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Author Topic: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios  (Read 85561 times)

AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #200 on: August 13, 2017, 04:40:24 AM »
The Younger Dryas cooling, in the Northern Hemisphere, began while the Antarctic Cold Reversal (ACR) was still ongoing, and the ACR ended in the midst of the Younger Dryas. Blunier, Thomas; et al., "Phase Lag of Antarctic and Greenland Temperature in the last Glacial...," in Abrantes, Fatima; Mix, Alan C., eds. (1999). Reconstructing Ocean History: A Window into the Future. New York: Kluwer Academic. ISBN 0-306-46293-1., pp. 121–138.

The GCM (Image 2) interestingly shows freezing conditions in estuaries of the Equatorial rivers (the Amazon and the Congo) while GCM delivers overall warming for SH and tropics. It is assumed from YD images 1 and 2 that the ACR had ended and thus SH SST had largely increased, but isolated pockets of cold existed because there were grounded ice bergs that were still melting - or SH GCM model is overstating the SH warmth and more of it was cooler.

Notable exceptions to overall SH warmth (image 2) are the large cold regions (i.e. the Chilean Coast of South America and Western and Southern Shores of Australia). It is here proposed that GCM probably overstates the SH warming, or there were significant persistent pile ups of ice bergs along the coast lines of South America (i.e. the Amazon cold anomaly), or the Western Equatorial Africa (i.e. the Congo anomaly). The failure of Ross Ice Shelf would be behind the Chilean cold anomaly, the Brazilian coastal anomaly (i.e. the Amazon cold spot), the Equatorial African anomaly (i.e. the Congo cold spot) and the failure of the Ronne Ice Shelf and other Antarctic shelves were behind the ice pile up on the southern and western shores of Australia.

The rapid cooling within one summer season is indicative of ice sheet / melt water lake collapse to cool the Northern Atlantic Ocean and its associated climate just within few weeks (Image 3). Teleconnections of such rapid cooling of ocean require large ice volume dumping which should have rapidly increased the sea level projecting a tongue of water beneath continental ice shelves world wide and making them to calve rapidly on both hemispheres due to a bending effect. German sea level fears may be well placed and correct in seeing coastal nuclear reactors as risk.


Thanks.

If one thinks of the cool/negative phase of the AMO as a minor representation of a Younger Dryas event; then the linked reference indicates that when the AMO is in a negative phase, this research would indicate that for the next two, or more, decades we can expect the tropical Pacific Ocean to be warmer than normal; i.e. that El Nino events will be more frequent and more intense, which particularly warms Antarctica and which indicates that for this period the GMSTA may well be above its average trend line:

KEWEI LYU, JIN-YI YU, AND HOUK PAEK (2017), "The Influences of the Atlantic Multidecadal Oscillation on the Mean Strength of the North Pacific Subtropical High during Boreal Winter", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0525.1

http://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0525.1
&
https://www.ess.uci.edu/~yu/PDF/Lyu-Yu-Paek.JCLI.2017.pdf

Abstract: "The Atlantic multidecadal oscillation (AMO) has been shown to be capable of exerting significant influences on the Pacific climate. In this study, the authors analyze reanalysis datasets and conduct forced and coupled experiments with an atmospheric general circulation model (AGCM) to explain why the winter North Pacific subtropical high strengthens and expands northwestward during the positive phase of the AMO. The results show that the tropical Atlantic warming associated with the positive AMO phase leads to a westward displacement of the Pacific Walker circulation and a cooling of the tropical Pacific Ocean, thereby inducing anomalous descending motion over the central tropical Pacific. The descending motion then excites a stationary Rossby wave pattern that extends northward to produce a nearly barotropic anticyclone over the North Pacific. A diagnosis based on the quasigeostrophic vertical velocity equation reveals that the stationary wave pattern also results in enhanced subsidence over the northeastern Pacific via the anomalous advections of vorticity and temperature. The anomalous barotropic anticyclone and the enhanced subsidence are the two mechanisms that increase the sea level pressure over the North Pacific. The latter mechanism occurs to the southeast of the former one and thus is more influential in the subtropical high region. Both mechanisms can be produced in forced and coupled AGCMs but are displaced northward as a result of stationary wave patterns that differ from those observed. This explains why the model-simulated North Pacific sea level pressure responses to the AMO tend to be biased northward."
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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #201 on: August 19, 2017, 06:56:33 PM »
The linked reference provides evidence that paleo subglacial lakes contributed to the abrupt collapse of the Pine Island Bay marine glacier about 11 kya.  The researchers recommend that models for other modern-day Antarctic marine glaciers (say PIG and Thwaites) should be recalibrated to better account for the influence of subglacial lakes:

