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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #700 on: May 03, 2018, 07:26:57 PM »
While the two attached images are not from the linked research, the first image (from 2000 Richard Alley data for Greenland) illustrates how quickly temperatures warmed in Greenland 15,000 kya; while the second image should how 14,700 to 13,5000 kya the subsequent Meltwater pulse 1A rapidly drove-up sea level (& I note that Meltwater pulse 1A appears to have been triggered by a collapse of portions of the Pine Island embayment marine glacier, see the last link about Meltwater pulse 1A).  This paleo-data illustrates how rapidly the bipolar seesaw can change global climate, and I note that we appear to be entering a parallel phase of bipolar seesaw, with rapidly shifting North Atlantic (see the immediate previous post) and North Pacific ocean circulation patterns, and with the PIG and Thwaites marine glaciers at risk of rapidly collapsing due to associated changes in local ocean circulation patterns:

Title: "Shift in ocean circulation triggered the end of the last ice age"

https://www.upi.com/Shift-in-ocean-circulation-triggered-the-end-of-the-last-ice-age/8381524574301/

Extract: ""This gives us an example of the way that different parts of the climate system are connected, so that changes in circulation in one region can drive changes in CO2 and oxygen all the way over on the other side of the planet," researcher Will Gray said.

The end of the last ice age was precipitated by a shift in the circulation of the North Pacific Ocean some 15,000 years ago.

Scientists modeled the ancient shifts in circulation and ocean-atmosphere gas exchange by measuring the chemical composition of foraminifera, the tiny fossil shells left behind by plankton. Their analysis -- published this week in the journal Nature Geoscience -- revealed an uptick in the amount of CO2 released by the North Pacific beginning 15,000 years ago. Previous studies have found evidence of shifting circulation patterns in the Atlantic at roughly the same time.

Earlier this month, another group of researchers published a study showing the Atlantic's circulation is slowing down. Scientists suggest a slowdown could significantly alter climate patterns across the globe.

"In our study we see very rapid changes in the climate of the North Pacific that we think are linked to past changes in ocean currents in the Atlantic," lead researcher Will Gray, an environmental scientist at St. Andrews, said in a news release. "This gives us an example of the way that different parts of the climate system are connected, so that changes in circulation in one region can drive changes in CO2 and oxygen all the way over on the other side of the planet.""

See also:

Gray et al. (2018), "Deglacial upwelling, productivity and CO₂ outgassing in the North Pacific Ocean", Nature Geoscience, doi: 10/1038/s4156-018-0108-6

https://www.nature.com/articles/s41561-018-0108-6

&

Title: "Meltwater pulse 1A"

https://en.wikipedia.org/wiki/Meltwater_pulse_1A
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #701 on: May 07, 2018, 11:39:01 PM »
The linked reference provides a mathematical framework for modeling cascading tipping mechanisms resulting in abrupt climate change; and as an illustration of this methodology it provides a conceptual model for coupling the North Atlantic Ocean Overturning Current and the ENSO system in the Pacific.  Consensus climate science should use such a methodology to better evaluate the risks associated with Hansen's ice-climate feedback mechanism:

Dekker, M. M., von der Heydt, A. S., and Dijkstra, H. A.: Cascading transitions in the climate system, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2018-26, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2018-26/
https://www.earth-syst-dynam-discuss.net/esd-2018-26/esd-2018-26.pdf

Abstract. We provide a theory of cascading tipping, i.e., a sequence of abrupt transitions occurring because a transition in one subsystem changes the background conditions for another subsystem. A mathematical framework of elementary deterministic cascading tipping points in autonomous dynamical systems is presented containing the double-fold, fold-Hopf, Hopf-fold and double-Hopf as most generic cases. Statistical indicators which can be used as early warning indicators of cascading tipping events in stochastic, non-stationary systems are suggested. The concept of cascading tipping is illustrated through a conceptual model of the coupled North Atlantic Ocean – El-Niño Southern Oscillation (ENSO) system, demonstrating the possibility of such cascading events in the climate system.
“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: Hansen et al paper: 3+ meters SLR by 2100
« Reply #702 on: May 10, 2018, 06:12:01 PM »
The linked article indicates that the ocean has been the main driver of Antarctic ice sheet retreat throughout the Holocene which has had an atypically warm plateau as compare to earlier interglacial periods (see also the Early Anthropocene thread, in the Science folder).  This implies that the WAIS is more susceptible to abrupt collapse than consensus climate science likes to admit, which implies that Hansen's ice-climate feedback mechanism is more likely to occur than considered by ESMs calibrated to the paleo record:

