Ice Apocalypse - Multiple Meters Sea Level Rise

[AbruptSLR]

The two attached (Bloomberg) images show how dramatically the coronavirus has reduced aerosol emissions from Guangzhou, China.  While this is impact is still relatively local, this response highlights the risk that a global pandemic could abruptly reduce anthropogenic aerosol emissions worldwide; which would cause an abrupt (although likely short-term) net increase in global radiative forcing.

[AbruptSLR]

The linked image retweeted by Hausfather illustrates how consensus climate science's focus on CO2 emissions can distract from associated increases in methane emissions.  Note how a significant portion of the change in energy related  CO2 emissions from 2018 to 2019 was related to the increasing switch from coal to natural gas; while natural gas from fracking has the same carbon footprint as coal so the global anthropogenic radiative forcing must have increased from 2018 to 2019, even is CO2 emissions flatlined.

[AbruptSLR]

Zeke Hausfather (Director of Climate and Energy at Breakthrough), has written an article (see the first image) discussing many of the means (logic) that consensus climate science will likely use to reduce the range of ECS recognized by AR6 as compared to that indicated by CMIP6 (see the second image).  Nevertheless, just because consensus climate science will likely be able to achieve in AR6 what Hausfather suggests; this does not mean that Earth Systems will respond in accordance with AR6's recommendations.

Title: "Cold Water on Hot Models"

https://thebreakthrough.org/issues/energy/cold-water-hot-models

[AbruptSLR]

The linked article indicates that 20% of the Amazon rainforest has already become a net source of carbon dioxide into the atmosphere:

Title: "Deforested parts of Amazon 'emitting more CO2 than they absorb'"

https://www.bbc.com/news/science-environment-51464694

Extract: "Results from a decade-long study of greenhouse gases over the Amazon basin appear to show around 20% of the total area has become a net source of carbon dioxide in the atmosphere."

[wdmn]

Zeke Hausfather (Director of Climate and Energy at Breakthrough), has written an article (see the first image) discussing many of the means (logic) that consensus climate science will likely use to reduce the range of ECS recognized by AR6 as compared to that indicated by CMIP6 (see the second image).  Nevertheless, just because consensus climate science will likely be able to achieve in AR6 what Hausfather suggests; this does not mean that Earth Systems will respond in accordance with AR6's recommendations.

Title: "Cold Water on Hot Models"

https://thebreakthrough.org/issues/energy/cold-water-hot-models

Meanwhile Patrick T. Brown posted this figure on twitter, stating:

"Is the higher climate sensitivity in the next generation of climate models credible? Our observationally-constrained ECS of the previous generation falls exactly on the ECS of the next generation. So I would vote yes, it's credible."
https://twitter.com/PatrickTBrown31/status/1227272506240712705

Referring to this paper: https://www.nature.com/articles/nature24672

As of 2017 when that paper was published it was possible to rule out an ECS lower than 2.5K based on observational data. The mean of such constrained models was ~3.8K which is the mean of the CMIP6 models.

[nanning]

Dear AbruptSLR, would it be possible to post slightly bigger graphs? In some cases I have difficulty reading the units and descriptions.
Of course I can click on the link but it would be nice to not have to.


I was unfamiliar with the Sv unit in oceanography so I looked it up and post it here because there may be other readers who don't know the unit.

https://en.wikipedia.org/wiki/Sverdrup
In oceanography, a sverdrup (symbol: Sv) is a non-SI unit of flow, with 1 Sv equal to 1 million cubic metres per second (260,000,000 US gal/s);[1][2] it is equivalent to the SI derived unit cubic hectometer per second (symbol: hm³/s or hm³⋅s⁻¹). It is used almost exclusively in oceanography to measure the volumetric rate of transport of ocean currents.

Interesting examples:
The water transport in the Gulf Stream gradually increases from 30 Sv in the Florida Current to a maximum of 150 Sv south of Newfoundland at 55°W longitude.[3]

The Antarctic Circumpolar Current, at approximately 125 Sv, is the largest ocean current.[4]

The entire global input of fresh water from rivers to the ocean is equal to about 1.2 Sv.[5]

[Tom_Mazanec]

So two different names for the exact same unit.
Sigh...

[AbruptSLR]

...
As of 2017 when that paper was published it was possible to rule out an ECS lower than 2.5K based on observational data. The mean of such constrained models was ~3.8K which is the mean of the CMIP6 models.

By examining the historical record, the authors of the linked reference find that about one-third of the models in CMIP5 underestimate the effective radiative forcing in the period from 1861-1880 to near present.  This means that on average CMIP5 underestimates climate sensitivity.

Andrews, T., Forster, P.M. Energy budget constraints on historical radiative forcing. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0696-1

https://www.nature.com/articles/s41558-020-0696-1

Abstract: "Radiative forcing is a fundamental quantity for understanding anthropogenic and natural drivers of past and future climate change, yet significant uncertainty remains in our quantification of radiative forcing and its model representation. Here we use instrumental measurements of historical global mean surface temperature change and Earth’s total heat uptake, alongside estimates of the Earth’s radiative response, to provide a top-down energy budget constraint on historical (1861–1880 to near-present) effective radiative forcing of 2.3 W m−2 (1.7–3.0W m−2; 5–95% confidence interval). This represents a near 40% reduction in the 5–95% uncertainty range assessed by the IPCC Fifth Assessment Report. Although precise estimates of effective radiative forcing in models do not widely exist, our results suggest that the effective radiative forcing may be too small in as many as one-third of climate models in the fifth phase of the Coupled Model Intercomparison Project. Improving model representation of radiative forcing should be a priority for modelling centres. This will reduce uncertainties in climate projections that have persisted for decades."

[AbruptSLR]

The linked reference indicates that the equatorward shift of the westerly jet stream (which is a bellwether for storminess) is more non-linear than previously assumed by consensus climate science.

Gang Chen et al. (06 February 2020), "Sensitivity of the latitude of the westerly jet stream to climate forcing", Geophysical Research Letters, https://doi.org/10.1029/2019GL086563

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL086563?af=R

Abstract
The latitude of the westerly jet stream is influenced by a variety of climate forcings, but their effects on the jet latitude often manifest as a tug‐of‐war between tropical forcing (e.g., tropical upper‐tropospheric warming) and polar forcing (e.g., Antarctic stratospheric cooling or Arctic amplification). Here we present a unified forcing‐feedback framework relating different climate forcings to their forced jet changes, in which the interactions between the westerly jet and synoptic eddies are synthesized by a zonal advection feedback, analogous to the feedback framework for assessing climate sensitivity. This framework is supported by a prototype feedback analysis in the atmospheric dynamical core of a climate model with diverse thermal and mechanical forcings. Our analysis indicates that the latitude of a westerly jet is most sensitive to the climate change‐induced jet speed changes near the tropopause. The equatorward jet shift also displays a larger deviation from linearity than the poleward counterpart.

Plain Language Summary
The westerly jet stream is perceived as the bellwether of midlatitude storminess, surface temperature extremes, and precipitation. The effects of different climate forcings, such as greenhouse gas warming and Antarctic ozone hole, on the westerly jet often result in large cancellations. Here we show the competing effects can be quantified by a unified forcing‐feedback framework. Our analysis demonstrates the critical role in jet shift of the zonal wind changes near the tropopause, which are associated with changes in the equator‐to‐pole temperature gradient under climate change. We also found that the equatorward jet shift is larger than the linear feedback prediction, but this nonlinear effect is small for a poleward jet shift.

Key Points
•   A prototype feedback analysis is developed for the westerly jet stream response to climate change
•   Jet latitude is most sensitive to the climate change‐induced jet speed changes near the tropopause
•   The equatorward jet shift exhibits a larger deviation from linearity than the poleward counterpart

[jai mitchell]

What we already knew

https://www.pnas.org/content/early/2020/02/10/1902469117.short?rss=1

Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica

Fifty years ago, it was speculated that the marine-based West Antarctic Ice Sheet is vulnerable to warming and may have melted in the past. Testing this hypothesis has proved challenging due to the difficulty of developing in situ records of ice sheet and environmental change spanning warm periods. We present a multiproxy record that implies loss of the West Antarctic Ice Sheet during the Last Interglacial (129,000 to 116,000 y ago), associated with ocean warming and the release of greenhouse gas methane from marine sediments. Our ice sheet modeling predicts that Antarctica may have contributed several meters to global sea level at this time, suggesting that this ice sheet lies close to a “tipping point” under projected warming.

[AbruptSLR]

What we already knew

https://www.pnas.org/content/early/2020/02/10/1902469117.short?rss=1

Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica

...

jai,

You beat me to this post but I provide the following post anyway, as it has a few more details, including the last sentence in the Abstract that I underlined:

The linked reference provides paleo-evidence that supports many aspects of the ice apocalypse scenario that I have previously discussed in this thread; however, it does indicate that there is still uncertainty about the time-scale at which such a scenario might unfold.  Also, to me, this evidence supports many aspects of the scenario cited in DeConto and Pollard (2016):

Chris S. M. Turney, Christopher J. Fogwill, Nicholas R. Golledge, Nicholas P. McKay, Erik van Sebille, Richard T. Jones, David Etheridge, Mauro Rubino, David P. Thornton, Siwan M. Davies, Christopher Bronk Ramsey, Zoë A. Thomas, Michael I. Bird, Niels C. Munksgaard, Mika Kohno, John Woodward, Kate Winter, Laura S. Weyrich, Camilla M. Rootes, Helen Millman, Paul G. Albert, Andres Rivera, Tas van Ommen, Mark Curran, Andrew Moy, Stefan Rahmstorf, Kenji Kawamura, Claus-Dieter Hillenbrand, Michael E. Weber, Christina J. Manning, Jennifer Young, and Alan Cooper (February 11, 2020), "Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica", PNAS, https://doi.org/10.1073/pnas.1902469117

https://www.pnas.org/content/early/2020/02/10/1902469117.short?rss=1

Significance
Fifty years ago, it was speculated that the marine-based West Antarctic Ice Sheet is vulnerable to warming and may have melted in the past. Testing this hypothesis has proved challenging due to the difficulty of developing in situ records of ice sheet and environmental change spanning warm periods. We present a multiproxy record that implies loss of the West Antarctic Ice Sheet during the Last Interglacial (129,000 to 116,000 y ago), associated with ocean warming and the release of greenhouse gas methane from marine sediments. Our ice sheet modeling predicts that Antarctica may have contributed several meters to global sea level at this time, suggesting that this ice sheet lies close to a “tipping point” under projected warming.

Abstract
The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG) (129 to 116 ky), which experienced warmer polar temperatures and higher global mean sea level (GMSL) (+6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (∼2 m), ocean thermal expansion, and melting mountain glaciers (∼1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic meridional overturning circulation in response to North Atlantic surface freshening. Here, we report a blue-ice record of ice sheet and environmental change from the Weddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS), which is underlain by major methane hydrate reserves. Constrained by a widespread volcanic horizon and supported by ancient microbial DNA analyses, we provide evidence for substantial mass loss across the Weddell Sea Embayment during the LIG, most likely driven by ocean warming and associated with destabilization of subglacial hydrates. Ice sheet modeling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multimeter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further amplify warming.

[AbruptSLR]

Dear AbruptSLR, would it be possible to post slightly bigger graphs? In some cases I have difficulty reading the units and descriptions.
Of course I can click on the link but it would be nice to not have to.

…

My time is limited, but I will see what I can do.

[jai mitchell]

ASLR

I was posting it yesterday but had a phone call and forgot 

The trouble I see is that we have no idea that the CPDW warming that is now fully documented on WAIS is (most likely) not something that a paleo analog can provide insight into.  The simple fact is that we have tweaked the Global atmospheric circ patterns far far far outside of any paleo analog.

[nanning]

Thanks for making that clear AbruptSLR. I withdraw my request .
It is hardly any effort for me to click on the link. You have your own methods. I am very grateful for all your efforts in informing us. I should not have asked.

[AbruptSLR]

ASLR

I was posting it yesterday but had a phone call and forgot 

The trouble I see is that we have no idea that the CPDW warming that is now fully documented on WAIS is (most likely) not something that a paleo analog can provide insight into.  The simple fact is that we have tweaked the Global atmospheric circ patterns far far far outside of any paleo analog.

jai,

Trying to communicate our true collective level of climate change risk to the general public is such a difficult task that I suspect that collectively we will have crossed numerous irreversible climate tipping points well before there is enough consensus to take effective action to reduce coming climate consequences this century.  Nevertheless, I will make another feeble attempt at trying to convey both the immediacy and magnitude of our current climate change risk, using Turney et al. (2020) as a foil.  As the current rate of increase of radiative forcing is several thousands of times faster than that leading into the Eemian (LIG or MIS5e), it is clear that Turney et al (2020)'s paleo-data cannot be taken to mean that the Eemian can be used as a simulation of future conditions this century.  Nevertheless, these paleo-findings can be used to encourage CMIP7 modelers to better model the ice-climate feedback mechanisms that CMIP6 discounted including:

1.  Turney et al (2020)'s finding makes it clear that Edwards et al. (2019)'s assessment of the likelihood of a MICI-type of WAIS collapse during the Eemian are out of date.  Note that Turney et al (2020) makes it clear that the WAIS contributed to at least 3.8m of sea level rise during the Eemian, while the first attached image indicates that previously consensus climate scientists only assumed that the WAIS contributed 2.5 m to sea level rise during the Eemian.

2.  The findings from the January 2020 Icefin robot (part of the ITGC) prove that the modified CDW in the subglacial cavities along the Thwaites Glacier grounding line (see the second image) is already 2C above the freezing point of water in the cavities.  Thus, one does not need to wait for the Southern Ocean waters to warm by less than an average of 2C (as was the case during the Eemian); as for key glaciers like the PIG and Thwaites Glacier, we are already there.

3. The third attached image illustrates how rapidly the PIIS calving front has retreated in recent decades through February 11, 2020; which is much quicker than assumed by CMIP6.  Thus, we do not need to wait two hundred years (as was the case for the Eemian) for such key ice shelves to collapse.

4.  The fourth image illustrates how rapidly the Beaufort Gyre energy budget has changed in recent years.  Thus, we do not need to wait for GIS ice melt to slow the MOC as a release of relatively freshwater from the Beaufort Gyre into the North Atlantic, will likely serve this function in the coming decades.

See also:

Title: "Ancient Antarctic ice melt increased sea levels by 3+ meters—and it could happen again"

https://phys.org/news/2020-02-ancient-antarctic-ice-sea-metersand.html

Extract: "Using data gained from their fieldwork, the team ran model simulations to investigate how warming might affect the floating ice shelves. These shelves currently buttress the ice sheets and help slow the flow of ice off the continent.

The results suggest a 3.8m sea level rise during the first thousand years of a 2°C warmer ocean. Most of the modelled sea level rise occurred after the loss of the ice shelves, which collapsed within the first two hundred years of higher temperatures.
…
Notably, the researchers warn that this tipping point may be closer than we think.

"The Paris Climate Agreement commits to restricting global warming to 2°C, ideally 1.5°C, this century," says Professor Turney.

"Our findings show that we don't want to get close to 2°C warming.""

[AbruptSLR]

18 years has made a big difference in the way the Thwaites Ice Tongue looks and behaves:

Title: "Thwaites Glacier Transformed"

https://earthobservatory.nasa.gov/images/146247/thwaites-glacier-transformed

Extract: "Notice the size of the glacier’s main ice tongue in 2001, when the glacier was advancing by about 4 kilometers per year. The large rift across the glacier eventually spawned Iceberg B-22 in 2002.

In the past ten years, the tongue has continued to fracture and separate from the Thwaites Eastern Ice Shelf. By the time the 2019 image was acquired, the main tongue had retreated substantially, and the ocean in front of Thwaites had become filled with mélange, a mixture of icebergs and sea ice.

Unlike Pine Island Glacier—which tends to shed large icebergs every few years (now almost annually)—the icebergs that now break from Thwaites are generally not large enough to be named and tracked by the U.S. National Ice Center. Instead, the glacier is constantly producing many small broken bits.

The melting of floating ice as it makes contact with the ocean is a key reason why the glacier is coming unglued. Seawater that is a few degrees above freezing is melting the ice shelf from below. Warm water has recently been recorded near the Thwaites Glacier grounding line—the location where the glacial ice rests on the seafloor.

“What the satellites are showing us is a glacier coming apart at the seams,” said Ted Scambos, a senior scientist at the University of Colorado. “Every few years a new area seems to be letting go and accelerating. Like taffy being stretched out, this glacier is being drawn into the ocean.”"

[AbruptSLR]

Another positive feedback mechanism that neither CMIP5, nor CMIP6, models do not adequately account for is climate change-driven changes in agricultural zones (see the attached image for RCP 8.5 2060-2080).  As cited in the linked open access reference 'Frontier soils contain up to 177 Gt of C, which might be subject to release, which is the equivalent of over a century of current United States CO2 emissions.'

Lee Hannah et al. (February 12, 2020), "The environmental consequences of climate-driven agricultural frontiers", PloS ONE, https://doi.org/10.1371/journal.pone.0228305

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0228305

Abstract
Growing conditions for crops such as coffee and wine grapes are shifting to track climate change. Research on these crop responses has focused principally on impacts to food production impacts, but evidence is emerging that they may have serious environmental consequences as well. Recent research has documented potential environmental impacts of shifting cropping patterns, including impacts on water, wildlife, pollinator interaction, carbon storage and nature conservation, on national to global scales. Multiple crops will be moving in response to shifting climatic suitability, and the cumulative environmental effects of these multi-crop shifts at global scales is not known. Here we model for the first time multiple major global commodity crop suitability changes due to climate change, to estimate the impacts of new crop suitability on water, biodiversity and carbon storage. Areas that become newly suitable for one or more crops are Climate-driven Agricultural Frontiers. These frontiers cover an area equivalent to over 30% of the current agricultural land on the planet and have major potential impacts on biodiversity in tropical mountains, on water resources downstream and on carbon storage in high latitude lands. Frontier soils contain up to 177 Gt of C, which might be subject to release, which is the equivalent of over a century of current United States CO2 emissions. Watersheds serving over 1.8 billion people would be impacted by the cultivation of the climate-driven frontiers. Frontiers intersect 19 global biodiversity hotspots and the habitat of 20% of all global restricted range birds. Sound planning and management of climate-driven agricultural frontiers can therefore help reduce globally significant impacts on people, ecosystems and the climate system.

Caption: Fig 1. Global climate-driven agricultural frontiers for RCP8.5 2060–2080.
Areas that transition from no current suitability for major commodity crops to suitability for one or more crops are depicted in blue, while currently uncultivated areas that transition to suitability for multiple major commodity crops are shown in red. Intensity of color indicates the level of agreement between simulations driven by different GCMs for the RCP 8.5 radiative concentration pathway. Terrestrial areas in white are either currently suitable for at least one modeled crop or, not suitable for any modeled crops in the projected climatic conditions. Suitability under current and projected climates is defined as universal agreement of suitability methods (EcoCrop, Maxent, Frequency of Extreme Temperatures).

[AbruptSLR]

18 years has made a big difference in the way the Thwaites Ice Tongue looks and behaves:

Title: "Thwaites Glacier Transformed"

https://earthobservatory.nasa.gov/images/146247/thwaites-glacier-transformed

..
Unlike Pine Island Glacier—which tends to shed large icebergs every few years (now almost annually)—the icebergs that now break from Thwaites are generally not large enough to be named and tracked by the U.S. National Ice Center. Instead, the glacier is constantly producing many small broken bits.

…

While I have discussed this matter in several prior posts, it has come to my attention that some reader do not understand why the Thwaites Ice Tongue breaks into numerous small (~ 1km to 5km) icebergs while the Pine Island Ice Shelf has been producing much larger icebergs when it calves, in recent years.  In my opinion, the most significant reason why the Thwaites Ice Tongue breaks into many smallish icebergs is that its glacial ice is pre-fractured in the pattern shown in the first image before the glacial ice crosses the final grounding line (at the base of the ice tongue).  Furthermore, in my opinion, this pre-fractured pattern in the glacial ice occurs when this ice passes over the sub-glacial cavity, upstream of the base of the ice tongue, due to tensile stresses induced in the ice when it looses basal support over the sub-glacial cavity (which I have previously call the 'Big Ear', as indicated by the title of the last attached image); as indicated in the last three attached images.

