Ice Apocalypse - Multiple Meters Sea Level Rise

[bluice]

One thing to bear in mind regarding sulphur reductions from shipping is that shipping, like population, is concentrated on the northern hemisphere. Because new regulations came into effect from Jan 1st we have not yet seen the full impact of high NH summer insolation and lower sulphur emissions.

To add insult to injury Covid-19 economic disruption has reduced aerosol emissions from land based sources and grounded a large portion of commercial aviation.

2020 might have more surprises waiting.

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2020 might have more surprises waiting.

In the attached image from Hausfather of his projection of GMSTA for 2020 using data thru March 2020; 2020 most likely would be the warmest year on record (particularly if low negative feedback from reduced aerosol emissions continue all year); which would surprise many people.

Caption: "Annual global average surface temperature anomalies from NASA plotted with respect to a 1981-2010 baseline. To-date 2020 values include January-March. Estimated 2020 annual value based on relationship between the January-March temperatures and annual temperatures since 1950. Chart by Carbon Brief using Highcharts"

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The linked references discuss uncertainty in TCRE and Carbon Budgets including findings from CMIP6.  Roughly they find that TCRE was largely the same in both CMIP5 and CMIP6; however, CMIP6 did a much better job of addressing carbon-cycle uncertainties which extends the range of possible changes in GMSTA (including lengthening the right-tail climate risks).  These references also confirm that permafrost degradation has been ignored by all consensus ESM projections; which represents yet another underestimated climate risk in the MIP projects.

Chris D Jones and Pierre Friedlingstein (2020), "Quantifying process-level uncertainty contributions to TCRE and Carbon Budgets for meeting Paris Agreement climate targets", Environmental Research Letters

https://iopscience.iop.org/article/10.1088/1748-9326/ab858a

Abstract
To achieve the goals of the Paris Agreement requires deep and rapid reductions in anthropogenic CO2 emissions, but uncertainty surrounds the magnitude and depth of reductions. Earth system models provide a means to quantify the link from emissions to global climate change. Using the concept of TCRE – the transient climate response to cumulative carbon emissions – we can estimate the remaining carbon budget to achieve 1.5 or 2 oC. But the uncertainty is large, and this hinders the usefulness of the concept. Uncertainty in carbon budgets associated with a given global temperature rise is determined by the physical Earth system, and therefore Earth system modelling has a clear and high priority remit to address and reduce this uncertainty. Here we explore multi-model carbon cycle simulations across three generations of Earth system models to quantitatively assess the sources of uncertainty which propagate through to TCRE. Our analysis brings new insights which will allow us to determine how we can better direct our research priorities in order to reduce this uncertainty. We emphasise that uses of carbon budget estimates must bear in mind the uncertainty stemming from the biogeophysical earth system, and we recommend specific areas where the carbon cycle research community needs to re-focus activity in order to try to reduce this uncertainty. We conclude that we should revise focus from the climate feedback on the carbon cycle to place more emphasis on CO2 as the main driver of carbon sinks and their long-term behaviour. Our proposed framework will enable multiple constraints on components of the carbon cycle to propagate to constraints on remaining carbon budgets.

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MacDougall, A. H., Frölicher, T. L., Jones, C. D., Rogelj, J., Matthews, H. D., Zickfeld, K., Arora, V. K., Barrett, N. J., Brovkin, V., Burger, F. A., Eby, M., Eliseev, A. V., Hajima, T., Holden, P. B., Jeltsch-Thömmes, A., Koven, C., Menviel, L., Michou, M., Mokhov, I. I., Oka, A., Schwinger, J., Séférian, R., Shaffer, G., Sokolov, A., Tachiiri, K., Tjiputra, J., Wiltshire, A., and Ziehn, T.: Is there warming in the pipeline? A multi-model analysis of the zero emission commitment from CO2, Biogeosciences Discuss., https://doi.org/10.5194/bg-2019-492, in review, 2020.

https://www.biogeosciences-discuss.net/bg-2019-492/

Abstract. The Zero Emissions Commitment (ZEC) is the change in global mean temperature expected to occur following the cessation of net CO2 emissions, and as such is a critical parameter for calculating the remaining carbon budget. The Zero Emissions Commitment Model Intercomparison Project (ZECMIP) was established to gain a better understanding of the potential magnitude and sign of ZEC, in addition to the processes that underlie this metric. Eighteen Earth system models of both full and intermediate complexity participated in ZECMIP. All models conducted an experiment where atmospheric CO2 concentration increases exponentially until 1000 PgC has been emitted. Thereafter emissions are set to zero and models are configured to allow free evolution of atmospheric CO2 concentration. Many models conducted additional second priority simulations with different cumulative emissions totals and an alternative idealized emissions pathway with a gradual transition to zero emissions. The inter-model range of ZEC 50 years after emissions cease for the 1000 PgC experiment is − 0.36 to 0.29 ºC with a model ensemble mean of −0.06 ºC, median of −0.05 ºC and standard deviation of 0.19 ºC. Models exhibit a wide variety of behaviours after emissions cease, with some models continuing to warm for decades to millennia and others cooling substantially. Analysis shows that both ocean carbon uptake and carbon uptake by the terrestrial biosphere are important for counteracting the warming effect from reduction in ocean heat uptake in the decades after emissions cease. Overall, the most likely value of ZEC on multi-decadal timescales is close to zero, consistent with previous model experiments.