Xavier Crosta et al. (2018), "Ocean as the main driver of Antarctic ice sheet retreat during the Holocene", Global and Planetary Change, https://doi.org/10.1016/j.gloplacha.2018.04.007

https://www.sciencedirect.com/science/article/pii/S0921818118300249

Abstract: "Ocean-driven basal melting has been shown to be the main ablation process responsible for the recession of many Antarctic ice shelves and marine-terminating glaciers over the last decades. However, much less is known about the drivers of ice shelf melt prior to the short instrumental era. Based on diatom oxygen isotope (δ18Odiatom; a proxy for glacial ice discharge in solid or liquid form) records from western Antarctic Peninsula (West Antarctica) and Adélie Land (East Antarctica), higher ocean temperatures were suggested to have been the main driver of enhanced ice melt during the Early-to-Mid Holocene while atmosphere temperatures were proposed to have been the main driver during the Late Holocene. Here, we present a new Holocene δ18Odiatom record from Prydz Bay, East Antarctica, also suggesting an increase in glacial ice discharge since ~4500 years before present (~4.5 kyr BP) as previously observed in Antarctic Peninsula and Adélie Land. Similar results from three different regions around Antarctica thus suggest common driving mechanisms. Combining marine and ice core records along with new transient accelerated simulations from the IPSL-CM5A-LR climate model, we rule out changes in air temperatures during the last ~4.5 kyr as the main driver of enhanced glacial ice discharge. Conversely, our simulations evidence the potential for significant warmer subsurface waters in the Southern Ocean during the last 6 kyr in response to enhanced summer insolation south of 60°S and enhanced upwelling of Circumpolar Deep Water towards the Antarctic shelf. We conclude that ice front and basal melting may have played a dominant role in glacial discharge during the Late Holocene."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #703 on: June 01, 2018, 10:14:45 PM »
Correctly modeling Hansen's ice-climate feedback mechanism requires a correct understanding the various factors that contribute to the Atlantic-Pacific asymmetry in deep water formation:

David Ferreira et al. (Volume publication date May 2018), "Atlantic-Pacific Asymmetry in Deep Water Formation", Annual Review of Earth and Planetary Sciences, Vol. 46:327-352 https://doi.org/10.1146/annurev-earth-082517-010045

https://www.annualreviews.org/doi/abs/10.1146/annurev-earth-082517-010045

Abstract: "While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, the Pacific Ocean does not. This asymmetric global overturning pattern has persisted for the past 2–3 million years, with evidence for different ventilation modes in the deeper past. In the current climate, the Atlantic-Pacific asymmetry occurs because the Atlantic is more saline, enabling deep convection. To what extent the salinity contrast between the two basins is dominated by atmospheric processes (larger net evaporation over the Atlantic) or oceanic processes (salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations of the present climate support a strong role for atmospheric processes as well as some modulation by oceanic processes. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary in different climate states."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #704 on: June 20, 2018, 03:51:30 PM »
These findings indicate that the implications of paleo records on the calibration of impacts of Hansen's ice-climate feedback mechanism on paleo-climate model projections, need to be revised:

R. F. Ivanovic et al. (04 June 2018), "Climatic Effect of Antarctic Meltwater Overwhelmed by Concurrent Northern Hemispheric Melt", Geophysical Research Letters, https://doi.org/10.1029/2018GL077623

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL077623

Abstract
Records indicate that 14,500 years ago, sea level rose by 12–22 m in under 340 years. However, the source of the sea level rise remains contentious, partly due to the competing climatic impact of different hemispheric contributions. Antarctic meltwater could indirectly strengthen the Atlantic Meridional Overturning Circulation (AMOC), causing northern warming, whereas Northern Hemisphere ice sheet meltwater has the opposite effect. This story has recently become more intriguing, due to increasing evidence for sea level contributions from both hemispheres. Using a coupled climate model with freshwater forcing, we demonstrate that the climatic influence of southern‐sourced meltwater is overridden by northern sources even when the Antarctic flux is double the North American contribution. This is because the Southern Ocean is quickly resalinized by Antarctic Circumpolar water. These results imply that the pattern of surface climate changes caused by ice sheet melting cannot be used to fingerprint the hemispheric source of the meltwater.
Plain Language Summary
The fastest major sea level rise ever recorded took place 14,500 years ago, when sea level rose by 12–22 m in under 340 years. The extra water came from melting ice sheets, which stretched across North America and northern Europe as well as Greenland and Antarctica. We ran a climate model to test the impact of different meltwater contributions from Antarctica and the Northern Hemisphere ice sheets (North America, Greenland, and Eurasia). Our simulations demonstrate that northern meltwater has a much stronger and longer lasting effect on ocean circulation and climate than Southern Hemisphere melt. Consequently, northern melting overrides the impact of southern melting even when the flux of water from North America is only half the magnitude of the Antarctic flux. This means that past climate records cannot be used to identify the contribution of meltwater from different ice sheets: the northern signal can override the southern signal.
“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: Hansen et al paper: 3+ meters SLR by 2100
« Reply #705 on: August 04, 2018, 08:10:57 PM »
The linked research provides more evidence that a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months.  This helps to confirm Hansen's ice-climate feedback projections:

G. Bromley et al. (06 April 2018), "Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields", Paleoceanography and Paleoclimatology, Vol. 33, Issue 4, https://doi.org/10.1002/2018PA003341

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2018PA003341

Abstract
Establishing the atmospheric expression of abrupt climate change during the last glacial termination is key to understanding driving mechanisms. In this paper, we present a new 14C chronology of glacier behavior during late‐glacial time from the Scottish Highlands, located close to the overturning region of the North Atlantic Ocean. Our results indicate that the last pulse of glaciation culminated between ~12.8 and ~12.6 ka, during the earliest part of the Younger Dryas stadial and as much as a millennium earlier than several recent estimates. Comparison of our results with existing minimum‐limiting 14C data also suggests that the subsequent deglaciation of Scotland was rapid and occurred during full stadial conditions in the North Atlantic. We attribute this pattern of ice recession to enhanced summertime melting, despite severely cool winters, and propose that relatively warm summers are a fundamental characteristic of North Atlantic stadials.

Plain Language Summary
Geologic data reveal that Earth is capable of abrupt, high‐magnitude changes in both temperature and precipitation that can occur well within a human lifespan. Exactly what causes these potentially catastrophic climate‐change events, however, and their likelihood in the near future, remains frustratingly unclear due to uncertainty about how they are manifested on land and in the oceans. Our study sheds new light on the terrestrial impact of so‐called “stadial” events in the North Atlantic region, a key area in abrupt climate change. We reconstructed the behavior of Scotland's last glaciers, which served as natural thermometers, to explore past changes in summertime temperature. Stadials have long been associated with extreme cooling of the North Atlantic and adjacent Europe and the most recent, the Younger Dryas stadial, is commonly invoked as an example of what might happen due to anthropogenic global warming. In contrast, our new glacial chronology suggests that the Younger Dryas was instead characterized by glacier retreat, which is indicative of climate warming. This finding is important because, rather than being defined by severe year‐round cooling, it indicates that abrupt climate change is instead characterized by extreme seasonality in the North Atlantic region, with cold winters yet anomalously warm summers.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #706 on: August 05, 2018, 08:01:01 AM »
Please see my question in reply to the indetical post in another thread.

https://forum.arctic-sea-ice.net/index.php/topic,1755.msg165786.html#msg165786

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #707 on: August 06, 2018, 05:56:14 PM »
sidd,

I replied in the other thread
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #708 on: August 15, 2018, 06:09:02 PM »
Future freshwater exports from the Arctic into the North Atlantic can come several sources including: a) the Beaufort Gyre, b) melting Arctic Sea Ice and c) ice mass loss from the Greenland Ice Sheet.  Furthermore, this Arctic freshwater can follow different pathways, and the cited reference indicates that these different pathways would have different (but significant) impacts on both the North Atlantic Convection and on the AMOC.  This research provide insights into Hansen's ice-climate feedback mechanism:

Wang, He, Sonya Legg, and Robert Hallberg, July 2018: The Effect of Arctic Freshwater Pathways on North Atlantic Convection and the Atlantic Meridional Overturning Circulation. Journal of Climate, 31(13), DOI:10.1175/JCLI-D-17-0629.1 .

https://journals.ametsoc.org/doi/10.1175/JCLI-D-17-0629.1
&
https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-17-0629.1

Abstract: "This study examines the relative roles of the Arctic freshwater exported via different pathways on deep convection in the North Atlantic and the Atlantic meridional overturning circulation (AMOC). Deep water feeding the lower branch of the AMOC is formed in several North Atlantic marginal seas, including the Labrador Sea, Irminger Sea, and the Nordic seas, where deep convection can potentially be inhibited by surface freshwater exported from the Arctic. The sensitivity of the AMOC and North Atlantic to two major freshwater pathways on either side of Greenland is studied using numerical experiments. Freshwater export is rerouted in global coupled climate models by blocking and expanding the channels along the two routes. The sensitivity experiments are performed in two sets of models (CM2G and CM2M) with different control simulation climatology for comparison. Freshwater via the route east of Greenland is found to have a larger direct impact on Labrador Sea convection. In response to the changes of freshwater route, North Atlantic convection outside of the Labrador Sea changes in the opposite sense to the Labrador Sea. The response of the AMOC is found to be sensitive to both the model formulation and mean-state climate."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #709 on: August 15, 2018, 11:37:39 PM »
Information from the linked reference can be used to help calibrate ESMs to properly account for Hansen's ice-climate feedback mechanism:

Ivanovic RF; Gregoire LJ; Burke A; Wickert AD; Valdes PJ; Ng HC; Robinson LF; McManus JF; Mitrovica JX; Lee L; Dentith JE (2018) Acceleration of northern ice sheet melt induces AMOC slowdown and northern cooling in simulations of the early last deglaciation, Paleoceanography and Paleoclimatology. doi: 10.1029/2017PA003308

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2017PA003308

Abstract
The cause of a rapid change in Atlantic Ocean circulation and northern cooling at the onset of Heinrich Stadial 1 ~18.5 ka is unclear. Previous studies have simulated the event using ice sheet and/or iceberg meltwater forcing, but these idealized freshwater fluxes have been unrealistically large. Here we use a different approach, driving a high‐resolution drainage network model with a recent time‐resolved global paleo‐ice sheet reconstruction to generate a realistic meltwater forcing. We input this flux to the Hadley Centre Coupled Model version 3 (HadCM3) climate model without adjusting the timing or amplitude and find that an acceleration in northern ice sheet melting (up to ~7.5 m/kyr global mean sea level rise equivalent) triggers a 20% reduction in the Atlantic Meridional Overturning Circulation. The simulated pattern of ocean circulation and climate change matches an array of paleoclimate and ocean circulation reconstructions for the onset of Heinrich Stadial 1, in terms of both rates and magnitude of change. This is achieved with a meltwater flux that matches constraints on sea level changes and ice sheet evolution around 19–18 ka. Since the rates of melting are similar to those projected for Greenland by 2200, constraining the melt rates and magnitude of climate change during Heinrich Stadial 1 would provide an important test of climate model sensitivity to future ice sheet melt.

Plain Language Summary
Atlantic Ocean circulation plays a key role in redistributing heat around Earth's surface, and thus has an important influence on our climate. Because of this, sudden shifts in Atlantic Ocean circulation can drive rapid climate changes. One such example is at the onset of “Heinrich Stadial 1”, 18.5 thousand years ago, when geological records show that Atlantic circulation weakened and the Northern Hemisphere cooled while the Southern Hemisphere warmed. At the time, huge ice sheets (several kilometers thick) covered much of North America and northern Europe. Climate model results suggest that the freshwater produced by these melting ice sheets is responsible for weakening the Atlantic Ocean circulation and triggering the abrupt climate changes captured in the geological records. This result helps to elucidate the complex interaction between ice sheets, ocean circulation, and climate, and how these interactions can lead to sudden shifts in climates of the past and, potentially, the future. Indeed, the rate of melting we adopt in the present model is comparable to the melting projected for the Greenland Ice Sheet by 2200.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #710 on: September 01, 2018, 04:44:05 PM »
While the linked reference ignores most of Hansen's ice-climate feedback mechanisms, it does correctly indicate that one major reason why the current range of ECS is not higher is that high latitude sea ice (particularly in the SH), has been reflecting a significant amount of radiative forcing back out into outer space.  While this consideration is important to recognize, it is also important to recognize that with continued global warming this SH sea ice extent could decrease relatively rapidly, which may contribute to increasing values of ECS in coming decades:

Qin Wen et al. (22 August 2018), "Decoding Hosing and Heating Effects on Global Temperature and Meridional Circulations in a Warming Climate", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0297.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0297.1

Abstract: "The global temperature changes under global warming result from two effects: one is the pure radiative heating effect caused by change of greenhouse gases, and the other is the freshwater effect related to changes in precipitation, evaporation and sea ice. The two effects are separated in a coupled climate model through sensitivity experiments in this study. It is indicated that freshwater change has a significant cooling effect, which can mitigate the global surface warming by as much as ~30%. Two significant regional cooling centres occur in the subpolar Atlantic and the Southern Ocean, respectively. The subpolar Atlantic cooling, also known as the “Warming Hole,” is triggered by sea-ice melting and the southward cold water advection from the Arctic Ocean, and is sustained by the weakened Atlantic meridional overturning circulation. The Southern Ocean surface cooling is triggered by sea-ice melting along the Antarctic, and is maintained by the enhanced northward Ekman flow. In these two regions, the effect of freshwater flux change dominates over that of radiation flux change, controlling the sea surface temperature change in the warming climate. The freshwater flux change also results in the Bjerknes compensation, with the atmosphere heat transport change compensating the ocean heat transport change by about 80% during the transient stage of global warming. In terms of global temperature and Earth’s energy balance, the freshwater change plays a stabilizing role in a warming climate."
“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: Hansen et al paper: 3+ meters SLR by 2100
« Reply #711 on: September 01, 2018, 04:56:31 PM »
The linked reference indicates that ice mass loss from both the Petermann and 79 North, Greenland marine terminating glaciers slows the AMOC more (over periods of less than 300 years) than does comparable ice mass loss from either Jacobshavn or Helheim glaciers.  This information has relevance to Hansen's ice-climate feedback, and which indicates that with continued global warming the ice-climate feedback may become stronger (for periods of less than 300 years) if/when the ice mass losses from Petermann and 79 North increase:

Liu, Y., Hallberg, R., Sergienko, O. et al. Clim Dyn (2018) 51: 1733. https://doi.org/10.1007/s00382-017-3980-7

https://link.springer.com/article/10.1007%2Fs00382-017-3980-7

Abstract: "Greenland Ice Sheet (GIS) might have lost a large amount of its volume during the last interglacial and may do so again in the future due to climate warming. In this study, we test whether the climate response to the glacial meltwater is sensitive to its discharging location. Two fully coupled atmosphere–ocean general circulation models, CM2G and CM2M, which have completely different ocean components are employed to do the test. In each experiment, a prescribed freshwater flux of 0.1 Sv is discharged from one of the four locations around Greenland—Petermann, 79 North, Jacobshavn and Helheim glaciers. The results from both models show that the AMOC weakens more when the freshwater is discharged from the northern GIS (Petermann and 79 North) than when it is discharged from the southern GIS (Jacobshavn and Helheim), by 15% (CM2G) and 31% (CM2M) averaged over model year 50–300 (CM2G) and 70–300 (CM2M), respectively. This is due to easier access of the freshwater from northern GIS to the deepwater formation site in the Nordic Seas. In the long term (> 300 year), however, the AMOC change is nearly the same for freshwater discharged from any location of the GIS. The East Greenland current accelerates with time and eventually becomes significantly faster when the freshwater is discharged from the north than from the south. Therefore, freshwater from the north is transported efficiently towards the south first and then circulates back to the Nordic Seas, making its impact to the deepwater formation there similar to the freshwater discharged from the south. The results indicate that the details of the location of meltwater discharge matter if the short-term (< 300 years) climate response is concerned, but may not be critical if the long-term (> 300 years) climate response is focused upon."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #712 on: September 08, 2018, 09:08:57 PM »
The linked reference presents findings that can be used to help calibrate Hansen's ice-climate feedback mechanism:

Pepijn Bakker & Matthias Prange (03 August 2018), "Response of the Intertropical Convergence Zone to Antarctic Ice Sheet Melt", Geophysical Research Letters, https://doi.org/10.1029/2018GL078659

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL078659

"Abstract
Past cooling events in the Northern Hemisphere have been shown to impact the location of the intertropical convergence zone (ITCZ) and therewith induce a southward shift of tropical precipitation. Here we use high resolution coupled ocean‐atmosphere simulations to show that reasonable past melt rates of the Antarctic Ice Sheet can similarly have led to shifts of the ITCZ, albeit in opposite direction, through large‐scale surface air temperature changes over the Southern Ocean. Through sensitivity experiments employing slightly negative to large positive meltwater fluxes, we deduce that meridional shifts of the Hadley cell and therewith the ITCZ are, to a first order, a linear response to Southern Hemisphere high‐latitude surface air temperature changes and Antarctic Ice Sheet melt rates. This highlights the possibility to use past episodes of anomalous melt rates to better constrain a possible future response of low latitude precipitation to continued global warming and a shrinking Antarctic Ice Sheet.

Plain Language Summary
Changes in high‐latitude climate can impact the tropical regions through so‐called atmospheric and oceanic teleconnections. Research has mostly focused on past southward shifts in the band of heavy tropical precipitation, called the intertropical convergence zone (ITCZ), linked to large‐scale cooling in the Northern Hemisphere resulting from large‐scale continental ice sheet buildup or a slowdown of the large‐scale Atlantic meridional ocean circulation. Here we use high resolution climate simulations to show that melting of the Antarctic Ice Sheet can similarly lead to northward shifts of the ITCZ and the displacement of the accompanying rain belt. Future melt rates of the Antarctic Ice Sheet are highly uncertain, but our work shows that it might have a nonnegligible impact on the tropical climate. Moreover, we find that because of the apparent linearity of the system under consideration, studying episodes of past changes in the size of the Antarctic Ice Sheet can help us constrain the possible changes in the low latitude hydroclimate."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #713 on: September 11, 2018, 12:03:47 AM »
Some more optimistic news: Forawhile now I have been hearing that late Eemian SLR spike may be be spurious. Evidence from Mallorca by Polyak (Victor, not Leonid) et al. lend weight to the thesis.

"Our sea-level record does not support the hypothesis of rapid sea-level fluctuations within MIS-5e. Instead, we suggest that melting of the polar ice sheets occurred early in the inter- glacial period, followed by gradual ice-sheet growth."

"Altogether, the data show that the MIS-5e highstand began by 126.6  ±​ 0.4 ka and ended no earlier than 116.0  ±​ 0.8 ka, representing 10.5 kyr of remarkable Western Mediterranean RSL stability between 1.4 and 2.9 m.a.p.s.l."

I find this striking because part of my concern for WAIS stability stems from the evidence for late Eemina sea level rise. If that did not actually happen, my concern is (slightly) diminished.

There is another presentation from a AGU which I cannot presently lay my hands on which argues along the same lines using plant fossil evidence. But early days, we shall see.

doi: 10.1038/s41561-018-0222-5


sidd



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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #714 on: September 11, 2018, 12:19:21 AM »
Some more optimistic news: Forawhile now I have been hearing that late Eemian SLR spike may be be spurious. Evidence from Mallorca by Polyak (Victor, not Leonid) et al. lend weight to the thesis.

"Our sea-level record does not support the hypothesis of rapid sea-level fluctuations within MIS-5e. Instead, we suggest that melting of the polar ice sheets occurred early in the inter- glacial period, followed by gradual ice-sheet growth."

"Altogether, the data show that the MIS-5e highstand began by 126.6  ±​ 0.4 ka and ended no earlier than 116.0  ±​ 0.8 ka, representing 10.5 kyr of remarkable Western Mediterranean RSL stability between 1.4 and 2.9 m.a.p.s.l."

I find this striking because part of my concern for WAIS stability stems from the evidence for late Eemina sea level rise. If that did not actually happen, my concern is (slightly) diminished.

There is another presentation from a AGU which I cannot presently lay my hands on which argues along the same lines using plant fossil evidence. But early days, we shall see.

doi: 10.1038/s41561-018-0222-5


sidd

Perhaps the authors ignored the fact that due to the fingerprint effect a collapse of the WAIS would have very little impact on sea level change in the Mediterranean (see the attached image).
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #715 on: September 11, 2018, 12:53:25 AM »
Re: icemelt sea level fingerprint

Unsurprisingly Polyak. et al. did consider this:

"melting of polar ice sheets during the LIG will also produce geographically variable sea-level changes that could result in an overestimation of the global signal by up to ~25% [5,18] . Examination of the patterns of sea-level change associated with the collapse of ice sheets during interglacial periods suggests that the Western Mediterranean will experience ~5% greater than average sea-level rise when either of the Antarctic Ice Sheets melt and ~5% less sea-level rise than the global average for melting of the Greenland Ice Sheet [19]. Therefore, equating GIA-corrected WesternMediterranean sea level with ESL does not present any obvious large biases."

Ref 5, 18 and 19 are all to papers with Mitrovica as an author. All very much worth reading.

sidd

Michael Hauber

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #716 on: September 12, 2018, 03:32:57 AM »


Perhaps the authors ignored the fact that due to the fingerprint effect a collapse of the WAIS would have very little impact on sea level change in the Mediterranean (see the attached image).

Your image shows that sea level change in the Mediterranean is a little above the global average.

I guess there is a reason I almost never look at these threads lol.
Climate change:  Prepare for the worst, hope for the best, expect the middle.