Furthermore, in my opinion, this behavior markedly increases the chance that an ice cliff face with over 100m of height above the water line may become exposed at the upstream side of the Big Ear subglacial cavity, if/when all of the downstream small icebergs float away (which might occur during the next one or two Super El Nino events).  Additionally, I remind readers that the Big Ear subglacial cavity occurs over the subglacial trough that leads directly into the BSB, and thus any ice cliff failure mechanism formed at the upstream side of this Big Ear subglacial cavity would likely propagate rapidly into the Byrd Subglacial Basin, BSB.

Edit: I note also that the accompanying images of the extent of the Big Ear subglacial cavity are for 2017; while it is now 2020, so the extent of this key subglacial cavity is almost certainly larger than indicates as it is reportedly substantially created by relatively warm modified circumpolar deep water, CDW, being circulated into the subglacial cavity by tidal action (indicated by the arrows in the second and third attached images).

[AbruptSLR]

The linked article about the risk of future abrupt 'dieback' of the Amazon rainforest concludes that this risk is real but that: "We are unlikely to know the vulnerability of the rainforest to climate change with any confidence until it is too late."

Title: "Guest post: Could climate change and deforestation spark Amazon ‘dieback’?"

https://www.carbonbrief.org/guest-post-could-climate-change-and-deforestation-spark-amazon-dieback

Extract: "Our model suggested that the CO2 effects had dominated over the 20th century – leading to a carbon sink in the intact rainforest. However, the model had the negative climate effects eventually winning out – resulting in an abrupt dieback of the Amazon rainforest from about 2040 onwards, when global warming had reached about 3C in this projection.
You can see this in the chart below, which shows how our model projected vegetation in the Amazon could change as the climate warmed through to 2100. It shows an Amazon dominated by trees (solid line) for decades, but then the fraction of the region that is covered by trees drops off dramatically through the middle of the 21st century. It is then replaced with grasses (dashed lines) and bare soil (dashed and dotted line).
…
Our findings were stark. However, recent research hints that Amazon forest may be more resilient to climate change. A lot of relevant research has flowed under the bridge since we published that dieback scenario in 2000 – some good news and some bad news for the forest.

First, the good news. It now seems that climate change is unlikely to be as damaging to the Amazon rainforest as we originally feared. In 2013, we discovered that the year-to-year variation in the annual increase in atmospheric CO2 allows us to estimate the sensitivity of tropical carbon sinks to climate change.
…
But there is also some less optimistic news. It now also seems that the CO2-fertilisation effect is unlikely to be as large as many early models assumed. This is because first and second generation climate-carbon cycle models did not include nutrient limitations on forest growth.
…
This, in combination with the dry season becoming long enough to permit regular natural fires, could see the forest transition to a permanent savannah. This would be characterised by a mixed tree and grassland system with an open canopy that allows the soil to become much hotter and drier, as well as store much less carbon.

Therefore, the twin pressures of deforestation and climate change on the Amazon rainforest remain a great concern. We are unlikely to know the vulnerability of the rainforest to climate change with any confidence until it is too late. However, we are sure that human-caused deforestation reduces the resilience of the forest to climate change and other stressors.

Many had thought the problem of Amazonian deforestation was on the path to being solved. The rate of deforestation dropped from a peak in 2004 of 28,000 square kilometres (km2) – equivalent to removing an area of forest almost the size of Belgium each year – to less than a fifth of that rate by 2014.

But that is all in the past now. With deforestation on the up and global warming continuing, there are, once again, multiple threats to the longevity of the Amazon rainforest."

[AbruptSLR]

The linked article tries to emphasize positive considerations associated with the risk of "… irreversible emissions of a permafrost 'tipping point'"; nevertheless, it concludes that: "… for permafrost, the science shows that thaw is already underway and the carbon it is releasing will already be contributing to our warming climate."  Furthermore, I not that if for any combination of reasons the NH atmosphere changes into an equable pattern this century (say due to the Equatorial Pacific SSTA increasing by 5C, say due to an abrupt slowdown of the MOC, caused say by an abrupt release of relatively fresh water from the Beaufort Gyre into the North Atlantic in coming decades), this carbon emissions from permafrost will definitely have effectively crossed an irreversible emission 'tipping point' that could sustain such equable conditions for a long time even without any more anthropogenic GHG emissions:

Title: "Guest post: The irreversible emissions of a permafrost ‘tipping point’"

https://www.carbonbrief.org/guest-post-the-irreversible-emissions-of-a-permafrost-tipping-point

Extract: "Scientists estimate that there is about twice as much carbon stored in permafrost as circulating in the atmosphere. This is approximately 1460bn-1600bn tonnes of carbon.

Most of it is currently frozen and preserved, but if even a small fraction is released into the atmosphere, the emissions would likely be large – potentially similar in magnitude to carbon release from other environmental fluxes, such as deforestation.
…
But, as things stand, permafrost thaw has already been observed in many locations in the Arctic. And as the recent special report on the ocean and cryosphere by the Intergovernmental Panel on Climate Change (IPCC) points out, warming this century will cause substantial emissions from permafrost:

“By 2100, near-surface permafrost area will decrease by 2-66% for RCP2.6 and 30–99% for RCP8.5. This could release 10s to 100s of gigatonnes of carbon as CO2 and methane to the atmosphere for RCP8.5, with the potential to accelerate climate change.”"

[AbruptSLR]

While the austral summer is rapidly coming to a close, the two attached images from the linked website show that from Nov 1, 2019 to Feb 13, 2020 the ASE region sustained an unusual high number of surface melt days; which likely contributed to the degradation of both the PIIS and the Thwaites Ice Shelf/Tongue.  Furthermore, as there was no El Nino event this ENSO season; the advection of warm CDW beneath these ice shelves/tongue have been typical; but when a strong El Nino event eventually occurs, I believe that not only will the degradation of the ice shelves/tongue be accelerated but also that any calved icebergs/bergy-bits will be more likely to float away; which would further accelerate subsequent degradation of the ice shelves/tongue by relieving congestion induced buttressing from these mélanges.

http://climato.be/cms/index.php?climato=the-2020-melt-season-over-antarctica-as-simulated-by-marv3-10

[AbruptSLR]

I chopped the attached graph  from a tweet by Deke Arndt into two pieces:

Tweet: "Deke Arndt‏ @DekeArndt Largest non El Niño monthly anomaly in the record. That rightmost grey bar just went where no grey bar has gone before."

[AbruptSLR]

While the orange dots are preliminary and the green crosses indicates readings from poorly mixed air masses; nevertheless, the range of both the orange and green symbols has increased significantly in recent years for atmospheric methane readings at Barrow, Alaska (see the attached image for atmospheric methane readings at Barrow for the years 2007 thru Feb 13, 2020).  To me, this is an indicator of increasing permafrost degradation in recent years:

Title: "Barrow Atmospheric Baseline Observatory, United States"

https://www.esrl.noaa.gov/gmd/dv/iadv/graph.php?code=BRW&program=ccgg&type=ts

Extract: "Data shown may be measurements of air collected approximately weekly in glass containers and returned to GMD for analysis or averages from air sampled semi-continuously at a GMD baseline observatory. Circle Symbols are thought to be regionally representative of a remote, well-mixed troposphere.

+ Symbols are thought to be not indicative of background conditions, and represent poorly mixed air masses influenced by local or regional anthropogenic sources or strong local biospheric sources or sinks.

A smooth curve and long-term trend may be fitted to the representative measurements when sufficient data exist. Data shown in ORANGE are preliminary. All other data have undergone rigorous quality assurance and are freely available from GMD, CDIAC, and WMO WDCGG."

[AbruptSLR]

The linked article focuses on the somewhat arbitrary consideration that some people have been overestimating the annual amount of methane currently discharged into the atmosphere from the Arctic Ocean associated with methane seeps in the seafloor.  However, associated study indicates that the amount of methane emitted from methane seeps is sensitive to bottom water temperatures, and the article concludes that:

"At 400 meters water depth we are already at the limit of the gas hydrate stability. If these waters warm merely by 1,3°C this hydrate lid will permanently lift, and the release will be constant." says Ferré."

Title: "Climate gas budgets highly overestimate methane discharge from Arctic Ocean"

https://www.sciencedaily.com/releases/2020/01/200113111052.htm

Extract: "We have found that seasonal differences in bottom water temperatures in the Arctic Ocean vary from 1,7°C in May to 3,5°C in August. The methane seeps in colder conditions decrease emissions by 43 percent in May compared to August." says oceanographer Benedicte Ferré, researcher at CAGE Centre for Arctic Gas Hydrate, Environment and Climate at UiT The Arctic University of Norway.

"Right now, there is a large overestimation in the methane budget. We cannot just multiply what we find in August by 12 and get a correct annual estimate. Our study clearly shows that the system hibernates during the cold season."
...
How methane will react in future ocean temperature scenarios is still unknown. The Arctic Ocean is expected to become between 3°C and a whopping 13°C warmer in the future, due to climate change. The study in question does not look into the future, but focuses on correcting the existing estimates in the methane emissions budget. However:

"We need to calculate the peculiarities of the system well, because the oceans are warming. The system such as this is bound to be affected by the warming ocean waters in the future." says Benedicte Ferré;.

A consistently warm bottom water temperature over a 12-month period will have an effect on this system.

"At 400 meters water depth we are already at the limit of the gas hydrate stability. If these waters warm merely by 1,3°C this hydrate lid will permanently lift, and the release will be constant." says Ferré."

Edit:

I forgot to mention that as the linked reference finds that prior estimates of current methane emissions from Arctic seafloor seeps were too high, as the current atmospheric methane concentrations are well known, this implies that some other source of methane emissions is higher than previously estimated (which might be coming from the recent acceleration of permafrost degradation).

[AbruptSLR]

There is relatively little new information cited in the linked article discussing a potential WAIS 'tipping point'; but it does emphasize that such a tipping point is likely to occur with a GMSTA someplace between 1.5C and 2C and that we are already around 1.1C and states that: '… the margins for avoiding this threshold are fine indeed.'

Title: "Guest post: How close is the West Antarctic ice sheet to a ‘tipping point’?" by Christina Hulbe

https://www.carbonbrief.org/guest-post-how-close-is-the-west-antarctic-ice-sheet-to-a-tipping-point

Extract: "The latest research says that the threshold for irreversible loss of the WAIS likely lies between 1.5C and 2C of global average warming above pre-industrial levels. With warming already at around 1.1C and the Paris Agreement aiming to limit warming to 1.5C or “well-below 2C”, the margins for avoiding this threshold are fine indeed.
…
The IPCC says:

“Beyond 2050, uncertainty in climate change induced SLR [sea level rise] increases substantially due to uncertainties in emission scenarios and the associated climate changes, and the response of the Antarctic ice sheet in a warmer world.”

The concern around the vulnerability of the WAIS principally lies in something called “marine ice sheet instability” (MISI) – “marine” because the base of the ice sheet is below sea level and “instability” for the fact that, once it starts, the retreat is self-sustaining.
…
There appears to be a second source of instability for marine ice sheets – one that comes into play if the ice shelves are lost entirely.
…
This process, illustrated below, is called “marine ice cliff instability” (MICI). The theory suggests that where the height of a glacier face exceeds around 100m above the ocean surface, the cliff will be too tall to support its own weight. It will, therefore, inevitably collapse, exposing a similarly tall cliff face behind it, which, too, will collapse. And so on."

[AbruptSLR]

A new Antarctic temperature record has just between set:

Title: "Antarctica Just Cracked a Disturbing New Temperature Record of 20 Degrees Celsius" Feb 14, 2020

https://www.sciencealert.com/antarctica-just-smashed-a-new-balmy-heat-record

Extract: "Scientists in Antarctica have recorded a new record temperature of 20.75 degrees Celsius (69.35 Fahrenheit), breaking the barrier of 20 degrees for the first time on the continent, a researcher said Thursday."

[AbruptSLR]

The linked article focuses on the somewhat arbitrary consideration that some people have been overestimating the annual amount of methane currently discharged into the atmosphere from the Arctic Ocean associated with methane seeps in the seafloor.  However, associated study indicates that the amount of methane emitted from methane seeps is sensitive to bottom water temperatures, and the article concludes that:

"At 400 meters water depth we are already at the limit of the gas hydrate stability. If these waters warm merely by 1,3°C this hydrate lid will permanently lift, and the release will be constant." says Ferré."

…

While I have more frequently cited the risk that the Beaufort Gyre poses to a slowing of the MOC; I also remind readers that the relatively freshwater accumulating is the Beaufort Gyre is also relatively warm and its eventual release from the gyre will not only send relatively warm fresh water into the North Atlantic, but also into the Arctic Ocean; which per the linked reference (previously cited in Reply #2672) would disrupt the halocline which in turn would reduce the Arctic Sea Ice extent beyond the summer season; which in turn would warm the Arctic Ocean waters due to the change in albedo; which puts the hydrate lid on the Arctic Ocean seafloor at greater risk of abruptly degrading in the coming decades.

Mary-Louise Timmermans John Toole and Richard Krishfield (29 Aug 2018), "Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins", Science Advances, Vol. 4, no. 8, eaat6773, DOI: 10.1126/sciadv.aat6773

https://advances.sciencemag.org/content/4/8/eaat6773

Abstract
Arctic Ocean measurements reveal a near doubling of ocean heat content relative to the freezing temperature in the Beaufort Gyre halocline over the past three decades (1987–2017). This warming is linked to anomalous solar heating of surface waters in the northern Chukchi Sea, a main entryway for halocline waters to join the interior Beaufort Gyre. Summer solar heat absorption by the surface waters has increased fivefold over the same time period, chiefly because of reduced sea ice coverage. It is shown that the solar heating, considered together with subduction rates of surface water in this region, is sufficient to account for the observed halocline warming. Heat absorption at the basin margins and its subsequent accumulation in the ocean interior, therefore, have consequences for Beaufort Gyre sea ice beyond the summer season.

[AbruptSLR]

With a hat-tip to vox_mundi, the linked reference found over 2 million Arctic permafrost methane emission hotspots during a recent airborne survey using state-of-the-art instrumentation.  This study suggests that thermokarst lakes are already becoming a significant source of methane emissions; which does not bode well for the prospect of increasing such methane emissions with continuing Arctic warming/amplification:

Clayton D. Elder et al. (10 February 2020), "Airborne Mapping Reveals Emergent Power Law of Arctic Methane Emissions", Geophysical Research Letters, https://doi.org/10.1029/2019GL085707

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL085707

Abstract
Methane (CH4) emissions from thawing permafrost amplify a climate warming feedback. However, upscaling of site‐level CH4 observations across diverse Arctic landscapes remains highly uncertain, compromising accuracy of current pan‐Arctic CH4 budgets and confidence in model forecasts. We report a 30,000‐km2 survey at 25‐m2 resolution (~1 billion observations) of CH4 hotspot patterns across Alaska and northwestern Canada using airborne imaging spectroscopy. Hotspots covered 0.2% of the surveyed area, concentrated in the wetland‐upland ecotone, and followed a two‐component power law as a function of distance from standing water. Hotspots decreased sharply over the first 40 m from standing water (y = 0.21×−0.649, R2 = 0.97), mirroring in situ flux observations. Beyond 40 m, CH4 hotspots diminished gradually over hundreds of meters (y = 0.004×−0.164, R2 = 0.99). This emergent property quantifies the distribution of strong methanogenic zones from site to regional scales, vastly improving metrics for scaling ground‐based CH4 inventories and validation of land models.

Plain Language Summary
Understanding Arctic methane emissions is crucial to forecasting the region's impact on global climate. Ongoing efforts suffer large uncertainties when upscaling emissions since direct observations rarely cover scales relevant to both process‐level (fine‐scale) biogeochemistry and land models that operate on much larger scales. We bridge these scale gaps via high‐resolution airborne detection of methane hotspots (25‐m2 pixels) across a 30,000‐km2 study domain. We quantified a key spatial property of Arctic methane emissions: their power law dependence on distance to nearest standing water. From the ground, we verified that wide‐ranging methane fluxes follow the same spatial power law pattern as domain‐wide hotspots. These conclusions can improve scaling of emissions in Arctic land models and potentially reduce the disparity between ground‐based and atmospheric emission budgeting.

[AbruptSLR]

In my opinion, if/when the PIIS calving front retreats upstream of the South Ice Shelf, SIS, (the first image shows the calving front on February 9, 2020); the second image (from the first linked reference) of ice shelves surface elevations circa 2012, indicates that there is a significant piece of the SIS that could calve off (i.e. the green area surrounded by blue).  Furthermore, the third image ( showing the 2009 to 2012 circulation pattern, from the second linked site) shows that relatively warm ocean water actively circulates beneath the SIS.  Also, I provide the fourth image that shows the mid-January 2014 grounding line location, for reference:

Shean, D. E., Joughin, I. R., Dutrieux, P., Smith, B. E., and Berthier, E.: Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica, The Cryosphere, 13, 2633–2656, https://doi.org/10.5194/tc-13-2633-2019, 2019.

https://www.the-cryosphere.net/13/2633/2019/

Abstract
Ocean-induced basal melting is responsible for much of the Amundsen Sea Embayment ice loss in recent decades, but the total magnitude and spatiotemporal evolution of this melt is poorly constrained. To address this problem, we generated a record of high-resolution digital elevation models (DEMs) for Pine Island Glacier (PIG) using commercial sub-meter satellite stereo imagery and integrated additional 2002–2015 DEM and altimetry data. We implemented a Lagrangian elevation change (Dh∕Dt) framework to estimate ice shelf basal melt rates at 32–256 m resolution. We describe this methodology and consider basal melt rates and elevation change over the PIG ice shelf and lower catchment from 2008 to 2015. We document the evolution of Eulerian elevation change (dh∕dt) and upstream propagation of thinning signals following the end of rapid grounding line retreat around 2010. Mean full-shelf basal melt rates for the 2008–2015 period were ∼82–93 Gt yr−1, with ∼200–250 m yr−1 basal melt rates within large channels near the grounding line, ∼10–30 m yr−1 over the main shelf, and ∼0–10 m yr−1 over the North shelf and South shelf, with the notable exception of a small area with rates of ∼50–100 m yr−1 near the grounding line of a fast-flowing tributary on the South shelf. The observed basal melt rates show excellent agreement with, and provide context for, in situ basal melt-rate observations. We also document the relative melt rates for kilometer-scale basal channels and keels at different locations on the ice shelf and consider implications for ocean circulation and heat content. These methods and results offer new indirect observations of ice–ocean interaction and constraints on the processes driving sub-shelf melting beneath vulnerable ice shelves in West Antarctica.
Caption for the second image: "Figure 3 October-December 2012 WorldView/GeoEye DEM mosaic of the PIG ice shelf.  Labels show regions discussed in text: North ice shelf. South ice shelf, Main ice shelf, "ice plain", and fast-flowing South ice shelf tributary.  White outline shows ~2011 grounding line. Elevation values are the corrected surface height (Eq. 1) above the EGM2008 geoid."

&

For the circulation pattern see:

http://nora.nerc.ac.uk/502263/1/1244341RevisedManuscript2.pdf

Caption for the third image: "Fig. 3. Observed and simulated hydrography and circulation in 2009 and 2012. A. Section of observed and simulated 2009 potential temperatures (color) and salinity (black contours) along the eastern Amundsen Sea trough and underneath the PIG ice shelf. White lines show the surface-referenced 27.47 and 27.75 isopycnals. The panel shows observations outside the PIG cavity, and simulation results within it. Observations are linearly interpolated from profiles (black triangles) indicated in figure 1B. B. Same as A but for the 2012 observations and simulation. C. Modeled potential temperature (color) and velocity (black vectors, every fifth vector is shown) averaged within 50 m of the seabed for the 2009 simulation. White vectors show the corresponding velocity observed by Autosub (binned on the model grid, see also Fig. S2A). The cyan line indicates the position of the section used in panels A and B. The white line indicates 750 m seabed depth. D. Same as C but for the difference between the 2012 and the 2009 simulations."

[AbruptSLR]

The linked reference assesses and evaluates the differences between climate sensitivity projected by CMIP5 models vs CMIP6 models.  The attached associated image indicates that the CMIP6 ECS distribution is bimodal, with one mode have an ECS of about 3C and the other having an ECS of about 5C.  As I doubt that the true pdf for ECS is bimodal; this bimodal distribution for CMIP6 likely is related to human bias.  While decision makers will likely use the associated uncertainty as an excuse for not taking more strident climate action; I view it as a significant risk that the 5C ECS mode may be correct.

Flynn, C. M. and Mauritsen, T.: On the Climate Sensitivity and Historical Warming Evolution in Recent Coupled Model Ensembles, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2019-1175, in review, 2020.

https://www.atmos-chem-phys-discuss.net/acp-2019-1175/

Abstract. The Earth's equilibrium climate sensitivity (ECS) to a doubling of atmospheric CO2, along with the transient 35 climate response (TCR) and greenhouse gas emissions pathways, determines the amount of future warming. Coupled climate models have in the past been important tools to estimate and understand ECS. ECS estimated from Coupled Model Intercomparison Project Phase 5 (CMIP5) models lies between 2.0 and 4.7 K (mean of 3.2 K), whereas in the latest CMIP6 the spread has increased: 1.8–5.5 K (mean of 3.7 K), with 5 out of 25 models exceeding 5 K. It is thus pertinent to understand the causes underlying this shift. Here we compare the CMIP5 and CMIP6 model ensembles, and find a systematic shift between CMIP eras to be unexplained as a process of random sampling from modeled forcing and feedback distributions. Instead, shortwave feedbacks shift towards more positive values, in particular over the Southern Ocean, driving the shift towards larger ECS values in many of the models. These results suggest that changes in model treatment of mixed-phase cloud processes and changes to Antarctic sea ice representation are likely causes of the shift towards larger ECS. Somewhat surprisingly, CMIP6 models exhibit less historical warming than CMIP5 models; the evolution of the warming suggests, however, that several of the models apply too strong aerosol cooling resulting in too weak mid 20th Century warming compared to the instrumental record.

Caption: "Figure 1. Histograms displaying number of CMIP5 (top) or CMIP6 (bottom) models that fall with 0.5 K ECS bins.  ECS mean value and standard deviation for CMIP5 and CMIP6 displayed in black and red, respectively, above each histogram."

[AbruptSLR]

Fracked natural gas does not only have a carbon footprint as heavy as that for coal; but it is so cheap and abundant that solar and wind power cannot compete with it, and it is driving utilities to build associated infrastructure that will ensure the use of natural gas for decades to come; all of which will slow progress in the fight against climate change.  Furthermore, virgin plastics made from natural gas is now cheaper than recycled plastics, making it difficult to move towards a circular economy.

Title: "Cheap natural gas is making it very hard to go green."

https://www.treehugger.com/fossil-fuels/cheap-natural-gas-making-it-very-hard-go-green.html

Extract: "We recently noted that the US is drowning in cheap natural gas, and that "Gasmaggedon" will make it even harder to electrify everything. Now we learn from Bloomberg Green that solar and wind power can't compete with gas that's this cheap. Naureen Malik and Brian Eckhouse write:

Gas is such a bargain that it’s being viewed less as a bridge fossil fuel, driving the world away from dirtier coal toward a clean-energy future, and more as a hurdle that could slow the trip down. Some forecasters are predicting prices will stay low for years, making it tough for states, cities and utilities to achieve their goals of being zero-carbon in power production by 2050 or earlier.
…
According to Jared Paben in Plastics Recycling Update, virgin plastics are now cheaper than recycled plastic, and there is too much of the stuff; Tison Keel of IHS Markit complains that "the supply-demand imbalance is expected to get worse with additional production capacity coming on-line. “What we have coming in the next couple of years is a large overbuild.”"

[Sciguy]

Fracked natural gas does not only have a carbon footprint as heavy as that for coal; but it is so cheap and abundant that solar and wind power cannot compete with it, and it is driving utilities to build associated infrastructure that will ensure the use of natural gas for decades to come; all of which will slow progress in the fight against climate change.  Furthermore, virgin plastics made from natural gas is now cheaper than recycled plastics, making it difficult to move towards a circular economy.

Title: "Cheap natural gas is making it very hard to go green."

https://www.treehugger.com/fossil-fuels/cheap-natural-gas-making-it-very-hard-go-green.html

Extract: "We recently noted that the US is drowning in cheap natural gas, and that "Gasmaggedon" will make it even harder to electrify everything. Now we learn from Bloomberg Green that solar and wind power can't compete with gas that's this cheap. Naureen Malik and Brian Eckhouse write:

Gas is such a bargain that it’s being viewed less as a bridge fossil fuel, driving the world away from dirtier coal toward a clean-energy future, and more as a hurdle that could slow the trip down. Some forecasters are predicting prices will stay low for years, making it tough for states, cities and utilities to achieve their goals of being zero-carbon in power production by 2050 or earlier.
…
According to Jared Paben in Plastics Recycling Update, virgin plastics are now cheaper than recycled plastic, and there is too much of the stuff; Tison Keel of IHS Markit complains that "the supply-demand imbalance is expected to get worse with additional production capacity coming on-line. “What we have coming in the next couple of years is a large overbuild.”"

Natural gas frackers are going bankrupt because the prices are so low.  They're already cutting production, so the amount of gas from gas-only fields will drop.

Currently, a lot of gas from oil fields is being vented and/or flared, which has a much worse impact on the greenhouse effect then if it's burned in a power plant. 

So the impacts of the current glut are that the natural gas producers will be out of business and venting/flaring will be reduced. 

And renewables are already cheaper than the cost of building new gas plants. While the low prices of gas may keep operating plants in business while prices are low, they aren't leading to new investment decisions to build new natural gas plants.  (The linked article is from September 2019).

https://www.fastcompany.com/90402331/its-now-cheaper-to-build-new-renewables-than-it-is-to-build-natural-gas-plants

Clean energy has reached a tipping point: It’s now cheaper to build and use a combination of wind, solar, batteries, and other clean tech in the U.S. than to build most proposed natural gas plants. Utilities want to spend $90 billion to build new gas plants and $30 billion to build new gas pipelines—but if they used renewables instead, consumers could save $29 billion in electricity bills, according to a new report from the nonprofit Rocky Mountain Institute.

“In 2019, given what is needed on the grid today, we show that these technologies have crossed the line and become the cheapest way to add electricity to the grid,” says Chaz Teplin, a manager in RMI’s electricity practice. “Going forward, that case is going to only accelerate because while the price of natural gas, for example, may fluctuate up and down, the cost to install new renewables is only going to continue to decrease.”

[AbruptSLR]

...

So the impacts of the current glut are that the natural gas producers will be out of business and venting/flaring will be reduced. 

...

I certainly hope that your are correct, but only time will tell what the future brings.

[interstitial]

Unfortunately the really low cost of natural gas this winter makes the September 2019 analysis Ken mentioned out of date. We used to use propane for heat but I put in a heat pump shortly after I started paying the bills here. Normally this is the time when propane  rates are highest but a week ago I got an advert for 1.49 which is close to the 1.19 low last summer and was the low a few years ago.

[AbruptSLR]

In the linked abstract of a presentation made at the December 2019 AGU Convention, Richard Alley et al. point out that ice-shelf stability is one of the most important considerations for determining whether future ice-cliff failure mechanisms may occur with continued global warming, and I note that CMIP6 models make very primitive assumptions about ice-shelf stability that do not appear to be what is currently happening seaward of the PIG and Thwaites Glacier.  Furthermore, Richard Alley et al.  support Hansen et al. (2016)'s observation that a cooling of the ocean surface (as is currently happening in the Southern Ocean) can direct more warm deep ocean water towards the bases of key ice shelves such as the PIIS, TEIS and the Thwaites Ice Tongue; which reduces their stability.  Richard Alley et al. also point out that ice-rafted debris (IRD) cannot occur with ice shelves intact, thus the factor than numerous IRD fields in both the Southern Ocean and the North Atlantic mean the ice-cliff failure mechanism likely occurred in paleo times under conditions similar to our current situation.

C51A-08 - “Then new problems came, from above and below…”: Heinrich Events and the future of West Antarctic ice (Invited)

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/587813

Abstract
Heinrich Events (HE), in particular H2, record ice-shelf loss and resulting ice-flow acceleration in a cold surface climate, with implications for the future of sea-level change. Essentially all ice shelves buttress ice inflow, and experience basal melting near the grounding line that reduces or eliminates ice-rafted debris (IRD) before calving. This understanding indicates that IRD pulses in cold climates record ice-shelf loss and not just faster flow with intact ice shelves. Ice-shelf loss has been observed recently in response to atmospheric warming (Larsen B), but also in response to oceanic warming (Jakobshavn) with shelf thinning and flow acceleration causing marginal rifting leading to shelf calving (Joughin et al. 2008 JGR), perhaps preconditioned by marginal troughs (K.E. Alley et al. 2019 SciAdv). As shown by Marcott et al. (2011 PNAS), surface cooling preceding HE allowed warm water to access the grounding zone of the Hudson Strait ice stream, and the IRD pulses then record the ice-shelf loss, accompanied by faster flow in response to loss of buttressing. H2 occurred at a minimum in atmospheric temperatures. Future warming could reach Larsen B-type conditions in West Antarctica. But, if ice-sheet mass loss stabilizes the water column and causes surface cooling but subsurface warming, similar or even greater instability may result, as confirmed by H2. Proper understanding of these processes implemented in models is essential for accurate projections.

[AbruptSLR]

Karen Alley et al (from a presentation at the December 2019 AGU Fall Meeting) discuss how basal channels in Antarctic ice shelves can work to destabilize such ice shelves leading to the type of accelerated calving as we have recently witness for the Pine Island Ice Shelf, PIIS.  In my opinion this behavior does not bode well for the stability of either the PIIS or the Thwaites Ice Tongue in coming decades.

C53C-1361 - Direct and indirect impacts of basal channels on ice-shelf stability

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/509049

Abstract
Basal channels are frequently found beneath the shear margins of fast-flowing ice shelves, where thinning due to channel formation likely contributes to reduced buttressing and decreased ice-shelf stability. Basal channels are also commonly found in the middle of ice shelves, particularly in areas where warm water is present. In either case, indirect effects on ice-shelf stability related to changes in buttressing and controls on basal melt rates are combined with direct effects, as stresses imparted by basal channels cause fractures, which may initiate calving events. We show that fractures form in association with basal channels on ice shelves throughout Antarctica, both at shear margins and at mid-shelf channels. Upstream channel growth is associated with channel deepening and the upstream propagation of channel-associated fractures on the Getz Ice Shelf. Because basal channels are widespread on Antarctic ice shelves, it is important to ascertain the balance of direct and indirect basal channel influences on ice-shelf stability and the capacity for basal channel change under evolving oceanic conditions.

[AbruptSLR]

Schwans et al. (a presentation at the December 2019 AGU Fall Meeting) indicates that the Eastern Shear Margin plays an important role in the future dynamics of the Thwaites Glacier.  Furthermore, I note that now that the PIIS is no longer buttressing the Southwest Tributary Glacier it is likely that the Thwaites Eastern Shear Margin will become more dynamic in coming years.

Title: "C53A-05 - Role of the Eastern Shear Margin in Thwaites Glacier’s Dynamics"

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/513156

Abstract
Thwaites Glacier’s (TG’s) accelerating mass loss and connection to major drainages in the WAIS make it the most likely means by which the ice sheet could rapidly destabilize and contribute to sea level rise (SLR).

Results using JPL’s Ice Sheet System Model (ISSM) show how the timing and rate of TG’s retreat into the interior of the WAIS is highly dependent on ill-constrained conditions at the bed and at/near the ice/ocean interface. Another uncertainty in projecting Thwaites’ retreat is whether its Eastern shear margin will remain stable or migrate.
A model ensemble containing various melt scenarios, bed types, initial shelf configurations, and shear margin forcings provides new insight into the relative importance of each of these forcings/conditions, and their interplay, in TG’s evolution over the next few centuries. Simulations activating the entire Eastern shear margin show that, regardless of bed character, this alters retreat patterns across TG’s main trunk, pointing to the margin as an important field target for future data collection efforts on Thwaites.

[AbruptSLR]

…

Chris S. M. Turney, Christopher J. Fogwill, Nicholas R. Golledge, Nicholas P. McKay, Erik van Sebille, Richard T. Jones, David Etheridge, Mauro Rubino, David P. Thornton, Siwan M. Davies, Christopher Bronk Ramsey, Zoë A. Thomas, Michael I. Bird, Niels C. Munksgaard, Mika Kohno, John Woodward, Kate Winter, Laura S. Weyrich, Camilla M. Rootes, Helen Millman, Paul G. Albert, Andres Rivera, Tas van Ommen, Mark Curran, Andrew Moy, Stefan Rahmstorf, Kenji Kawamura, Claus-Dieter Hillenbrand, Michael E. Weber, Christina J. Manning, Jennifer Young, and Alan Cooper (February 11, 2020), "Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica", PNAS, https://doi.org/10.1073/pnas.1902469117

https://www.pnas.org/content/early/2020/02/10/1902469117.short?rss=1

…

First, the following extract from Turney et al. (2020) makes it clear how important the bipolar seesaw mechanism is w.r.t. potential future ice mass loss from Antarctica (possibly triggered by a release of relatively fresh/warm water from the Beaufort Gyre in coming decades).

Extract from Turney et al. (2020): "Recent work has proposed that the iceberg-rafted Heinrich 11 event between 135 and 130 ky (during Termination II) may have significantly reduced North Atlantic Deep Water (NADW) formation and shut down the Atlantic meridional overturning circulation (AMOC) (42), resulting in net heat accumulation in the Southern Hemisphere (the bipolar seesaw pattern of northern cooling and southern warming) (43, 44) (Fig. 4A). Under this scenario, surface cooling during Heinrich 11 increased the northern latitudinal temperature gradient and caused a southward migration of the Intertropical Convergence Zone and midlatitude Southern Hemisphere westerly airflow (14, 45). Importantly, Heinrich 11 was probably one of the largest of the iceberg-rafting events over the last 140 ky (including H-1 and H-2) and during a time of likely weakened AMOC (42). In the Southern Ocean, the associated northward Ekman transport of cool surface waters (something akin to today; Fig. 1A) was likely compensated by increased delivery of relatively warm and nutrient-rich Circumpolar Deep Water (CDW) toward the Antarctic margin (14, 34, 43, 45, 46), potentially leading to enhanced thermal erosion of ice at exposed grounding lines (43, 47). This interpretation is supported by the enriched benthic foraminifera 13C values into the LIG (46), a proxy for the influence of NADW on CDW in the south, implying northern (warmer) waters were reaching far south for much of this period (and a cause of persistent loss of ice volume) (Fig. 2I). The unambiguous precise correlation between the Patriot Hills ice and West Antarctic marine records (34) afforded by the Termination II tephra demonstrates that the warming recorded in the BIA is coincident with a major, well-documented peak in marine temperatures and productivity around the Antarctic continent and in the Southern Ocean (34, 45, 46) (Fig. 2). The subsequent delivery of large volumes of associated freshwater into the Southern Ocean during the LIG would have reduced Antarctic Bottom Water (AABW) production (46), resulting in increased deepwater formation in the North Atlantic (43, 48, 49) (Fig. 4C). Recent modeling results suggest that increased heat transport beneath the ice shelves can drive extensive grounding-line retreat, triggering substantial drawdown of the Antarctic ice sheet (2, 14, 20) (Fig. 4B). Of concern, warming of the ocean cavity in the WSE is projected to increase during the 21st century (50)."

Second, the linked article makes it clear that the ice-rafted debris (IRD) already found on the seafloor of the Southern Ocean supported the concept that MICI-types of ice mass loss may be in our future and it discusses efforts to obtain more extensive such evidence (see image).

Title: "Antarctica’s iceberg graveyard could reveal the ice sheet’s future"

https://www.sciencenews.org/article/antarctica-iceberg-graveyard-climate-change

Extract: "“By looking at material carried by icebergs that calved off of the continent, we should be able to infer which sectors of the ice sheet were most unstable in the past,” Raymo says. “We can correlate the age and mineralogy of the ice-rafted debris to the bedrock in the section of Antarctica from which the bergs originated.”

Icebergs breaking off from the edges of Antarctica’s ice sheet tend to stay close to the continent, floating counterclockwise around the continent. But when the bergs reach the Weddell Sea, on the eastern side of the peninsula, they are shunted northward through a region known as Iceberg Alley toward warmer waters in the Scotia Sea.
…
But Antarctica may have played a larger role than once thought. In a study published in Nature in 2014, Kuhn, Weber and other colleagues reported that ice-rafted debris from that time period, as recorded in relatively short sediment cores from Iceberg Alley, often occurred in large pulses lasting a few centuries to millennia. Those data suggested that the southernmost continent was shedding lots of bergs much more quickly during those times than once thought.
…
“The existing [ice core] record from Iceberg Alley taught us Antarctica lost ice through a threshold reaction,” Weber says. That means that when the continent reached a certain transition point, there was sudden and massive ice loss rather than just a slow, gradual melt.

“We have rather firm evidence that this threshold is passed once the ice sheet loses contact with the underlying ocean floor,” he says, adding that at that point, the shedding of ice becomes self-sustaining, and can go on for centuries. “With mounting evidence of recent ice-mass loss in many sectors of West Antarctica of a similar fashion, we need to be concerned that a new ice-mass loss event is already underway, and there is no stopping it.”"

&

Title: "Deep-Sea Drillers Investigate Shedding of Antarctic Icebergs"

https://blogs.ei.columbia.edu/2019/03/25/iodp-icebergs-antarctica-climate-change/

Third, the first linked video illustrates how dramatically the Antarctic iceberg flux has increased from 1976 to 2019.

Title: "Icebergs Alive - Iceberg flux 1976-2019"



Fourth, the second linked video illustrates how much the Thwaites Glacier ice flow velocity has increased through 2019.

Title: "Thwaites Glacier Along Flow Ice Speed"

[blumenkraft]

And here as GIF i found.

(Click to play)

[AbruptSLR]

In the linked 2018 Carbon Brief article Hausfather both tries to explain 'How scientists estimate 'climate sensitivity' and tries to support the AR5 consensus ranges for ECS and TCR; which in my opinion discounts much of the actual climate change risk that we are currently facing.  Examples of how consensus climate scientists (including Hausfather) are discounting the risk of higher effective climate sensitivity include:

1. They created definitions of 'climate sensitivity' that discount effective climate sensitivity risks such as abrupt ice sheet mass loss, and sea ice albedo flip, this century.

2. They discount the early activation of various 'slow' feedback mechanisms such as the early upwelling of warm circumpolar deep water, CDW, that is currently accelerating ice shelf calving in Antarctic.

3. They general give too much weight to calculations of climate sensitivity based on short-term observations that are biased by the 'faux hiatus'.

4. They discount the fact that both effective ECS and effective TCR increase with continued forcing and thus the longer we wait to take effective action to stop climate change the harder it will be to take effective action.

Title: "Explainer: How scientists estimate 'climate sensitivity'" by Zeke Hausfather, 2018

https://skepticalscience.com/explainer-how-scientists-estimate-climate-sensitivity.html

Extract: "Climate sensitivity refers to the amount of global surface warming that will occur in response to a doubling of atmospheric CO2 concentrations compared to pre-industrial levels."

CO2 has increased from its pre-industrial level of 280 parts per million (ppm) to around 408 ppm today. Without actions to reduce emissions concentrations are likely to reach 560 ppm – double pre-industrial levels – around the year 2060.

There are three main measures of climate sensitivity that scientists use. The first is equilibrium climate sensitivity (ECS). The Earth’s climate takes time to adjust to changes in CO2 concentration. For example, the extra heat trapped by a doubling of CO2 will take decades to disperse down through the deep ocean. ECS is the amount of warming that will occur once all these processes have reached equilibrium.

The second is transient climate response (TCR). This is the amount of warming that might occur at the time when CO2 doubles, having increased gradually by 1% each year. TCR more closely matches the way the CO2 concentration has changed in the past. It differs from ECS because the distribution of heat between the atmosphere and oceans will not yet have reached equilibrium.

A third way of looking at climate sensitivity, Earth system sensitivity (ESS), includes very long-term Earth system feedbacks, such as changes in ice sheets or changes in the distribution of vegetative cover.
…
A 2017 paper by Dr Cristian Proistosescu and Prof Peter Huybers at Harvard University found that amplifying feedbacks that play a large role in ECS in climate models have not fully kicked in for current climate conditions. A similar paper by Prof Kyle Armourof the University of Washington suggests feedbacks will increase by about 25% from today’s transient warming as the Earth moves towards equilibrium.

This means that sensitivity estimates based on instrumental warming to date would be on the low side, as they would not capture the larger role of feedbacks in future warming. The authors suggest that “accounting for these…brings historical records into agreement with model-derived ECS estimates”.

This is in part because feedbacks depend strongly on the spatial pattern of warming. Prof Armour elaborates in a discussion on the Climate Lab Book website:

“Nearly all GCMs [global climate models] show global radiative feedbacks changing over time under forcing, with effective climate sensitivity increasing as equilibrium is approached. As a result, climate sensitivity estimated from transient warming appears smaller than the true value of ECS…

As far as we can tell, the physical reason for this effect is that the global feedback depends on the spatial pattern of surface warming, which changes over time…One nice example is the sea-ice albedo feedback in the Southern Ocean: because warming has yet to emerge there, that positive (destabilising) feedback has yet to be activated.

This means that even perfect knowledge of global quantities (surface warming, radiative forcing, heat uptake) is insufficient to accurately estimate ECS; you also have to predict how radiative feedbacks will change in the future.”"

See also:

https://www.climate-lab-book.ac.uk/2016/reconciling-estimates-of-climate-sensitivity/#comment-2565

Extract: "Caldeira & Myrhvold (2013) and the standard “Gregory approach” use simulations where CO2 jumps by 300% immediately (“abrupt4xCO2”) and then you see what happens. In those cases dT/dt is big and then slows down. That’s because forcing is big and causes immediate heating. But if you plot T vs F (F being net top-of-atmosphere imbalance here) you see that dT/dF, which is related to feedbacks, changes with time in a way that means feedbacks get more-positive as warming goes on.

In 1pctCO2 simulations the forcing increases linearly from zero, but the temperature change accelerates. Taking the model average T and looking at the trends for each 30 year period within years 0-120 you get trends in C/decade of: +0.21, +0.27, +0.31, +0.34. Warming accelerates under transient CO2 increases in models.

The differences comes down to dT/dt versus dT/dF. Rugenstein & Knutti is a good place to look for more info and work by people like Armour, Held, Gettelman, Kay & Shell helps explain the physics."

[AbruptSLR]

I re-post the following in order to emphasize that abrupt iceberg calving (without ice shelves being present, resulting in ice-rafted debris as shown in the attached image) not only occurred in much of the WAIS but also in portions of the EAIS in paleo-times.  If this pattern is repeated in the future is could lead to over a century of ice sheet-climate positive feedback for more global warming even without additional anthropogenic radiative forcing after we have reached a MICI tipping point (say beginning in the ASE and then moving progressively to other Antarctic regions):

The linked reference discusses the paleo stability (instability) of the Wilkes Land continental margin (EAIS) in response to the early Pliocene ocean warming (which are conditions that the Earth could approximately replicate before 2100):

Melissa A. Hansen, Sandra Passchier, Boo-Keun Khim, Buhan Song & Trevor Williams (2015), "Threshold behavior of a marine-based sector of the East Antarctic Ice Sheet in response to early Pliocene ocean warming", Paleoceanography, DOI: 10.1002/2014PA002704

http://onlinelibrary.wiley.com/doi/10.1002/2014PA002704/abstract

Abstract: "We investigate the stability of the East Antarctic Ice Sheet (EAIS) on the Wilkes Land continental margin, Antarctica, utilizing a high-resolution record of ice-rafted debris (IRD) mass accumulation rates (MAR) from Integrated Ocean Drilling Program Site U1359. The relationship between orbital variations in the IRD record and climate drivers was evaluated to capture changes in the dynamics of a marine-based ice sheet in response to early Pliocene warming. Three IRD MAR excursions were observed and confirmed via scanning electron microscope microtextural analysis of sand grains. Time series analysis of the IRD MAR reveals obliquity-paced expansions of the ice sheet to the outer shelf prior to ~4.6 Ma. A decline in the obliquity and a transition into a dominant precession response of IRD MAR occur at ~4.6 Ma along with a decline in the amplitude of IRD MAR maxima to low background levels between ~4.0 and ~3.5 Ma. We speculate that as sea surface temperatures began to peak above 3°C during the early Pliocene climatic optimum, the ice shelves thinned, leading to a greater susceptibility to precession-forced summer insolation and the onset of persistent retreat of a marine-based portion of the EAIS."

[AbruptSLR]

Per the linked NASA website, the global January 2020 LOTI Anomaly vs 1951-1980 was 1.17^oC, and the first attached image give the zonal mean LOTI anomaly vs 1951-1980 for January 2020; which makes me wonder what the people living near 60^o north latitude (like Oslo, Norway) will experience during January 2050:

https://data.giss.nasa.gov/gistemp/maps/index_v4.html

Edit:

The second attached image (from the same website) gives the January 2020 LOTI Anomaly vs 1951-1980; which shows that not only are the people living near Oslo, Norway, effected but also almost all of Siberia (with its extensive permafrost regions) and much of Canada near Hudson Bay (with its extensive sea ice area).

Edit2:

For those who forgot, to convert 1951-1980 temp departures to pre-industrial add: + 0.256 Celsius (so 1.17C with a 1951-1980 baseline converts to +1.426C vs pre-industrial)

[bluice]

Indeed so.

In approximately 60 % of Finland, January 2020 was the mildest in recorded history.

In the record-breaking areas, this January was generally 7–8 degrees milder than usual. The reference period consists of the average from 1981–2010. "In many areas, the average temperature of January was equivalent to typical conditions in late March and early April,"

https://en.ilmatieteenlaitos.fi/press-release/1243129338

And there’s hardly any ice on the Baltic Sea.

[Human Habitat Index]

Per the linked NASA website, the global January 2020 LOTI Anomaly vs 1951-1980 was 1.17^oC, and the first attached image give the zonal mean LOTI anomaly vs 1951-1980 for January 2020; which makes me wonder what the people living near 60^o north latitude (like Oslo, Norway) will experience during January 2050:

https://data.giss.nasa.gov/gistemp/maps/index_v4.html

Edit:

The second attached image (from the same website) gives the January 2020 LOTI Anomaly vs 1951-1980; which shows that not only are the people living near Oslo, Norway, effected but also almost all of Siberia (with its extensive permafrost regions) and much of Canada near Hudson Bay (with its extensive sea ice area).

Edit2:

For those who forgot, to convert 1951-1980 temp departures to pre-industrial add: + 0.256 Celsius (so 1.17C with a 1951-1980 baseline converts to +1.426C vs pre-industrial)

Do you use 1750 baseline ?

[kassy]

Only 58 cm...

The Antarctica factor: Model uncertainties reveal upcoming sea level risk

Within this century already, due to Antarctica alone global sea level might rise up to three times as much as it did in the last century. This is a finding of an exceptionally comprehensive comparison of state-of-the-art computer models from around the world.

"While we saw about 19 centimeter of sea-level rise in the past 100 years, Antarctic ice-loss could lead to up to 58 centimeter within this century. Coastal planning cannot merely rely on the best guess. It requires a risk analysis. Our study provides exactly that: The sea level contribution of Antarctica is very likely not going to be more than 58 centimeters."

...

The researchers accounted for a number of uncertainties in the computations, from the atmospheric warming response to carbon emissions to oceanic heat transport to the Southern ocean. 16 ice sheet/ modeling groups comprised of 36 researchers from 27 institutes contributed to the new study, which was coordinated by PIK. A similar study six years earlier had to rely on the output of only five ice sheet models. This development reflects the increasing importance of research on the Antarctic ice sheet.

https://www.sciencedaily.com/releases/2020/02/200214084904.htm

I guess few or none have the MICI process in them?
 
Its 580/80 or 7,25 mm per year.

Meltwater pulse 1A (MWP1a) is the name used by Quaternary geologists, paleoclimatologists, and oceanographers for a period of rapid post-glacial sea level rise, between 13,500 and 14,700 years ago, during which global sea level rose between 16 meters (52 ft) and 25 meters (82 ft) in about 400–500 years, giving mean rates of roughly 40–60 mm (0.13–0.20 ft)/yr.[1]

I would bet against the ensemble outcome if i wasn´t dead by then...oh well. 

[AbruptSLR]

Per the linked NASA website, the global January 2020 LOTI Anomaly vs 1951-1980 was 1.17^oC, and the first attached image give the zonal mean LOTI anomaly vs 1951-1980 for January 2020; which makes me wonder what the people living near 60^o north latitude (like Oslo, Norway) will experience during January 2050:

https://data.giss.nasa.gov/gistemp/maps/index_v4.html

Edit:

The second attached image (from the same website) gives the January 2020 LOTI Anomaly vs 1951-1980; which shows that not only are the people living near Oslo, Norway, effected but also almost all of Siberia (with its extensive permafrost regions) and much of Canada near Hudson Bay (with its extensive sea ice area).

Edit2:

For those who forgot, to convert 1951-1980 temp departures to pre-industrial add: + 0.256 Celsius (so 1.17C with a 1951-1980 baseline converts to +1.426C vs pre-industrial)

Do you use 1750 baseline ?

The +0.256 conversion factor is to the late 19th century.

[rboyd]

Per the linked NASA website, the global January 2020 LOTI Anomaly vs 1951-1980 was 1.17^oC, and the first attached image give the zonal mean LOTI anomaly vs 1951-1980 for January 2020; which makes me wonder what the people living near 60^o north latitude (like Oslo, Norway) will experience during January 2050:

https://data.giss.nasa.gov/gistemp/maps/index_v4.html

Edit:

The second attached image (from the same website) gives the January 2020 LOTI Anomaly vs 1951-1980; which shows that not only are the people living near Oslo, Norway, effected but also almost all of Siberia (with its extensive permafrost regions) and much of Canada near Hudson Bay (with its extensive sea ice area).

Edit2:

For those who forgot, to convert 1951-1980 temp departures to pre-industrial add: + 0.256 Celsius (so 1.17C with a 1951-1980 baseline converts to +1.426C vs pre-industrial)

Do you use 1750 baseline ?

The +0.256 conversion factor is to the late 19th century.

Add 0.2 degrees centigrade to use 1750 as a baseline.

Countries in the Paris climate agreement set a target of keeping warming below 2 degrees Celsius by curbing carbon emissions compared to their preindustrial levels. But a new study shows that the preindustrial level used in the agreement, based on temperature records from the late 19th century, doesn't account for a potential century of rising temperatures caused by carbon dioxide emissions. Accounting for those gases, released from about 1750 to 1875, would add another one-fifth of a degree to the baseline temperature, the study found

Published yesterday in Nature Climate Change, the research suggests there's less time than previously believed to address global warming, said Michael Mann, a climatologist at Pennsylvania State University.

The study estimates that there may have already been 0.2 degree Celsius of warming, or 0.36 degree Fahrenheit, built into Earth, he said. That means the Paris Agreement would have to be more aggressive, according to the study, which was also written by researchers from the universities of Edinburgh and Reading in the United Kingdom.

“When you take that into account, it turns out we have 40 percent less carbon to burn than we thought we had,” Mann said

https://www.scientificamerican.com/article/the-world-may-have-less-time-to-address-climate-change-than-scientists-thought/

[rboyd]

The full-year 2019 LOTI-GISS temperature rise is 0.98 degrees centigrade above the baseline, which gives me 1.24 degrees centigrade versus late 19th century, BUT the World Meteorological Organization put 2019 at 1.1 degrees centigrade above the late 19th century.

I know that the WMO averages five data sets including Hadley, NOAA and NASA, and that the NOAA interpolation techniques (for areas without measured temperatures) give lower temperatures than NASA GISS and some data sets simply ignore non-covered areas. From the quote below by the WMO, seems like the NASA-GISS gives the highest temperatures, but that may be because it is more accurately including the areas not covered by temperature monitoring locations. If so, the WMO is giving a misleading picture by mixing NASA-GISS with less accurate data sets, as well as not baselining to 1750 for pre-industrial.

It seems that the WMO uses reanalysis data sets to fill in the gaps, would be interesting to see an analysis between NASA-GISS interpolation and this reanalysis to see which is more accurate. The WMO is implicitly stating that NASA GISS is estimating on the hot side.

With NASA GISS vs 1750, 1.24+0.2, we were pretty much at 1.5 degrees last year, and even closer in 2016 (short by only 0.02 degrees). Reporting that may have helped focus policy makers mind's a bit better.

The spread between the five data sets was 0.15°C with both the lowest (1.05°C) and the highest (1.20°C) being more than 1°C warmer than the pre-industrial baseline.

Modern temperature records began in 1850. WMO uses datasets (based on monthly climatological data from Global Observing Systems) from the United States National Oceanic and Atmospheric Administration, NASA’s Goddard Institute for Space Studies, and the United Kingdom’s Met Office Hadley Centre and the University of East Anglia’s Climatic Research Unit in the United Kingdom. 

It also uses reanalysis datasets from the European Centre for Medium Range Weather Forecasts and its Copernicus Climate Change Service, and the Japan Meteorological Agency.  This method combines millions of meteorological and marine observations, including from satellites, with models to produce a complete reanalysis of the atmosphere. The combination of observations with models makes it possible to estimate temperatures at any time and in any place across the globe, even in data-sparse areas such as the polar regions.

https://public.wmo.int/en/media/press-release/wmo-confirms-2019-second-hottest-year-record

[AbruptSLR]

The linked RealClimate article by Mauri Pelto, 2009; reminds us that in 1978 John Mercer argued that a major deglaciation of the WAIS might begin circa 2028, and that in 1981 Terry Hughes argued that such a major deglaciation would likely begin in the Pine Island Bay of the Amundsen Sea Embayment, ASE. Furthermore, Pelto indicated that the evidence through 2009 supported these arguments by Mercer and Hughes; however, to date neither the CMIP community nor the IPCC accept the likelihood of such an occurrence in the near future.

That said, the first image (from Rignot, 2008) and the second image (from Vaughan et al 2006) show that the Pine Island Glacier and the Thwaites Glacier catchment basins abut each other; which may lead to a synergistic degradation of the stability of both catchment basins in coming years.  This is particularly true regarding the potential interaction between the Pine Island Ice Shelf's (PIIS) South Ice Shelf (SIS) and the Southwest Tributary Glacier's (SWT) ice shelf as indicated by third image showing the 2012 PIIS ice surface elevation and the fourth image showing the interface between the SWT ice shelf and the SIS for February 18, 2020 which shows a faint rift about 1km upstream from the calving face.

Title: "Is Pine Island Glacier the Weak Underbelly of the West Antarctic Ice Sheet?", RealClimate Guest post by Mauri Pelto, November 9, 2009

http://www.realclimate.org/index.php/archives/2009/11/is-pine-island-glacier-the-weak-underbelly-of-the-west-antarctic-ice-sheet/

Extract: "A different example, from the same time period, was the 1978 publication by the late John Mercer, Ohio State U., who argued that a major deglaciation of the West Antarctic Ice Sheet (WAIS) may be in progress within 50 years. This conclusion was based on the fact that the WAIS margin was ringed with stabilizing ice shelves, and that much of the ice sheet is grounded below sea level. The loss of ice shelves — Mercer proposed — would allow the ice sheet to thin, grounding lines to retreat and the ice sheet to disintegrate via calving. This is a much faster means of losing mass than melting in place. Mercer further commented that the loss of ice shelves on the Antarctic Peninsula, as has since been observed, would be an indicator that this process of ice sheet loss due to global warming was underway.

Mercer’s ideas led Terry Hughes (1981) (my doctoral advisor at U. of Maine) to propose that the WAIS had a “weak underbelly” in Pine Island Bay. This bay in the Amundsen Sea is where the Pine Island Glacier (PIG) and Thwaites Glacier reach the sea. These are the only two significant outlet glaciers draining the north side of the WAIS. Together they drain 20% of the WAIS. Hughes called this area the “weak underbelly” because these glaciers lack the really huge ice shelves Ross Ice Shelf and the Ronne-Filchner Ice Shelf in which most other large WAIS outlet glaciers terminate.
…
The evidence does indicate that one of the basic underlying principles, proposed by Mercer and Hughes, of what can stabilize or destabilize WAIS was right on the money. The evidence reviewed does not fully confirm the weak underbelly hypothesis, but it provides enough evidence that we had best monitor the situation and expand our attempts to understand it."

[AbruptSLR]

...
With NASA GISS vs 1750, 1.24+0.2, we were pretty much at 1.5 degrees last year, and even closer in 2016 (short by only 0.02 degrees). Reporting that may have helped focus policy makers mind's a bit better.

The spread between the five data sets was 0.15°C with both the lowest (1.05°C) and the highest (1.20°C) being more than 1°C warmer than the pre-industrial baseline.

Modern temperature records began in 1850. WMO uses datasets (based on monthly climatological data from Global Observing Systems) from the United States National Oceanic and Atmospheric Administration, NASA’s Goddard Institute for Space Studies, and the United Kingdom’s Met Office Hadley Centre and the University of East Anglia’s Climatic Research Unit in the United Kingdom. 

It also uses reanalysis datasets from the European Centre for Medium Range Weather Forecasts and its Copernicus Climate Change Service, and the Japan Meteorological Agency.  This method combines millions of meteorological and marine observations, including from satellites, with models to produce a complete reanalysis of the atmosphere. The combination of observations with models makes it possible to estimate temperatures at any time and in any place across the globe, even in data-sparse areas such as the polar regions.

https://public.wmo.int/en/media/press-release/wmo-confirms-2019-second-hottest-year-record

For ease of reference I re-post my Reply #724, which is relevant to this topic:

I note that Hawkins et al (2017) defines the pre-industrial baseline to be from 1720-1800 for determining GMSTA, and indicates that as both the CMIP5 and the AR5 projections were baselined to the 1896-2005 baseline (see first image that gives various AR5 baselines), one needs to add between 0.55 and 0.80C (which has a mean value of 0.675C) to the published CMIP5 and AR5 projections values to get correct values for GMSTA.

As the second image from the second linked article by Clive Best indicates that the mean value of the CMIP5 runs for RCP 8.5 in 2040 is about 1.7C, this implies that referenced to pre-industrial for RCP 8.5 (which is less aggressive than SSP5-Baseline) GMSTA in 2040 would be about 2.375C (which is above Mid-Pliocene conditions):

Ed Hawkins et al. (2017), "Estimating Changes in Global Temperature since the Preindustrial Period", BAMS, https://doi.org/10.1175/BAMS-D-16-0007.1

https://journals.ametsoc.org/doi/full/10.1175/BAMS-D-16-0007.1

Abstract: "The United Nations Framework Convention on Climate Change (UNFCCC) process agreed in Paris to limit global surface temperature rise to “well below 2°C above pre-industrial levels.” But what period is preindustrial? Somewhat remarkably, this is not defined within the UNFCCC’s many agreements and protocols. Nor is it defined in the IPCC’s Fifth Assessment Report (AR5) in the evaluation of when particular temperature levels might be reached because no robust definition of the period exists. Here we discuss the important factors to consider when defining a preindustrial period, based on estimates of historical radiative forcings and the availability of climate observations. There is no perfect period, but we suggest that 1720–1800 is the most suitable choice when discussing global temperature limits. We then estimate the change in global average temperature since preindustrial using a range of approaches based on observations, radiative forcings, global climate model simulations, and proxy evidence. Our assessment is that this preindustrial period was likely 0.55°–0.80°C cooler than 1986–2005 and that 2015 was likely the first year in which global average temperature was more than 1°C above preindustrial levels. We provide some recommendations for how this assessment might be improved in the future and suggest that reframing temperature limits with a modern baseline would be inherently less uncertain and more policy relevant."
&

Extract: "We have examined estimates of historical radiative forcings to determine which period might be most suitable to be termed preindustrial and used several approaches to estimate a change in global temperature since this preindustrial reference period. The main conclusions are as follows:

1.   The 1720–1800 period is most suitable to be defined as preindustrial in physical terms, although we have incomplete information about the radiative forcings and very few direct observations during this time. However, this definition offers a target period for future analysis and data collection to inform this issue.
2.   The 1850–1900 period is a reasonable pragmatic surrogate for preindustrial global mean temperature. The available evidence suggests it was slightly warmer than 1720–1800 by around 0.05°C, but this is not statistically significant.
3.   We assess a likely range of 0.55°–0.80°C for the change in global average temperature from preindustrial to 1986–2005.
4.   We also consider a likely lower bound on warming from preindustrial to 1986–2005 of 0.60°C, implying that the AR5 estimate of warming was probably too small and that 2015 was the first year to be more than 1°C above preindustrial levels."

&

Title: "A comparison of CMIP5 Climate Models with HadCRUT4.6" January 21, 2019 by Clive Best

http://clivebest.com/blog/?p=8788

Caption for the second image: Model comparisons to HadCRUT4.6. Spaghetti are individual annual model results for each RCP. Solid curves are model ensemble annual averages.