly due to their large inertia. Ice-volume contributions to future SLR will therefore reflect delayed responses to GHG emissions, developing climate system feedbacks, and future emissions. The large and fast-growing disequilibrium between accelerated climate forcing and slow/lagging response thus creates a strong potential for rapid sea-level adjustments. The current disequilibrium may be evaluated by comparing present-day conditions with geological data that illustrate the likely climate-system state if it had been given sufficient time to respond completely to the change in forcing.

...It is less straightforward to use geological data to answer the second question because present-day climate change due to rapid GHG emissions is: (a) unprecedentedly rapid relative to changes due to orbital forcing and climate system feedbacks, and (b) becoming warmer than a normal interglacial. Regardless, geological observations can at least provide a sound natural context for modern trends and future projections.


Laurent

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #95 on: December 17, 2013, 09:27:51 PM »
AbruptSLR
The 300 meters was above current level and happened 70 million years ago, there was no interglacial at that time ! The water that was there, is still there, not gone into space !
We were in an interglacial era for around 1 million years (with a cycle of around 120.000 years) but this may be over now, we may be heading toward something else.
I never encontered explanation of why we were in an interglacial era but my guess is that the earth is losing energy and a big part of the CO2 was stored in the ground.

The 65 meters figure is well known but if it is based on the calculation below, then it is absolutely wrong ! not the calcul but the interpretation !
It is said we have around 30 millions km3 of ice around the world (mainly in Antarctica 29)
The surface of the oceans is roughly 70% of the earth surface (radius of the earth 6370 km, so the total surface is 4 x pi x 6370 x 6370 ~ 510 millions de km2)  wich is 357 millions de km2.

If all the ice melts 30 / 357 = 0,084 km = 84 meters. May be a little less because all the ice is not completely grounded.

But this calcul assume the thermal expension is 0, wich is wrong, I have seen 50 % (no source)
This calculation assume there is no isostatic rebound, wich is wrong, you cannot remove billions of tons without any effect on the crust !

Lennart van der Linde

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #96 on: December 17, 2013, 09:49:05 PM »
Diffenbaugh & Field (2013) stress that warming this century will be at least ten times faster than any other comparable warming in the past 65 million years, as ASLR and Rohling et al already pointed out:
http://climate-institute.webstarts.com/uploads/Natural_systems_climate_change_Field_Nature_2013.pdf

They say:
"the Paleocene Eocene Thermal Maximum (PETM) encompassed warming of at least 5°C in <10,000 years, a rate of change up to 100-fold slower than that projected for RCP8.5 and 10-fold slower than that projected for RCP2.6 ... Terrestrial ecosystems have experienced widespread changes in climate over the past century. It is highly likely that those changes will intensify in the coming decades, unfolding at a rate that is at least an order of magnitude—and potentially several orders of magnitude—more rapid than the changes to which terrestrial ecosystems have been exposed during the past 65 million years."

Also see figure S1 in their supplementary material:
http://www.sciencemag.org/content/suppl/2013/08/01/341.6145.486.DC1/Diffenbaugh-SM.pdf

So to me it seems at least quite possible, if not likely, that future SLR will be faster than any SLR in the past 65 million years, including Meltwater Pulse 1A.

AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #97 on: December 18, 2013, 02:24:50 AM »
Laurent,

Thanks for the corrections about paleo sea levels, as according to the attached image from Wikipedia sea level has been may have been somewhere between 200m and 400m higher than today in the distant past.
“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: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #98 on: December 18, 2013, 11:33:35 AM »
As to the speed of current and future warming compared to past warmings, this paper by Wright & Schaller suggests that the PETM warming 55 million years ago may have happened much faster than up to the 10.000 years suggested by earlier research:
http://geology.rutgers.edu/images/Publications_PDFS/Wright_Schaller_2013.pdf

They conclude the planet warmed 5 degrees C in possibly as little as 13 years, which they themselves regard as probably controversial, as they explain in their press release:
http://news.rutgers.edu/research-news/new-finding-shows-climate-change-can-happen-geological-instant/20131003#.UlQlTWRgYY5

However, since there were no ice sheets back then, this possibly extremely fast warming seems not very relevant for the study of the potential speed of future SLR.

AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #99 on: December 18, 2013, 04:25:57 PM »
Further to Laurent's point that most current SLR projections do not consider the glacial isostatic rebound of the WAIS, I provide the first image of the bedmap2 bottom elevations (with the ice removed without GIA), in contract to the second image of the antarctic bottom elevations (with the ice removed and with GIA.  It is very clear that the indicated rebound will add several meters to future SLR.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson