Ice Apocalypse - Multiple Meters Sea Level Rise

[RoxTheGeologist]

As continued global warming should increase the frequency with which atmospheric rivers reach Greenland, we may be in for some rude surprises in the coming decades (w.r.t. increasing rates of ice mass loss from the Greenland Ice Sheet):

William Neff (2018), "Atmospheric rivers melt Greenland", Nature Climate Change 8, 857-858, DOI: https://doi.org/10.1038/s41558-018-0297-4

http://www.nature.com/articles/s41558-018-0297-4

Abstract: "Recent years have seen increased melting of the Greenland Ice Sheet, contributing to accelerated rates of sea-level rise.  New research suggests that this melting due to an increased frequency of atmospheric rivers, narrow filaments of moist air moving polewards."

It worries me that we have this huge gravitationally unstable mass of ice on top of Greenland that is gradually warming, getting wet and having more snow piled on top of it, causing more pressure melting at it's base. The only thing keeping it up is the friction along it's base and its mechanical integrity. Once it loses mechanical integrity all bets are off. Whats to stop the whole damn thing sliding into the ocean in chunks?

An underlying principle in geology is that "The present is the key to the past". Unfortunately that doesn't really help us understand events that might happen once every 100,000 years.

[Hefaistos]

It worries me that we have this huge gravitationally unstable mass of ice on top of Greenland that is gradually warming, getting wet and having more snow piled on top of it, causing more pressure melting at it's base. The only thing keeping it up is the friction along it's base and its mechanical integrity. Once it loses mechanical integrity all bets are off. Whats to stop the whole damn thing sliding into the ocean in chunks?
...

I don't think it's "gravitationally unstable", especially as compared to parts of Antarctic's ice.
It's got to be a very slow process warming the glaciers up, especially as it seems that Greenland is about to replace the Arctic sea as the north cold pole, once ASI is gone.

Even if there are 'rain rivers' coming in, the quantity of rain water is negligible compared to the thousands of meters of glacier ice.
"Whats to stop the whole damn thing sliding into the ocean in chunks?" - I wouldn't worry about this particular scenario.

[Sleepy]

Are you sure about that Hefaistos?

[magnamentis]

just in case that someone's understanding is otherwise, sea ice does NOT add to weight of the region, it will displace the amount of weight in water equivalent. only land-ice would add weight, hence in case that greenland keeps it's approximate ice-volume for another while not much (nothing ) will change and in case greenland would loose a lot of it's ice-shield the balance should improve because a lot of weight (mass) that's not centered by now would disappear while in the centers, south and north there won't be much of a mass-shift.


antarctic ice-shield is sufficiently centered over the pole and the north pole i mentioned above.

only should greenland significantly gain ice volume would things be different while i'm sure, in that case so would other regions and neutralize some (most) of the effect.

[AbruptSLR]

just in case that someone's understanding is otherwise, sea ice does NOT add to weight of the region, it will displace the amount of weight in water equivalent. only land-ice would add weight, hence in case that greenland keeps it's approximate ice-volume for another while not much (nothing ) will change and in case greenland would loose a lot of it's ice-shield the balance should improve because a lot of weight (mass) that's not centered by now would disappear while in the centers, south and north there won't be much of a mass-shift.


antarctic ice-shield is sufficiently centered over the pole and the north pole i mentioned above.

only should greenland significantly gain ice volume would things be different while i'm sure, in that case so would other regions and neutralize some (most) of the effect.

In order to further help avoid confusion, the weight of sea ice is opposed by the opposite force of buoyancy, meaning that it is essentially free floating; however, the great majority of the Greenland Ice Sheet, GIS, consists of marine-terminating glaciers that have a very large component of something called Volume above Floatation.  This means that marine glaciers and marine-terminating glaciers rest on the seafloor, and the weight of the volume above floatation holds these glaciers down from floating.  Thus all portions of the volume above floatation for the GIS (and the EAIS and WAIS) would contribute to sea-level-raise if they were to either melt, and/or move/slide/calve into water depths so deep that they float.

Edit, see also:

Title: "Calculating glacier ice volumes and sea level equivalents"

http://www.antarcticglaciers.org/glaciers-and-climate/estimating-glacier-contribution-to-sea-level-rise/

Extract:

Table 1. Sea level equivalent (SLE) from various land ice sources. From IPCC AR5 (Vaughan et al, 2013).

Ice on land                                   Sea level equivalent (m)
Antarctic Ice Sheet                                           58.3
Greenland Ice Sheet                                         7.36
Glaciers and ice caps                                        0.41

[Hefaistos]

Are you sure about that Hefaistos?

Yeah. In comparison to e.g. WAIS we shouldn't worry too much about GIS.

GIS rests in a 'cradle' of mountain chains. Sure, there are some weak spots, but with Greenland becoming the new Northern cold pole, I suppose dramatic melt due to 'rain rivers' will be restrained.

+Historical evidence from Eemian:

"Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present."

https://www.nature.com/articles/nature11789

[Sleepy]

Are you sure about that Hefaistos?

Yeah. In comparison to e.g. WAIS we shouldn't worry too much about GIS.

Of course, because Greenland melt will end up in the the southern hemisphere and Antarctic melt will end up here. As for the rest, I wouldn't be sure or suppose anything with current warming rates.

[AbruptSLR]

It seems to me that the behavior of the NEGIS during the Holocene Optimum ~7.8 – 1.2 ka, provides a point of concern as to how much ice mass loss may occur for this key marine terminating ice stream in the coming decades:

Nicolaj K. Larsen et al. (14 May 2018), "Instability of the Northeast Greenland Ice Stream over the last 45,000 years", Nature Communications, Volume 9, Article number: 1872, doi:10.1038/s41467-018-04312-7

http://www.nature.com/articles/s41467-018-04312-7

Abstract: "The sensitivity of the Northeast Greenland Ice Stream (NEGIS) to prolonged warm periods is largely unknown and geological records documenting such long-term changes are needed to place current observations in perspective. Here we use cosmogenic surface exposure and radiocarbon ages to determine the magnitude of NEGIS margin fluctuations over the last 45 kyr (thousand years). We find that the NEGIS experienced slow early Holocene ice-margin retreat of 30–40 m a−1, likely as a result of the buttressing effect of sea-ice or shelf-ice. The NEGIS was ~20–70 km behind its present ice-extent ~41–26 ka and ~7.8–1.2 ka; both periods of high orbital precession index and/or summer temperatures within the projected warming for the end of this century. We show that the NEGIS was smaller than present for approximately half of the last ~45 kyr and is susceptible to subtle changes in climate, which has implications for future stability of this ice stream."

[litesong]

I don't think it's "gravitationally unstable", especially as compared to parts of Antarctic's ice......  Even if there are 'rain rivers' coming in, the quantity of rain water is negligible compared to the thousands of meters of glacier ice.

First, comparing Greenland to Antarctica can't be done for many reasons, one being that West Antarctica is nearly a set of above sea level islands & underwater grounding rock islands. Second, already the center core of Greenland is in uplift. Third, those 'rain rivers' aren't considered "iffy", since Greenland is losing sea ice, as much as 400+ cubic kilometers per year, even tho total solar irradiation has been low for 12 years. When the Pineapple Express pours on our Cascade Mountains in Washington state, the rain rivers, not only pour into our valleys, but melt the snows & glaciers, which also exit with the rains. Some of our glaciers are gone & the majority on in recession. When the sun upgrades to normal, will Hefaistos consider Greenland 'rain rivers' iffy, when Greenland ice loss hits 1000 cubic kilometers per year, or 5000 per year, or 10,000 per year? 

[Sleepy]

We’ve entered some profoundly unfamiliar planetary territory.
https://mashable.com/article/climate-change-carbon-pollution-15-million-years/

[Hefaistos]

I don't think it's "gravitationally unstable", especially as compared to parts of Antarctic's ice......  Even if there are 'rain rivers' coming in, the quantity of rain water is negligible compared to the thousands of meters of glacier ice.

First, comparing Greenland to Antarctica can't be done for many reasons, one being that West Antarctica is nearly a set of above sea level islands & underwater grounding rock islands. Second, already the center core of Greenland is in uplift. Third, those 'rain rivers' aren't considered "iffy", since Greenland is losing sea ice, as much as 400+ cubic kilometers per year, even tho total solar irradiation has been low for 12 years. When the Pineapple Express pours on our Cascade Mountains in Washington state, the rain rivers, not only pour into our valleys, but melt the snows & glaciers, which also exit with the rains. Some of our glaciers are gone & the majority on in recession. When the sun upgrades to normal, will Hefaistos consider Greenland 'rain rivers' iffy, when Greenland ice loss hits 1000 cubic kilometers per year, or 5000 per year, or 10,000 per year?

Sorry, but when you quoted me, you omitted an important part of the argument. Here is what I wrote: "I don't think it's "gravitationally unstable", especially as compared to parts of Antarctic's ice.
It's got to be a very slow process warming the glaciers up, especially as it seems that Greenland is about to replace the Arctic sea as the north cold pole, once ASI is gone.
Even if there are 'rain rivers' coming in, the quantity of rain water is negligible compared to the thousands of meters of glacier ice."

GIS is on high altitudes, it's freezing temperatures most of the year. Rain rivers will eat the ice sheet away on the edges, at lower altitudes, but higher up, where most of GIS is, 'rain rivers' will be 'snow cannons', and the snow that falls will eventually be compressed to form new ice.

[AbruptSLR]

While certainly the WAIS is more susceptible to rapid collapse from hydrofacturing of ice shelves followed by cliff failures of the subsequently exposed marine glacier ice cliffs; nevertheless, the GIS has a significant number of marine terminating glacier that are subject to accelerating rates of cliff failures (with continued global warming) as indicated by the linked reference and associated image:

Tanja Schlemm and Anders Levermann (2018), "A simple stress-based cliff-calving law", The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-205

https://www.the-cryosphere-discuss.net/tc-2018-205/tc-2018-205.pdf

Abstract. Over large coastal regions in Greenland and Antarctica the ice sheet calves directly into the ocean. In contrast to ice-shelf calving, an increase in cliff calving directly contributes to sea-level rise and a monotonously increasing calving rate with ice thickness can constitute a self-amplifying ice loss mechanism that may significantly alter sea-level projections both of Greenland and Antarctica. Here we seek to derive a minimalistic stress-based parameterization for cliff calving. To this end we compute the stress field for a glacier with a simplified two-dimensional geometry from the two-dimensional Stokes equation. First we assume a constant yield stress to derive the failure region at the glacier front from the stress field within the ice sheet. Secondly, we assume a constant response time of ice failure due to exceedance of the yield stress. With this strongly constraining but very simple set of assumption we propose a cliff-calving law where the calving rate follows a power-law dependence on the freeboard of the ice with exponents between 2 and 3 depending on the relative water depth at the calving front. The critical freeboard below which the ice front is stable decreases with increasing relative water depth of the calving front. For a dry water front it is, for example, 75m. The purpose of this study is not to provide a comprehensive calving law, but to derive a particularly simple equation with a transparent and minimalistic set of assumptions.

Edit: At risk of stating the obvious, as the calving face retreats down a negatively slope into a marine basin such as either the Byrd Subglacial Basin, BSB (in West Antarctica), or the central basin beneath the Greenland Ice Sheet, both the relative water depth and the freeboard of the associated ice cliff increase which leads to a positive feedback on the rate of acceleration of calving.  Furthermore, the keel draft of the associated calved icebergs are always shallower than the associated water depth, and thus the associated icebergs may float out of the glacier gateway into the open ocean, and/or contribute immediately to sea level rise by floating above the submerged basin floor and pushing associate water out the glacier gateway into the open ocean.

Edit2: Of course it is also true that if the calving face of marine glacier retreats into a submerged basin (like BSB or the central Greenland Basin) that the calved icebergs might (or might not) form a sufficiently dense ice mélange that could buttress and thus inhibit further ice cliff failures until the ice mélange disperses.

[AbruptSLR]

Pretty scary news (that CaCO₃ is currently being dissolved from the seafloor) even for Halloween, in that this happened during the PETM, and it took Earth over 100,000 years to recover from that event:

Olivier Sulpis, Bernard P. Boudreau, Alfonso Mucci, Chris Jenkins, David S. Trossman, Brian K. Arbic, and Robert M. Key (published ahead of print October 29, 2018), "Current CaCO₃ dissolution at the seafloor caused by anthropogenic CO₂", PNAS, https://doi.org/10.1073/pnas.1804250115

http://www.pnas.org/content/early/2018/10/23/1804250115

Significance
The geological record contains numerous examples of “greenhouse periods” and ocean acidification episodes, where the spreading of corrosive (CO₂-enriched) bottom waters enhances the dissolution of CaCO₃ minerals delivered to the seafloor or contained within deep-sea sediments. The dissolution of sedimentary CaCO₃ neutralizes excess CO₂, thus preventing runaway acidification, and acts as a negative-feedback mechanism in regulating atmospheric CO₂ levels over timescales of centuries to millennia. We report an observation-based indication and quantification of significant CaCO₃ dissolution at the seafloor caused by man-made CO₂. This dissolution is already occurring at various locations in the deep ocean, particularly in the northern Atlantic and near the Southern Ocean, where the bottom waters are young and rich in anthropogenic CO₂.

Abstract
Oceanic uptake of anthropogenic CO₂ leads to decreased pH, carbonate ion concentration, and saturation state with respect to CaCO₃ minerals, causing increased dissolution of these minerals at the deep seafloor. This additional dissolution will figure prominently in the neutralization of man-made CO₂. However, there has been no concerted assessment of the current extent of anthropogenic CaCO₃ dissolution at the deep seafloor. Here, recent databases of bottom-water chemistry, benthic currents, and CaCO₃ content of deep-sea sediments are combined with a rate model to derive the global distribution of benthic calcite dissolution rates and obtain primary confirmation of an anthropogenic component. By comparing preindustrial with present-day rates, we determine that significant anthropogenic dissolution now occurs in the western North Atlantic, amounting to 40–100% of the total seafloor dissolution at its most intense locations. At these locations, the calcite compensation depth has risen ∼300 m. Increased benthic dissolution was also revealed at various hot spots in the southern extent of the Atlantic, Indian, and Pacific Oceans. Our findings place constraints on future predictions of ocean acidification, are consequential to the fate of benthic calcifiers, and indicate that a by-product of human activities is currently altering the geological record of the deep sea.

[litesong]

Rain rivers will eat the ice sheet away on the edges, at lower altitudes, but higher up, where most of GIS is, 'rain rivers' will be 'snow cannons', and the snow that falls will eventually be compressed to form new ice.

With AGW warming the planet, some warmer snows which used to "be compressed to form new ice" aren't forming new ices. Also, any rain that is falling is warmer rain, that melts more snow & ice. Classic examples are lower latitude mountains which are now losing their glaciers. Our Washington state Cascade Mountains are losing glaciers rapidly, even on Mt. Rainier. Many of our late summer rivers into early fall have decreased their mass flow rates due to no longer existing glaciers which used to supply river & creek waters in the last times before fall rains & snows began. Increasing AGW effects as at the low latitude conditions, are already nibbling at the fringes of Greenland (& yes, at Antarctica too) & surprisingly at higher Greenland elevations.
 Yeah, the Greenland Ice Sheet is not stable.

[litesong]

We’ve entered some profoundly unfamiliar planetary territory.
https://mashable.com/article/climate-change-carbon-pollution-15-million-years/

First, it was less than 600,000 years ago, then 600,000 years ago, then 800,000 years ago. Now scientists are saying CO2 is higher than 15 million years ago? This here AGW stuff.... its a time machine.

[Sleepy]

Unfortunately litesong, no-one has invented a time machine that can take us back.
It's the speed that's the big issue here, followed by the speed and then in third place, the speed.

Using the Eeemian as an analogy, with Greenland as the new "cold pole" doesn't really work. First, we now know that the year-to-year variability in SMB can be high and is highly dependent on the weather. Second, the ice on Greenland covers "only" ~1,700,000 km², the Arctic Ocean ~14,000,000 km². Third, during the Eemian it was warmer summers that melted the ice thanks to different orbital parameters. Fourth, CO₂ levels during the Eemian peaked around 280ppm.



Hopefully GRACE-FO starts producing soon. It won't help us mitigate though.

[AbruptSLR]

The linked research indicates that: a) the oceans have absorbed 60% heat than assumed by AR5; b) The carbon budget assumed by AR5 must be decreased by at least 25%; and c) the range of climate sensitivity is higher than assumed by AR5:

Title: "Earth's oceans have absorbed 60 percent more heat than previously thought"

https://m.phys.org/news/2018-10-earth-oceans-absorbed-percent-previously.html

Extract: "First author Laure Resplandy, an assistant professor of geosciences and the Princeton Environmental Institute, said that her and her co-authors' estimate is more than 60 percent higher than the figure in the 2014 Fifth Assessment Report on climate change from the United Nations Intergovernmental Panel on Climate Change (IPCC).
…
Scientists know that the ocean takes up roughly 90 percent of all the excess energy produced as the Earth warms, so knowing the actual amount of energy makes it possible to estimate the surface warming we can expect, said co-author Ralph Keeling, a Scripps Oceanography geophysicist and Resplandy's former postdoctoral adviser.

"The result significantly increases the confidence we can place in estimates of ocean warming and therefore helps reduce uncertainty in the climate sensitivity, particularly closing off the possibility of very low climate sensitivity," Keeling said.
…
The researchers' findings suggest that if society is to prevent temperatures from rising above that mark, emissions of carbon dioxide, the chief greenhouse gas produced by human activities, must be reduced by 25 percent compared to what was previously estimated, Resplandy said."

See also:
 
Resplandy et al. (Oct 31 2018), "Quantification of ocean heat uptake from changes in atmospheric O₂ and CO₂ composition", Nature 563, 105-108, doi: https://doi.org/10.1038/s41586-018-0651-8

http://www.nature.com/articles/s41586-018-0651-8

Finally, I note that Resplandy's calculation that the carbon budget should be reduced by 25% is essentially the same thing as saying that TCR is 25% larger than estimated by AR5.

[AbruptSLR]

The linked reference indicates that 128 kya, the bipolar seesaw contributed significantly to the warming of the Antarctic and Southern Ocean temperatures, due ice melting in the Northern Hemisphere.  This supports Hanson's ice-climate feedback mechanism and further indicates that ice mass loss from Greenland will accelerated ice mass loss from Antarctica:

Max D. Holloway et al. (23 October 2018), "Simulating the 128‐ka Antarctic Climate Response to Northern Hemisphere Ice Sheet Melting Using the Isotope‐Enabled HadCM3", Geophysical Research Letters, https://doi.org/10.1029/2018GL079647

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL079647

Abstract
Warmer than present Antarctic and Southern Ocean temperatures during the last interglacial, approximately 128,000 years ago, have been attributed to changes in north‐south ocean heat transport, causing opposing hemispheric temperature anomalies. We investigate the magnitude of Antarctic warming and Antarctic ice core isotopic enrichment in response to Northern Hemisphere meltwater input during the early last interglacial. A 1,600‐year HadCM3 simulation driven by 0.25 Sv of meltwater input reproduces 50–60% of the peak Southern Ocean summer sea surface temperature anomaly, sea ice retreat, and ice core isotope enrichment. We also find a robust increase in the proportion of cold season precipitation during the last interglacial, leading to lower isotopic values at the Antarctic ice core sites. These results suggest that a HadCM3 simulation including 0.25 Sv for 3,000–4,000 years would reconcile the last interglacial observations, providing a potential solution for the last interglacial missing heat problem.

Plain Language Summary
The Antarctic isotope and temperature maximum, which occurred approximately 128,000 years Before Present (yBP) during the warmer than present last interglacial period, is hypothesized to have resulted from a slowdown in northward ocean heat transport due to ice sheet melting into the North Atlantic—a mechanism known as the bipolar seesaw. We test this hypothesis by running and analyzing long, fully coupled, isotope‐enabled climate model simulations, which include meltwater entering the North Atlantic, for this critical period 128,000 yBP. Results are evaluated against ocean and ice core data. After 1,600 years, we simulate 55% of the peak Southern Ocean summer sea surface temperature anomaly, 50% of the estimated winter sea ice retreat, and 60% of the ice core isotope enrichment reconstructed during the early last interglacial Antarctic climate optimum.

[Sleepy]

Hopefully GRACE-FO starts producing soon. It won't help us mitigate though.

I'm a bit sleepy but amazing timing by NASA and GFZ. 

News | November 1, 2018
GRACE-FO Resumes Data Collection
https://www.jpl.nasa.gov/news/news.php?feature=7276

[AbruptSLR]

While in other threads I have stated that I would no longer post in the ASIF, I have decided that as the risk of abrupt sea level rise, SLR, this century is so much higher than many decisionmakers appreciate; I will periodically post in this one ASIF thread.  In this regard, I make a few posts illustrating how decisionmakers are confused about the topic of abrupt SLR, and I begin by providing the first linked reference by Pattyn (2018), which points out that many (most) current consensus ice-sheet model projections of Antarctic Ice Sheet, AIS, contribution to SLR used inappropriate equilibrium initial states for their models; while dynamical initial states are necessary for short-term projections on the order of decades.  Furthermore, Pattyn (2018) notes that such dynamical initial conditions need to properly account for not only Marine Ice Sheet Instability, MISI, but also for Marine Ice Cliff Instability, MICI, and for hydro-fracturing mechanisms (see the first attached image).

Frank Pattyn (2018 Jul 16), "The paradigm shift in Antarctic ice sheet modelling", Nat Commun. 2018; 9: 2728; doi:  10.1038/s41467-018-05003-z

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6048022/

Abstract: "The Antarctic ice sheet is one of the largest potential contributors to future sea level rise. Predicting its future behaviour using physically-based ice sheet models has been a bottleneck for the past decades, but major advances are ongoing."
…
Extract: "A key aspect of projecting future Antarctic mass loss with dynamical ice sheet models is related to the initial state of the model. Since ice sheet models were initially applied for palaeo-climatic studies on long time scales, initialisation was generally obtained from a long spin-up time leading to a steady-state ice sheet (both in terms of geometry and thermodynamics). However, for predictions on shorter time scales (decades to centuries), a stable spin-up generally leads to an ice sheet geometry far different from the one currently observed, which is one of the reasons why such ice sheet models may respond differently than observations suggest. Moreover, using a steady-state for initialising the ice sheet prevents models from properly accounting for the dynamical mass losses observed over the last decade, as the present-day ice sheet is not in steady state. Motivated by the increasing ice sheet imbalance of the ASE glaciers over the last 20 years, and supported by the recent boom in satellite data availability, data-assimilation methods are progressively used to evaluate unknown fields using time-evolving states accounting for the transient nature of observations and the model dynamics."

Next I note that, Bronselaer et al (2018) used an AIS model that does not account for MICI nor hydro-fracturing (which are not likely to be significant before 2040) to show that by 2040 upwelling of relatively warm circumpolar deep water, CDW, around Antarctic will shift the potential ice melting temperature difference upward from below 1,000 m depth to roughly 750 m depth, and will increasingly advect this warm CDW towards the grounding line (see the second attached image) for key marine glaciers such as the Pine Island Glacier, PIG (see the third image wrt the water depth of the grounding line) and the Thwaites Glacier (see the fourth image).  What is critical to note wrt Bronselaer et al (2018) is that by 2040 the temperature of the Southern Ocean would be thousands of years from full equilibrium, but for key AIS marine glaciers both the top and bottom ice surfaces exposed to air and water respectively will experience ice mass loss sufficient to trigger localized MICI and hydro-fracturing mechanisms (if they had been included in Bronselaer et al (2018)'s model.

Bronselaer, B. et al. (2018) Change in future climate due to Antarctic meltwater, Nature, doi:s41586-018-0712-z

https://www.nature.com/articles/s41586-018-0712-z

Abstract: "Meltwater from the Antarctic Ice Sheet is projected to cause up to one metre of sea-level rise by 2100 under the highest greenhouse gas concentration trajectory (RCP8.5) considered by the Intergovernmental Panel on Climate Change (IPCC). However, the effects of meltwater from the ice sheets and ice shelves of Antarctica are not included in the widely used CMIP5 climate models, which introduces bias into IPCC climate projections. Here we assess a large ensemble simulation of the CMIP5 model ‘GFDL ESM2M’ that accounts for RCP8.5-projected Antarctic Ice Sheet meltwater. We find that, relative to the standard RCP8.5 scenario, accounting for meltwater delays the exceedance of the maximum global-mean atmospheric warming targets of 1.5 and 2 degrees Celsius by more than a decade, enhances drying of the Southern Hemisphere and reduces drying of the Northern Hemisphere, increases the formation of Antarctic sea ice (consistent with recent observations of increasing Antarctic sea-ice area) and warms the subsurface ocean around the Antarctic coast. Moreover, the meltwater-induced subsurface ocean warming could lead to further ice-sheet and ice-shelf melting through a positive feedback mechanism, highlighting the importance of including meltwater effects in simulations of future climate."

Caption for the second attached image: "Fig. 5 | Mechanism for ocean warming. a, Hovmoller diagram of the meltwater-induced ocean temperature anomaly, averaged along the Antarctic coast, as a function of time. The black dotted line indicates the maximum warming in a given year. b, c, Schematic of the meltwater-induced Southern Ocean subsurface warming, shown as a zonal-mean cross-section. In the pre-industrial state (b), isopycnals (black lines) are tilted towards the ocean surface by westerly winds (black circles, directed out of the page), away from the continental shelf, with an upward heat flux transporting heat from the warm CDW (orange water) towards the cooler surface (blue water), as shown by the red arrow. In the perturbed state (c), meltwater from the Antarctic Ice Sheet freshens the surface (blue), depressing isopycnals (solid to dashed black lines) so that isopycnal mixing transports heat towards the continent rather than towards the ocean surface (red arrow), leading to coastal warming at depth around the shelf and cooling at the surface."

[AbruptSLR]

As a follow-on to my last post I note that, Pollard, DeConto & Alley (2018) use their Antarctic Ice Sheet, AIS, model with ice-cliff and hydrofracturing failure mechanisms together with ice mélange back pressures calibrated to that currently observed for the Jakobshavn marine terminating glacier in Greenland.  Pollard et al (2018) then assumed the abrupt imposition of warm mid-Pliocene climate conditions (which roughly have a GMSTA above pre-industrial of over 1.5C and ocean water temperatures beneath the ice of key AIS marine glaciers comparable to those found by Bronselaer et al (2018) after 2040).  Assuming these approximations Antarctica could look like the illustrations shown in column 'b' in the first image, and may contributed about 3 m to SLR, by roughly 2090, per panel 'a' of the second attached image.  Furthermore, the third attached image (from Hansen (2018)) show that currently GMSTA is about 1.05C and that the most recent two La Ninas imply a warming rate of 0.38°C per decade; which indicates that by 2040 GMSTA may be over 1.8C (which would match Mid-Pliocene conditions).  Finally, the last attached image (from Hansen et al (2016)) shows gold colored curves for abrupt ice sheet mass loss beginning circa 2040, that show such an ice mass loss would temporarily cool GMSTA, but would also temporarily increase the global energy imbalance, which implies an abrupt & temporary increase in climate sensitivity that would wreak severe storm activity around the planet:

David Pollard, Robert M. DeConto, Richard B. Alley (13 March 2018), "A continuum model of ice mélange and its role during retreat of the Antarctic Ice Sheet", Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-28

https://www.geosci-model-dev-discuss.net/gmd-2018-28/gmd-2018-28.pdf

Abstract: "Rapidly retreating thick ice fronts can generate large amounts of mélange (floating ice debris), which may affect episodes of rapid retreat of Antarctic marine ice. In modern Greenland fjords, mélange provides substantial back pressure on calving ice faces, which slows ice-front velocities and calving rates. On the much larger scales of West Antarctica, it is unknown if mélange could clog seaways and provide enough back pressure to act as a negative feedback slowing retreat.  Here we describe a new mélange model, using a continuum mechanical formulation that is computationally feasible for long-term continental Antarctic applications. It is tested in an idealized rectangular channel and calibrated very basically using observed modern conditions in Jakobshavn fjord, West Greenland. The model is then applied to drastic retreat of Antarctic ice in response to warm mid-Pliocene climate. With mélange parameter values that yield reasonable modern Jakobshavn results, Antarctic marine ice still retreats drastically in the Pliocene simulations, with little slowdown despite the huge amounts of mélange generated. This holds both for the rapid early collapse of West Antarctica, and later retreat into major East Antarctic basins. If parameter values are changed to make the mélange much more resistive to flow, far outside the range for reasonable Jakobshavn results, West Antarctica still collapses and retreat is slowed or prevented only in a few East Antarctic basins."

[Sleepy]

Welcome back ASLR.

[AbruptSLR]

As I said that I would make a few posts (which I take to mean three posts today), I provide the following like to an article that cites research that confirms that current ice mass loss is contributing (see blue line in the attached image) to the drift of the Earth's rotational axis about the poles:

Scientists Identified Three Reasons Responsible for Earth’s Spin Axis Drift

http://www.geologyin.com/2018/09/scientists-identified-three-reasons.html

Extract: "A typical desk globe is designed to be a geometric sphere and to rotate smoothly when you spin it. Our actual planet is far less perfect—in both shape and in rotation.

Earth is not a perfect sphere. When it rotates on its spin axis—an imaginary line that passes through the North and South Poles—it drifts and wobbles. These spin-axis movements are scientifically referred to as "polar motion." Measurements for the 20th century show that the spin axis drifted about 4 inches (10 centimeters) per year. Over the course of a century, that becomes more than 11 yards (10 meters).

Using observational and model-based data spanning the entire 20th century, NASA scientists have for the first time identified three broadly-categorized processes responsible for this drift—contemporary mass loss primarily in Greenland, glacial rebound, and mantle convection.

"The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis. But recently, many researchers have speculated that other processes could have potentially large effects on it as well," said first author Surendra Adhikari of NASA's Jet Propulsion Laboratory in Pasadena, California."

[AbruptSLR]

Welcome back ASLR.

With a limited bandwidth

Thanks,
ASLR

[oren]

Great to see you back ASLR, even if on a limited fashion. Your scientific contributions are sorely missed. Hopefully they will increase again as time goes by, as there are many subjects you have been covering that have been suffering as a result of your absence.

[Lennart van der Linde]

Good to see you back, ASLR!

[Stephan]

Thank you for having you back. We have missed your contributions.

[AbruptSLR]

Thank you all.

&

As stated in the first linked article, when Hansen et al. (2016) clearly presented their case/scenarios for abrupt SLR and associated coming superstorms in the coming decades; it "… met with skepticism from a number of other climate scientists."  However, this first linked article and the associated reference by Alessandro Silvano et al (18 Apr 2018), provides some concrete evidence that at least portions of Hansen's ice-climate feedback mechanism (e.g. reduced global overturning circulation) are already being activated. 

Title: "One of the most worrisome predictions about climate change may be coming true"

http://www.columbia.edu/~jeh1/mailings/2018/Mooney.2018.WorrisomePredictionsMayComeTrue.WP.pdf

Extract: "Two years ago, former NASA climate scientist James Hansen and a number of colleagues laid out a dire scenario in which gigantic pulses of fresh water from melting glaciers could upend the circulation of the oceans, leading to a world of fast-rising seas and even superstorms.

Hansen’s scenario was based on a computer simulation, not hard data from the real world, and met with skepticism from a number of other climate scientists. But now, a new oceanographic study appears to have confirmed one aspect of this picture — in its early stages, at least.

The new research, based on ocean measurements off the coast of East Antarctica, shows that melting Antarctic glaciers are indeed freshening the ocean around them. And this, in turn, is blocking a process in which cold and salty ocean water sinks below the sea surface in winter, forming “the densest water on the Earth,” in the words of study lead author Alessandro Silvano, a researcher with the University of Tasmania in Hobart."

&

Alessandro Silvano et al (18 Apr 2018), "Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water", Science Advances, Vol. 4, no. 4, eaap9467, DOI: 10.1126/sciadv.aap9467

http://advances.sciencemag.org/content/4/4/eaap9467

Abstract: "Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise."

Indeed, the second reference Caesar et al. (2018) (and the associated linked RealClimate article), provide further proof that the AMOC is slowing as projected by Hansen et al (2016).

Caesar et al. (April 12, 2018) "Observed fingerprint of a weakening Atlantic Ocean overturning circulation", Nature, Vol 556, http://doi.org/10.1038/s41586-018-0006-5

https://www.nature.com/articles/s41586-018-0006-5.epdf?author_access_token=d9GwXXnkYQw6itiGny0ZW9RgN0jAjWel9jnR3ZoTv0OdzeJ18XkImxSDnyYEEsE8cCDHkcmVSlMgRd2VzekBpzVfe728uOBU7B1e8unrLGpKyeWhlTvQKe6JHGdYV8iLm4nND7KgW4aTVEUH8xo0AA%3D%3D

Abstract: "The Atlantic meridional overturning circulation (AMOC)—a system of ocean currents in the North Atlantic—has a major impact on climate, yet its evolution during the industrial era is poorly known owing to a lack of direct current measurements. Here we provide evidence for a weakening of the AMOC by about 3 ± 1 sverdrups (around 15 per cent) since the mid-twentieth century. This weakening is revealed by a characteristic spatial and seasonal sea-surface temperature ‘fingerprint’—consisting of a pattern of cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region—and is calibrated through an ensemble of model simulations from the CMIP5 project. We find this fingerprint both in a high-resolution climate model in response to increasing atmospheric carbon dioxide concentrations, and in the temperature trends observed since the late nineteenth century. The pattern can be explained by a slowdown in the AMOC and reduced northward heat transport, as well as an associated northward shift of the Gulf Stream. Comparisons with recent direct measurements from the RAPID project and several other studies provide a consistent depiction of record-low AMOC values in recent years."

See also:

Title: "If you doubt that the AMOC has weakened, read this"

http://www.realclimate.org/index.php/archives/2018/05/if-you-doubt-that-the-amoc-has-weakened-read-this/

Furthermore, the third linked reference (Pedro et al. (2018)) demonstrates that the bipolar seesaw (associated with changes in the global overturning circulation) is indeed part of a larger 'interhemispheric coupling' that is a bigger part of Hansen's ice-climate feedback mechanism.  However, while Pedro et al (2018) focus on calibrating their computer model for 'interhemispheric coupling' first triggered by ice mass loss from the Greenland Ice Sheet, GIS; the associated first image clearly shows paleo-evidence that 'interhemispheric coupling' triggered by ice mass loss from the Antarctic Ice Sheet, AIS, leads to an abrupt warming of the GIS.  This indicates that if my various posts in this thread are correct that the AIS may contribute multiple meters to SLR in the coming decades, then this will likely trigger a rapid warming of the GIS in the subsequent decades; which would then drive further abrupt SLR & more superstorms.

Joel B. Pedro , Markus Jochum, Christo Buizert, Feng He, Stephen Barker & Sune O. Rasmussen (15 July 2018), "Beyond the bipolar seesaw: Toward a process understanding of interhemispheric coupling", Quaternary Science Reviews, Volume 192, , Pages 27-46, https://doi.org/10.1016/j.quascirev.2018.05.005

https://www.sciencedirect.com/science/article/pii/S0277379117310351

Abstract: "The thermal bipolar ocean seesaw hypothesis was advanced by Stocker and Johnsen (2003) as the ‘simplest possible thermodynamic model’ to explain the time relationship between Dansgaard–Oeschger (DO) and Antarctic Isotope Maxima (AIM) events. In this review we combine palaeoclimate observations, theory and general circulation model experiments to advance from the conceptual model toward a process understanding of interhemispheric coupling and the forcing of AIM events. We present four main results: (1) Changes in Atlantic heat transport invoked by the thermal seesaw are partially compensated by opposing changes in heat transport by the global atmosphere and Pacific Ocean. This compensation is an integral part of interhemispheric coupling, with a major influence on the global pattern of climate anomalies. (2) We support the role of a heat reservoir in interhemispheric coupling but argue that its location is the global interior ocean to the north of the Antarctic Circumpolar Current (ACC), not the commonly assumed Southern Ocean. (3) Energy budget analysis indicates that the process driving Antarctic warming during AIM events is an increase in poleward atmospheric heat and moisture transport following sea ice retreat and surface warming over the Southern Ocean. (4) The Antarctic sea ice retreat is itself driven by eddy-heat fluxes across the ACC, amplified by sea-ice–albedo feedbacks. The lag of Antarctic warming after AMOC collapse reflects the time required for heat to accumulate in the ocean interior north of the ACC (predominantly the upper 1500 m), before it can be mixed across this dynamic barrier by eddies."

Finally for this post, the second attached image from the Sentinel satellite for Nov 23 2018, shows that the Southwest Tributary Ice Shelf is no longer blocked by the Pine Island Ice Shelf; which means that the ice flow velocity of the Southwest Tributary Glacier is currently accelerating; which in turn means that the east shear margin of the Thwaites Glacier (see the third image) well progressively offer less stabilization to the Thwaites Glacier; which in turn may well trigger the abrupt collapse of major portions of the Byrd Subglacial Basin within the next one to two decades (when considering concurrent influences from the ENSO & ASL interactions).

[RealityCheck]

Good to see your postings here again, ASLR. Welcome back from me too. I long ago concluded that this is this single most important thread on the forum. So thanks for your renewed contributions, if only here...

[John_The_Elder]

Great to see you back. You are one of the best!

[AbruptSLR]

Great to see you back ASLR, even if on a limited fashion. Your scientific contributions are sorely missed. Hopefully they will increase again as time goes by, as there are many subjects you have been covering that have been suffering as a result of your absence.

oren,

You (& others who are so inclined) should feel free to re-post any information that I provide in this thread to other threads where you feel that contrarians (and/or those who err on the side of least drama) are putting their collective thumbs on the scales.

For example, in the 'Hansen e al paper: 3+ meters SLR by 2100' thread, Reply #713 indicated that the findings of Polyak et al. (2018) that "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.", induced sidd to state:

"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."

https://forum.arctic-sea-ice.net/index.php/topic,1327.700.html

In this regard, I note that the correct interpretation of paleo-SLR data is notoriously challenging and includes many uncertainties that could easily change Polyak et al. (2018)'s conclusions such as is illustrated by their own Fig. 3 (see the first attached image), including:

1. They show that their calculated RSL values (ranging from +1.4m to well over +14m) depend significantly on what GIA model and GIA assumptions that they utilize.
2. Their simplified GIA assumptions do not effectively consider phased ice mass loss scenarios from the NH and the SH.

See also:

Title: "Scientists find stable sea levels during last interglacial"

https://www.sciencedaily.com/releases/2018/09/180910111314.htm

Extract: ""This is the most accurate, best resolved sea level record for MIS-5e of the last interglacial period," said Polyak. "It provides exceptionally accurate timing of the sea level history during the above mentioned period and shows that it rose to 6 meters above present sea level ~127,000 years ago, it would have gradually fell to 2 meters by 122,000 years ago, and would have stayed at that elevation for the remainder of the sea level highstand to 116,000 years ago," says Onac. "The results suggest that if the pre-industrial temperature will be surpassed by 1.5 to 2°C, sea level will respond and rise 2 to 6 meters (7 to 20 feet) above present sea level.""

& see:

Victor J. Polyak, Bogdan P. Onac, Joan J. Fornós, Carling Hay, Yemane Asmerom, Jeffrey A. Dorale, Joaquín Ginés, Paola Tuccimei, Angel Ginés. A highly resolved record of relative sea level in the western Mediterranean Sea during the last interglacial period. Nature Geoscience, 2018; DOI: 10.1038/s41561-018-0222-5

https://www.nature.com/articles/s41561-018-0222-5

Abstract: "The magnitude and trajectory of sea-level change during marine isotope stage (MIS) 5e of the last interglacial period is uncertain. In general, sea level may have been 6–9 m above present sea level, with one or more oscillations of up to several metres superimposed. Here we present a well-dated relative sea-level record from the island of Mallorca in the western Mediterranean Sea for MIS-5e, based on the occurrence of phreatic overgrowths on speleothems forming near sea level. We find that relative sea-level in this region was within a range of 2.15 ±  0.75 m above present levels between 126,600 ±  400 and 116,000 ±  800 years ago, although centennial-scale excursions cannot be excluded due to some gaps in the speleothem record. We corrected our relative sea-level record for glacio-isostatic adjustment using nine different glacial isostatic models. Together, these models suggest that ice-equivalent sea-level in Mallorca peaked at the start of MIS-5e then gradually decreased and stabilized by 122,000 years ago, until the highstand termination 116,000 years ago. 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 interglacial period, followed by gradual ice-sheet growth."

Additional information Supplementary information is available for this paper at https://doi.org/10.1038/ s41561-018-0222-5.


As further evidence that Polyak et al. (2018) may be erring on the side of least drama, Stocchi et al. (2018) find that: "Evidences of two MIS 5e RSL stands are found in Mallorca, northern Tyrrhenian coast of Italy, southeastern Sardinia and Tunisia."; which directly contradicts Polyak et al. (2018)'s conclusion.

See:

Stocchi et al. (2018), "MIS 5e relative sea-level changes in the Mediterranean Sea: Contribution of isostatic disequilibrium", Quaternary Science Reviews 185, 122-134, https://doi.org/10.1016/j.quascirev.2018.01.004

http://www.staff.science.uu.nl/~boer0160/docs/Stocchi_etal_QSR_2018.pdf

Abstract: "Sea-level indicators dated to the Last Interglacial, or Marine Isotope Stage (MIS) 5e, have a twofold value. First, they can be used to constrain the melting of Greenland and Antarctic Ice Sheets in response to global warming scenarios. Second, they can be used to calculate the vertical crustal rates at active margins. For both applications, the contribution of glacio- and hydro-isostatic adjustment (GIA) to vertical displacement of sea-level indicators must be calculated. In this paper, we re-assess MIS 5e sea-level indicators at 11 Mediterranean sites that have been generally considered tectonically stable or affected by mild tectonics. These are found within a range of elevations of 2–10 m above modern mean sea level. Four sites are characterized by two separate sea-level stands, which suggest a two-step sea-level highstand during MIS 5e. Comparing field data with numerical modeling we show that (i) GIA is an important contributor to the spatial and temporal variability of the sea-level highstand during MIS 5e, (ii) the isostatic imbalance from the melting of the MIS 6 ice sheet can produce a >2.0 m sea-level highstand, and (iii) a two-step melting phase for the Greenland and Antarctic Ice Sheets reduces the differences between observations and predictions. Our results show that assumptions of tectonic stability on the basis of the MIS 5e records carry intrinsically large uncertainties, stemming either from uncertainties in field data and GIA models. The latter are propagated to either Holocene or Pleistocene sea-level reconstructions if tectonic rates are considered linear through time."

Extract: "Conclusions
1. The observed range of MIS 5e RSL highstand from 11 tectonically stable sites in the Mediterranean is comprised between 2 and 10m above present msl.  The observed highstands are not necessarily coeval.  Evidences of two MIS 5e RSL stands are found in Mallorca, northern Tyrrhenian coast of Italy, southeastern Sardinia and Tunisia.
2. The GIA-induced RSL changes across the Mediterranean are characterized by significant regional variability throughout the MIS 5e.  The Earth is in isostatic imbalance and a generalized RSL above present sea level is predicted. …
3. According to GIA, the MIS 5e RSL highstand occurs at different times as a function of the geographical location in the Mediterranean.
4. To precisely quantify the GrIS and AIS retreat during MIS5e on the basis on RSL data, requires that the maximum extent, thickness and retreat of the MIS 6 ice sheets, and in particular of Fennoscandia, are constrained.
5. A two-step melting chronology where the GrIS and AIS retreat is out of phase is capable of reconciling predictions and observation provided that the GIA processes are included.
6. Neglecting the uncertainties that are related to RSL indicators and GIA may lead to over or underestimations of local crustal motions even at sites that are considered tectonically stable.  As a consequence, we suggest that caution should be exercised when extrapolating long-term tectonic rates from MIS 5e shorelines."

Furthermore Barlow et al. (2018) find no evidence that RSL fell (note that it takes longer to form new ice sheets and it can take for them to collapse) significantly from the circa 127kya peak (see the second attached image) during the MIS 5e (Eemian).

Barlow NLM, McClymont EL, Whitehouse PL, Stokes CR, Jamieson SSR, Woodroffe SA, Bentley MJ, Callard SL, Ó Cofaigh C, Evans DJA, Horrocks JR, Lloyd JM, Long AJ, Margold M, Roberts DH & Sanchez-Montes ML (2018), "Lack of evidence for a substantial sea-level fluctuation within the Last Interglacial", Nature Geoscience, vol. 11, 627–634, https://doi.org/10.1038/s41561-018-0195-4

https://www.nature.com/articles/s41561-018-0195-4

Abstract: "During the Last Interglacial, global mean sea level reached approximately 6 to 9 m above the present level. This period of high sea level may have been punctuated by a fall of more than 4 m, but a cause for such a widespread sea-level fall has been elusive. Reconstructions of global mean sea level account for solid Earth processes and so the rapid growth and decay of ice sheets is the most obvious explanation for the sea-level fluctuation. Here, we synthesize published geomorphological and stratigraphic indicators from the Last Interglacial, and find no evidence for ice-sheet regrowth within the warm interglacial climate. We also identify uncertainties in the interpretation of local relative sea-level data that underpin the reconstructions of global mean sea level. Given this uncertainty, and taking into account our inability to identify any plausible processes that would cause global sea level to fall by 4 m during warm climate conditions, we question the occurrence of a rapid sea-level fluctuation within the Last Interglacial. We therefore recommend caution in interpreting the high rates of global mean sea-level rise in excess of 3 to 7 m per 1,000 years that have been proposed for the period following the Last Interglacial sea-level lowstand."

Extract: "In conclusion, reconstructions of GMSL during the LIG4,5 have raised the intriguing possibility that fluctuations in ice-sheet volume occurred within the interglacial, that is, ice sheets regrew and then decayed. We have considered several possible driving mechanisms, acting alone or in combination, for multimetre changes in GMSL during the LIG. We find that the current understanding of ice-sheet histories during MIS 6 is not adequate enough to rule out the possibility that limitations in the modelling of the solid Earth response could be contributing to the appearance of a GMSL fall during the LIG3,11. However, if the GMSL fall was driven by changes in ice-sheet mass balance, it would require 1.15–3.45 million km3 of ice to form in less than 1,000 years; we found little geomorphological or sedimentary evidence for such substantial ice-sheet regrowth during the LIG. It is also clear that large uncertainties associated with the interpretation of some local RSL data that underpin the reconstructed GMSL curve remain. Taken together, our analysis leads us to question the occurrence of a rapid GMSL fall within the LIG, which also raises important questions about the very high reconstructed rates of GMSL rise following the lowstand; reported to be approximately 3 to 7 m kyr–1 (ref. 5).

We conclude that it is critical that future reconstructions of GMSL during the LIG include a range of realistic ice-sheet scenarios from the preceding glacial (MIS 6); take into account the impact of dynamic topography on the reconstructed elevations of former RSLs; and assemble a geographically and temporally widespread dataset of local RSL, with careful interpretation of fossil sea-level indicators with respect to tidal datums and accurate chronologies. Until these issues are better resolved, we would urge caution in using rates of GMSL rise from the LIG to project future sea-level changes.
…
5. Kopp, R. E., Simons, F. J., Mitrovica, J. X., Maloof, A. C. & Oppenheimer, M. A probabilistic assessment of sea level variations within the last interglacial stage. Geophys. J. Int. 193, 711–716 (2013)."


Finally, the third attached image from Austermann et al. (2017) indicates that correctly paleo-SLR data to account for dynamic topography (DT) can increase calculated estimates of paleo-SLR by about a meter in the Western Mediterranean during MIS 5e (Eemian);

Austermann J, Mitrovica JX, Huybers P and Rovere A (2017), "Detection of a dynamic topography signal in last interglacial sea-level records", Science Advances, vol. 3(7), e1700457, https://doi.org/10.1126/sciadv.1700457

http://advances.sciencemag.org/content/3/7/e1700457

Abstract: "Estimating minimum ice volume during the last interglacial based on local sea-level indicators requires that these indicators are corrected for processes that alter local sea level relative to the global average. Although glacial isostatic adjustment is generally accounted for, global scale dynamic changes in topography driven by convective mantle flow are generally not considered. We use numerical models of mantle flow to quantify vertical deflections caused by dynamic topography and compare predictions at passive margins to a globally distributed set of last interglacial sea-level markers. The deflections predicted as a result of dynamic topography are significantly correlated with marker elevations (>95% probability) and are consistent with construction and preservation attributes across marker types. We conclude that a dynamic topography signal is present in the elevation of last interglacial sea-level records and that the signal must be accounted for in any effort to determine peak global mean sea level during the last interglacial to within an accuracy of several meters."

Extract: "A complication in all these studies is that various geodynamic processes contribute to the present elevation of paleo sea level records (. A notable example of these processes is tectonic uplift or subsidence at active plate boundaries [for example, see Zazo et al. (9)], which often leads to the exclusion of these sites in reconstructions of past GMSL. Another important deformational process is the response of the Earth system to changes in ice and ocean loading during ice age cycles (10, 11), or glacial isostatic adjustment (GIA), a process first studied in the context of the LIG by Lambeck and Nakada (12). The accuracy of model-derived corrections for this global process is subject to uncertainties in ice history and mantle viscoelastic structure [for example, see Lambeck et al. (13)]. Additionally, the redistribution of sediment can lead to sea level changes through the buildup of topography and loading-induced deformation of the solid Earth and gravity field (14, 15).

Earth’s surface is further deflected by viscous stresses associated with buoyancy variations and flow within Earth’s convective mantle that can alter the elevation of sea-level markers subsequent to their formation (16–22). Effects of this so-called dynamic topography (DT) on the current elevation of sea-level markers dating to the mid-Pliocene (~3 million years ago) have been documented (23–25) and imply meter-scale displacements for LIG sea-level markers (24). Kopp et al. (4) incorporated uncertainties due to vertical land movement and applied nonzero rates in several passive margin regions. Although this correction may implicitly include the DT process, effects of DT are generally not addressed in sea level studies of Pleistocene interglacials and have not previously been shown to be detectable during the LIG. Here, we quantify and analyze the effects of DT on globally distributed markers of local peak sea level during the LIG."

Best,
ASLR

[Shared Humanity]

AbruptSLR...just wanted to say that I am happy to see you still posting here.

[Alison]

Missed ya ASLR. 

[AbruptSLR]

Thanks again for all of the well wishes.

Additionally, to be clear past interglacial periods do not service as analogues for projecting future modern-day climate change; for which state-the-art Earth System Models, ESMs, (with ice-cliff and hydrofracturing mechanisms included) are the best tool for projecting coming climate change.  That said, paleo-information from past glacial and interglacial periods can be helpful in calibrating ESM projections.  In this regard the first linked reference (& associated article) by Rehfeld et al (2018) demonstrates that: "… AWI researchers have now demonstrated that, though climate change has decreased around the globe from glacial to interglacial periods, the difference is by no means as pronounced as previously assumed."  This of course means that climate sensitivity (which is positively correlated with climate variability) is currently higher than consensus scientists previously assumed:

Kira Rehfeld et al, Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene, Nature (2018). DOI: 10.1038/nature25454

https://www.nature.com/articles/nature25454

Abstract: "Changes in climate variability are as important for society to address as are changes in mean climate1. Contrasting temperature variability during the Last Glacial Maximum and the Holocene can provide insights into the relationship between the mean state of the climate and its variability. However, although glacial–interglacial changes in variability have been quantified for Greenland, a global view remains elusive. Here we use a network of marine and terrestrial temperature proxies to show that temperature variability decreased globally by a factor of four as the climate warmed by 3–8 degrees Celsius from the Last Glacial Maximum (around 21,000 years ago) to the Holocene epoch (the past 11,500 years). This decrease had a clear zonal pattern, with little change in the tropics (by a factor of only 1.6–2. and greater change in the mid-latitudes of both hemispheres (by a factor of 3.3–14). By contrast, Greenland ice-core records show a reduction in temperature variability by a factor of 73, suggesting influences beyond local temperature or a decoupling of atmospheric and global surface temperature variability for Greenland. The overall pattern of reduced variability can be explained by changes in the meridional temperature gradient, a mechanism that points to further decreases in temperature variability in a warmer future."

See also:
Title: "Researchers compare global temperature variability in glacial and interglacial periods"

https://phys.org/news/2018-02-global-temperature-variability-glacial-interglacial.html

Extract: "On the basis of a unique global comparison of data from core samples extracted from the ocean floor and the polar ice sheets, AWI researchers have now demonstrated that, though climate change has decreased around the globe from glacial to interglacial periods, the difference is by no means as pronounced as previously assumed."

To better quantify the implications of Rehfeld et al (2018)'s finding, the following linked reference by Dessler & Forster (2018) clearly demonstrate that the likely range for ECS in the period from 2000 to 2017 was 2.4 to 4.6C (with a mode and a mean of 2.9 and 3.3C, respectively) as opposed to AR5's cited likely range of 1.5 to 4.5C.

Furthermore, it is important to remember that ECS is not a fixed value but rather is projected to increase with continued global warming, this century:

A. E. Dessler and P.M. Forster (07 August 2018), "An estimate of equilibrium climate sensitivity from interannual variability', Journal of Geophysical Research Atmospheres, https://doi.org/10.1029/2018JD028481

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD028481?campaign=wolacceptedarticle

Abstract
Estimating the equilibrium climate sensitivity (ECS; the equilibrium warming in response to a doubling of CO2) from observations is one of the big problems in climate science. Using observations of interannual climate variations covering the period 2000 to 2017 and a model‐derived relationship between interannual variations and forced climate change, we estimate ECS is likely 2.4‐4.6 K (17‐83% confidence interval), with a mode and median value of 2.9 and 3.3 K, respectively. This analysis provides no support for low values of ECS (below 2 K) suggested by other analyses. The main uncertainty in our estimate is not observational uncertainty, but rather uncertainty in converting observations of short‐term, mainly unforced climate variability to an estimate of the response of the climate system to long‐term forced warming.

Plain language summary
Equilibrium climate sensitivity (ECS) is the amount of warming resulting from doubling carbon dioxide. It is one of the important metrics in climate science because it is a primary determinant of how much warming we will experience in the future. Despite decades of work, this quantity remains uncertain: the last IPCC report stated a range for ECS of 1.5‐4.5 deg. Celsius. Using observations of interannual climate variations covering the period 2000 to 2017, we estimate ECS is likely 2.4‐4.6 K. Thus, our analysis provides no support for the bottom of the IPCC's range."

You can obtain a copy of the paper here:

https://drive.google.com/file/d/1nt4YEMLc0AwWEAHtHAcwDEVzHkyKj1G-/view

Finally, Dessler & Forster (2018)'s findings combined with those of Brown & Caldeira 2017 https://www.nature.com/articles/nature24672 and Caldwell 2018 https://journals.ametsoc.org/doi/10.1175/JCLI-D-17-0631.1 should place best estimates of the current value of ECS at 3.5 or greater.  This is important in that it increases the probability of abrupt ice mass loss from the WAIS within the next couple of decades.  Also, Rehfeld et al (2018)'s findings confirm Hansen's projections about the coming of superstorms when the ice mass loss from the WAIS cools the surface of the Southern Ocean, and warms the tropical oceans, thus increasing the atmospheric thermal gradient from the tropics to the poles.

[AbruptSLR]

From Replies #219 & #220 there is a strong case to be made that key portions of the Antarctic Ice Sheet may be initially subject to cliff-failures and hydrofracturing by about 2040 when GMSTA may be between 1.5 and 1.8C above pre-industrial.  Furthermore, the first linked reference Zhuan et al. (2018) demonstrates that climate sensitivity [aka climate model response (M) combined with internal climate variability (V)] dominates the rate of increase of GMSTA vs GHG emissions in this timeframe.  Unfortunately, contrarians (and/or those who prefer to err on the side of least drama) like to point at incomplete and biased definitions of climate sensitivity that give low estimates ECS, and TCR, which decision makers are all too willing to use in their policies.  Therefore, in this post I provide some more insight as to why the true ECS values (over the next 20 years) is higher that the ~3C value recommended by IPCC.

Meijia Zhuan et al. (12 November 2018), "A method for investigating the relative importance of three components in overall uncertainty of climate projections", International Journal of Climatology, https://doi.org/10.1002/joc.5920

https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/joc.5920

Abstract: "Climate model response (M) and greenhouse gas emissions (S) uncertainties are consistently estimated as spreads of multi‐model and multi‐scenario climate change projections. There has been less agreement in estimating internal climate variability (V). In recent years, an initial condition ensemble (ICE) of a climate model has been developed to study V. ICE is simulated by running a climate model using an identical climate forcing but different initial conditions. Inter‐member differences of an ICE manifestly represent V. However, ICE has been barely used to investigate relative importance of climate change uncertainties. Accordingly, this study proposes a method of using ICEs, without assuming V as constant, for investigating the relative importance of climate change uncertainties and its temporal‐spatial variation. Prior to investigating temporal‐spatial variation in China, V estimated using ICE was compared to that using multi‐model individual time series at national scale. Results show that V using ICE is qualitatively similar to that using multi‐model individual time series for temperature. However, V is not constant for average and extreme precipitations. V and M dominate before 2050s especially for precipitation. S is dominant in the late 21st century especially for temperature. Mean temperature change is projected to be 30%‐70% greater than its uncertainty until 2050s, while uncertainty becomes 10%‐40% greater than the change in the late 21st century. Precipitation change uncertainty overwhelms its change by 70%‐150% throughout 21st century. Cold regions (e.g. northern China, Qinghai‐Tibetan Plateau) tend to have greater temperature change uncertainties. In dry regions (e.g. northwest China), all three uncertainties tend to be great for changes in average and extreme precipitations. This study emphasizes the importance of considering climate change uncertainty in impact studies, especially taking into account that V is irreducible in the future. Using ICEs without assuming V as constant is an appropriate approach to study climate change uncertainty."
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First, Skeie et al. (2018) demonstrate that: "Sensitivity analysis performed by merging the upper (0–700m) and the deep-ocean OHC or using only one OHC dataset (instead of four in the main analysis) both give an enhancement of the mean ECSinf by about 50% from our best estimate."  Thus considering increases in ocean heat content considerable increases estimates of effective ECS above those currently used by policymakers and indeed that used by Hansen et al. (2016).  Furthermore, we all need to remember that the ocean has been warming from pre-industrial conditions for nearly 270 years, and unlike previous interglacial warming periods, the oceans had the entire Holocene to absorb heat, which, is important when evaluating the stability of subsea methane hydrates (particularly in the Arctic Ocean).

Skeie, R. B., Berntsen, T., Aldrin, M., Holden, M., and Myhre, G.: Climate sensitivity estimates – sensitivity to radiative forcing time series and observational data, Earth Syst. Dynam., 9, 879-894, https://doi.org/10.5194/esd-9-879-2018, 2018.

https://www.earth-syst-dynam.net/9/879/2018/
https://www.earth-syst-dynam.net/9/879/2018/esd-9-879-2018.pdf

Abstract: "Inferred effective climate sensitivity (ECSinf) is estimated using a method combining radiative forcing (RF) time series and several series of observed ocean heat content (OHC) and near-surface temperature change in a Bayesian framework using a simple energy balance model and a stochastic model. The model is updated compared to our previous analysis by using recent forcing estimates from IPCC, including OHC data for the deep ocean, and extending the time series to 2014. In our main analysis, the mean value of the estimated ECSinf is 2.0°C, with a median value of 1.9°C and a 90% credible interval (CI) of 1.2–3.1°C. The mean estimate has recently been shown to be consistent with the higher values for the equilibrium climate sensitivity estimated by climate models. The transient climate response (TCR) is estimated to have a mean value of 1.4°C (90% CI 0.9–2.0°C), and in our main analysis the posterior aerosol effective radiative forcing is similar to the range provided by the IPCC. We show a strong sensitivity of the estimated ECSinf to the choice of a priori RF time series, excluding pre-1950 data and the treatment of OHC data. Sensitivity analysis performed by merging the upper (0–700m) and the deep-ocean OHC or using only one OHC dataset (instead of four in the main analysis) both give an enhancement of the mean ECSinf by about 50% from our best estimate."
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Second, not only do we need to consider heat absorbed by the oceans, but Sallee (2018) notes that: "Since 2006, an estimated 60%–90% of global ocean heat content change associated with global warming is based in the Southern Ocean."  Thus most of this recent increase in ocean heat content is available to destabilize key Antarctic marine glaciers (see the first attached image & associated caption below).

Sallée, J.-B. (2018), "Southern Ocean warming", Oceanography 31(2), https://doi.org/10.5670/oceanog.2018.215.

https://tos.org/oceanography/article/southern-ocean-warming
https://tos.org/oceanography/assets/docs/31-2_sallee.pdf

Abstract: "The Southern Ocean plays a fundamental role in global climate. With no continental barriers, it distributes climate signals among the Pacific, Atlantic, and Indian Oceans through its fast-flowing, energetic, and deep-reaching dominant current, the Antarctic Circumpolar Current. The unusual dynamics of this current, in conjunction with energetic atmospheric and ice conditions, make the Southern Ocean a key region for connecting the surface ocean with the world ocean’s deep seas. Recent examinations of global ocean temperature show that the Southern Ocean plays a major role in global ocean heat uptake and storage. Since 2006, an estimated 60%–90% of global ocean heat content change associated with global warming is based in the Southern Ocean. But the warming of its water masses is inhomogeneous. While the upper 1,000 m of the Southern Ocean within and north of the Antarctic Circumpolar Current are warming rapidly, at a rate of 0.1°–0.2°C per decade, the surface subpolar seas south of this region are not warming or are slightly cooling. However, subpolar abyssal waters are warming at a substantial rate of ~0.05°C per decade due to the formation of bottom waters on the Antarctic continental shelves. Although the processes at play in this warming and their regional distribution are beginning to become clear, the specific mechanisms associated with wind change, eddy activity, and ocean-ice interaction remain areas of active research, and substantial challenges persist to representing them accurately in climate models."

Caption for first image: "FIGURE 1. Schematic showing temperature trends in different layers of the Southern Ocean. The layers are defined as main water masses of the Southern Ocean: Subtropical Water (TW), Mode Water (MW), Intermediate Water (IW), Circumpolar Deep Water (CDW), and Bottom Water (BW). Black arrows show the main overturning pathways in the basin, and the dashed black contours show a vertical slice of the deep-reaching Antarctic Circumpolar Current circulating clockwise around the Antarctic continent. The red arrows and associated numbers represent processes at play in the warming of the Southern Ocean and are discussed in the text: 1 increased surface stratification and shallowing of CDW layer, 2 increased heat uptake in the subpolar basins, 3 increased northward heat transport associated with increased subpolar heat uptake, 4 reduced eddy- mediated southward heat transport across the Antarctic Circumpolar Current, 5 intrusion of CDW onto the continental shelves, and 6 warming of the bottom water ventilating the abyssal ocean."

Second, Purkey & Johnson show that the increase in the Antarctic Westerly wind velocities associated with the Antarctic ozone hole has advected the warm CDW southward when it can more easily destabilize key marine glaciers.  As shown in the second accompanying image figure 4a the warm CDW has surged from the north into the Weddell-Enderby Basin at depths shallower than 1000m (depths that can feed directly into the Filchner Trough leading beneath the FRIS. 

Sarah G. Purkey and Gregory C. Johnson (2012), "Global Contraction of Antarctic Bottom Water between the 1980s and 2000s", Journal of Climate, https://doi.org/10.1175/JCLI-D-11-00612.1

https://journals.ametsoc.org/doi/10.1175/JCLI-D-11-00612.1

Abstract: "A statistically significant reduction in Antarctic Bottom Water (AABW) volume is quantified between the 1980s and 2000s within the Southern Ocean and along the bottom-most, southern branches of the meridional overturning circulation (MOC). AABW has warmed globally during that time, contributing roughly 10% of the recent total ocean heat uptake. This warming implies a global-scale contraction of AABW. Rates of change in AABW-related circulation are estimated in most of the world’s deep-ocean basins by finding average rates of volume loss or gain below cold, deep potential temperature (θ) surfaces using all available repeated hydrographic sections. The Southern Ocean is losing water below θ = 0°C at a rate of −8.2 (±2.6) × 106 m3 s−1. This bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near-surface recovery, apparently through a southward surge of Circumpolar Deep Water from the north. To the north, smaller losses of bottom waters are seen along three of the four main northward outflow routes of AABW. Volume and heat budgets below deep, cold θ surfaces within the Brazil and Pacific basins are not in steady state. The observed changes in volume and heat of the coldest waters within these basins could be accounted for by small decreases to the volume transport or small increases to θ of their inflows, or fractional increases in deep mixing. The budget calculations and global contraction pattern are consistent with a global-scale slowdown of the bottom, southern limb of the MOC."

Caption: "FIG. 4. (a)–(c) Total rates of volume change for select basins (legends) below each potential isotherm (DV curves, solid lines) with 95% confidence intervals (shading) along three of the four northward pathways for AABW out of the Southern Ocean from south to north (orange through green to purple). Minimum u values spreading from the orange to the green basins (lower horizontal black lines) and the green to the purple basins (upper horizontal black lines) are estimated from a climatology (Gouretski and Koltermann 2004). Color-coded numbers along the right axis indicate mean depths of selected us for the corresponding basin."
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Third, Hansen has warned that changing ENSO patterns (due to global warming) are disproportionately working to destabilize Antarctic marine glaciers, and as noted by Cha et al (2018), all the changes in the ENSO pattern that Hansen warned about are coming true now (i.e. more frequent El Nino events, less frequent La Nina events, and more frequent warming of the Nino 3 region that is primarily responsible for advecting tropical Pacific Ocean heat energy to West Antarctica via atmospheric Rossby waves)

Sang‐Chul Cha et al. (05 November 2018), "A Recent Shift Toward an El Niño‐Like Ocean State in the Tropical Pacific and the Resumption of Ocean Warming", Geophysical Research Letters, https://doi.org/10.1029/2018GL080651

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL080651

Abstract
Since approximately 2011, the tropical Pacific has been sharply shifting toward an opposite phase to that observed in the previous decade. This shift has coincided with a recent resumption of global warming after a hiatus in the 2000s. Based on a model‐data analysis using an ensemble empirical mode decomposition, we identified a distinct low‐frequency mode of the sea level in the tropical Pacific and showed its connection to global ocean warming and the suppression of global warming during the early 2000s, as well as the resumption of warming during recent years. Hindcast and model experiments conducted to illustrate the physical mechanism linking the decadal mode to the Pacific Decadal Oscillation‐related trade winds, which regulate the strength of the Equatorial Undercurrent and the surface temperature of the tropical Pacific Ocean, revealed an El Niño‐like state for the last several years.

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Fourth, I noted that freshwater hosing of the North Atlantic from both ice mass loss from Greenland [see Bondzio et al. (2018) and Ying et al. (2018)] and from a likely pulse of low salinity water released from the Beaufort Sea Gyre (likely sometime in the next two decades); would further slow the global overturning current [see Buarque et al (2018)]; which via the bipolar seesaw mechanism will both further destabilize Antarctic marine glaciers and will increase tropical ocean surface temperatures.

Johannes H. Bondzio et al. (15 November 2018), "Control of ocean temperature on Jakobshavn Isbræ's present and future mass loss", Geophysical Research Letters, https://doi.org/10.1029/2018GL079827

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL079827

Abstract
Large uncertainties in model parameterizations and input datasets make projections of future sea level rise contributions of outlet glaciers challenging. Here, we introduce a novel technique for weighing large ensemble model simulations that uses information of key observables. The approach is robust to input errors and yields calibrated means and error estimates of a glacier's mass balance. We apply the technique to Jakobshavn Isbræ, using a model that includes a dynamic calving law, and closely reproduce the observed behavior from 1985 until 2018 by forcing the model with ocean temperatures only. Our calibrated projection suggests that the glacier will continue to retreat and contribute about 5.1 mm to eustatic sea level rise by 2100 under present‐day climatic forcing. Our analysis shows that the glacier's future evolution will strongly depend on the ambient oceanic setting.

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Jun Ying et al. (2018), "Inter-model uncertainty in the change of ENSO’s amplitude under global warming: Role of the response of atmospheric circulation to SST anomalies", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0456.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0456.1

Abstract: "This study investigates the mechanism of the large inter-model uncertainty in the change of ENSO’s amplitude under global warming, based on 31 CMIP5 models. We find that the uncertainty in ENSO’s amplitude is significantly correlated to that of the change in the response of atmospheric circulation to SST anomalies (SSTAs) in the eastern equatorial Pacific Niño3 region. This effect of the atmospheric response to SSTAs mainly influences the uncertainty in ENSO’s amplitude during El Niño (EN) phases, but not during La Niña (LN) phases, showing pronounced nonlinearity. The effect of the relative SST warming and the present-day response of atmospheric circulation to SSTAs are the two major contributors to the inter-model spread of the change in the atmospheric response to SSTAs, of which the latter is more important. On the one hand, models with a stronger (weaker) mean-state SST warming in the eastern equatorial Pacific, relative to the tropical-mean warming, favor a larger (smaller) increase in the change in the response of atmospheric circulation to SSTAs in the eastern equatorial Pacific during EN. On the other hand, models with a weaker (stronger) present-day response of atmospheric circulation to SSTAs during EN tend to exhibit a larger (smaller) increase in the change under global warming. The result implies that an improved simulation of the present-day response of atmospheric circulation to SSTAs could be effective in lowering the uncertainty in ENSO’s amplitude change under global warming."

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Ramos Buarque, S. and Salas y Melia, D.: Link between the North Atlantic Oscillation and the surface mass balance components of the Greenland Ice Sheet under preindustrial and last interglacial climates: a study with a coupled global circulation model, Clim. Past, 14, 1707-1725, https://doi.org/10.5194/cp-14-1707-2018, 2018.

https://www.clim-past.net/14/1707/2018/

Abstract. The relationship between the surface mass balance (SMB) components (accumulation and melting) of the Greenland Ice Sheet (GrIS) and the North Atlantic Oscillation (NAO) is examined from numerical simulations performed with a new atmospheric stretched grid configuration of the Centre National de Recherches Météorologiques Coupled Model (CNRM-CM) version 5.2 under three periods: preindustrial climate, a warm phase (early Eemian, 130kaBP) and a cool phase (late Eemian, 115kaBP) of the last interglacial. The horizontal grid of the atmospheric component of CNRM-CM5.2 is stretched from the tilted pole on Baffin Bay (72°N, 65°W) in order to obtain a higher spatial resolution on Greenland. The correlation between simulated SMB anomalies averaged over Greenland and the NAO index is weak in winter and significant in summer (about 0.6 for the three periods). In summer, spatial correlations between the NAO index and SMB components display different patterns from one period to another. These differences are analyzed in terms of the respective influence of the positive and negative phases of the NAO on accumulation and melting. Accumulation in south Greenland is significantly correlated with the positive (negative) phase of the NAO in a warm (cold) climate. Under preindustrial and 115kaBP climates, melting along the margins is more correlated with the positive phase of the NAO than with its negative phase, whereas at 130kaBP it is more correlated with the negative phase of the NAO in north and northeast Greenland.

[AbruptSLR]

As my last post was limited by the 2000 word limit per post, I continue here:

Fifth, Chen et al (2018) illustrates the risk of increasing atmospheric methane emissions from hydrates as the Arctic Ocean warms and its current patterns change.

Leifer, I., Chen, F. R., McClimans, T., Muller Karger, F., and Yurganov, L.: Satellite ice extent, sea surface temperature, and atmospheric methane trends in the Barents and Kara Seas, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-237, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-237/

Abstract. Over a decade (2003–2015) of satellite data of sea-ice extent, sea surface temperature (SST), and methane (CH4) concentrations in lower troposphere over 10 focus areas within the Barents and Kara Seas (BKS) were analyzed for anomalies and trends relative to the Barents Sea. Large positive CH4 anomalies were discovered around Franz Josef Land (FJL) and offshore west Novaya Zemlya in early fall. Far smaller CH4 enhancement was found around Svalbard, downstream and north of known seabed seepage. SST increased in all focus areas at rates from 0.0018 to 0.15°Cyr−1, CH4 growth spanned 3.06 to 3.49ppbyr−1.
The strongest SST increase was observed each year in the southeast Barents Sea in June due to strengthening of the warm Murman Current (MC), and in the south Kara Sea in September. The southeast Barents Sea, the south Kara Sea and coastal areas around FJL exhibited the strongest CH4 growth over the observation period. Likely sources are CH4 seepage from subsea permafrost and hydrate thawing and the petroleum reservoirs underlying the central and east Barents Sea and the Kara Sea. The spatial pattern was poorly related to seabed depth. However, the increase in CH4 emissions over time may be explained by a process of shoaling of strengthening warm ocean currents that would also advect the CH4 to areas where seasonal deepening of the surface ocean mixed layer depth leads to ventilation of these water masses. Continued strengthening of the MC will further increase heat transfer to the BKS, with the Barents Sea ice-free in ~15 years. We thus expect marine CH4 flux to the atmosphere from this region to continue increasing.
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Sixth, Zamanian et al. (2018) shows that CO₂ emission from soil inorganic carbon into the atmosphere with continued warming has been likely underestimated.

Kazem Zamanian et al. (08 October 2018), "Contribution of soil inorganic carbon to atmospheric CO2: More important than previously thought", Global Change Biology, https://doi.org/10.1111/gcb.14463

https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.14463

Extract: "We conclude that, considering the factors mentioned by Datta and Mandal (2018), our estimation (Zamanian et al., 2018) of CO2 fluxes from carbonates by N fertilization (7.5 × 1012 g C year−1) and from liming of acidic soils (273 × 1012 g C year−1) as accurate as it can be done to date is possibly an underestimation."

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Seventh, the next two articles show that the size of the Antarctic ozone hole (which increases the Westerly wind velocity over the Southern Ocean & thus shift the warm CDW shoreward) is still significant and will remain significant until well after the 2040 timeframe considered in this post.

Title: "Antarctic ozone hole grows, but not by much"

https://cosmosmagazine.com/geoscience/antarctic-ozone-hole-grows-but-not-by-much

Extract: "The hole, which peaks every year at the end of the southern winter, topped out at about 22.9 million square kilometres – almost three times the area of the continental US – and was the thirteenth largest out of the past 40.
And while that’s not exactly cause for unrestrained celebration, it is, say scientists at NASA's Goddard Space Flight Centre in Maryland, which monitors the phenomenon, testament to the tentative success of the 1987 Montreal Protocol, which led to the phasing out of man-made ozone-depleting substances.
“Chlorine levels in the Antarctic stratosphere have fallen about 11% from the peak year in 2000.
"This year’s colder temperatures would have given us a much larger ozone hole if chlorine was still at levels we saw back in the year 2000.”
The size of the ozone hole is directly affected by annual temperatures, with warmer weather restricting its growth. Warm averages in 2016 led to a hole 19.7 million kilometres in area, but it increased in 2018 on the back of the coldest run of temperatures since 1979."

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Title: "Hole in Earth's Ozone Layer Could Be Closed in 2060s, UN Report Says"

https://weather.com/news/news/2018-11-07-ozone-hole-healing/

Extract: "The ozone hole over the Antarctic is expected to be closed in the 2060s, the report said. Other areas in the atmosphere could recover even earlier if all goes as planned."
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Eight, while not related to climate sensitivity, the following article and Velders et al. (2015), illustrate that if the Kigali Amendment to the Montreal Protocol prove ineffective, radiative forcing from HFCs could increase significantly in the coming decades [see the attached image from Velders et al. (2015)]

Title: "Fast-Rising Demand for Air Conditioning Is Adding to Global Warming. The Numbers Are Striking."

https://insideclimatenews.org/news/11112018/climate-change-home-air-conditioning-half-degree-global-warming-by-2100

Extract: "With window units set to more than triple by 2050, home air conditioning is on pace to add half a degree Celsius to global warming this century, a new report says."

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Guus J.M.Velders et al. (2015), "Future atmospheric abundances and climate forcings from scenarios of global and regional hydrofluorocarbon (HFC) emissions", Atmospheric Environment, Volume 123, Part A, December 2015, Pages 200-209, https://doi.org/10.1016/j.atmosenv.2015.10.071

https://www.sciencedirect.com/science/article/pii/S135223101530488X
https://ac.els-cdn.com/S135223101530488X/1-s2.0-S135223101530488X-main.pdf?_tid=16e884ef-7981-4c7b-b1a0-f211d675a9bd&acdnat=1543182231_4fac32e869522e2e888d45a5a2229aeb

Abstract: "Hydrofluorocarbons (HFCs) are manufactured for use as substitutes for ozone-depleting substances that are being phased out globally under Montreal Protocol regulations. While HFCs do not deplete ozone, many are potent greenhouse gases that contribute to climate change. Here, new global scenarios show that baseline emissions of HFCs could reach 4.0–5.3 GtCO2-eq yr−1 in 2050. The new baseline (or business-as-usual) scenarios are formulated for 10 HFC compounds, 11 geographic regions, and 13 use categories. The scenarios rely on detailed data reported by countries to the United Nations; projections of gross domestic product and population; and recent observations of HFC atmospheric abundances. In the baseline scenarios, by 2050 China (31%), India and the rest of Asia (23%), the Middle East and northern Africa (11%), and the USA (10%) are the principal source regions for global HFC emissions; and refrigeration (40–58%) and stationary air conditioning (21–40%) are the major use sectors. The corresponding radiative forcing could reach 0.22–0.25 W m−2 in 2050, which would be 12–24% of the increase from business-as-usual CO2 emissions from 2015 to 2050. National regulations to limit HFC use have already been adopted in the European Union, Japan and USA, and proposals have been submitted to amend the Montreal Protocol to substantially reduce growth in HFC use. Calculated baseline emissions are reduced by 90% in 2050 by implementing the North America Montreal Protocol amendment proposal. Global adoption of technologies required to meet national regulations would be sufficient to reduce 2050 baseline HFC consumption by more than 50% of that achieved with the North America proposal for most developed and developing countries."

[AbruptSLR]

As this is the Ice Apocalypse thread, we cannot neglect to consider the fact that the current high rate of anthropogenic radiative forcing (at least 100 times faster than during the PETM) increases the risk that a cascade (domino effect) of activated positive feedback mechanisms could drive the Earth irreversibly towards a 'hothouse' condition, if we allow the Earth to temporarily reach Mid-Pliocene conditions (which will cause abrupt ice mass loss from Antarctica), as shown in Steffen et al. (2018) & the three associated images, and the associated article.

Will Steffen, Johan Rockström, Katherine Richardson, Timothy M. Lenton, Carl Folke, Diana Liverman, Colin P. Summerhayes, Anthony D. Barnosky, Sarah E. Cornell, Michel Crucifix, Jonathan F. Donges, Ingo Fetzer, Steven J. Lade, Marten Scheffer, Ricarda Winkelmann, Hans Joachim Schellnhuber (2018), "Trajectories of the Earth System in the Anthropocene", Proc. Nat. Acad. Sci., https://doi.org/10.1073/pnas.1810141115

http://www.pnas.org/content/115/33/8252

Abstract: "We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a “Hothouse Earth” pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System—biosphere, climate, and societies—and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values."
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Title: "Climate Change Could Have a Domino Effect"

https://www.chemistryviews.org/details/news/1023141/Climate_Change_Could_Have_a_Domino_Effect.html

Extract: "The initial domino stones could form the tipping points, which already react to a relatively small increase in global temperatures, such as the melting of the West Antarctic and Greenland Ice Sheet and the Arctic sea ice. As this continues to fuel warming through positive feedback loops, it could then be "swept" by tipping points with slightly higher thresholds, such as the Gulf Stream ocean current or the Southern Ocean's buffering of global CO2. Once such a cascade is triggered, it might cause a runaway effect that could catapult Earth's climate out of its stable phase even as human emissions are reduced. The earth could be 4–5 °C warmer than pre-industrial temperatures and have sea levels 10–60 m higher than today."
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Furthermore, Fischer et al. (2018) (& the associated article) supports the concern that if we allow the world to reach Mid-Pliocene conditions we could lock-in a cascade of positive feedbacks that could effectively double the current value of climate sensitivity.

Fischer et al. (2018), "Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond", Nature Geoscience, vol. 11, 474–485, https://doi.org/10.1038/s41561-018-0146-0

https://www.nature.com/articles/s41561-018-0146-0

Abstract: "Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the preindustrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise."

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Title: "Global warming may be twice what climate models predict"

https://phys.org/news/2018-07-global-climate.html

Extract: "Observations of past warming periods suggest that a number of amplifying mechanisms, which are poorly represented in climate models, increase long-term warming beyond climate model projections," said lead author, Prof Hubertus Fischer of the University of Bern.

"This suggests the carbon budget to avoid 2°C of global warming may be far smaller than estimated, leaving very little margin for error to meet the Paris targets."

To get their results, the researchers looked at three of the best-documented warm periods, the Holocene thermal maximum (5000-9000 years ago), the last interglacial (129,000-116,000 years ago) and the mid-Pliocene warm period (3.3-3 million years ago).

The warming of the first two periods was caused by predictable changes in the Earth's orbit, while the mid-Pliocene event was the result of atmospheric carbon dioxide concentrations that were 350-450ppm – much the same as today."
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Furthermore, Liu et al. (2018) confirms that a sufficient perturbance of the AMOC into the Arctic Ocean (say due to abrupt ice mass loss from Antarctic beginning in 2040) could lead "… to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated."  Such possible activation of the positive Arctic ice-albedo mechanism, could then trigger other positive feedback mechanisms.

Wei Liu et al. (2018), "The mechanisms of the Atlantic Meridional Overturning Circulation slowdown induced by Arctic sea ice decline", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0231.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0231.1

Abstract: "We explore the mechanisms by which Arctic sea ice decline affects the Atlantic Meridional Overturning Circulation (AMOC) in a suite of numerical experiments perturbing Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ∼100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these bouyancy anomalies, and therefore to the AMOC slowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal wind-driven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection."

Edit: To help convey how close we currently are to reaching Mid-Pliocene conditions, I attach the fourth image of Fischer et al. (2018) Figure 1.

[AbruptSLR]

 I re-post the following from the Potential Collapse Scenario for the WAIS" thread

"Based on my interpretation of the two linked references, I suspect that local ice cliff failures near the base of the Thwaites Ice Tongue (see the four images) will begin sometime 2025 and 2033, and will be initiated due to influences from Super El Nino events in that timeframe:

Yu, H., Rignot, E., Morlighem, M., & Seroussi, H. (2017). Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics. The Cryosphere, 11(3), 1283, doi:10.5194/tc-11-1283-2017

https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017.pdf
https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017-assets.html

Abstract. "Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades.  Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing.  We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA’s Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations.  We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and iceberg calving."

Extract: "In our simulations, we find that crevasses propagate significantly faster near the ice front when the ice shelf is shortened.
…
The reason for the propagation of crevasses is the existence of a nonhydrostatic condition of ice immediately downstream of the grounding line, which is not accounted for in simplified models that assume hydrostatic equilibrium everywhere on the ice shelf.  We also find that calving is enhanced in the presence of pre-existing surface crevasses or shorter ice shelves or when the ice front is undercut.  We conclude that it is important to consider the full stress regime of ice in the grounding line region to replicate the conditions conducive to calving events, especially the nonhydrostatic condition that is critical to propagate the crevasses."

&

The second linked reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of extreme El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent.""

[AbruptSLR]

As a follow-on to my last post, the first  image shows the deepwater changes across the Amundsen Sea continental shelf through which the warm CDW flows towards the grounding lines of key marine glaciers.

The second image shows a computer simulation of the pattern of warm CDW flow in the Amundsen Sea continental shelf area; which indicates how warm CDW can flow from the PIG to the Thwaites grounding line.

The third image shows that the submerged ridge seaward of Thwaites can help direct the warm CDW come from the PIG towards the 'trough' that crosses the Thwaites ice plug.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.

Next, the second linked reference indicates that from January to June the ASL typically moves from about 110 degrees W (where it is in position to help direct warm CDW into the ASE) to about 150 degrees W (where it does not help to direct warm CDW into the ASE).  I note also that:

(a) As the SAM has become more positive, due to global warming, the ASL has become more intensity and has tended to drift more to the west than previously; and

(b) El Nino events do not typically occur in the January to June timeframe but rather in the October to Dec timeframe, which helps to explain way more warm CDW flows into the ASE during El Nino events

Turner, J., Phillips, T., Hosking, J. S., Marshall, G. J. and Orr, A. (2013), The Amundsen Sea low. Int. J. Climatol., 33: 1818–1829. doi: 10.1002/joc.3558

http://onlinelibrary.wiley.com/doi/10.1002/joc.3558/abstract

Abstract: "We develop a climatology of the Amundsen Sea low (ASL) covering the period 1979–2008 using ECMWF operational and reanalysis fields. The depth of the ASL is strongly influenced by the phase of the Southern annular mode (SAM) with positive (negative) mean sea level pressure anomalies when the SAM is negative (positive). The zonal location of the ASL is linked to the phase of the mid-tropospheric planetary waves and the low moves west from close to 110°W in January to near 150°W in June as planetary waves 1 to 3 amplify and their phases shift westwards. The ASL is deeper by a small, but significant amount, during the La Niña phase of El Niño-Southern Oscillation (ENSO) compared to El Niño. The difference in depth of the low between the two states of ENSO is greatest in winter. There is no statistically significant difference in the zonal location of the ASL between the different phases of ENSO. Over 1979–2008 the low has deepened in January by 1.7 hPa dec−1 as the SAM has become more positive. It has also deepened in spring and autumn as the semi-annual oscillation has increase in amplitude over the last 30 years. An increase in central pressure and eastward shift in March has occurred as a result of a cooling of tropical Pacific SSTs that altered the strength of the polar front jet."


Finally, the third linked 2017 reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of Super El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent."

[AbruptSLR]

The linked article & associated reference provide evidence that during the Holocene the sea line on the Texas coastline rose by several meters within a period of decades, almost certainly due to collapsing glaciers:

Title: "Oceans Can Rise in Sudden Bursts"

https://www.scientificamerican.com/article/oceans-can-rise-in-sudden-bursts/

Extract: "Fossilized corals off Texas show that in the past, sea level rose several meters in just decades, probably due to collapsing glaciers"

&

Pankaj Khanna, André W. Droxler, Jeffrey A. Nittrouer, John W. Tunnell Jr & Thomas C. Shirley (2017), "Coralgal reef morphology records punctuated sea-level rise during the last deglaciation", Nature Communications, https://doi.org/10.1038/s41467-017-00966-x

https://www.nature.com/articles/s41467-017-00966-x

Abstract: "Coralgal reefs preserve the signatures of sea-level fluctuations over Earth’s history, in particular since the Last Glacial Maximum 20,000 years ago, and are used in this study to indicate that punctuated sea-level rise events are more common than previously observed during the last deglaciation. Recognizing the nature of past sea-level rises (i.e., gradual or stepwise) during deglaciation is critical for informing models that predict future vertical behavior of global oceans. Here we present high-resolution bathymetric and seismic sonar data sets of 10 morphologically similar drowned reefs that grew during the last deglaciation and spread 120km apart along the south Texas shelf edge. Herein, six commonly observed terrace levels are interpreted to be generated by several punctuated sea-level rise events forcing the reefs to shrink and backstep through time. These systematic and common terraces are interpreted to record punctuated sea-level rise events over timescales of decades to centuries during the last deglaciation, previously recognized only during the late Holocene."

[wili]

Sorry not to say this sooner--good to have you back, bro! Your posts are always deeply appreciated, and were sorely missed in your absence!

[AbruptSLR]

Sorry not to say this sooner--good to have you back, bro! Your posts are always deeply appreciated, and were sorely missed in your absence!

wili,

Thank you.

Also, as an official El Nino for the 2018-2019 ENSO season will almost certainly be declared in either December or January, I provide the linked article and associated linked reference that provides statistical evidence that El Nino events significantly accelerate ice mass loss from the ice shelves in the Amundsen Sea Embayment; which further destabilizes the key marine glaciers in this region:

Title: "El Nino's long reach to Antarctic ice"

https://www.bbc.com/news/science-environment-42614412

Extract: "ENSO is recognised to have global influence, altering patterns of rainfall and drought, for example. And in the southern polar region, it appears to influence atmospheric pressure fields.

One in particular, referred to as the Amundsen Sea Low, governs both regional winds and ocean circulation.

During an El Niño, this fosters higher snowfall rates on shelves, raising their height, but it also pulls more warm water up from the deep which can get under the shelves and melt them.

The combined effect leads to a loss in mass of the shelves. In a big El Niño phase, like the one in 1997/98, this reduction can be equivalent in scale to that stemming from the ongoing, long-term negative thinning trend.

"That means for a short period of time you are adding the two together. And that's key information to put into computer models if you want to properly represent the dynamics of these systems," explained Dr Paolo, who has now moved to the US space agency.

In La Niña years, the reverse happens: less snowfall, but also less melting on the shelves' undersides. This works briefly to slow the ongoing, long-term negative trend. "


See also:

Paolo, F. S., Padman, L., Fricker, H. A., Adusumilli, S., Howard, S., & Siegfried, M. R. (2018). Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation. Nature Geoscience, 11(2), 121–126. doi:10.1038/s41561-017-0033-0

https://www.nature.com/articles/s41561-017-0033-0

&

Title: "Strong chance of a new El Niño forming by early 2019"

https://www.bbc.com/news/science-environment-46347451

Best,
ASLR

[AbruptSLR]

In September 2012 the Thwaites Ice Tongue flow rate surged and continued flowing at a high rate through the end of 2012 (and this high flow rate can be associated with the surface elevation depression shown in the first image)

In this regards, the linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014 (see the last three attached images):

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf

Abstract. We present conventional and swath altimetry data from CryoSat-2, revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica (TWG). Much of the drainage happened in less than 6 months, with an apparent connection between three lakes spanning more than 130 km. Hydro-potential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed largescale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events. This shows that there are important limitations in the ability of hydro-potential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."

There is more information on the June 2013 to Jan 2014 drainage of four subglacial lakes beneath the Thwaites Glacier.  The article is entitled: "Hidden lakes drain below West Antarctica’s Thwaites Glacier".

http://www.washington.edu/news/2017/02/08/hidden-lakes-drained-under-west-antarcticas-thwaites-glacier/

Extract: "Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.
…
Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, Smith said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain."

Obviously, when these subglacial lakes have refilled by the basal meltwater drainage system, in the coming decades, Thwaites will be primed for another surge.

[AbruptSLR]

In regards to my last post, the linked reference (see also the first attached image and associated caption below, and the second image that shows the basal meltwater drainage system beneath Thwaites) provides more evidence of high geothermal flux and associated basal melt water beneath the Thwaites Glacier, both of which will threaten its future stability, and they both work to refill the recently drainage subglacial lakes beneath Thwaites:

Dustin M. Schroeder, Donald D. Blankenship, Duncan A. Young, and Enrica Quartini, (2014), "Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet", PNAS, doi: 10.1073/pnas.1405184111

http://www.pnas.org/content/early/2014/06/04/1405184111.abstract

http://www.pnas.org/content/suppl/2014/06/04/1405184111.DCSupplemental

Also see:
http://www.utexas.edu/news/2014/06/10/antarctic-glacier-melting/

Caption: "This map shows the locations of geothermal flow underneath Thwaites Glacier in West Antarctica that were identified with airborne ice-penetrating radar. The dark magenta triangles show where geothermal flow exceeds 150 milliwatts per square meter, and the light magenta triangles show where flow exceeds 200 milliwatts per square meter. Letters C, D and E denote high melt areas: in the western-most tributary, C; adjacent to the Crary mountains, D; and in the upper portion of the central tributaries, E. Credit: University of Texas Institute Geophysics"

[AbruptSLR]

Calculation of the remaining carbon budget has been made using unsafe assumptions, including: use of TCR instead of ECS, use of too low of a value of TCR, use of incomplete model projections, use of models that do not consider chaos theory even though the climate is chaotic, use of out-of-date data, using unsafe assumptions about the negative radiative forcing from aerosols, incorporation of too much faith in world leaders to limit carbon emissions, no consideration of freshwater hosing, radiative forcing scenarios are too low, assumed losses of carbon sinks are too optimistic, assuming that geoengineering is feasible.  In consideration of this the US DOE initially started a program called Accelerated Climate Modeling for Energy, ACME; which has subsequently been renamed Energy-Exascale-Earth System Model, E3SM, in an attempt to better understand the actual nature of our collective situation w.r.t. coming climate change.  E3SM models/hardware are expected be continuously updated for several decades; nevertheless, the version of the E3SM model extant at the end of 2017 is currently being used in the CMIP6 program which will heavily influence the coming AR6 findings.  As E3SM is currently the most advanced (but still imperfect) climate model, I provide the following discussion and links related to this matter.

As indicated in the first linked article, preliminary runs of the 2017 version of the E3SM model project that the current value of ECS might have a mean value of about 5.2C (& this high value is likely attributable to the state-of-the-art way that E3SM models aerosols and cloud feedback mechanisms).

While some consensus scientists (like Bjorn Stevens) have said that it is difficult to determine whether the 2017 version of E3SM CMIP6 projections will be any more relevant than other models in the CMIP6 program; I believe that these findings from the world's most advanced ESM warrant the adoptions of the Precautionary Principle, particularly as the 2017 version of E3SM only partially addresses Hansen's ice-climate feedback mechanism:

Title: "DOE’s maverick climate model is about to get its first test"
doi:10.1126/science.aau0578

http://www.sciencemag.org/news/2018/05/does-maverick-climate-model-about-get-its-first-test

Extract: "In 2017, after President Donald Trump took office and pulled the nation out of the Paris climate accords, DOE dropped "climate" from the project name. The new name, the Energy Exascale Earth System Model (E3SM), better reflects the model's focus on the entire Earth system, says project leader David Bader of Lawrence Livermore National Laboratory in California.
..
One preliminary result, on the climate's sensitivity to carbon dioxide (CO2), will "raise some eyebrows," Bader says. Most models estimate that, for a doubling of CO2 above preindustrial levels, average global temperatures will rise between 1.5°C and 4.5°C. The E3SM predicts a strikingly high rise of 5.2°C, which Leung suspects is due to the way the model handles aerosols and clouds. And like many models, the E3SM produces two bands of rainfall in the tropics, rather than the one seen in nature near the equator.

The first test of the E3SM will be its performance in CMIP6. Nearly three dozen modeling groups, including newcomers from South Korea, India, Brazil, and South Africa, are expected to submit results to the intercomparison between now and 2020."

Furthermore, the second linked pdf and associated videos, present some of the findings from the 2017 runs (prior to the CMIP6 runs), including the first attached image comparing hindcastes by the 2017 version of the E3SM model versions other 2017 runs by other advanced ESM models.  While the E3SM (2017) runs may not be sufficiently calibrated to matches its greater-than-normal degree of nonlinear responses, nevertheless the first attached image indicates that E3SM (2017) projected that higher than consensus negative forcing from anthropogenic radiative forcing has masked most of the consequences of the calculated 5.2C value of ECS up to the 2016-17 timeframe.  Even if E3SM (2017) is too responsive to radiative forcing, its projection highlight the potential extreme risks that humanity is taking by assuming that the recent potential high values of negative aerosol forcing are not masking current high values of ECS.  One disturbing possible conclusion from this E3SM (2017) projection might be that since ECS is dependent on the rate of forcing, the sharp global decline in global anthropogenic aerosol negative forcing after the 1990's may have triggered higher values of ECS.  Furthermore, if the E3SM (2017) projection indeed to demonstrate that ECS is very sensitive to the rate of radiative forcing, this would diminish the relevance of paleo-determined values for ECS as the rate of forcing in the past was from hundreds to many thousands of times slower that in modern times.

Title: "E3SM v1 Water Cycle Model for DECK and CMIP6 Submissions by Chris Golaz (of January 25, 2018)":

https://e3sm.org/wp-content/uploads/2018/10/2018-01-25_AllHands_Golaz_opt.pdf

&
See also:

E3SM All-Hands Presentations
https://e3sm.org/about/events/all-hands-presentations/
&
Energy Exascale Earth System Model
https://esgf-node.llnl.gov/projects/e3sm/
&

The following the linked references present findings from E3SM model runs from near the end of 2017, or early 2018, which illustrate that: a) Atmospheric module EAMv1 of E3SM still does not fully simulate cloud feedback mechanisms [see Xie et al. (2018)]; b) Land Ice module of E3SM does not include either the ice-cliff nor the hydrofracturing failure mechanisms [see the second attached image & Hoffman et al. (2018)]; and c) the E3SM module for projecting the potential loss of the Thwaites Ice Shelf is still relatively primitive.

Shaocheng Xie et al. (04 October 2018), "Understanding Cloud and Convective Characteristics in Version 1 of the E3SM Atmosphere Model", JAMES, https://doi.org/10.1029/2018MS001350

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018MS001350

Abstract: "This study provides comprehensive insight into the notable differences in clouds and precipitation simulated by the Energy Exascale Earth System Model Atmosphere Model version 0 and version 1 (EAMv1). Several sensitivity experiments are conducted to isolate the impact of changes in model physics, resolution, and parameter choices on these differences. The overall improvement in EAMv1 clouds and precipitation is primarily attributed to the introduction of a simplified third‐order turbulence parameterization Cloud Layers Unified By Binormals (along with the companion changes) for a unified treatment of boundary layer turbulence, shallow convection, and cloud macrophysics, though it also leads to a reduction in subtropical coastal stratocumulus clouds. This lack of stratocumulus clouds is considerably improved by increasing vertical resolution from 30 to 72 layers, but the gain is unfortunately subsequently offset by other retuning to reach the top‐of‐atmosphere energy balance. Increasing vertical resolution also results in a considerable underestimation of high clouds over the tropical warm pool, primarily due to the selection for numerical stability of a higher air parcel launch level in the deep convection scheme. Increasing horizontal resolution from 1° to 0.25° without retuning leads to considerable degradation in cloud and precipitation fields, with much weaker tropical and subtropical short‐ and longwave cloud radiative forcing and much stronger precipitation in the intertropical convergence zone, indicating poor scale awareness of the cloud parameterizations. To avoid this degradation, significantly different parameter settings for the low‐resolution (1°) and high‐resolution (0.25°) were required to achieve optimal performance in EAMv1."

Plain Language Summary
The Energy Exascale Earth System Model (E3SM) is a new and ongoing U.S. Department of Energy (DOE) climate modeling effort to develop a high‐resolution Earth system model specifically targeting next‐generation DOE supercomputers to meet the science needs of the nation and the mission needs of DOE. The increase of model resolution along with improvements in representing cloud and convective processes in the E3SM atmosphere model version 1 has led to quite significant model behavior changes from its earlier version, particularly in simulated clouds and precipitation. To understand what causes the model behavior changes, this study conducts sensitivity experiments to isolate the impact of changes in model physics, resolution, and parameter choices on these changes. Results from these sensitivity tests and discussions on the underlying physical processes provide substantial insight into the model errors and guidance for future E3SM development.
&

Matthew J. Hoffman et al . (2018), MPAS-Albany Land Ice (MALI): a variable-resolution ice sheet model for Earth system modeling using Voronoi grids", Geosci. Model Dev., 11, 3747–3780, https://doi.org/10.5194/gmd-11-3747-2018

https://www.geosci-model-dev.net/11/3747/2018/gmd-11-3747-2018.pdf

Abstract. We introduce MPAS-Albany Land Ice (MALI) v6.0, a new variable-resolution land ice model that uses unstructured Voronoi grids on a plane or sphere. MALI is built using the Model for Prediction Across Scales (MPAS) framework for developing variable-resolution Earth system model components and the Albany multi-physics code base for the solution of coupled systems of partial differential equations, which itself makes use of Trilinos solver libraries. MALI includes a three-dimensional first-order momentum balance solver (Blatter–Pattyn) by linking to the Albany-LI ice sheet velocity solver and an explicit shallow ice velocity solver. The evolution of ice geometry and tracers is handled through an explicit first-order horizontal advection scheme with vertical remapping. The evolution of ice temperature is treated using operator splitting of vertical diffusion and horizontal advection and can be configured to use either a temperature or enthalpy formulation. MALI includes a mass-conserving subglacial hydrology model that supports distributed and/or channelized drainage and can optionally be coupled to ice dynamics. Options for calving include “eigencalving”, which assumes that the calving rate is proportional to extensional strain rates. MALI is evaluated against commonly used exact solutions and community benchmark experiments and shows the expected accuracy. Results for the MISMIP3d benchmark experiments with MALI’s Blatter–Pattyn solver fall between published results from Stokes and L1L2 models as expected. We use the model to simulate a semi-realistic Antarctic ice sheet problem following the initMIP protocol and using 2 km resolution in marine ice sheet regions. MALI is the glacier component of the Energy Exascale Earth System Model (E3SM) version 1, and we describe current and planned coupling to other E3SM components.
&

Hoffman, M., J. Fyke, S. Price, X. Asay-Davis, and M. Perego (in prep.): Effects of ice shelf melt variability on the evolution of Thwaites Glacier, West Antarctica. Geophys. Res. Lett

https://www.colorado.edu/lab/icesheetclimate/publications

Therefore, if my prior estimates are correct that Pollard, DeConto and Alley (2018) projected Antarctic ice mass losses for Mid-Pliocene conditions may begin circa 2040; then E3SM projections may well prove to be unsafe.

The discussion at the linked Pik-Postdam website considers the probability that tipping cascades of significantly interlinked positive feedback mechanisms might potentially leading to abrupt climate change, particularly if perturbated by a collapse of key Antarctic marine glaciers:

Title: "DominoES project    Domino Effects in the Earth System: Can Antarctica tip climate policy?"

https://www.pik-potsdam.de/research/projects/activities/dominoes

Extract: "Tipping elements are components of the Earth system that could be pushed into qualitatively different states by small external perturbations, with profound environmental impacts possibly endangering the livelihoods of millions of people. There are indications for significant interlinkages between climate tipping elements and even the potential for tipping cascades or domino effects from the climate to the social sphere. We will assess these effects for a highly relevant tipping chain connecting climatic tipping elements like Antarctica and Greenland with potential social tipping processes in public opinion formation and climate policy changes, and their societal implications.

DominoES is a joint project by the Potsdam Institute for Climate Impact Research (PIK) and the Leibniz Institute for the Social Sciences (GESIS) funded by the Leibniz Association (2017 - 2020)."

For those who do not understand dynamical sensitivity, I note that it is related to the influence of climate attractors (from chaos theory), which can capture energy from radiative forcing and progressively ratchet-up climate states (see the last two attached images).

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The Last Glacial Termination, LGT, occurred from 18,000 to 11,650 kya, and the following reference, reconstructs the dynamic response of the Antarctic ice sheets to warming in this period in order to better evaluate Hansen's ice-climate feedback mechanisms.  The abstract from the second linked reference concludes: "Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections.  With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise."

Fogwill, et. al. (2017), "Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the last Glacial Termination", Scientific Reports 7, Article number 39979, doi:10.1038/srep39979

https://www.nature.com/articles/srep39979


Also a rain-dominated Arctic would be affected by Hansen's ice-climate feedback mechanism driven by a WAIS collapse beginning circa 2040 (which almost all ESM projections currently ignore), and or pulses of methane emission from thermokarst lakes.   Also the second linked reference assumes that ECS is only around 3C.

Richard Bintanja and Olivier Andry (2017), “Towards a rain-dominated Arctic”, Geophysical Research Abstracts Vol. 19, EGU2017-4402

http://meetingorganizer.copernicus.org/EGU2017/EGU2017-4402.pdf

Abstract: “Current climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, very little is known about future changes in rain/snow distribution in the Arctic, notwithstanding the importance for hydrology and biology. Here we use 37 state-of-the-art climate models in standardised twenty-first century (2006–2100) simulations to show that 70◦ – 90◦N average annual Arctic snowfall will actually decrease, despite the strong increase in precipitation, and that most of the additional precipitation in the future (2091– 2100) will fall as rain. In fact, rain is even projected to become the dominant form of precipitation in the Arctic region. This is because Arctic atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rain/snowfall will heavily impact Arctic hydrology (e.g. river discharge, permafrost melt), climatology (e.g. snow, sea ice albedo and melt) and ecology (e.g. water and food availability).”

See also the following linked reference:

R. Bintanja et al. Towards a rain-dominated Arctic, Nature Climate Change (2017). DOI: 10.1038/nclimate3240

http://www.nature.com/nclimate/journal/v7/n4/full/nclimate3240.html

Extract: "Rain causes more (extensive) permafrost melt [Refs. 7,26], which most likely leads to enhanced emissions of terrestrial methane [Ref. 27] (a powerful greenhouse gas), more direct runoff (a smaller seasonal delay) and concurrent freshening of the Arctic Ocean [Ref 18]. Rainfall also diminishes snow cover extent and considerably lowers the surface albedo of seasonal snow, ice sheets and sea ice [Ref. 9] , reinforcing surface warming and amplifying the retreat of ice and snow; in fact, enhanced rainfall will most likely accelerate sea-ice retreat by lowering its albedo (compared with that of fresh snowfall) "

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For those interested in an overview of atmospheric bridges, oceanic tunnels and global climatic telecommunications, I offer the following linked 2007 open access reference.  However, I warn that it only provides a low level overview and does not explicitly address issues such as ice-climate feedback (ala Hansen et al 2016) nor issues like the role of Agulhus Leakage in the bipolar seesaw mechanism:

Zhengyu Liu & Mike Alexander (23 June 2007), "Atmospheric bridge, oceanic tunnel, and global climatic teleconnections', Reviews of Geophysics; DOI: 10.1029/2005RG000172

http://onlinelibrary.wiley.com/doi/10.1029/2005RG000172/full

Abstract: "We review teleconnections within the atmosphere and ocean, their dynamics and their role in coupled climate variability. We concentrate on teleconnections in the latitudinal direction, notably tropical-extratropical and interhemispheric interactions, and discuss the timescales of several teleconnection processes. The tropical impact on extratropical climate is accomplished mainly through the atmosphere. In particular, tropical Pacific sea surface temperature anomalies impact extratropical climate variability through stationary atmospheric waves and their interactions with midlatitude storm tracks. Changes in the extratropics can also impact the tropical climate through upper ocean subtropical cells at decadal and longer timescales. On the global scale the tropics and subtropics interact through the atmospheric Hadley circulation and the oceanic subtropical cell. The thermohaline circulation can provide an effective oceanic teleconnection for interhemispheric climate interactions."

The first attached image shows an oceanic Rossby Wave Train that can propagate from the Equatorial Pacific to West Antarctica in a timeframe of months.

The second image shows that during a paleo (45 kya) North Atlantic hosing (D-O) event, warm Gulf Stream water flowed under the less saline (but colder) surface water in order to warm the Norwegian Sea.  Also, the third image shows that under extant conditions with both cool North Pacific and North Atlantic ocean temperatures, atmospheric Rossby waves can still telecommunicate heat from the tropical oceans directly to Arctic regions (as indicated).

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The linked reference points out that per their 1D models the Arctic continental shelf methane hydrate stability zone (HSZ) can take ~ 10 to 20 kyrs to respond to changes in initial temperature conditions associated with the end of the last ice age.  However, while it is pleasant to think of middle of the 10 to 20 kya range, as the attached image indicates the Holocene began about 11 kya and thus we should now start to see portions of the HSZ becoming unstable due to the global temperature increase leading to the beginning of the Holocene.  This emphasizes that modelers need to get their initial conditions correct:

Valentina V. Malakhova & Alexey V. Eliseev (2017), "The role of heat transfer time scale in the evolution of the subsea permafrost and associated methane hydrates stability zone during glacial cycles", Global and Planetary Change, https://doi.org/10.1016/j.gloplacha.2017.08.007

http://www.sciencedirect.com/science/article/pii/S0921818117301273

Abstract: "Climate warming may lead to degradation of the subsea permafrost developed during Pleistocene glaciations and release methane from the hydrates, which are stored in this permafrost. It is important to quantify time scales at which this release is plausible. While, in principle, such time scale might be inferred from paleoarchives, this is hampered by considerable uncertainty associated with paleodata. In the present paper, to reduce such uncertainty, one–dimensional simulations with a model for thermal state of subsea sediments forced by the data obtained from the ice core reconstructions are performed. It is shown that heat propagates in the sediments with a time scale of ∼ 10-20 kyr. This time scale is longer than the present interglacial and is determined by the time needed for heat penetration in the unfrozen part of thick sediments. We highlight also that timings of shelf exposure during oceanic regressions and flooding during transgressions are important for simulating thermal state of the sediments and methane hydrates stability zone (HSZ). These timings should be resolved with respect to the contemporary shelf depth (SD). During glacial cycles, the temperature at the top of the sediments is a major driver for moving the HSZ vertical boundaries irrespective of SD. In turn, pressure due to oceanic water is additionally important for SD ≥ 50 m. Thus, oceanic transgressions and regressions do not instantly determine onset s of HSZ and/or its disappearance. Finally, impact of initial conditions in the subsea sediments is lost after ∼ 100 kyr. Our results are moderately sensitive to intensity of geothermal heat flux."

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While this thread goes well beyond Hansen's ice-climate feedback mechanisms; nevertheless, Hansen's basic position on this matter lies at the heart of this thread.  Therefore, I note that it is a clear example of scientific reticence that consensus climate science has not highly cited Hansen et al. (2016), " Ice Melt, Sea Level Rise, and Superstorms", as discussed in the first linked documents (also see the attached image showing Hansen's illustration of both the ocean stratification and precipitation feedback mechanisms):

James Hansen (October 26, 2017), "Scientific Reticence: a DRAFT Discussion" and "Scientific Reticence and the Fate of Humanity"

http://www.columbia.edu/~jeh1/mailings/2017/20171026_ScientificReticence.pdf
https://unfccc.int/event/abibimman-foundation-james-hansen-scientific-reticence-a-threat-to-humanity-and-nature

Extract: "Frank Dentener, an editor of Atmospheric Chemistry and Physics, in a recent note to me observed that Ice Melt, Sea Level Rise, and Superstorms, hereafter Ice Melt, was not highly cited or mainstream in climate impact discussions. He was concerned because he thought it important for peer-reviewed extreme scenarios to be included in the upcoming IPCC AR6 cycle."
&

Furthermore, the second linked reference indicates that consensus climate science has been largely ignoring Hansen's warnings about fat-tail climate risks since well before 2007, and I note that the longer we wait to take effective action the worse our climate situation becomes:

Hansen (2007), "Scientific Reticence and Sea Level Rise", Environmental Research Letters, Volume 2, Number 2, doi:10.1088/1748-9326/2/2/024002

http://iopscience.iop.org/article/10.1088/1748-9326/2/2/024002
https://arxiv.org/abs/physics/0703220

Abstract: "I suggest that a "scientific reticence" is inhibiting communication of a threat of potentially large sea level rise. Delay is dangerous because of system inertias that could create a situation with future sea level changes out of our control. I argue for calling together a panel of scientific leaders to hear evidence and issue a prompt plain-written report on current understanding of the sea level change issue."

Finally for this post, I note that no matter how much reticence that consensus climate scientists have (or have not) exhibited; I believe that climate science has presented adequate information (even considering the associated uncertainties) for global decision makers to take far greater measures to fight climate change then what they currently have planned.  Until decision makers are willing to open their collective eyes (or become replaced by decision makers who are willing to open their eyes) and take the large number of fat-tailed risks that we face serious; the only out-come that I can see for the path that we are currently taking is socio-economic collapse sometime before 2060.

Title: "A Failure of Imagination on Climate Risks"

http://www.resilience.org/stories/2017-07-26/a-failure-of-imagination-on-climate-risks/

Extract: "Climate change is an existential risk that could abruptly end human civilisation because of a catastrophic “failure of imagination” by global leaders to understand and act on the science and  evidence before them.

At the London School of Economics in 2008, Queen Elizabeth questioned: “Why did no one foresee the timing, extent and severity of the Global Financial Crisis?” The British Academy answered a year later: “A psychology of denial gripped the financial and corporate world… [it was] the failure of the collective imagination of many bright people… to understand the risks to the system as a whole”.

A “failure of imagination” has also been identified as one of the reasons for the breakdown in US intelligence around the 9/11 attacks in 2001.

A similar failure is occurring with climate change today.

The problem is widespread at the senior levels of government and global corporations. A 2016 report, Thinking the unthinkable, based on interviews with top leaders around the world, found that:

“A proliferation of ‘unthinkable’ events… has revealed a new fragility at the highest levels of corporate and public service leaderships. Their ability to spot, identify and handle unexpected, non-normative events is… perilously inadequate at critical moments… Remarkably, there remains a deep reluctance, or what might be called ‘executive myopia’, to see and contemplate even the possibility that ‘unthinkables’ might happen, let alone how to handle them."

Such failures are manifested in two ways in climate policy. At the political, bureaucratic and business level in underplaying the high-end risks and in failing to recognise that the existential risk of climate change is totally different from other risk categories. And at the research level in underestimating the rate of climate change impact and costs, along with an under-emphasis on, and poor communication of, those high-end risks."

In my next several posts I plan on citing several significant potential sources of fat-tailed risks that could contribute to a cascade (domino effect) of tipping points potentially driving the Earth Systems into progressively high states of activation (with higher climate attractors and higher climate sensitivities), if mankind doesn't get off our current BAU pathway immediately (which most likely will not happen).

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As one example of a fat-tailed risk that could contribute to a cascade of tipping point feedback and forcing mechanisms, the linked article is entitled: "Draining huge African peatland a threat to climate: study", this significant GHG source is missing from AR5.  A collapse of the WAIS beginning in 2040 could activate this huge source of possible GHG emissions well before the end of this century:

https://www.yahoo.com/news/draining-huge-african-peatland-threat-climate-study-195730012.html

Extract: "A swampy forest in central Africa the size of England covers previously unknown carbon stocks equivalent to three years' worth of global CO2 emissions, scientists revealed Wednesday.
Draining these peatlands for agriculture, or reduced rainfall due to climate change, would release massive amounts of planet-warming greenhouse gases, they warned in a study published in Nature magazine.

"We found 30 billion tonnes of carbon that nobody knew was there," said Simon Lewis, co-lead author of the study and a professor at the University of Leeds.

"If the Congo Basin peatlands were to be destroyed, it would release billions of tonnes of CO2 into the atmosphere," he told AFP."

Edit, see also the following linked article that indicates that the Congo Basin peatlands formed during the Holocene and thus this fat-tailed risk is not accounted for in models of paleo interglacial periods:

Title: "Guest post: A plan to solve the mysteries of Congo’s vast tropical peatland"

https://www.carbonbrief.org/guest-post-a-plan-to-solve-mysteries-of-congos-vast-tropical-peatland

Extract: "Radiocarbon dating at the base of the peat – up to five metres below the surface – has revealed that the peatland began to form about 10,000 years ago – when central Africa became warmer and wetter as the Earth emerged from the last ice age.
…
Critically, our initial discovery of the peatland included no data from the DRC, which we believe houses two-thirds of the peatland area and its associated carbon stocks. Our new work will test this hypothesis and provide the first data-driven maps of the peatlands in the DRC.

Peatlands are important not just in terms of removing carbon from the atmosphere: the waterlogged conditions means these wetlands also release large quantities of the greenhouse gas methane."