Title: "Geoscientific evidence for subglacial lakes"

https://www.sciencedaily.com/releases/2017/06/170601082228.htm

Extract: "During expeditions to the Amundsen Sea with the Research Icebreaker Polarstern in 2006 and 2010, AWI researchers and their international colleagues collected sediment cores that they now confirm are from subglacial lakes. "The cores, which are up to ten metres long, were collected at a water depth of 750 metres. The lake sediments are currently buried under a four-metre thick layer of marine sediment on the seafloor," Kuhn reports. They were retrieved from valleys on the ocean floor that were situated under the Antarctic Ice Sheet in the Earth's distant past. "We have now verified that, during the last glacial period, there were also subglacial lakes under a massively thick ice sheet in Pine Island Bay in the southern Amundsen Sea.

Satellite-monitoring shows that the movement of water from one lake to another can cause glaciers draining the Antarctic Ice Sheet to move more quickly. "This aspect needs to be taken into account in models designed to make predictions on the future behaviour and dynamics of ice masses, and with them, the degree to which the sea level will rise," explains AWI marine geologist Kuhn. According to a second study, which Kuhn contributed to and was published in Nature Communications on 17 March 2017, he added: "We have every reason to believe that there are more subglacial lakes in the Antarctic -- and more so in the last glacial period -- than has been previously assumed. In addition, icecaps like those on the sub-Antarctic island South Georgia and ice sheets reacted much more sensitively and rapidly to climate changes than previously assumed.""

See also:

1.   Gerhard Kuhn, Claus-Dieter Hillenbrand, Sabine Kasten, James A. Smith, Frank O. Nitsche, Thomas Frederichs, Steffen Wiers, Werner Ehrmann, Johann P. Klages, José M. Mogollón. Evidence for a palaeo-subglacial lake on the Antarctic continental shelf. Nature Communications, 2017; 8: 15591 DOI: 10.1038/NCOMMS15591

2.   Alastair G. C. Graham, Gerhard Kuhn, Ove Meisel, Claus-Dieter Hillenbrand, Dominic A. Hodgson, Werner Ehrmann, Lukas Wacker, Paul Wintersteller, Christian dos Santos Ferreira, Miriam Römer, Duanne White, Gerhard Bohrmann. Major advance of South Georgia glaciers during the Antarctic Cold Reversal following extensive sub-Antarctic glaciation. Nature Communications, 2017; 8: 14798 DOI: 10.1038/ncomms14798
“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 #202 on: August 30, 2017, 11:17:19 PM »
The linked article discusses findings from a new study reported in Nature that compares the current rates of radiative forcing, RF, with those that occurred during the PETM, and reconfirms that we are currently driving Earth Systems with RF with much fast rates than during the PETM:

Title: "New study: We’re outpacing the most radical climate event we know of"

https://arstechnica.com/science/2017/08/new-study-were-outpacing-the-most-radical-climate-event-we-know-of/

Extract: "To find a sudden warming that's driven entirely by greenhouse gases, you have to go back 56 million years to the Paleocene-Eocene Thermal Maximum (PETM). At the start of the PETM, a geologically sudden surge of carbon dioxide into the atmosphere caused warming and a large change in the ocean's pH. It took well over 100,000 years for conditions to return to anything normal. During that time, the extinction rate rose, and many ecosystems were disrupted or shifted by thousands of miles.

But understanding the PETM has proven a challenge, as it's not clear how much carbon entered the atmosphere or where it came from. A new paper in today's issue of Nature takes existing information about carbon dioxide levels and isotope ratios and combines them with data on the amount of carbon that dissolved into the oceans. The results provide a new indication of how much carbon entered the atmosphere—10,000 gigatonnes—and suggests volcanoes put it there.
Somewhat disturbingly, however, the data reinforces past indications that the PETM was relatively slow compared to our current carbon binge."
“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 #203 on: September 13, 2017, 05:45:35 PM »
The linked reference provides a paleo study of the WAIS's sensitivity to warming of the Southern Ocean:

Johannes Sutter, Paul Gierz, Klaus Grosfeld, Malte Thoma, Gerrit Lohmann (2016), "Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse", Geophysical Research Letters, DOI: 10.1002/2016GL067818

http://onlinelibrary.wiley.com/doi/10.1002/2016GL067818/full

Abstract: "The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 m in the last warm era, of which probably not much more than 2 m are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3-D thermomechanical ice sheet model forced by an atmosphere-ocean general circulation model (AOGCM). Our results show that high LIG sea levels cannot be reproduced with the atmosphere-ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2–3°C, accounting for a sea level rise of 3–4 m during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming."

See also:

Title: "How stable is the West Antarctic Ice Sheet?"

https://www.awi.de/nc/en/about-us/service/press/press-release/how-stable-is-the-west-antarctic-ice-sheet.html

Extract: "[05. February 2016]  A future warming of the Southern Ocean caused by rising greenhouse gas concentrations in the atmosphere may severely disrupt the stability of the West Antarctic Ice Sheet. The result would be a rise in the global sea level by several metres. A collapse of the West Antarctic Ice Sheet may have occurred during the last interglacial period 125,000 years ago, a period when the polar surface temperature was around two degrees Celsius higher than today. This is the result of a series of model simulations which the researchers of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have published online in the journal Geophysical Research Letters."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Laurent

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #204 on: September 14, 2017, 12:52:47 PM »
Someone here was saying that the Eemian was 0.5°c +/-0.3°c. Here the article says 2°c that is quite a big difference ! where is the truth ?

AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #205 on: September 14, 2017, 04:45:53 PM »
Someone here was saying that the Eemian was 0.5°c +/-0.3°c. Here the article says 2°c that is quite a big difference ! where is the truth ?


Laurent,

The linked reference indicates that the Eemian was punctuated by a number of hosing events that impacted the MOC.  Thus by cherry picking time periods, both values of GMSTA could be correct; however, as CMIP5 projections do not include such hosing events, so we cannot use the Eemian record as an analog for the AR5 projections.

Karin F.Helmens et al (2015), "Major cooling intersecting peak Eemian Interglacial warmth in northern Europe", Quaternary Science Reviews 122, DOI: 10.1016/j.quascirev.2015.05.018

http://www.sciencedirect.com/science/article/pii/S0277379115002231

Abstract: "The degree of climate instability on the continent during the warmer-than-present Eemian Interglacial (around ca. 123 kyr ago) remains unsolved. Recently published high-resolution proxy data from the North Atlantic Ocean suggest that the Eemian was punctuated by abrupt events with reductions in North Atlantic Deep Water formation accompanied by sea-surface temperature cooling. Here we present multi-proxy data at an unprecedented resolution that reveals a major cooling event intersecting peak Eemian warmth on the North European continent. Two independent temperature reconstructions based on terrestrial plants and chironomids indicate a summer cooling of the order of 2-4 °C. The cooling event started abruptly, had a step-wise recovery, and lasted 500-1000 yr. Our results demonstrate that the common view of relatively stable interglacial climate conditions on the continent should be revised, and that perturbations in the North Atlantic oceanic circulation under warmer-than-present interglacial conditions may also lead to abrupt and dramatic changes on the adjacent continent."

See also: "Eemian"
https://en.wikipedia.org/wiki/Eemian

Best,
ASLR
« Last Edit: September 15, 2017, 12:18:20 AM 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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AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #206 on: September 14, 2017, 05:24:51 PM »
Laurent,

Here is information from Hansen et al (2013), on your question (however, different researchers give different values):

James Hansen, Makiko Sato, Gary Russell, Pushker Kharecha (16 September 2013), "Climate sensitivity, sea level and atmospheric carbon dioxide", Philosophical Transactions of the Royal Society A, DOI: 10.1098/rsta.2012.0294

http://rsta.royalsocietypublishing.org/content/371/2001/20120294

Abstract: "Cenozoic temperature, sea level and CO2 covariations provide insights into climate sensitivity to external forcings and sea-level sensitivity to climate change. Climate sensitivity depends on the initial climate state, but potentially can be accurately inferred from precise palaeoclimate data. Pleistocene climate oscillations yield a fast-feedback climate sensitivity of 3±1°C for a 4 W m−2 CO2 forcing if Holocene warming relative to the Last Glacial Maximum (LGM) is used as calibration, but the error (uncertainty) is substantial and partly subjective because of poorly defined LGM global temperature and possible human influences in the Holocene. Glacial-to-interglacial climate change leading to the prior (Eemian) interglacial is less ambiguous and implies a sensitivity in the upper part of the above range, i.e. 3–4°C for a 4 W m−2 CO2 forcing. Slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify the total Earth system sensitivity by an amount that depends on the time scale considered. Ice sheet response time is poorly defined, but we show that the slow response and hysteresis in prevailing ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state dependence of climate sensitivity, finding an increased sensitivity towards warmer climates, as low cloud cover is diminished and increased water vapour elevates the tropopause. Burning all fossil fuels, we conclude, would make most of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change."

Best,
ASLR
« Last Edit: September 15, 2017, 12:19:07 AM 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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Laurent

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #207 on: September 15, 2017, 12:15:12 AM »
Thank you Abruptslr !
This graph from the ice cores in this link https://en.wikipedia.org/wiki/Eemian show me that there was an average at 0.8°c and a peak at 1.5°c (that is what I read) ok I get that different scientists give different results...
« Last Edit: September 15, 2017, 12:30:53 AM by Laurent »

AbruptSLR

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Re: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios
« Reply #208 on: September 16, 2017, 12:43:46 AM »
Thank you Abruptslr !
This graph from the ice cores in this link https://en.wikipedia.org/wiki/Eemian show me that there was an average at 0.8°c and a peak at 1.5°c (that is what I read) ok I get that different scientists give different results...


If this graph is showing local temperatures in Antarctica, then do not forget to divide by an Antarctic Amplification factor of between 2 and 3 to GMSTA.

Edit:

The linked reference finds an Antarctic Amplification of 2 to 3 time GMSTA; which is higher than that observed over the satellite era:

Kurt M. Cuffey, Gary D. Clow, Eric J. Steig, Christo Buizert, T. J. Fudge, Michelle Koutnik, Edwin D. Waddington, Richard B. Alley, and Jeffrey P. Severinghaus (2016), "Deglacial temperature history of West Antarctica", PNAS, vol. 113 no. 50, 14249–14254, doi: 10.1073/pnas.1609132113

http://www.pnas.org/content/113/50/14249

Abstract: "The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8 ∘  11.3±1.8∘ C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted."

Extract: "Of greatest immediate interest, however, is our demonstration that the global deglacial temperature change was amplified by a factor of 2–3 in the Antarctic, that Antarctic warming was largely achieved by 15 ka in coherence with records from Southern Hemisphere mountain ranges, and that climate models of the deglaciation perform well on average, but that the ones with lowest sensitivity can be discounted. The early warming of the Southern Hemisphere, which our study helps to quantify, arose from combined effects of reduced northward oceanic heat transport, increased insolation, and increasing atmospheric CO2. Quantitative simulation of this phenomenon could provide an illuminating challenge for model studies."
« Last Edit: September 16, 2017, 12:49:30 AM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson