Ice Apocalypse - Multiple Meters Sea Level Rise

[AbruptSLR]

The linked reference provides a new map of geothermal heat flux, GHF, for Antarctic and it presents new data indicating high GHF in the Thwaites Glacier region.  This increases the risk of an MICI-type of failure in the BSB initiating in the Thwaites Glacier gateway.

Weisen Shen et al. (20 June 2020), "A Geothermal heat flux map of Antarctica empirically constrained by seismic structure", Geophysical Research Letters, https://doi.org/10.1029/2020GL086955

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL086955?af=R

Abstract
The geothermal heat flux (GHF) is an important boundary condition for modeling the movement of the Antarctic ice‐sheet, but is difficult to measure systematically at a continental scale. Earlier GHF maps suffer from low resolution and possibly biased assumptions in tectonism and crustal heat generation, resulting in significant uncertainty. We present a new GHF map for Antarctica constructed by empirically relating the upper mantle structure to known GHF in the continental US. The new map, compared with previously seismologically determined one, has improved resolution and lower uncertainties. New features in this map include high GHF in the southern Transantarctic Mountains where warmer uppermost mantle is introduced by lithospheric removal and in the Thwaites Glacier region. Additionally, a modest GHF in the central West Antarctic Rift system near the Siple Coast and an absence of large‐scale regions with GHF greater than 90 mW/m2 are found.

Plain Language Summary
The flow of the heat from Earth's interior into the ice‐sheet of Antarctica, or geothermal heat flux, has been poorly constrained but is important for understanding the movement of the ice‐sheet. In this study, we present a new map of the geothermal heat flux estimated from the latest studies of the seismic structure of Antarctica. This is accomplished by directly relating seismic wave speeds with heat flux for the continental United States, a place where many local heat flux measurements have been collected. The new map contains features that have not been reported before. For example, we find that more heat is coming out from the base of the southern Transantarctic Mountains, which is perhaps related to the missing thick and cold lithosphere beneath that region. We also report that part of West Antarctica may have lower geothermal heat flux than previously reported. The new map will help model the movement of the Antarctic ice‐sheet and predict its future.

[gerontocrat]

Can you really model something that you don't understand? Yes, you can. But it will definitely be GIGO.

Yes you can and it will not necessarily be GIGO.

Before the nature of gravity was described by Newton models were constructed to determine the trajectory of cannonballs.

Scientists in Ancient Egypt modelled the annual floods of the Nile and predicted whether it would be a good or bad year. They knew nowt of the seasonal rains in the headwaters of the Blue Nile.

Priests in Neolithic times designed monuments such as Stonehenge relying on predictions of the movement of the sun in the heavens.

[Hefaistos]

Geron,
your examples are valid, but not relevant.
Gravity always pulls downward.
The Nile always flows only in one direction.
Planets and stars always move in the same way.
By plain observation you can spot reliable patterns.

But what about cloud feedbacks? Some of the clouds have positive feedback, some have negative.
Cloud feedback tend to be negative in the tropics, positive elsewhere.
Aerosols play an important role, but how, and where, and for which types of clouds?
Convective processes and cloud feedbacks happen on smaller scales (grid sizes) than the models can handle. And even if they had this data, there isn't enough computational capacity available.
You don't even have observations on the relevant scale.
Without observations you have no valid data.
Without theories that cover all relevant cloud and aerosol processes, you have no valid model.
Without computational capacity your deficient data and model built on incomplete theories will indeed produce only GIGO.

There is a research initiative to resolve these issues, The World Climate Research Programme (WCRP) Grand Challenge on Clouds, Circulation, and Climate Sensitivity.
They write in a white paper: "Limited understanding of clouds is the major source of uncertainty in Climate Sensitivity, but also contributes substantially to persistent biases in modelled circulation systems..."
"The spread of climate sensitivity estimates is unacceptably large, mostly as a result of uncertain changes in clouds. This uncertainty can be thought of as the ‘cloud problem’. The cloud problem contributes to an inability to usefully constrain the upper bound, and the relative reliability, of differing estimates of climate sensitivity."

https://wcrp-climate.org/component/content/article/61-gc-clouds-circulation?catid=30&Itemid=267

[AbruptSLR]

The linked reference shows that carbon budgets only work to achieve the Paris target if one ignores all of the uncertainties associated with:

a) The practicability of negative emission capacities,
b) Non-CO2 radiative forcers like methane, and
c) High-end projections for climate sensitivity.

Thus relying on carbon budgets sounds like risky business to me.

Sanderson, B.: The role of prior assumptions in carbon budget calculations, Earth Syst. Dynam., 11, 563–577, https://doi.org/10.5194/esd-11-563-2020, 2020.

https://esd.copernicus.org/articles/11/563/2020/

Abstract
Cumulative emissions budgets and net-zero emission target dates are often used to frame climate negotiations (Frame et al., 2014; Millar et al., 2016; Van Vuuren et al., 2016; Rogelj et al., 2015b; Matthews et al., 2012). However, their utility for near-term policy decisions is confounded by uncertainties in future negative emissions capacity (Fuss et al., 2014; Smith et al., 2016; Larkin et al., 2018; Anderson and Peters, 2016), in the role of non-CO2 forcers (MacDougall et al., 2015) and in the long-term Earth system response to forcing (Rugenstein et al., 2019; Knutti et al., 2017; Armour, 2017). Such uncertainties may impact the utility of an absolute carbon budget if peak temperatures occur significantly after net-zero emissions are achieved, the likelihood of which is shown here to be conditional on prior assumptions about the long-term dynamics of the Earth system. In the context of these uncertainties, we show that the necessity and scope for negative emissions deployment later in the century can be conditioned on near-term emissions, providing support for a scenario framework which focuses on emissions reductions rather than absolute budgets (Rogelj et al., 2019b).

[Hefaistos]

Something is going wrong at Moyhu as for instance, the first attached image from the linked Moyhu website shows that no month in 2020 has been the warmest on record.

http://www.moyhu.org.s3.amazonaws.com/data/freq/ncep.html

Yet, NOAA, NASA and Copernicus (see the second attached image where Hausfather uses Copernicus data thru the end of May 2020 to project that 2020 will be the warmest year on record) all indicate that all months thru May 2020 were the warmest on record.

Thus until Moyhu's data falls in line with the observed NOAA, NASA and Copernicus observed data, I am inclined to ignore all data from Moyhu.

There seems to be some issues with the NCEP V1 data, or the feed.
It has been discussed on the Moyhu blog, also by Karsten Haustein (sign. KarSteN):

https://moyhu.blogspot.com/2020/05/ncepncar-reanalysis-surface-temperature.html
https://moyhu.blogspot.com/2020/06/ncepncar-reanalysis-may-2020-surface.html

Karsten Haustein discusses issues with the NCEP reanalysis in depth here:
http://www.karstenhaustein.com/reanalysis/info.php

[AbruptSLR]

...
There seems to be some issues with the NCEP V1 data, or the feed.
It has been discussed on the Moyhu blog, also by Karsten Haustein (sign. KarSteN):

https://moyhu.blogspot.com/2020/05/ncepncar-reanalysis-surface-temperature.html
https://moyhu.blogspot.com/2020/06/ncepncar-reanalysis-may-2020-surface.html

Karsten Haustein discusses issues with the NCEP reanalysis in depth here:
http://www.karstenhaustein.com/reanalysis/info.php

My opinion is that if Moyhu and Haustein know the they have a problem with the NCEP V1 data being bad; then they should have the integrity of either not posting the data that they know to be wrong or at least to post a warning on their websites, clearly visible and right next to the bad data.

[AbruptSLR]

The linked article indicates that climate denial is not a victimless crime and that more lawsuits are being filed against perpetrators:

Title: "DC Sues Fossil Fuel Giants for Decades of Spending Millions to 'Mislead Consumers and Discredit Climate Science in Pursuit of Profits'"

https://www.commondreams.org/news/2020/06/25/dc-sues-fossil-fuel-giants-decades-spending-millions-mislead-consumers-and-discredit

Extract: "Climate denial is not a victimless crime. Now, one by one states and local governments are stepping up to hold the perpetrators accountable."

[AbruptSLR]

Per the linked June 2020 document, the Trump Administration wants to open up about 82% of the National Petroleum Reserve in Alaska to oil/gas leases and drilling:

Title: "National Petroleum Reserve in Alaska - Integrated Activity Plan and Environmental Impact Statement"

https://www.blm.gov/sites/blm.gov/files/NPR-A_Final-IAP-EIS_Volume%201_ExecSummary_Ch1-3_References_Glossary.pdf

Extract: "Alternative E (Preferred Alternative)
Alternative E would make the most land open to leasing (approximately 18.7 million acres, or 82 percent of the NPR-A’s subsurface estate)."

[AbruptSLR]

The linked article advises that immediate steps need to be taken to prevent tropical forests from crossing a temperature tipping point:

Title: "Temperature Tipping Point for Tropical Forests Identified – Scientists Recommend Immediate Steps"

https://scitechdaily.com/temperature-tipping-point-for-tropical-forests-identified-scientists-recommend-immediate-steps/

Extract: "All living things have tipping points: points of no return, beyond which they cannot thrive. A new report in Science shows that maximum daily temperatures above 32.2 degrees Celsius (about 90 degrees Fahrenheit) cause tropical forests to lose stored carbon more quickly. To prevent this escape of carbon into the atmosphere, the authors, including three scientists affiliated with the Smithsonian Tropical Research Institute (STRI) in Panama, recommend immediate steps to conserve tropical forests and stabilize the climate."

[AbruptSLR]

In the attached tweet, Gavin Schmidt reminds people to stop saying that Arctic Amplification is twice   the GMSTA, because it is currently over three times GMSTA.

[AbruptSLR]

The linked reference reminds us that aerosol-cloud interactions together cloud feedback are the primary reasons that the high-end CMIP6 models have higher ECS values than those projected by CMIP5.  However, the reference fails to point out that E3SMv1's projection of a TCR value of 2.93C is primarily due to freshwater hosing mechanisms that most of the other high-end CMIP6 models either downplay or ignore.  Thus, if E3SMv1 is correct about TCR then the world could experience much high GMSTA values in coming decades than currently acknowledged by consensus climate science:

Gerald A. Meehl, Catherine A. Senior, Veronika Eyring, Gregory Flato, Jean-Francois Lamarque, Ronald J. Stouffer, Karl E. Taylor and Manuel Schlund, (24 June 2020), “Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models”, Science Advances, DOI: 10.1126/sciadv.aba1981

https://advances.sciencemag.org/content/6/26/eaba1981

Abstract
For the current generation of earth system models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), the range of equilibrium climate sensitivity (ECS, a hypothetical value of global warming at equilibrium for a doubling of CO2) is 1.8°C to 5.6°C, the largest of any generation of models dating to the 1990s. Meanwhile, the range of transient climate response (TCR, the surface temperature warming around the time of CO2 doubling in a 1% per year CO2 increase simulation) for the CMIP6 models of 1.7°C (1.3°C to 3.0°C) is only slightly larger than for the CMIP3 and CMIP5 models. Here we review and synthesize the latest developments in ECS and TCR values in CMIP, compile possible reasons for the current values as supplied by the modeling groups, and highlight future directions. Cloud feedbacks and cloud-aerosol interactions are the most likely contributors to the high values and increased range of ECS in CMIP6.

[AbruptSLR]

The linked reference confirms that freshwater hosing in the North Atlantic and likely in the Southern Ocean contribute to a slowing down of the AMOC; which in turn reduces the ocean's ability to sequester anthropogenically generated heat.  This indicates that future climate change models (like those for CMIP7) need to do a much better job of modeling freshwater hosing mechanisms:

Shineng Hu, Shang-Ping Xie and Wei Liu (2020), "Global pattern formation of net ocean surface heat flux response to greenhouse warming", J. Climate, https://doi.org/10.1175/JCLI-D-19-0642.1

https://journals.ametsoc.org/jcli/article/doi/10.1175/JCLI-D-19-0642.1/348583/Global-pattern-formation-of-net-ocean-surface-heat?searchresult=1

Abstract
This study examines global patterns of net ocean surface heat flux changes (Δ𝑄𝑛𝑒𝑡) under greenhouse warming in an ocean-atmosphere coupled model based on a heat budget decomposition. The regional structure of Δ𝑄𝑛𝑒𝑡 is primarily shaped by ocean heat divergence changes (ΔOHD): excessive heat is absorbed by higher-latitude oceans (mainly over the North Atlantic and the Southern Ocean), transported equatorward, and stored in lower-latitude oceans with the rest being released to the tropical atmosphere. The overall global pattern of ΔOHD is primarily due to the circulation change and partially compensated by the passive advection effect, except for the Southern Ocean that requires further investigations for a more definitive attribution. The mechanisms of North Atlantic surface heat uptake are further explored. In another set of global warming simulations, a perturbation of freshwater removal is imposed over the subpolar North Atlantic to largely offset the CO2-induced changes in the local ocean vertical stratification, barotropic gyre, and the Atlantic meridional overturning circulation (AMOC). Results from the freshwater perturbation experiments suggest that a significant portion of the positive Δ𝑄𝑛𝑒𝑡 over the North Atlantic under greenhouse warming is caused by the Atlantic circulation changes, perhaps mainly by the slowdown of AMOC, while the passive advection effect can contribute to the regional variations of Δ𝑄𝑛𝑒𝑡. Our results imply that ocean circulation changes are critical for shaping global warming pattern and thus hydrological cycle changes.

[AbruptSLR]

The linked article indicates that the Southern Ocean may suck less CO2 from the atmosphere in the future due to a combination of the Antarctic ozone hole and increasing atmospheric GHG concentrations:

Title: "In Antarctica, the Sinister Stirrings of Climate Change"

https://thewire.in/environment/climate-change-antarctica-southern-ocean

Extract: "The world’s oceans take up more than a quarter of the carbon humans are emitting into the atmosphere, partially mitigating the greenhouse effect of that carbon. And the Southern Ocean accounts for nearly 40% of this marine carbon absorption, even though it makes up only one-fifth of Earth’s ocean surface area. There could be enormous consequences for our already warming planet from even a small reduction in the Southern Ocean’s ability to suck up carbon from the atmosphere.

Scientists say this reduction may already be happening, and they suspect that the westerlies in the Southern Hemisphere, which are stronger than their northern counterparts because they blow mostly over open water, are to blame. Records of actual wind speeds, as well as estimates of wind speeds from measurements of atmospheric pressure, provide clear signs that the westerlies in both hemispheres are shifting toward the poles and intensifying. Climate models show that these changes are partly due to global warming, and research is afoot to determine if they are hindering the Southern Ocean’s capacity to pull carbon out of the atmosphere."

[AbruptSLR]

This is a reminder that the linked reference concludes that if GHG concentration approach Eocene levels, ECS will accelerate rapidly as indicated by the following extract:

"Our simulations exhibit increasing equilibrium climate sensitivity with warming and suggest an Eocene sensitivity of more than 6.6°C, much greater than the present-day value (4.2°C)."

Jiang Zhu, Christopher J. Poulsen, Jessica E. Tierney. Simulation of Eocene extreme warmth and high climate sensitivity through cloud feedbacks. Science Advances, 2019; 5 (9): eaax1874 DOI: 10.1126/sciadv.aax1874

https://advances.sciencemag.org/content/5/9/eaax1874

Abstract
The Early Eocene, a period of elevated atmospheric CO2 (>1000 ppmv), is considered an analog for future climate. Previous modeling attempts have been unable to reproduce major features of Eocene climate indicated by proxy data without substantial modification to the model physics. Here, we present simulations using a state-of-the-art climate model forced by proxy-estimated CO2 levels that capture the extreme surface warmth and reduced latitudinal temperature gradient of the Early Eocene and the warming of the Paleocene-Eocene Thermal Maximum. Our simulations exhibit increasing equilibrium climate sensitivity with warming and suggest an Eocene sensitivity of more than 6.6°C, much greater than the present-day value (4.2°C). This higher climate sensitivity is mainly attributable to the shortwave cloud feedback, which is linked primarily to cloud microphysical processes. Our findings highlight the role of small-scale cloud processes in determining large-scale climate changes and suggest a potential increase in climate sensitivity with future warming.

[AbruptSLR]

The linked reference describes an early application of a highly theoretical statistical method to potentially reduce climate uncertainty in families of climate models with multiple forcing scenarios like CMIP6.  However, much work remains to clarify climate implications under conditions of strong forcing such as would occur under a potential future cascade of nonlinear tipping points (including a potential MICI-type of collapse of the WAIS this century):

Valerio Lembo et al, Beyond Forcing Scenarios: Predicting Climate Change through Response Operators in a Coupled General Circulation Model, Scientific Reports (2020). DOI: 10.1038/s41598-020-65297-2

https://www.nature.com/articles/s41598-020-65297-2

Abstract
Global Climate Models are key tools for predicting the future response of the climate system to a variety of natural and anthropogenic forcings. Here we show how to use statistical mechanics to construct operators able to flexibly predict climate change. We perform our study using a fully coupled model - MPI-ESM v.1.2 - and for the first time we prove the effectiveness of response theory in predicting future climate response to CO2 increase on a vast range of temporal scales, from inter-annual to centennial, and for very diverse climatic variables. We investigate within a unified perspective the transient climate response and the equilibrium climate sensitivity, and assess the role of fast and slow processes. The prediction of the ocean heat uptake highlights the very slow relaxation to a newly established steady state. The change in the Atlantic Meridional Overturning Circulation (AMOC) and of the Antarctic Circumpolar Current (ACC) is accurately predicted. The AMOC strength is initially reduced and then undergoes a slow and partial recovery. The ACC strength initially increases due to changes in the wind stress, then undergoes a slowdown, followed by a recovery leading to a overshoot with respect to the initial value. Finally, we are able to predict accurately the temperature change in the North Atlantic.

Extract: "Article
Open Access
Published: 26 May 2020
Beyond Forcing Scenarios: Predicting Climate Change through Response Operators in a Coupled General Circulation Model
Valerio Lembo, Valerio Lucarini & Francesco Ragone
Scientific Reports volume 10, Article number: 8668 (2020) Cite this article

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Abstract
Global Climate Models are key tools for predicting the future response of the climate system to a variety of natural and anthropogenic forcings. Here we show how to use statistical mechanics to construct operators able to flexibly predict climate change. We perform our study using a fully coupled model - MPI-ESM v.1.2 - and for the first time we prove the effectiveness of response theory in predicting future climate response to CO2 increase on a vast range of temporal scales, from inter-annual to centennial, and for very diverse climatic variables. We investigate within a unified perspective the transient climate response and the equilibrium climate sensitivity, and assess the role of fast and slow processes. The prediction of the ocean heat uptake highlights the very slow relaxation to a newly established steady state. The change in the Atlantic Meridional Overturning Circulation (AMOC) and of the Antarctic Circumpolar Current (ACC) is accurately predicted. The AMOC strength is initially reduced and then undergoes a slow and partial recovery. The ACC strength initially increases due to changes in the wind stress, then undergoes a slowdown, followed by a recovery leading to a overshoot with respect to the initial value. Finally, we are able to predict accurately the temperature change in the North Atlantic.


Extract: "Clearly, in some applications one may want to test accurately to what extent nonlinear effects are relevant, as the theory is also applicable to higher orders. Some insights into the non linear component of the response could also be obtained by appropriately combining forcings differing in sign and magnitude. Nonetheless, being based on a perturbative approach, response theory (linear and nonlinear) has, by definition, only a limited range of applicability (e.g. one cannot use it to treat arbitrarily strong forcings). Still, the non-applicability of response theory has itself fundamental implications for the knowledge of the dynamics of the system one is studying. At a tipping point (or critical transition) the negative feedbacks of a system are overcome by the positive ones and any linear Green function diverges as a result of the increase in the time correlations of the system due to a critical Ruelle-Pollicott pole, signalling the crisis of the chaotic attractor68. Instead, near a critical transition, response operators do not converge unless one considers very weak forcings. The experimental design provided here is thus also a clear and mathematically sound strategy for the study of conditions leading to tipping points and their role for the climate response in state-of-the-art climate models."

[sidd]

That Lembo paper is interesting, i commented on it in another thread; it seems useful if the result is robust for other models.  But now that i think about it, i seem to recall other papers using similar technique, (perhaps some from Hansen?), but they dont explicitly invoke the whole Green's function formalism.

Also token quibble: i wish they had called it a Green's function and not a Green function.

sidd

[kassy]

Unknown currents in Southern Ocean have been observed with help of seals

Using state-of-the-art ocean robots and scientific sensors attached to seals, researchers have for the first time observed small and energetic ocean currents in the Southern Ocean. The currents are critical at controlling the amount of heat and carbon moving between the ocean and the atmosphere -- information vital for understanding our global climate and how it may change in the future

...

These papers present for the first time upper ocean currents of approximately 0.1-10 km in size. These currents, which are invisible to satellite and ship-based data, are seen to interact with strong Southern Ocean storms and with physical processes occurring under sea ice.

"Using the data collected by the seals, we're able to look at the impact these upper ocean currents have underneath the sea ice for the first time. It's a really valuable insight into what was previously completely unknown in the Southern Ocean," says Dr Louise Biddle, Department of Marine Sciences, University of Gothenburg.

The winter had assumed to be a "quiet" time due to the dampening effect of sea ice on the ocean's surface. However, the two studies show that these upper ocean currents have a significant effect on the ocean during winter.

Unprecedented high-resolution measurements

Some of the findings by Sebastiaan Swart and his team gives further insight how these observed ocean currents work. Their study highlights that during times when there are no storms and winds are weak, upper ocean currents start to become much more energetic. This energy enhances the rate of ocean mixing and transport of properties, like heat, carbon and nutrients, around the ocean and into the deep ocean.

...

https://www.sciencedaily.com/releases/2020/06/200626114754.htm

[AbruptSLR]

I find it disturbing that the linked reference indicates that many consensus climate scientists primarily attribute the North Atlantic warming hole (or Cold Blob) to a slow-down of that AMOC; while in fact both the Cold Blob and the slow-down of the AMOC is primarily related to meltwater hosing from Greenland.  This indicates to me that many consensus climate science models should be upgraded to include freshwater hosing from meltwater:

Keil, P. et al. (2020) Multiple drivers of the North Atlantic warming hole, Nature Climate Change, doi:10.1038/s41558-020-0819-8

https://www.nature.com/articles/s41558-020-0819-8

Abstract: "Despite global warming, a region in the North Atlantic ocean has been observed to cool, a phenomenon known as the warming hole. Its emergence has been linked to a slowdown of the Atlantic meridional overturning circulation, which leads to a reduced ocean heat transport into the warming hole region. Here we show that, in addition to the reduced low-latitude heat import, increased ocean heat transport out of the region into higher latitudes and a shortwave cloud feedback dominate the formation and temporal evolution of the warming hole under greenhouse gas forcing. In climate model simulations of the historical period, the low-latitude Atlantic meridional overturning circulation decline does not emerge from natural variability, whereas the accelerating heat transport to higher latitudes is clearly attributable to anthropogenic forcing. Both the overturning and the gyre circulation contribute to the increased high-latitude ocean heat transport, and therefore are critical to understand the past and future evolutions of the warming hole."

See also:

Title: "Scientists shed light on human causes of North Atlantic’s ‘cold blob’"

https://www.carbonbrief.org/scientists-shed-light-on-human-causes-of-north-atlantics-cold-blob

Extract: "Previous research has linked the warming hole to a weakening of an ocean current in the North Atlantic, which brings heat up from the tropics.

Now a new study – published in Nature Climate Change – suggests that a number of other factors are also involved. These include “changes in the high latitude ocean circulation” and the cool sea surface creating “more low-level clouds”, the lead author tells Carbon Brief."

[AbruptSLR]

That Lembo paper is interesting, i commented on it in another thread; it seems useful if the result is robust for other models.  But now that i think about it, i seem to recall other papers using similar technique, (perhaps some from Hansen?), but they dont explicitly invoke the whole Green's function formalism.

Also token quibble: i wish they had called it a Green's function and not a Green function.

sidd

Hansen frequently used Green's function in past papers, but he has also used something that he calls a climate response function (see attached) that has a similar shape as the Green's functions that he sometimes used in the past.

Edit: The linked 2018 paper by Hansen et al. presents one example of where he has used a Green's function.

Title: "Climate Change in a Nutshell: The Gathering Storm"

http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf

[AbruptSLR]

The linked reference (& associated article) indicates that for the past 3-decades the South Pole has warmed at a rate three times that of the GMSTA in the same period:

Clem, K.R., Fogt, R.L., Turner, J. et al. Record warming at the South Pole during the past three decades. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0815-z

https://www.nature.com/articles/s41558-020-0815-z

& for free access:

https://www.nature.com/articles/s41558-020-0815-z.epdf?sharing_token=w9XdPzT3YfCdh6rdcwGi_9RgN0jAjWel9jnR3ZoTv0NZj9FMZf-OGYzRW4VVW5B-YJpPLoSDHzkgSCgtnA_D7es2dbumPxZKq9QTEsmNWyUuXgj6YeXiSohzwkcz1BXl33ZAQhxpEqPDVVRlsLAhhIzV4k3o1Cv_TFYGM5fBni0gE_2bYeXWMQ0Sa0nqdzfApIKsphbpre0NWb8AqpvzZ11jbXfIvzIxH0XnWuFdmTMByDOG5nc3BbCQ9JdCcaJhZNy_IqKlq_N_OMT-Bga5SQ%3D%3D&tracking_referrer=www.cbc.ca

Abstract: "Over the last three decades, the South Pole has experienced a record-high statistically significant warming of 0.61 ± 0.34 °C per decade, more than three times the global average. Here, we use an ensemble of climate model experiments to show this recent warming lies within the upper bounds of the simulated range of natural variability. The warming resulted from a strong cyclonic anomaly in the Weddell Sea caused by increasing sea surface temperatures in the western tropical Pacific. This circulation, coupled with a positive polarity of the Southern Annular Mode, advected warm and moist air from the South Atlantic into the Antarctic interior. These results underscore the intimate linkage of interior Antarctic climate to tropical variability. Further, this study shows that atmospheric internal variability can induce extreme regional climate change over the Antarctic interior, which has masked any anthropogenic warming signal there during the twenty-first century."

See also:

Title: "South Pole warmed 3 times the global rate over the past 30 years, new study suggests"

https://www.cbc.ca/news/technology/south-pole-warming-1.5631435

Extract: "A new study has found that the South Pole has warmed at least three times the global warming rate over the past 30 years."

[AbruptSLR]

Per the linked reference, beaver behavior is accelerating permafrost degradation:

Benjamin M. Jones, Ken D Tape, Jason Clark, Ingmar Nitze, Guido Grosse and Jeff Disbrow, (30 June 2020), “Increase in beaver dams controls surface water and thermokarst dynamics in an Arctic tundra region, Baldwin Peninsula, northwestern Alaska”, Environmental Research Letters.
DOI: 10.1088/1748-9326/ab80f1

https://iopscience.iop.org/article/10.1088/1748-9326/ab80f1

Abstract: "Beavers are starting to colonize low arctic tundra regions in Alaska and Canada, which has implications for surface water changes and ice-rich permafrost degradation. In this study, we assessed the spatial and temporal dynamics of beaver dam building in relation to surface water dynamics and thermokarst landforms using sub-meter resolution satellite imagery acquired between 2002 and 2019 for two areas in northwestern Alaska. In a 100 km2 study area near Kotzebue, the number of dams increased markedly from 2 to 98 between 2002 and 2019. In a 430 km2 study area encompassing the entire northern Baldwin Peninsula, the number of dams increased from 94 to 409 between 2010 and 2019, indicating a regional trend. Correlating data on beaver dam numbers with surface water area mapped for 12 individual years between 2002 and 2019 for the Kotzebue study area showed a significant positive correlation (R2 = 0.61; p < .003). Beaver-influenced waterbodies accounted for two-thirds of the 8.3 % increase in total surface water area in the Kotzebue study area during the 17-year period. Beavers specifically targeted thermokarst landforms in their dam building activities. Flooding of drained thermokarst lake basins accounted for 68 % of beaver-influenced surface water increases, damming of lake outlets accounted for 26 %, and damming of beaded streams accounted for 6 %. Surface water increases resulting from beaver dam building likely exacerbated permafrost degradation in the region, but dam failure also factored into the drainage of several thermokarst lakes in the northern Baldwin Peninsula study region, which could promote local permafrost aggradation in freshly exposed lake sediments. Our findings highlight that beaver-driven ecosystem engineering must be carefully considered when accounting for changes occurring in some permafrost regions, and in particular, regional surface water dynamics in low Arctic and Boreal landscapes."

[AbruptSLR]

The linked reference suggests that as the Earth warms natural ecosystems such as freshwaters will release more methane than expected from predictions based on temperature increases alone:

Yizhu Zhu, Kevin J. Purdy, Özge Eyice, Lidong Shen, Sarah F. Harpenslager, Gabriel Yvon-Durocher, Alex J. Dumbrell, Mark Trimmer. Disproportionate increase in freshwater methane emissions induced by experimental warming. Nature Climate Change, 2020; DOI: 10.1038/s41558-020-0824-y

https://www.nature.com/articles/s41558-020-0824-y

Abstract: "Net emissions of the potent GHG methane from ecosystems represent the balance between microbial methane production (methanogenesis) and oxidation (methanotrophy), each with different sensitivities to temperature. How this balance will be altered by long-term global warming, especially in freshwaters that are major methane sources, remains unknown. Here we show that the experimental warming of artificial ponds over 11 years drives a disproportionate increase in methanogenesis over methanotrophy that increases the warming potential of the gases they emit. The increased methane emissions far exceed temperature-based predictions, driven by shifts in the methanogen community under warming, while the methanotroph community was conserved. Our experimentally induced increase in methane emissions from artificial ponds is, in part, reflected globally as a disproportionate increase in the capacity of naturally warmer ecosystems to emit more methane. Our findings indicate that as Earth warms, natural ecosystems will emit disproportionately more methane in a positive feedback warming loop."

[AbruptSLR]

The linked reference confirms that the AMOC is projected to continue slowing with continued global warming:

Wei Liu  et al. (26 Jun 2020), "Climate impacts of a weakened Atlantic Meridional Overturning Circulation in a warming climate", Science Advances, Vol. 6, no. 26, eaaz4876, DOI: 10.1126/sciadv.aaz4876

https://advances.sciencemag.org/content/6/26/eaaz4876

Abstract
While the Atlantic Meridional Overturning Circulation (AMOC) is projected to slow down under anthropogenic warming, the exact role of the AMOC in future climate change has not been fully quantified. Here, we present a method to stabilize the AMOC intensity in anthropogenic warming experiments by removing fresh water from the subpolar North Atlantic. This method enables us to isolate the AMOC climatic impacts in experiments with a full-physics climate model. Our results show that a weakened AMOC can explain ocean cooling south of Greenland that resembles the North Atlantic warming hole and a reduced Arctic sea ice loss in all seasons with a delay of about 6 years in the emergence of an ice-free Arctic in boreal summer. In the troposphere, a weakened AMOC causes an anomalous cooling band stretching from the lower levels in high latitudes to the upper levels in the tropics and displaces the Northern Hemisphere midlatitude jets poleward.

[sidd]

Thanks for that Jones paper (open access, it is a wonderful thing.) 

I notice some of the same authors as the wonderfully named "Tundra be Dammed" paper i commented on in 2018. Time flies, and beavers rest not. Unlike us humans.

https://forum.arctic-sea-ice.net/index.php/topic,434.msg182505.html#msg182505

sidd

[Hefaistos]

I find it disturbing that the linked reference indicates that many consensus climate scientists primarily attribute the North Atlantic warming hole (or Cold Blob) to a slow-down of that AMOC; while in fact both the Cold Blob and the slow-down of the AMOC is primarily related to meltwater hosing from Greenland.  This indicates to me that many consensus climate science models should be upgraded to include freshwater hosing from meltwater:

Keil, P. et al. (2020) Multiple drivers of the North Atlantic warming hole, Nature Climate Change, doi:10.1038/s41558-020-0819-8

https://www.nature.com/articles/s41558-020-0819-8

Abstract: "Despite global warming, a region in the North Atlantic ocean has been observed to cool, a phenomenon known as the warming hole. Its emergence has been linked to a slowdown of the Atlantic meridional overturning circulation, which leads to a reduced ocean heat transport into the warming hole region. Here we show that, in addition to the reduced low-latitude heat import, increased ocean heat transport out of the region into higher latitudes and a shortwave cloud feedback dominate the formation and temporal evolution of the warming hole under greenhouse gas forcing. In climate model simulations of the historical period, the low-latitude Atlantic meridional overturning circulation decline does not emerge from natural variability, whereas the accelerating heat transport to higher latitudes is clearly attributable to anthropogenic forcing. Both the overturning and the gyre circulation contribute to the increased high-latitude ocean heat transport, and therefore are critical to understand the past and future evolutions of the warming hole."

See also:

Title: "Scientists shed light on human causes of North Atlantic’s ‘cold blob’"

https://www.carbonbrief.org/scientists-shed-light-on-human-causes-of-north-atlantics-cold-blob

Extract: "Previous research has linked the warming hole to a weakening of an ocean current in the North Atlantic, which brings heat up from the tropics.

Now a new study – published in Nature Climate Change – suggests that a number of other factors are also involved. These include “changes in the high latitude ocean circulation” and the cool sea surface creating “more low-level clouds”, the lead author tells Carbon Brief."

There is a lot of talk about a slowdown of the AMOC, and a lot of CMIP modelling takes it as a given thing in their future scenarios.

However, the evidence for a slowdown of AMOC is rather weak, as it relies on data that are disputed.
The causes of the eventual slowdown are also disputed.

No evidence of a slowdown are to be seen in recent data. Here as measured at different places.
(data taken from KNMI site)

[Hefaistos]

The theme of AMOC slowdown is also covered in this post:

https://forum.arctic-sea-ice.net/index.php/topic,2205.msg240256.html#msg240256

The chart gives no support at all for a slowdown.

"A time series of AMOC transport (MOCρ ) at the OVIDE section (eastern subpolar gyre: Portugal to Cape Farewell) for 1993–2017, constructed from altimetry and hydrography. The gray line is from altimetry combined with a time-mean of Argo velocities; the green curve is low-pass filtered using a 2-year running mean. The black curve is from altimetry and Argo. Red circles are estimates from OVIDE hydrography with associated errors given by the red lines. The mean of the gray curve is given by the black dashed line (Updated from Mercier et al., 2015)."

[AbruptSLR]

Per the linked open access reference:

"The AMOC has been observed to slow down over the past decade in the Rapid Climate Change (RAPID) array at 26.5°N in the North Atlantic, although this AMOC slowdown can be part of natural climate variability, considering the relatively short observational period."

Wei Liu et al. (26 Jun 2020), Climate impacts of a weakened Atlantic Meridional Overturning Circulation in a warming climate", Science Advances, Vol. 6, no. 26, eaaz4876< DOI: 10.1126/sciadv.aaz4876

https://advances.sciencemag.org/content/6/26/eaaz4876

Abstract
While the Atlantic Meridional Overturning Circulation (AMOC) is projected to slow down under anthropogenic warming, the exact role of the AMOC in future climate change has not been fully quantified. Here, we present a method to stabilize the AMOC intensity in anthropogenic warming experiments by removing fresh water from the subpolar North Atlantic. This method enables us to isolate the AMOC climatic impacts in experiments with a full-physics climate model. Our results show that a weakened AMOC can explain ocean cooling south of Greenland that resembles the North Atlantic warming hole and a reduced Arctic sea ice loss in all seasons with a delay of about 6 years in the emergence of an ice-free Arctic in boreal summer. In the troposphere, a weakened AMOC causes an anomalous cooling band stretching from the lower levels in high latitudes to the upper levels in the tropics and displaces the Northern Hemisphere midlatitude jets poleward.

[AbruptSLR]

The findings of the linked open access reference show that the millennial-scale global cooling began approximately 6,500 years ago when the long-term average global temperature topped out at around 0.7°C warmer than the mid-19th century. Since then, accelerating greenhouse gas emissions have contributed to global average temperatures that are now surpassing 1°C above the mid-19th century.  Thus, we are well into a range of climate response not seen since the Eemian:

Kaufman, D., McKay, N., Routson, C. et al. Holocene global mean surface temperature, a multi-method reconstruction approach. Sci Data 7, 201 (2020). https://doi.org/10.1038/s41597-020-0530-7

https://www.nature.com/articles/s41597-020-0530-7

Abstract: "An extensive new multi-proxy database of paleo-temperature time series (Temperature 12k) enables a more robust analysis of global mean surface temperature (GMST) and associated uncertainties than was previously available. We applied five different statistical methods to reconstruct the GMST of the past 12,000 years (Holocene). Each method used different approaches to averaging the globally distributed time series and to characterizing various sources of uncertainty, including proxy temperature, chronology and methodological choices. The results were aggregated to generate a multi-method ensemble of plausible GMST and latitudinal-zone temperature reconstructions with a realistic range of uncertainties. The warmest 200-year-long interval took place around 6500 years ago when GMST was 0.7 °C (0.3, 1. warmer than the 19th Century (median, 5th, 95th percentiles). Following the Holocene global thermal maximum, GMST cooled at an average rate −0.08 °C per 1000 years (−0.24, −0.05). The multi-method ensembles and the code used to generate them highlight the utility of the Temperature 12k database, and they are now available for future use by studies aimed at understanding Holocene evolution of the Earth system."

[AbruptSLR]

The linked article discusses the risks of megaslumps in Siberia due to Artic Amplification.

Title: "A Disastrous Summer in the Arctic"

https://www.newyorker.com/news/annals-of-a-warming-planet/a-disastrous-summer-in-the-arctic

Extract: "The permafrost found in the area surrounding Verkhoyansk is some of the deepest and oldest in the world, descending as much as five thousand feet. Closer to the surface, a type of ice-rich permafrost known as yedoma is particularly vulnerable to rapid thaws. The result is thermokarst, the strange and sometimes shocking topography that forms as the land slides, sags, and sinks. Mysterious sinkholes suddenly appear, drunken forests fall, and hillocks destroy farmland. One of Russia’s most extreme examples of thermokarst, known as the Batagay megaslump, is a two-hundred-and-eighty-foot-deep, half-mile-wide depression, situated just outside Verkhoyansk. It first began forming as a small gully in the nineteen-sixties, because of deforestation, but has grown significantly in recent years, exposing the remains of ancient creatures, including musk ox, a cave lion, a Pleistocene wolf, a woolly mammoth, and an almost perfectly preserved, forty-thousand-year-old foal. While exciting for scientists and tusk hunters, the megaslump is another sign of the challenges that people in the region—home to several indigenous cultures and languages, including Sakha, Evenki, Even, and others—face if they want to remain on their land. Some locals call it a gateway to the underworld, which seems appropriate, as the slump releases more and more methane. Researchers who have been to the slump say that they can hear the thuds, booms, and cracks of the thawing ice. This summer, the sound will be especially loud."

[Hefaistos]

Per the linked open access reference:

"The AMOC has been observed to slow down over the past decade in the Rapid Climate Change (RAPID) array at 26.5°N in the North Atlantic, although this AMOC slowdown can be part of natural climate variability, considering the relatively short observational period."

Wei Liu et al. (26 Jun 2020), Climate impacts of a weakened Atlantic Meridional Overturning Circulation in a warming climate", Science Advances, Vol. 6, no. 26, eaaz4876< DOI: 10.1126/sciadv.aaz4876

https://advances.sciencemag.org/content/6/26/eaaz4876

That whole paper is built on computer simulations with a GCM model and applying only the RCP8.5 scenario.
That alone disqualifies the results, as we aren't following the RCP8.5 due to the strong development of renewables.

Secondly, the paper enforces a very strong decline in the AMOC, a decline that has no support in the actual data that we have today, see chart.
Caption: "Fig. 1 AMOC strength and global mean surface air temperature in CCSM4 historical and RCP8.5 simulations and sensitivity experiment AMOC_fx. (A) From 1850 to 1980, the AMOC strength is adopted from CCSM4 historical simulation (purple, ensemble mean; light purple, ensemble spread). After 1980, the AMOC strength from CCSM4 historical and RCP8.5 simulations (AMOC_fx) is shown as green (purple) curve for ensemble mean and light green (light purple) shading for ensemble spread. The AMOC strength is defined as the maximum of the annual mean stream function below 500 m in the North Atlantic."

Furthermore, the paper uses AMOC data up until 2017 which are claimed to show a slight slowdown of the AMOC. Developments since then seem to contradict that.
As Smeed et al write:
"Our results show that the previously reported decline of the AMOC (Smeed et al., 2014) has been arrested, but the length of the observational record of the AMOC is still short relative to the time scales of importantdecadal variations that exist in the Atlantic. Understanding is therefore constantly evolving. What we identify as a changed state of the AMOC in this study may well prove to be part of a decadal oscillation superposed on a multidecadal cycle."


https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL076350

[AbruptSLR]

The linked article (& associated linked reference) discuss new findings about the behavior of the Ross Ice Shelf, RIS, and the extract notes that meltwater from such Antarctic ice shelves are, and in the future will continue, impacting the MOC by slowing it down:

Title: "What an ocean hidden under Antarctic ice reveals about our planet’s future climate"

https://theconversation.com/what-an-ocean-hidden-under-antarctic-ice-reveals-about-our-planets-future-climate-139110

Extract: " There are indeed hidden ocean cavities around Antarctica, and our latest research explores how the ocean circulates underneath the continent’s ice shelves - large floating extensions of the ice on land that rise and fall with the tides.
…
What is less well understood, but also potentially a massive agent for change, is the impact of meltwater on the global thermohaline circulation, an oceanic transport loop that sees the ocean cycle from the abyss off the coast of Antarctica to tropical surface waters every 1,000 years or so.

Antarctic ice shelves are like a pit stop in this loop and so what happens in Antarctica resonates globally. Faster melting ice shelves will change the ocean stratification, with repercussions for global ocean circulation - and one result of this appears to be greater climate variability.

See also:

Craig Stevens et al. (June 29, 2020), "Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting", PNAS, https://doi.org/10.1073/pnas.1910760117

https://www.pnas.org/content/early/2020/06/23/1910760117

Significance
This study describes measurements of the ocean beneath the center of the Ross Ice Shelf, the Earth’s largest ice shelf. Ice shelves experience melting from below by the ocean and so are vulnerable to a warming climate system. We present the second dataset ever collected from this region, the first having been gathered 40 y prior. Our data provide a basis for better understanding the complex processes that drive melting. They illustrate the degree of variability in the mid-water column, a region largely ignored in modeling. We also observed ephemeral refreezing on the ice shelf underside, with implications for both melt rate and upper ocean dynamics. This insight emphasizes the importance of in situ observations in undersampled environments.

Abstract
The stability of large Antarctic ice shelves has important implications for global sea level, sea ice area, and ocean circulation. A significant proportion of ice mass loss from these ice shelves is through ocean-driven melting which is controlled by largely unobserved oceanic thermodynamic and circulatory processes in the cavity beneath the ice shelf. Here we use direct measurements to provide evidence of the changing water column structure in the cavity beneath the Ross Ice Shelf, the planet’s largest ice shelf by area. The cavity water column data exhibit both basal and benthic boundary layers, along with evidence of tidally modulated and diffusively convecting internal mixing processes. A region of thermohaline interleaving in the upper–middle water column indicates elevated diffusion and the potential to modify the cavity circulation. The measurements were recorded using the Aotearoa New Zealand Ross Ice Shelf Program hot water drill borehole melted in the central region of the shelf in December 2017 (HWD2), only the second borehole through the central region of the ice shelf, following J9 in 1977. These data, and comparison with the 1977 data, provide valuable insight into ice shelf cavity circulation and aid understanding of the evolution of the presently stable Ross Ice Shelf.

[AbruptSLR]

The linked reference cites direct observation that the AMOC is continuing to slow and states:

"There has been a long-term reduction in ocean heat transport of 0.17 PW from 1.32 PW before 2009 to 1.15 PW after 2009 (2009–16) on an annual average basis associated with a 2.5-Sv (1 Sv ≡ 106 m3 s−1) drop in the Atlantic meridional overturning circulation (AMOC)."

Harry L. Bryden et al. (2020), "Reduction in Ocean Heat Transport at 26°N since 2008 Cools the Eastern Subpolar Gyre of the North Atlantic Ocean", J. Climate, 33 (5): 1677–1689, https://doi.org/10.1175/JCLI-D-19-0323.1

https://journals.ametsoc.org/jcli/article/33/5/1677/347129/Reduction-in-Ocean-Heat-Transport-at-26-N-since

Abstract: "Northward ocean heat transport at 26°N in the Atlantic Ocean has been measured since 2004. The ocean heat transport is large—approximately 1.25 PW, and on interannual time scales it exhibits surprisingly large temporal variability. There has been a long-term reduction in ocean heat transport of 0.17 PW from 1.32 PW before 2009 to 1.15 PW after 2009 (2009–16) on an annual average basis associated with a 2.5-Sv (1 Sv ≡ 106 m3 s−1) drop in the Atlantic meridional overturning circulation (AMOC). The reduction in the AMOC has cooled and freshened the upper ocean north of 26°N over an area following the offshore edge of the Gulf Stream/North Atlantic Current from the Bahamas to Iceland. Cooling peaks south of Iceland where surface temperatures are as much as 2°C cooler in 2016 than they were in 2008. Heat uptake by the atmosphere appears to have been affected particularly along the path of the North Atlantic Current. For the reduction in ocean heat transport, changes in ocean heat content account for about one-quarter of the long-term reduction in ocean heat transport while reduced heat uptake by the atmosphere appears to account for the remainder of the change in ocean heat transport."

[AbruptSLR]

The linked reference provides current information about meridional energy transport (MET) within the MOC.  It discusses variability with regard to: latitude (see the attached image) and climate variability.  In general it indicates that MET is increasing with time as global warming increases and as the MOC slows down (which resulting in more heat accumulation):

Liu, Y., Attema, J., Moat, B., and Hazeleger, W.: Synthesis and evaluation of historical meridional heat transport from midlatitudes towards the Arctic, Earth Syst. Dynam., 11, 77–96, https://doi.org/10.5194/esd-11-77-2020, 2020.

https://esd.copernicus.org/articles/11/77/2020/

Abstract
Meridional energy transport (MET), both in the atmosphere (AMET) and ocean (OMET), has significant impact on the climate in the Arctic. In this study, we quantify AMET and OMET at subpolar latitudes from six reanalysis data sets. We investigate the differences between the data sets and we check the coherence between MET and the Arctic climate variability at interannual timescales. The results indicate that, although the mean transport in all data sets agrees well, the spatial distributions and temporal variations of AMET and OMET differ substantially among the reanalysis data sets. For the ocean, only after 2007, the low-frequency signals in all reanalysis products agree well. A further comparison with observed heat transport at 26.5∘ N and the subpolar Atlantic, and a high-resolution ocean model hindcast confirms that the OMET estimated from the reanalysis data sets are consistent with the observations. For the atmosphere, the differences between ERA-Interim and the Japanese 55-year Reanalysis (JRA-55) are small, while the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) differs from them. An extended analysis of linkages between Arctic climate variability and AMET shows that atmospheric reanalyses differ substantially from each other. Among the chosen atmospheric products, ERA-Interim and JRA-55 results are most consistent with those from coupled climate models. For the ocean, the Ocean Reanalysis System 4 (ORAS4) and Simple Ocean Data Assimilation version 3 (SODA3) agree well on the relation between OMET and sea ice concentration (SIC), while the GLobal Ocean reanalyses and Simulations version 3 (GLORYS2V3) deviates from those data sets. The regressions of multiple fields in the Arctic on both AMET and OMET suggest that the Arctic climate is sensitive to changes of meridional energy transport at subpolar latitudes in winter. Given the good agreement on the diagnostics among assessed reanalysis products, our study suggests that the reanalysis products are useful for the evaluation of energy transport. However, assessments of products with the AMET and OMET estimated from reanalysis data sets beyond interannual timescales should be conducted with great care and the robustness of results should be evaluated through intercomparison, especially when studying variability and interactions between the Arctic and midlatitudes.

[AbruptSLR]

The linked open access reference includes discussion of possible future conditions under which the East Siberian Arctic Shelf, ESAS, may contribute high fluxes of methane into the atmosphere:

Puglini, M., Brovkin, V., Regnier, P., and Arndt, S.: Assessing the potential for non-turbulent methane escape from the East Siberian Arctic Shelf, Biogeosciences, 17, 3247–3275, https://doi.org/10.5194/bg-17-3247-2020, 2020.

https://www.biogeosciences.net/17/3247/2020/

Abstract
The East Siberian Arctic Shelf (ESAS) hosts large yet poorly quantified reservoirs of subsea permafrost and associated gas hydrates. It has been suggested that the global-warming induced thawing and dissociation of these reservoirs is currently releasing methane (CH4) to the shallow coastal ocean and ultimately the atmosphere. However, a major unknown in assessing the contribution of this CH4 flux to the global CH4 cycle and its climate feedbacks is the fate of CH4 as it migrates towards the sediment–water interface. In marine sediments, (an)aerobic oxidation reactions generally act as a very efficient methane sink. However, a number of environmental conditions can reduce the efficiency of this biofilter. Here, we used a reaction-transport model to assess the efficiency of the benthic methane filter and, thus, the potential for benthic methane escape across a wide range of environmental conditions that could be encountered on the East Siberian Arctic Shelf. Results show that, under steady-state conditions, anaerobic oxidation of methane (AOM) acts as an efficient biofilter. However, high CH4 escape is simulated for rapidly accumulating and/or active sediments and can be further enhanced by the presence of organic matter with intermediate reactivity and/or intense local transport processes, such as bioirrigation. In addition, in active settings, the sudden onset of CH4 flux triggered by, for instance, permafrost thaw or hydrate destabilization can also drive a high non-turbulent methane escape of up to 19 µmol CH4 cm−2 yr−1 during a transient, multi-decadal period. This “window of opportunity” arises due to delayed response of the resident microbial community to suddenly changing CH4 fluxes. A first-order estimate of non-turbulent, benthic methane efflux from the Laptev Sea is derived as well. We find that, under present-day conditions, non-turbulent methane efflux from Laptev Sea sediments does not exceed 1 Gg CH4 yr−1. As a consequence, we conclude that previously published estimates of ocean–atmosphere CH4 fluxes from the ESAS cannot be supported by non-turbulent, benthic methane escape.
Extract: "High methane escape (up to 11–19 µmol CH4 cm−2 yr−1 corresponding to 2.6–4.5 TgCH4 yr−1 if upscaled to the ESAS) can occur during a transient period following the onset of methane flux from the deep sediments. Under these conditions, substantial methane escape from sediments requires the presence of active fluid flow that supports a significant and rapid upward migration of the SMTZ in response to the onset of CH4 flux from below. Such rapid and pronounced movements create a window of opportunity for non-turbulent methane escape by inhibiting the accumulation of AOM-performing biomass within the SMTZ – mainly through thermodynamic constraints – thereby perturbing the efficiency of the AOM biofilter. The magnitude of methane effluxes, as well as the duration of this window of opportunity, is largely controlled by the active flow velocity. In addition, results of transient scenario runs indicated that the characteristic response time of the AOM biofilter is of the order of few decades (20–30 years), thus exceeding seasonal–interannual variability. Consequently, seasonal variation of bottom methane and seawater sulfates exert a negligible effect on methane escape through the sediment–water interface."

[AbruptSLR]

...

Keil, P. et al. (2020) Multiple drivers of the North Atlantic warming hole, Nature Climate Change, doi:10.1038/s41558-020-0819-8

https://www.nature.com/articles/s41558-020-0819-8

Abstract: "Despite global warming, a region in the North Atlantic ocean has been observed to cool, a phenomenon known as the warming hole. Its emergence has been linked to a slowdown of the Atlantic meridional overturning circulation, which leads to a reduced ocean heat transport into the warming hole region. Here we show that, in addition to the reduced low-latitude heat import, increased ocean heat transport out of the region into higher latitudes and a shortwave cloud feedback dominate the formation and temporal evolution of the warming hole under greenhouse gas forcing. In climate model simulations of the historical period, the low-latitude Atlantic meridional overturning circulation decline does not emerge from natural variability, whereas the accelerating heat transport to higher latitudes is clearly attributable to anthropogenic forcing. Both the overturning and the gyre circulation contribute to the increased high-latitude ocean heat transport, and therefore are critical to understand the past and future evolutions of the warming hole."
...

Here is another reminder that the quoted research indicates that the AMOC is currently slowing (particularly since 2015); which is a major risk factor for high values of TCR in coming decades:

Title: "Why Earth has a stubborn spot that's cooling"

https://mashable.com/article/cold-blob-atlantic-ocean-climate-change/

Extract: "There's mounting evidence, which this study further supports, that a major ocean current called the "Atlantic Meridional Overturning Circulation (AMOC) — which acts somewhat like a conveyor belt as it transports warm tropical water up into the North Atlantic Ocean — is slowing down. Scientists suspect the slowdown is driven by "off-the-charts" melting of the Greenland ice sheet, which has resulted in freshwater pouring into the North Atlantic Ocean.
…
Oceanographers expect AMOC to slow down as freshwater, newly melted in a rapidly heating Arctic, pours into the North Atlantic. The persistent cold blob provides compelling evidence of this already happening. "The AMOC is projected to slow down as a response to increasing greenhouse gases in the atmosphere," said Daniel Whitt, an oceanographer at the National Center for Atmospheric Research who also had no role in the study.
…
What's more, Keil and his team found that a circulation of water traveling in a loop around the North Atlantic itself, called the "subpolar gyre," has been sending heat out of this region. The gyre, circulating counter-clockwise, carries relatively warmer waters farther north, into the Arctic Ocean. It's a profoundly complicated system, Keil said, noting that his team is preparing an entirely separate study focusing just on what's driving this gyre (the research is led by Rohit Ghosh, who also studies ocean trends at the Max Planck Institute for Meteorology.)

The important point is this gyre acts to transport warmer waters out of the North Atlantic, further cooling the cold blob.
…
The researchers also showed that clouds played a role, though smaller, in sustaining the cold blob.

They found the cooler ocean surface produces more low-level clouds, a cloud type that's thick and "reflects more sunlight and thereby further cools the surface," said Keil. This means the warming hole is "strengthening" itself in a feedback loop, explained Keil, as more cooling creates more reflective clouds, which in turn creates more cooling.

The role of clouds in the North Atlantic, however, is a new, emerging finding that will certainly need continued observation, said NASA's Willis."

[AbruptSLR]

While the warming that occurred from the Last Glacial Maximum to the Holocene Thermal Maximum (or Holocene Climate Optimum) is not a direct analogy for the anthropogenically driven global warming that we are currently experiencing; nevertheless, the assessment of this period presented in the linked article indicates that freshwater hosing into the North Atlantic can rapidly accelerate global warming due to the associated slowing of the AMOC and the resulting bipolar seesaw mechanism:

Title: "Explainer: How the rise and fall of CO2 levels influenced the ice ages"

https://www.carbonbrief.org/explainer-how-the-rise-and-fall-of-co2-levels-influenced-the-ice-ages

Extract: "While scientists used to think that CO2 lagged temperatures by 600 to 1,000 years during deglaciation, a number of recent studies have suggested that the lag is considerably smaller or even too small to detect. It is challenging to precisely match up CO2 records and temperature records from ice cores as there is a delay between new snowfall on an ice sheet (that traps the air bubbles) and then that snow slowly compressing into ice.
…
Specifically, Shakun and colleagues argue that changes in orbital cycles triggered initial melting of ice sheets in the northern hemisphere. This caused large amounts of freshwater to pour into the oceans as ice sheets melted, disrupting the Atlantic Meridional Overturning Circulation (AMOC), which, in turn, cooled the northern hemisphere and warmed the southern hemisphere.

This southern hemisphere warming caused ocean releases of CO2, which, in turn, warmed the entire planet.
…
While there is a clear relationship between CO2 and temperature over the past million years, it is difficult to extrapolate to future changes to the Earth’s climate. For example, at the end of the last ice age atmospheric CO2 concentrations increased by around 50% while global temperatures increased by around 4C. If CO2 were the only factor at work, this would imply a very high sensitivity of the climate to CO2 – around 8C per doubling CO2, far higher than current estimates based on climate models and other lines of evidence."

[Hefaistos]

Here is another reminder that the quoted research indicates that the AMOC is currently slowing (particularly since 2015); which is a major risk factor for high values of TCR in coming decades:

ASLR, your statement (bolded by me) is not correct.
AMOC is stable during the period from 2015 to 2019, even showing a slight increase.
Please see the charts i posted in reply #3424 and reply #3425:

The RAPID arrays show:
At 26N, a slight increase
At Upper Mid Ocean, stable
Florida Straits, stable
Ekman at 26N, a slight increase
OVIDE section, a slight increase

What's the evidence you can provide that "AMOC is currently slowing (particularly since 2015)"?

https://forum.arctic-sea-ice.net/index.php/topic,2205.msg271113.html#msg271113

I believe that Smeed et al got it right in their recent paper, when they write:
"Our results show that the previously reported decline of the AMOC (Smeed et al., 2014) has been arrested, but the length of the observational record of the AMOC is still short relative to the time scales of importantdecadal variations that exist in the Atlantic. Understanding is therefore constantly evolving. What we identify as a changed state of the AMOC in this study may well prove to be part of a decadal oscillation superposed on a multidecadal cycle."

In other words, what we're seeing is natural variations, and there is currently no evidence of a declining AMOC, specifically not since 2015.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL076350

[Tom_Mazanec]

ASLR, what would be the result of a loss of AMOC? Without a Gulf Stream would Europe and the eastern Us and Canada actually cool?

[AbruptSLR]

ASLR, what would be the result of a loss of AMOC? Without a Gulf Stream would Europe and the eastern Us and Canada actually cool?

First, I believe that in coming decades that the AMOC/MOC will slow abruptly (due to one or more freshwater hosing events), but not stop entirely.

Second, yes that would mean that the Gulf (of Mexico) Stream would also slow abruptly which (if if were to happen) would clearly cool Western Europe, the northeast coast of the US and eastern Canada; while at the same time the great majority of surface temperatures for the rest of the world would warm abruptly until the MOC re-established itself some century or two, in the future, after the freshwater hosing event has dissipated.

[AbruptSLR]

The linked reference indicates that when the AMOC slowed prior to the last interglacial (LIG) this warmed the subsurface ocean temperature adjoining marine, and marine-terminating, glaciers; which resulted in sea levels that were six to nine meters higher than today. 

Clark, P.U., He, F., Golledge, N.R. et al. Oceanic forcing of penultimate deglacial and last interglacial sea-level rise. Nature 577, 660–664 (2020). https://doi.org/10.1038/s41586-020-1931-7

https://www.nature.com/articles/s41586-020-1931-7

Abstract: "Sea-level histories during the two most recent deglacial–interglacial intervals show substantial differences despite both periods undergoing similar changes in global mean temperature and forcing from greenhouse gases. Although the last interglaciation (LIG) experienced stronger boreal summer insolation forcing than the present interglaciation, understanding why LIG global mean sea level may have been six to nine metres higher than today has proven particularly challenging. Extensive areas of polar ice sheets were grounded below sea level during both glacial and interglacial periods, with grounding lines and fringing ice shelves extending onto continental shelves. This suggests that oceanic forcing by subsurface warming may also have contributed to ice-sheet loss analogous to ongoing changes in the Antarctic and Greenland ice sheets. Such forcing would have been especially effective during glacial periods, when the Atlantic Meridional Overturning Circulation (AMOC) experienced large variations on millennial timescales, with a reduction of the AMOC causing subsurface warming throughout much of the Atlantic basin. Here we show that greater subsurface warming induced by the longer period of reduced AMOC during the penultimate deglaciation can explain the more-rapid sea-level rise compared with the last deglaciation. This greater forcing also contributed to excess loss from the Greenland and Antarctic ice sheets during the LIG, causing global mean sea level to rise at least four metres above modern levels. When accounting for the combined influences of penultimate and LIG deglaciation on glacial isostatic adjustment, this excess loss of polar ice during the LIG can explain much of the relative sea level recorded by fossil coral reefs and speleothems at intermediate- and far-field sites."

Edit: Obviously, this study supports the concept that ice-climate feedbacks can contribute to abrupt climate change, for example when the Beaufort Gyre eventually releases a surge of relative warm, relatively fresh, water into the North Atlantic it may likely slow the AMOC; which might lead to abrupt sea level rise.

This is a reminder that Clark et al. (2020) indicates that the WAIS is less stable than consensus climate science has been assuming:

Title: "Warming oceans could cause Antarctic Ice Sheet collapse, sea level rise"

https://phys.org/news/2020-02-oceans-antarctic-ice-sheet-collapse.html

Extract: "A new study suggests the Western Antarctic Ice Sheet is less stable than researchers once thought. As in the past, its collapse in the future is likely."

[AbruptSLR]

The linked reference confirms that the AMOC is projected to continue slowing with continued global warming:

Wei Liu  et al. (26 Jun 2020), "Climate impacts of a weakened Atlantic Meridional Overturning Circulation in a warming climate", Science Advances, Vol. 6, no. 26, eaaz4876, DOI: 10.1126/sciadv.aaz4876

https://advances.sciencemag.org/content/6/26/eaaz4876

Abstract
While the Atlantic Meridional Overturning Circulation (AMOC) is projected to slow down under anthropogenic warming, the exact role of the AMOC in future climate change has not been fully quantified. Here, we present a method to stabilize the AMOC intensity in anthropogenic warming experiments by removing fresh water from the subpolar North Atlantic. This method enables us to isolate the AMOC climatic impacts in experiments with a full-physics climate model. Our results show that a weakened AMOC can explain ocean cooling south of Greenland that resembles the North Atlantic warming hole and a reduced Arctic sea ice loss in all seasons with a delay of about 6 years in the emergence of an ice-free Arctic in boreal summer. In the troposphere, a weakened AMOC causes an anomalous cooling band stretching from the lower levels in high latitudes to the upper levels in the tropics and displaces the Northern Hemisphere midlatitude jets poleward.

Some in this thread have suggested that the recent observed cooling of the lower levels of the troposphere is an indication that climate sensitivity is relatively low; however, the quoted reference indicates that instead it is an indication that the AMOC is slowing (see the bolded text in the abstract); which to me is an indication that in coming decades TCR will be much higher (near 2.93C) than assumed by consensus climate science.

[AbruptSLR]

....

Armitage, T.W.K., Manucharyan, G.E., Petty, A.A. et al. Enhanced eddy activity in the Beaufort Gyre in response to sea ice loss. Nat Commun 11, 761 (2020). https://doi.org/10.1038/s41467-020-14449-z

https://www.nature.com/articles/s41467-020-14449-z?utm_medium=affiliate&utm_source=commission_junction&utm_campaign=3_nsn6445_deeplink_PID8099906&utm_content=deeplink

Abstract: "The Beaufort Gyre freshwater content has increased since the 1990s, potentially stabilizing in recent years. The mechanisms proposed to explain the stabilization involve either mesoscale eddy activity that opposes Ekman pumping or the reduction of Ekman pumping due to reduced sea ice–ocean surface stress. However, the relative importance of these mechanisms is unclear. Here, we present observational estimates of the Beaufort Gyre mechanical energy budget and show that energy dissipation and freshwater content stabilization by eddies increased in the late-2000s. The loss of sea ice and acceleration of ocean currents after 2007 resulted in enhanced mechanical energy input but without corresponding increases in potential energy storage. To balance the energy surplus, eddy dissipation and its role in gyre stabilization must have increased after 2007. Our results imply that declining Arctic sea ice will lead to an increasingly energetic Beaufort Gyre with eddies playing a greater role in its stabilization."

..."

This is a reminder that both the quoted reference, and the linked associated article, indicate that the Beaufort Gyre has already accumulated sufficient excess freshwater to lead both to abrupt Arctic Sea Ice loss and to an abrupt slowdown of the AMOC anytime in the coming decades. 

Title: "Climate Change Is Intensifying Arctic Ocean Currents"

https://eos.org/articles/climate-change-is-intensifying-arctic-ocean-currents

Extract: "“For the past few decades, the Beaufort Gyre has rotated in a clockwise direction, driven by the wind. When ice covers the surface of the ocean, it’s harder for the wind to push the ocean around. But as this protective barrier of sea ice shrinks (and the remaining ice becomes thinner and more mobile), wind is able to put more energy into the rotation of the Beaufort Gyre.
...
Since the 1990s, the Beaufort Gyre has accumulated around 8,000 cubic kilometers of additional fresh water, enough to cover all of California in 60 feet [18 meters] of water.
...
The Arctic Ocean has enough warm water at depth to melt the ice pack multiple times, but it is isolated from the surface by cold and fresh—more buoyant—surface waters. Enhanced upwards mixing of this heat could lead to further ice pack melt.
...
Changes in Arctic Ocean currents—or in the Beaufort Gyre specifically—could alter the amount of cold, relatively fresh water coming down from the Arctic. This reduction of cool fresh water could disrupt the warm Atlantic current and cool Europe substantially.
..,
Both Armitage and Johnson said that this study also highlights the need for oceanographic models with increased resolution. Many of the current models are not able to resolve features like eddies, and because eddies play an important role in the dynamics of the Beaufort Gyre, higher-resolution models are necessary for accuracy. And having accurate models of the Arctic Ocean—and how it will be affected by climate change—may be very important for future global climate predictions.”

[AbruptSLR]

The linked open access reference indicates that:

"Heatwaves have increased in intensity, frequency and duration, with these trends projected to worsen under enhanced global warming."

Perkins-Kirkpatrick, S.E., Lewis, S.C. Increasing trends in regional heatwaves. Nat Commun 11, 3357 (2020). https://doi.org/10.1038/s41467-020-16970-7

https://www.nature.com/articles/s41467-020-16970-7

Abstract: "Heatwaves have increased in intensity, frequency and duration, with these trends projected to worsen under enhanced global warming. Understanding regional heatwave trends has critical implications for the biophysical and human systems they impact. Until now a comprehensive assessment of regional observed changes was hindered by the range of metrics employed, underpinning datasets, and time periods examined. Here, using the Berkeley Earth temperature dataset and key heatwave metrics, we systematically examine regional and global observed heatwave trends. In almost all regions, heatwave frequency demonstrates the most rapid and significant change. A measure of cumulative heat shows significant increases almost everywhere since the 1950s, mainly driven by heatwave days. Trends in heatwave frequency, duration and cumulative heat have accelerated since the 1950s, and due to the high influence of variability we recommend regional trends are assessed over multiple decades. Our results provide comparable regional observed heatwave trends, on spatial and temporal scales necessary for understanding impacts."

[AbruptSLR]

The linked video discusses finding from the 2020 ATOMIC campaign to study shallow convection clouds off the coast of Barbados from January thru February 2020.  This campaign observed several differences from projections from consensus climate models of regional shallow altitude cloud formation that merit further improvement of existing models:

Title: "Atlantic Tradewind Ocean-atmosphere Mesoscale Interaction Campaign (ATOMIC)"

[AbruptSLR]

Arctic Amplification is accelerating rapidly:

Title: "Rapid Arctic meltdown in Siberia alarms scientists"

https://www.washingtonpost.com/climate-environment/rapid-arctic-meltdown-in-siberia-alarms-scientists/2020/07/03/4c1bd6a6-bbaa-11ea-bdaf-a129f921026f_story.html

Extract: "In Siberia and across much of the Arctic, profound changes are unfolding more rapidly than scientists anticipated only a few years ago. Shifts that once seemed decades away are happening now, with potentially global implications.
...
Much of Siberia experienced an exceptionally mild winter, followed by a warmer-than- average spring, and it has been among the most unusually warm regions of the world during 2020. During May, parts of Siberia saw an average monthly temperature that was a staggering 18 degrees Fahrenheit (10 Celsius) above average for the month, according to the European Union’s Copernicus Climate Change Service.
...
The persistent warmth has helped to fuel wildfires, eviscerate sea ice and destabilize homes and other buildings constructed on thawing permafrost. It allegedly even contributed to a massive fuel spill in Norilsk in late May that prompted Russian President Vladimir Putin to declare a state of emergency in the environmentally sensitive region.
...
Already, sea ice in the vicinity of Siberia is running at record-low levels for any year since reliable satellite monitoring began in 1979.

Scientists have long maintained that the Arctic is warming twice as fast as the rest of the world. But in reality, the region is now warming at nearly three times the global average. Data from NASA shows that since 1970, the Arctic has warmed by an average of 5.3 degrees (2.94 Celsius), compared with the global average of 1.71 degrees (0.95 Celsius) during the same period. Scientists refer to the phenomenon as “Arctic amplification.”
...
Sea ice typically reaches its minimum in September, he noted. Ice melt accelerates in Greenland during June and July. Wildfires have the potential to worsen as summer drags on. Intense summer storms can cause permafrost degradation and worsen coastal erosion."

[Hefaistos]

The linked reference confirms that the AMOC is projected to continue slowing with continued global warming:

Wei Liu  et al. (26 Jun 2020), "Climate impacts of a weakened Atlantic Meridional Overturning Circulation in a warming climate", Science Advances, Vol. 6, no. 26, eaaz4876, DOI: 10.1126/sciadv.aaz4876

https://advances.sciencemag.org/content/6/26/eaaz4876

Abstract
While the Atlantic Meridional Overturning Circulation (AMOC) is projected to slow down under anthropogenic warming, the exact role of the AMOC in future climate change has not been fully quantified. Here, we present a method to stabilize the AMOC intensity in anthropogenic warming experiments by removing fresh water from the subpolar North Atlantic. This method enables us to isolate the AMOC climatic impacts in experiments with a full-physics climate model. Our results show that a weakened AMOC can explain ocean cooling south of Greenland that resembles the North Atlantic warming hole and a reduced Arctic sea ice loss in all seasons with a delay of about 6 years in the emergence of an ice-free Arctic in boreal summer. In the troposphere, a weakened AMOC causes an anomalous cooling band stretching from the lower levels in high latitudes to the upper levels in the tropics and displaces the Northern Hemisphere midlatitude jets poleward.

Some in this thread have suggested that the recent observed cooling of the lower levels of the troposphere is an indication that climate sensitivity is relatively low; however, the quoted reference indicates that instead it is an indication that the AMOC is slowing (see the bolded text in the abstract); which to me is an indication that in coming decades TCR will be much higher (near 2.93C) than assumed by consensus climate science.

What if the AMOC instead is in a strengthening cycle? This is suggested be several recent papers. How do you then explain the decreasing tropospheric temperatures?

"Surface predictor of overturning circulation and heat content change in the subpolar North Atlantic"
Desbruyères et al, 2019, Ocean Sci., 15, 809–817

Abstract
The Atlantic Meridional Overturning Circulation (AMOC) impacts ocean and atmosphere temperatures on a wide range of temporal and spatial scales. Here we use observational datasets to validate model-based inferences on the usefulness of thermodynamics theory in reconstructing AMOC variability at low frequency, and further build on this reconstruction to provide prediction of the near-future (2019–2022) North Atlantic state. An easily observed surface quantity – the rate of warm to cold transformation of water masses at high latitudes – is found to lead the observed AMOC at 45∘ N by 5–6 years and to drive its 1993–2010 decline and its ongoing recovery, with suggestive prediction of extreme intensities for the early 2020s. We further demonstrate that AMOC variability drove a bi-decadal warming-to-cooling reversal in the subpolar North Atlantic before triggering a recent return to warming conditions that should prevail at least until 2021. Overall, this mechanistic approach of AMOC variability and its impact on ocean temperature brings new key aspects for understanding and predicting climatic conditions in the North Atlantic and beyond."

From the Conclusions:
"In this paper we have provided observationally based evidence of a tight causal relationship between low-frequency changes in the rate of surface-forced water mass transformation in the eastern SPG /Subpolar Gyre/, the variability in the overturning circulation at 45∘ N, and ocean heat content trends in the SPG. The 5-year delay between surface property changes in the SPG and downstream circulation changes suggests good skills for short-term predictability in the region from the sole use of ocean surface and air–sea interface measurements. Here, a strong intensification of the overturning and associated heat transport from 2010 is found to persist until the early 2020s, driving a new significant reversal of climatic condition in the SPG as temperatures rapidly rise from their last minimum of 2017. "

Enjoy the full text:
https://os.copernicus.org/articles/15/809/2019/

Caption Figure 4. The AMOC and SFOC time series. (a) Annual anomalies in the maximum AMOC (blue) and the maximum SFOC (red) at 45 N (in Sv), with the latter shifted 5 years forward (lag of maximum correlation). The reference (time-mean) period is 1996–2013. Thick lines show 7-year low-pass-filtered time series. The right-hand side axis displays the corresponding heat transport anomalies. The original time line for SFOC is given in the top x axis. (b) The 7-year low-pass-filtered time series of anomalies in the maximum SFOC at 45 N (red – shifted 5 years forward), the maximum SFOC at the OSNAP line (green – shifted 4 years forward) decomposed into contributions from the eastern (thin) and western (dashed) basins, and the maximum SFOC at the GIS sills (yellow – shifted 3 years forward). Shading indicates the ensemble standard errors for each variable.

Caption  Figure 5. OHC time series. Detrended anomalies in OHC within
the upper SPG (0–1000 m; 10–70W, 45–65 N; black, in joules)
and MHT -driven OHC anomalies north of 45 N (blue, in joules).
Shading indicates the ensemble standard errors for each variable.
The SFOC -driven OHC prediction for 2017–2022 is shown in red,
with its associated error based on the historical predictive skills of
SFOC (Eq. 6). The green patch indicates the “cold blob” era driven
by extreme air–sea flux events (Josey et al., 2018).

[Hefaistos]

Another paper about the ongoing strengthening of the AMOC:

"Pending recovery in the strength of the meridional overturning circulation at 26°N"

by Moat et al, in Ocean Science, forthcoming  (still in peer review)

Abstract. The strength of the Atlantic meridional overturning circulation (AMOC) at 26°N has now been continuously measured by the RAPID array over the period Apr 2004 - Sept 2018. This record provides unique insight into the variability of the large-scale ocean circulation, previously only measured by sporadic snapshots of basin-wide transports from
hydrographic sections. The continuous measurements have unveiled striking variability on timescales of days to a decade, driven largely by wind-forcing, contrasting with previous expectations about a slowly-varying, buoyancy forced large-scale ocean circulation. However, these measurements were primarily observed during a warm state of the Atlantic Multidecadal
Variability (AMV) which has been steadily declining since a peak in 2008-2010. In 2013-2015, a period of strong buoyancyforcing by the atmosphere drove intense watermass transformation in the subpolar North Atlantic and provides a unique opportunity to investigate the response of the large-scale ocean circulation to buoyancy forcing. Modelling studies suggest that the AMOC in the subtropics responds to such events with an increase in overturning transport, after a lag of 3-9 years. At 45°N, observations suggest that the AMOC may already be increasing. ..."

https://www.researchgate.net/publication/338658885_Pending_recovery_in_the_strength_of_the_meridional_overturning_circulation_at_26_N

Figure 3 The total AMOC at 10-day resolution (a), can be decomposed into a seasonal cycle (b), interannual variability (c)...

[AbruptSLR]

I note that many consensus climate models, that do not consider freshwater hosing, project that the AMOC will strengthen in coming decades; while many advanced climate models, that at least partially account for freshwater hosing events, project that the AMOC will continue to weaken in coming decades.

[AbruptSLR]

The linked article & open access associated reference indicate that Earth's magnetic field can change direction at a rate of up to 10o per year; which indicates that in the extreme case the magnetic poles could 100 percent flip in as little as 18 years.  This new research includes evaluation of evidence from paleo periods when there was major changes in ice sheet size.

Title: "Earth's magnetic field can change 10 times faster than previously thought"

https://www.sciencedaily.com/releases/2020/07/200706094136.htm

Extract: "A new study by the University of Leeds and University of California at San Diego reveals that changes in the direction of the Earth's magnetic field may take place 10 times faster than previously thought."

See also:

Christopher J. Davies, Catherine G. Constable. Rapid geomagnetic changes inferred from Earth observations and numerical simulations. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-16888-0

https://www.nature.com/articles/s41467-020-16888-0

Abstract: "Extreme variations in the direction of Earth’s magnetic field contain important information regarding the operation of the geodynamo. Paleomagnetic studies have reported rapid directional changes reaching 1° yr−1, although the observations are controversial and their relation to physical processes in Earth’s core unknown. Here we show excellent agreement between amplitudes and latitude ranges of extreme directional changes in a suite of geodynamo simulations and a recent observational field model spanning the past 100 kyrs. Remarkably, maximum rates of directional change reach  ~10° yr−1, typically during times of decreasing field strength, almost 100 times faster than current changes. Detailed analysis of the simulations and a simple analogue model indicate that extreme directional changes are associated with movement of reversed flux across the core surface. Our results demonstrate that such rapid variations are compatible with the physics of the dynamo process and suggest that future searches for rapid directional changes should focus on low latitudes."

Extract: "New global time-dependent field models for periods preceding the Holocene are revealing geomagnetic field behaviour that is not represented in the relatively short historical record."

[AbruptSLR]

The linked paper discusses "… common features of climate delay discourses …"

Lamb, W. F. et al. (2020) Discourses of climate delay, Global Sustainability, doi.org/10.1017/sus.2020.13

https://www.cambridge.org/core/journals/global-sustainability/article/discourses-of-climate-delay/7B11B722E3E3454BB6212378E32985A7

Non-technical summary
‘Discourses of climate delay’ pervade current debates on climate action. These discourses accept the existence of climate change, but justify inaction or inadequate efforts. In contemporary discussions on what actions should be taken, by whom and how fast, proponents of climate delay would argue for minimal action or action taken by others. They focus attention on the negative social effects of climate policies and raise doubt that mitigation is possible. Here, we outline the common features of climate delay discourses and provide a guide to identifying them.