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Jones, C. D., Frölicher, T. L., Koven, C., MacDougall, A. H., Matthews, H. D., Zickfeld, K., Rogelj, J., Tokarska, K. B., Gillett, N. P., Ilyina, T., Meinshausen, M., Mengis, N., Séférian, R., Eby, M., and Burger, F. A.: The Zero Emissions Commitment Model Intercomparison Project (ZECMIP) contribution to C4MIP: quantifying committed climate changes following zero carbon emissions, Geosci. Model Dev., 12, 4375–4385, https://doi.org/10.5194/gmd-12-4375-2019, 2019.

https://www.geosci-model-dev.net/12/4375/2019/

Abstract
The amount of additional future temperature change following a complete cessation of CO2 emissions is a measure of the unrealized warming to which we are committed due to CO2 already emitted to the atmosphere. This “zero emissions commitment” (ZEC) is also an important quantity when estimating the remaining carbon budget – a limit on the total amount of CO2 emissions consistent with limiting global mean temperature at a particular level. In the recent IPCC Special Report on Global Warming of 1.5 ∘C, the carbon budget framework used to calculate the remaining carbon budget for 1.5 ∘C included the assumption that the ZEC due to CO2 emissions is negligible and close to zero. Previous research has shown significant uncertainty even in the sign of the ZEC. To close this knowledge gap, we propose the Zero Emissions Commitment Model Intercomparison Project (ZECMIP), which will quantify the amount of unrealized temperature change that occurs after CO2 emissions cease and investigate the geophysical drivers behind this climate response. Quantitative information on ZEC is a key gap in our knowledge, and one that will not be addressed by currently planned CMIP6 simulations, yet it is crucial for verifying whether carbon budgets need to be adjusted to account for any unrealized temperature change resulting from past CO2 emissions. We request only one top-priority simulation from comprehensive general circulation Earth system models (ESMs) and Earth system models of intermediate complexity (EMICs) – a branch from the 1 % CO2 run with CO2 emissions set to zero at the point of 1000 PgC of total CO2 emissions in the simulation – with the possibility for additional simulations, if resources allow. ZECMIP is part of CMIP6, under joint sponsorship by C4MIP and CDRMIP, with associated experiment names to enable data submissions to the Earth System Grid Federation. All data will be published and made freely available.

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Increases in sea surface temperature, SST, is an important factor for determining climate sensitivity.  Thus, the linked reference indicating that SSTs around the world are surging upward in recent years due high values of ocean heat uptake in recent decades, is not good news.

Bablu Sinha et al. (22 April 2020), "Surging of global surface temperature due to decadal legacy of ocean heat uptake", Journal of Climate, https://doi.org/10.1175/JCLI-D-19-0874.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0874.1

Abstract
Global surface warming since 1850 consisted of a series of slowdowns (hiatus) followed by surges. Knowledge of a mechanism to explain how this occurs would aid development and testing of interannual to decadal climate forecasts. In this paper a global climate model is forced to adopt an ocean state corresponding to a hiatus (with negative Interdecadal Pacific Oscillation, IPO, and other surface features typical of a hiatus) by artificially increasing the background diffusivity for a decade before restoring it to its normal value and allowing the model to evolve freely. This causes the model to develop a decadal surge which overshoots equilibrium (resulting in a positive IPO state) leaving behind a modified, warmer climate for decades. Water mass transformation diagnostics indicate that the heat budget of the tropical Pacific is a balance between large opposite signed terms: surface heating/cooling due to air-sea heat flux is balanced by vertical mixing and ocean heat transport divergence. During the artificial hiatus, excess heat becomes trapped just above the thermocline and there is a weak vertical thermal gradient (due to the high artificial background mixing). When the hiatus is terminated, by returning the background diffusivity to normal, the thermal gradient strengthens to pre-hiatus values so that the mixing (diffusivity x thermal gradient) remains roughly constant. However, since the base layer just above the thermocline remains anomalously warm this implies a warming of the entire water column above the trapped heat which results in a surge followed by a prolonged period of elevated surface temperatures.

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The linked reference indicates that there is more than four times the amount of coarse dust in the atmosphere than climate scientists previously thought.  Furthermore, as coarse dust induces a positive feedback mechanism for global warming, this may mean that aerosol feedback is more negative than previously thought so possibly as the world emits fewer aerosols, global warming may well accelerate.  Furthermore, if climate change increases global mean wind velocities it is possible that even more coarse dust will be launched into the atmosphere in the future, and if so this would increase climate sensitivity with continued global warming:

Adeyemi A. Adebiyi and Jasper F. Kok (08 Apr 2020), "Climate models miss most of the coarse dust in the atmosphere", Science Advances, Vol. 6, no. 15, eaaz9507, DOI: 10.1126/sciadv.aaz9507

https://advances.sciencemag.org/content/6/15/eaaz9507/

Abstract
Coarse mineral dust (diameter, ≥5 μm) is an important component of the Earth system that affects clouds, ocean ecosystems, and climate. Despite their significance, climate models consistently underestimate the amount of coarse dust in the atmosphere when compared to measurements. Here, we estimate the global load of coarse dust using a framework that leverages dozens of measurements of atmospheric dust size distributions. We find that the atmosphere contains 17 Tg of coarse dust, which is four times more than current climate models simulate. Our findings indicate that models deposit coarse dust out of the atmosphere too quickly. Accounting for this missing coarse dust adds a warming effect of 0.15 W·m−2 and increases the likelihood that dust net warms the climate system. We conclude that to properly represent the impact of dust on the Earth system, climate models must include an accurate treatment of coarse dust in the atmosphere.

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The linked reference indicates that cryoturbic diapirs could accelerate future thawing of permafrost; which would accelerate the associated emissions of future GHGs from permafrost regions.

Mitsuaki Ota et al. (07 February 2020), "Could Cryoturbic Diapirs Be Key for Understanding Ecological Feedbacks to Climate Change in High Arctic Polar Deserts?" JGR Biogeosciences, https://doi.org/10.1029/2019JG005263

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JG005263

Abstract
High Arctic polar deserts cover 26% of the Arctic. Increasing temperatures are predicted to significantly alter polar desert freeze‐thaw and biogeochemical cycles, with important implications for greenhouse gas emissions. However, the mechanisms underlying these changing cycles are still highly uncertain. Cryoturbic, carbon‐rich Bhy horizons (diapirs) in frost boils are key nutrient sources for Salix arctica. We hypothesized that diapirism leads to organic carbon characteristics that alter microbial pathways, which then control root foraging and greenhouse gas production. During July and August 2013, we characterized soil properties and examined gross nitrogen transformation rates in frost boils both with and without diapirs in two High Arctic polar deserts (dolomite and granite) near Alexandra Fjord (78°51′N 75°54′W), Ellesmere Island, Nunavut, Canada. Diapiric frost boils had 18% higher soil organic carbon in the dolomitic and 9% higher in the granitic deserts, and 29% higher total dissolved nitrogen in the dolomitic desert. However, diapirs decreased gross nitrogen mineralization rates by 30% in the dolomitic and by 48% in the granitic deserts. Attenuated total reflectance Fourier transformed mid‐infrared spectroscopy revealed greater concentrations of polysaccharides and recalcitrant carbon in diapiric versus nondiapiric frost boils. These increased polysaccharide concentrations likely facilitate diapirism as soil viscosity increases with polysaccharides. Lower microbial activity or ectomycorrhizae that are known to colonize S. arctica may accumulate total dissolved nitrogen in diapirs. Our results suggest geomorphologic‐plant‐microbe interactions may underlie important patterns of geochemical cycling in arctic systems. Thus, polar desert frost boils should represent a key focus of future investigations of climate change in arctic systems.

Plain Language Summary
Arctic ecology and climate are intricately interconnected. During short summers, the upper soil layers thaw, allowing biological activities. Recent warming in polar deserts has influenced key thaw processes and plant‐microbe interactions with soil nutrients. Polar desert ecosystems cover 26% of the Arctic and are expected to transform dramatically with further warming, with important implications for climate‐ecology feedbacks.
To evaluate feedbacks in polar deserts, we focused on cryoturbic diapirism (buoyant nutrient patches above the permafrost), which is expected to increase with warming. We investigated soil properties and microbial activities in frost boils (density‐driven circulations of sediments above the permafrost). We found that diapirism increased recalcitrant soil organic carbon, which decreased microbial activities. Interestingly, we found that microbes and/or plants may augment diapirism by enhanced polysaccharide production increasing soil viscosity. Despite low organic carbon quality, the dominant vascular plant species, Salix arctica, increased root biomass and nitrogen uptake from diapirs, suggesting a mutualistic relationship between S. arctica and microbes. Under warming air temperatures, permafrost degradation releases stored organic matter, which may enhance nutrient cycling via diapirism. Therefore, our study suggests that diapirism may represent ecological change in High Arctic polar deserts in response to global warming.

See also:
Title: "Floating Patches of Soil Nutrients in Soil Help Explain Arctic Thawing"

https://eos.org/research-spotlights/floating-patches-of-soil-nutrients-in-soil-help-explain-arctic-thawing

Extract: "Nutrient-rich diapirs have a complex relationship with soil microbes and play an important role in carbon and nitrogen nutrient cycling, making them crucial for understanding feedbacks in the Arctic."

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The linked Nature comment/article (which I have cited previously) provides clear mathematics as to how to define a concept that I have not emphasized enough, which is that a climate emergency can be defined as the product of climate risk (R) times climate urgency (U) and illustrated in the formula below (from the article).

Emergency = R × U = p × D × τ / T

Where risk (R) as the probability of something happening (p) multiplied by damage (D), and where Urgency (U) is the time it takes one to react to an issue (τ) divided by the intervention time left to avoid a bad outcome (T).

While a great many of my posts have focused on my belief that (R) is higher than most decision makers understand, I have generally only implied that (U) [say it would take 30-years to reach net zero emissions (τ) while say the time left before the Beaufort Gyre discharges a significant amount of freshwater hosing of 10-years (T) giving a (U) of 3].

Thus, here I would like to emphasize that in my opinion consensus climate scientists underemphasize both (R) and (U) and thus doubly underemphasize our true state of climate emergency:

Timothy M. Lenton, Johan Rockström, Owen Gaffney, Stefan Rahmstorf, Katherine Richardson, Will Steffen & Hans Joachim Schellnhuber (2019), "Climate tipping points — too risky to bet against", Nature, 575, 592-595, doi: 10.1038/d41586-019-03595-0

https://www.nature.com/articles/d41586-019-03595-0

Extract: "The growing threat of abrupt and irreversible climate changes must compel political and economic action on emissions.
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Politicians, economists and even some natural scientists have tended to assume that tipping points in the Earth system — such as the loss of the Amazon rainforest or the West Antarctic ice sheet — are of low probability and little understood. Yet evidence is mounting that these events could be more likely than was thought, have high impacts and are interconnected across different biophysical systems, potentially committing the world to long-term irreversible changes.

Here we summarize evidence on the threat of exceeding tipping points, identify knowledge gaps and suggest how these should be plugged. We explore the effects of such large-scale changes, how quickly they might unfold and whether we still have any control over them.
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EMERGENCY: DO THE MATHS

We define emergency (E) as the product of risk and urgency. Risk (R) is defined by insurers as probability (p) multiplied by damage (D). Urgency (U) is defined in emergency situations as reaction time to an alert (τ) divided by the intervention time left to avoid a bad outcome (T).

Thus:

E = R × U = p × D × τ / T

The situation is an emergency if both risk and urgency are high. If reaction time is longer than the intervention time left (τ / T > 1), we have lost control.

We argue that the intervention time left to prevent tipping could already have shrunk towards zero, whereas the reaction time to achieve net zero emissions is 30 years at best. Hence we might already have lost control of whether tipping happens. A saving grace is that the rate at which damage accumulates from tipping — and hence the risk posed — could still be under our control to some extent."

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In the linked 2017 RealClimate article Rahmstorf and Levermann make the case the global GHG emissions must peak by 2020.  I guess that we will all find out in a few years whether the global socio-economic system manages to meet/sustain that target/date:

Title: " Why global emissions must peak by 2020" by Stefan Rahmstorf and Anders Levermann

http://www.realclimate.org/index.php/archives/2017/06/why-global-emissions-must-peak-by-2020/comment-page-4/

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With a hat tip to interstitial I provide the following two linked open access references about updated bathymetry for key marine glaciers in the ASE, and I re-post interstitial's image showing how the bathymetry of the Thwaites gateway at base of the Thwaites Ice Tongue is deep enough to sustain ice-cliff failure mechanisms that could propagate upstream into the BSB once/if initiated:

Jordan, T. A., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R. D., Graham, A. G. C., and Paden, J. D.: New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-294, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2019-294/

Abstract. Ice shelves play a critical role in the long-term stability of ice sheets through their buttressing effect. The underlying bathymetry and cavity thickness are key inputs for modelling future ice sheet evolution. However, direct observation of sub-ice shelf bathymetry is time consuming, logistically risky, and in some areas simply not possible. Here we use airborne gravity anomaly data to provide new estimates of sub-ice shelf bathymetry outboard of the rapidly changing West Antarctic Thwaites Glacier, and beneath the adjacent Dotson and Crosson Ice Shelves. This region is of especial interest as the low-lying inland reverse slope of the Thwaites glacier system makes it vulnerable to marine ice sheet instability, with rapid grounding-line retreat observed since 1993 suggesting this process may be underway. Our results confirm a major marine channel > 800 m deep extends to the front of Thwaites Glacier, while the adjacent ice shelves are underlain by more complex bathymetry. Comparison of our new bathymetry with ice shelf draft reveals that ice shelves formed since 1993 comprise a distinct population where the draft conforms closely to the underlying bathymetry, unlike the older ice shelves which show a more uniform depth of the ice base. This indicates that despite rapid basal melting in some areas, these “new” ice shelves are not yet in equilibrium with the underlying ocean system. We propose qualitative models of how this transient ice-shelf configuration may have developed.

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Hogan, K. A., Larter, R. D., Graham, A. G. C., Arthern, R., Kirkham, J. D., Totten Minzoni, R., Jordan, T. A., Clark, R., Fitzgerald, V., Anderson, J. B., Hillenbrand, C.-D., Nitsche, F. O., Simkins, L., Smith, J. A., Gohl, K., Arndt, J. E., Hong, J., and Wellner, J.: Revealing the former bed of Thwaites Glacier using sea-floor bathymetry, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-25, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2020-25/

Abstract. The geometry of the sea floor beyond Thwaites Glacier (TG) is a major control on the routing of warm ocean waters towards the ice stream’s grounding zone, which has led to increased mass loss through sub-ice-shelf melting and resulting accelerated ice flow. Nearshore topographic highs act as pinning points for the Thwaites Ice Shelf and potentially provide barriers to warm water incursions. To date, few vessels have been able to access this area due to persistent sea-ice and iceberg cover. This critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project, with more than 2000 km2 of new multibeam echo-sounder data (MBES) were acquired offshore TG. Here, these data along with legacy MBES datasets are compiled to produce a set of standalone bathymetric grids for the inner Amundsen Sea shelf beyond both Pine Island and Thwaites glaciers. At TG, the bathymetry is dominated by a > 1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some parts having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf, suggesting a positive feedback mechanism for ice-shelf ungrounding. Knowing that this offshore area is a former bed for TG, we applied a novel spectral approach to investigate bed roughness and find that derived power spectra can be approximated using an inverse-square law, a result that is consistent with spectra for bed profiles from the modern TG. Using existing ice-flow theory, we also make a first assessment of the form drag (basal drag contribution) for ice flow over this topography. Ice flowing over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting in the grounding zone today. We show that the sea-floor bathymetry is an analogue for extant bed areas of TG and that more can be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. Comparisons with existing regional bathymetric compilations for the area show that high-frequency (finer than 5 km) bathymetric variability beyond Antarctic ice shelves can only be resolved by observations such as MBES and that without these data calculations of the capacity of bathymetric troughs, and thus oceanic heat flux, may be significantly underestimated. This work meets the requirements of recent numerical ice-sheet and ocean modelling studies that have recognised the need for accurate and high-resolution bathymetry to determine warm water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.

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The linked reference (& associated article) indicate that ozone-depleting substances, ODSs, likely have contributed to up to half of the observed Arctic Amplification in recent decades.  While many consensus climate scientists that these finding to be a ray of hope that the continued success of the Montreal Protocol could soon contribute to a reduction in future Arctic Amplification. 

While, not trying to be a 'Jeremiah', I note that the current (temporary) large ozone hole in the Arctic likely implies that the true situation w.r.t. ODSs and Arctic Amplification may not be as simple as many consensus climate scientists are hoping.  For instance, it is believed that the current Arctic ozone hole due to a cooling down in the stratosphere above the Arctic, thus:

1. One theory for this stratospheric cooling is that as the temperature of the sea in the North Pacific warms up, this has the effect of creating a cooling in the stratosphere in the Arctic.  If this is so, then continued warming of the North Pacific SST would likely contribute to more frequent Arctic ozone holes in the future.

2. Another theory is that when the ozone depletes this actually promotes cooling in the upper atmosphere because the ozone absorbs a lot of sunlight, so the less ozone the more cooling down.  If so, this would also imply that Arctic ozone holes may become more frequent in the future.

3. The Trump Administration has recently rescinded US regulations requiring monitoring and reporting of ODS leaks from a large class of refrigeration units.  If other countries use the COVID-19 crisis to temporarily suspend efforts to control ODS leaks then Arctic Amplification might actually accelerate in the near future.

Polvani, L.M., Previdi, M., England, M.R. et al. Substantial twentieth-century Arctic warming caused by ozone-depleting substances. Nat. Clim. Chang. 10, 130–133 (2020). https://doi.org/10.1038/s41558-019-0677-4

https://www.nature.com/articles/s41558-019-0677-4

Abstract
The rapid warming of the Arctic, perhaps the most striking evidence of climate change, is believed to have arisen from increases in atmospheric concentrations of GHGs since the Industrial Revolution. While the dominant role of carbon dioxide is undisputed, another important set of anthropogenic GHGs was also being emitted over the second half of the twentieth century: ozone-depleting substances (ODS). These compounds, in addition to causing the ozone hole over Antarctica, have long been recognized as powerful GHGs. However, their contribution to Arctic warming has not been quantified. We do so here by analysing ensembles of climate model integrations specifically designed for this purpose, spanning the period 1955–2005 when atmospheric concentrations of ODS increased rapidly. We show that, when ODS are kept fixed, forced Arctic surface warming and forced sea-ice loss are only half as large as when ODS are allowed to increase. We also demonstrate that the large impact of ODS on the Arctic occurs primarily via direct radiative warming, not via ozone depletion. Our findings reveal a substantial contribution of ODS to recent Arctic warming, and highlight the importance of the Montreal Protocol as a major climate change-mitigation treaty.

See also:

Title: "The unexpected link between the ozone hole and Arctic warming"

https://theconversation.com/the-unexpected-link-between-the-ozone-hole-and-arctic-warming-130438

Extract: "But why has the Arctic warmed more than the tropics and the mid-latitudes?

We now know that this is due, in part, to tiny concentrations of very powerful greenhouse gases — ozone-depleting substances such as chlorofluorocarbons (CFCs).
…
To explore the contribution of ozone-depleting substances to late-20th century warming, we ran a climate model over the period from 1955 to 2005. One of the simulations incorporated all of the various historical climate drivers — those that warm the climate, like carbon dioxide, methane, nitrous oxide and ozone-depleting substances, and those that cool the climate, like volcanic particulate matter. The second simulation had all the historical climate drivers, except the ozone-depleting substances.
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Comparing the two model simulations revealed that global warming was reduced by one-third and Arctic warming by one-half when the ozone-depleting substances were not included in our simulation.
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Why do ozone-depleting substances have such a large impact despite their very small atmospheric concentrations? First, these chemicals are very potent greenhouse gases, a fact that we have known for a long time. Second, in the late-20th century, warming from carbon dioxide is partially cancelled out by the cooling that comes from particulate matter in the atmosphere, allowing CFCs and other ozone-depleting substances to contribute substantially to warming.

Finally, when it comes to Arctic amplification, we know that this phenomenon arises from feedbacks within the climate system that act to enhance warming, and this is exactly what we find in our model simulations. In the simulation without ozone-depleting substances, the climate feedbacks were weaker than in the simulation with them, resulting in less Arctic amplification."

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The linked reference cited findings from E3SM indicating that while current ice mass loss from Antarctic ice-shelf melting is relatively small compared to the volume of Southern Ocean CDW; nevertheless, the meltwater from Antarctic ice shelf mass loss is located close to regions of convention of the MOC and that the associated increase in sea-ice formation and strong density stratification near the Antarctic coast resulting in more upwelling of CDW (which I note could accelerate local ice mass loss) and an out-sized influence on MOC overturning in the Southern Ocean (which I note could slow the MOC resulting in an increase in Tropical Ocean SSTA).

Hyein Jeong, Xylar S. Asay-Davis, Adrian K. Turner, Darin S. Comeau, and Stephen F. Price (17 April 2020), "Impacts of ice-shelf melting on water mass transformation in the Southern Ocean from E3SM simulations", Journal of Climate, https://doi.org/10.1175/JCLI-D-19-0683.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0683.1?af=R

Abstract
The Southern Ocean overturning circulation is driven by winds, heat fluxes, and freshwater sources. Among these sources of freshwater, Antarctic sea-ice formation and melting play the dominant role. Even though ice-shelf melt is relatively small in magnitude, it is located close to regions of convection, where it may influence dense water formation. Here, we explore the impacts of ice-shelf melting on Southern Ocean water mass transformation (WMT) using simulations from the Energy Exascale Earth System Model (E3SM) both with and without the explicit representation of melt fluxes from beneath Antarctic ice shelves. We find that ice-shelf melting enhances transformation of Upper Circumpolar Deep Water (UCDW), converting it to lower density values. While the overall differences in Southern Ocean WMT between the two simulations are moderate, freshwater fluxes produced by ice-shelf melting have a further, indirect impact on the Southern Ocean overturning circulation through their interaction with sea-ice formation and melting, which also cause considerable upwelling. We further find that surface freshening and cooling by ice-shelf melting causes increased Antarctic sea-ice production and stronger density stratification near the Antarctic coast. In addition, ice-shelf melting causes decreasing air temperature, which may be directly related to sea-ice expansion. The increased stratification reduces vertical heat transport from the deeper ocean. Although the addition of ice-shelf melting processes leads to no significant changes in Southern Ocean WMT, the simulations and analysis conducted here point to a relationship between increased Antarctic ice-shelf melting and the increased role of sea ice in Southern Ocean overturning.

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Many consensus climate scientists indicate that they believe that anthropogenic radiative forcing impacts on the oceans occur only on the scale of centuries to millennia; however, the linked reference indicates that anthropogenic influences in the industrial era have resulted in abrupt (primarily in the late 20th century) and unprecedented warming of the water in the Icelandic Basin, due to changes in the North Atlantic subpolar gyre (SPG).  Thus I am concerned that an abrupt freshwater hosing event into the North Atlantic (such as from the Beaufort Gyre and/or from the GIS) could trigger the SPG to push relatively warm subtropical ocean water still further into higher latitudes where it would likely have negative impacts on Arctic sea ice area and possibly on Arctic Ocean methane hydrates:

Peter T. Spooner et al. (17 April 2020), Exceptional 20th century ocean circulation in the Northeast Atlantic", Geophysical Research Letters, https://doi.org/10.1029/2020GL087577

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL087577?af=R

Abstract
The North Atlantic subpolar gyre (SPG) connects tropical and high latitude waters, playing a leading role in deep‐water formation, propagation of Atlantic water into the Arctic, and as habitat for many ecosystems. Instrumental records spanning recent decades document significant decadal variability in SPG circulation, with associated hydrographic and ecological changes. Emerging longer‐term records provide circumstantial evidence that the North Atlantic also experienced centennial trends during the 20th century. Here, we use marine sediment records to show that there has been a long‐term change in SPG circulation during the industrial era, largely during the 20th century. Moreover, we show that the shift and late 20th century SPG configuration were unprecedented in the last 10,000 years. Recent SPG dynamics resulted in an expansion of subtropical ecosystems into new habitats and likely also altered the transport of heat to high latitudes.

Plain Language Summary
The Northeast Atlantic is of crucial importance for the global climate system and marine ecosystems. We can use sediment from the bottom of the ocean to reconstruct how the Northeast Atlantic has changed over thousands of years. In this study we present the first evidence that 20th century Northeast Atlantic surface ocean circulation was unusual compared to the last 10,000 years. This change caused a replacement of cool, subpolar waters with warmer subtropical waters near Iceland, and has impacted the distribution of marine organisms. The most striking aspect of our work is the exceptional nature of the shift in the 20th century (in contrast to thousands of years of relative stability), with implications for understanding future change.

Key Points
•   Ocean sediments suggest that the Iceland Basin warmed during the industrial era
•   Basin‐wide sub‐polar gyre circulation change contributed to warming during this period
•   Late 20th century subpolar gyre state unprecedented in the last 10,000 years

[AbruptSLR]

I provide the link to the cited reference not because ice sheet models are currently accurate enough to make valid ice mass loss projections (as they are not), but rather because the linked research represents an improvement on prior consensus ice sheet model projections, and it helps to identify the importance of model initialization procedures and assumptions.  Also, I note that the ice shelves in the ASE are currently in much worse condition than assumed by this reference.

Alevropoulos-Borrill, A. V., Nias, I. J., Payne, A. J., Golledge, N. R., and Bingham, R. J.: Ocean-forced evolution of the Amundsen Sea catchment, West Antarctica, by 2100, The Cryosphere, 14, 1245–1258, https://doi.org/10.5194/tc-14-1245-2020, 2020.

https://www.the-cryosphere.net/14/1245/2020/

Abstract
The response of ice streams in the Amundsen Sea Embayment (ASE) to future climate forcing is highly uncertain. Here we present projections of 21st century response of ASE ice streams to modelled local ocean temperature change using a subset of Coupled Model Intercomparison Project (CMIP5) simulations. We use the BISICLES adaptive mesh refinement (AMR) ice sheet model, with high-resolution grounding line resolving capabilities, to explore grounding line migration in response to projected sub-ice-shelf basal melting. We find a contribution to sea level rise of between 2.0 and 4.5 cm by 2100 under RCP8.5 conditions from the CMIP5 subset, where the mass loss response is linearly related to the mean ocean temperature anomaly. To account for uncertainty associated with model initialization, we perform three further sets of CMIP5-forced experiments using different parameterizations that explore perturbations to the prescription of initial basal melt, the basal traction coefficient and the ice stiffening factor. We find that the response of the ASE to ocean temperature forcing is highly dependent on the parameter fields obtained in the initialization procedure, where the sensitivity of the ASE ice streams to the sub-ice-shelf melt forcing is dependent on the choice of parameter set. Accounting for ice sheet model parameter uncertainty results in a projected range in sea level equivalent contribution from the ASE of between −0.02 and 12.1 cm by the end of the 21st century.

[AbruptSLR]

If the linked reference's finding that part of the E3SM version 1 projected high value of TCR is due to a projected slowing of the AMOC; then this may well be because E3SM version 1 did a better job of evaluating the influence of freshwater hosing from glacier meltwater; then this implies that ice-climate feedbacks may likely have a much higher impact on increasing climate sensitivity than consensus climate science is currently acknowledging.

Aixue Hu et al. (17 April 2020), "Role of AMOC in transient climate response to greenhouse gas forcing in two coupled models", Journal of Climate, https://doi.org/10.1175/JCLI-D-19-1027.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-1027.1?af=R

Abstract
As the greenhouse gas concentrations increase, a warmer climate is expected. However, numerous internal climate processes can modulate the primary radiative warming response of the climate system to rising greenhouse gas forcing. Here the particular internal climate process that we focus on is the Atlantic Meridional Overturning Circulation (AMOC) – an important global scale feature of ocean circulation that serves to transport heat and other scalars, and we address the question of how the mean strength of AMOC can modulate the transient climate response. While the Community Earth System Model version 2 (CESM2) and the Energy Exascale Earth System Model version 1 (E3SM1) have very similar equilibrium/effective climate sensitivity, our analysis suggests that a weaker AMOC contributes in part to the higher transient climate response to a rising greenhouse gas forcing seen in E3SM1 by permitting a faster warming of the upper ocean and a concomitant slower warming of the subsurface ocean. Likewise the stronger AMOC in CESM2 by permitting a slower warming of the upper ocean leads in part to a smaller transient climate response. Thus, while the mean strength of AMOC does not affect the equilibrium/effective climate sensitivity, it is likely to play an important role in determining the transient climate response on the centennial timescale.

[AbruptSLR]

While the linked reference presents high-quality scientific findings, it is sad to me to read about how much methane is being emitted from the Permian Basin in Texas.

Yuzhong Zhang et al. (22 Apr 2020), "Quantifying methane emissions from the largest oil-producing basin in the United States from space", Science Advances, Vol. 6, no. 17, eaaz5120, DOI: 10.1126/sciadv.aaz5120

https://advances.sciencemag.org/content/6/17/eaaz5120

Abstract
Using new satellite observations and atmospheric inverse modeling, we report methane emissions from the Permian Basin, which is among the world’s most prolific oil-producing regions and accounts for >30% of total U.S. oil production. Based on satellite measurements from May 2018 to March 2019, Permian methane emissions from oil and natural gas production are estimated to be 2.7 ± 0.5 Tg a−1, representing the largest methane flux ever reported from a U.S. oil/gas-producing region and are more than two times higher than bottom-up inventory-based estimates. This magnitude of emissions is 3.7% of the gross gas extracted in the Permian, i.e., ~60% higher than the national average leakage rate. The high methane leakage rate is likely contributed by extensive venting and flaring, resulting from insufficient infrastructure to process and transport natural gas. This work demonstrates a high-resolution satellite data–based atmospheric inversion framework, providing a robust top-down analytical tool for quantifying and evaluating subregional methane emissions.

[AbruptSLR]

The linked reference (and associated article) indicate that the US oil & gas industry's emissions of methane were 15% higher than previously assumed between 2014 and 2018 (and it may be more considering the emissions from the Permian formation in Texas discussed in my previous post).

Anthony R. Ingraffea, Paul A. Wawrzynek, Renee Santoro and Martin Wells (April 9, 2020), " Reported Methane Emissions from Active Oil and Gas Wells in Pennsylvania, 2014–2018", Environ. Sci. Technol., https://doi.org/10.1021/acs.est.0c00863

https://pubs.acs.org/doi/abs/10.1021/acs.est.0c00863

Abstract
Oil/gas well integrity failures are a common but poorly constrained source of methane emissions to the atmosphere. As of 2014, Pennsylvania requires gas and oil well operators to report gas losses, both fugitive and process, from all active and unplugged abandoned gas and oil wells. We analyze 589,175 operator reports and find that lower-bound reported annual methane emissions averaged 22.1 Gg (−16.9, +19.5) between 2014 and 2018 from 62,483 wells, an average of only 47% of the statewide well inventory for those years. Extrapolating to the 2019 oil and gas well inventory yields well average emissions of 55.6 Gg CH4. These emissions are not currently included in the state’s oil and gas emission inventory. We also assess compliance in reporting among operators and note anomalies in reporting and apparent workarounds to reduce reported emissions. Suggestions for improving the accuracy and reliability in reporting and reducing emissions are offered.

See also:

Title: "Oil and gas methane emissions in US are at least 15% higher than we thought"

https://www.dailyclimate.org/fracking-methane-leaks-2645817522.html

Extract: "The new study, conducted by researchers at Cornell University and published in the journal Environmental Science and Technology, looked at 589,175 operator reports on methane leaks from both fracking and conventional oil and gas wells in Pennsylvania from 2014-2018. The researchers found that methane emissions in the state are at least 15 percent higher than previously thought—and they believe a similar under-counting is happening at the national level.

"Another 15 percent of methane going into the atmosphere that we didn't know about is very significant for climate change in the short term," Tony Ingraffea, professor emeritus of engineering at Cornell and the study's lead author, told EHN."

[AbruptSLR]

The linked preprint of a PNAS reference emphasizes that model differences in tropical cloud feedbacks is a source of uncertainty in current projections of regional climate change.  This represents a climate risk w.r.t. potential freshwater hosing events that might slow the MOC and consequently impact tropical cloud cover.

Cristian Proistosescu, David S. Battisti, Kyle Armour and Gerard H. Roe (2020), "Equilibrium climate sensitivity controls uncertainty in regional climate change over the 21st century" Preprint from PNAS.

https://eartharxiv.org/v7ndp/

Abstract: "Improved projections of local temperature change over the 21st century are essential for evaluating impacts and setting policy targets.  Uncertainty in these projections is due to two approximately equal factors: uncertainty in greenhouse gas emissions, and uncertainty in the response of climate to those emissions. For the latter, it is well known that climate models all have a similar global pattern of warming.  Here, we show that differences among projections of warming also share a common pattern of variability.  Specifically, the leading empirical orthogonal function (EOF) of inter-model differences strongly resembles the ensemble-mean response itself.  This pattern explains 60% of the total variance in projected regional warming, with higher fractions of variance explained over tropics and mid-latitudes.  When projected onto the model residuals, it is strongly correlated (r² = 0.9) with Equilibrium Climate Sensitivity (ECS), and more-weakly correlated with the Transient Climate Response (TCR, r² = 0.6). We show how this strong correlation between equilibrium global warming and transient regional warming uncertainty arises due to the large scales over which the atmosphere mixes energetic perturbations.  The dominant source of variance in both ECS and 21st-century warming are low-latitude feedbacks, whereas TCR is more sensitive to uncertainties in CO₂ radiative forcing and ocean heat uptake.  The results imply that throughout the tropics and mid-latitudes, and especially over land, most of the uncertainty in local temperature projections is due to model differences in tropical cloud feedbacks."

[AbruptSLR]

The linked 2018 article cites plenty of evidence that the MOC is currently slowing down (which is an indication of both high TCR and high ECS):

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

http://www.realclimate.org/index.php/archives/2018/05/if-you-doubt-that-the-amoc-has-weakened-read-this/comment-page-2/

Extract: "So, while there is obviously the need to understand the ocean circulation changes in the North Atlantic in more detail, I personally have no more doubts that the conspicuous ‘cold blob’ in the subpolar Atlantic is indeed due to a long-term decline of the northward heat transport by the AMOC."

[AbruptSLR]

The linked article discusses evidence that the Amazon rainforest will be prone to an increased number of wildfires in 2020:

Title: "Satellite data show Amazon rainforest likely drier, more fire-prone this year"

https://news.mongabay.com/2020/04/satellite-data-show-amazon-rainforest-likely-drier-more-fire-prone-this-year/

Extract:
•   "Satellite data show regions of the Amazon with severe negative changes in soil moisture and groundwater, meaning this year will likely be drier than 2019.
•   While a severe drought is unlikely, a drier year may increase the spread of wildfires and trigger an earlier spike in deforestation rates, experts say.
•   Although weather forecasts for the Amazon are highly unpredictable, which could potentially reverse the current deficit, climate models by Brazil’s Center for Weather Forecasting and Climate Research (CPTEC) show no indication of above-average precipitation in the coming months.
•   A technical report by the Amazon Environmental Research Institute (IPAM) published this week anticipates a surge in fires caused by the deforestation spike of 2019, as the modus operandi of land grabbers is to deforest one year then set fire the next, in order to successfully transform forest into farmland and pastures."

[AbruptSLR]

One probable explanation to the 'Fermi Paradox' is that: "…  climate change induced by "energy intensive" civilizations may prevent sustainability within such civilizations, thus explaining the paradoxical lack of evidence for intelligent extraterrestrial life."

Title: "Fermi paradox"

https://en.wikipedia.org/wiki/Fermi_paradox

Extract: "The Fermi paradox, named after Italian-American physicist Enrico Fermi, is the apparent contradiction between the lack of evidence for extraterrestrial civilizations and various high estimates for their probability (such as some optimistic estimates for the Drake equation).
…
There have been many attempts to explain the Fermi paradox, primarily suggesting that intelligent extraterrestrial beings are extremely rare, that the lifetime of such civilizations is short, or that they exist but (for various reasons) we see no evidence.
…
Using extinct civilizations such as Easter Island (Rapa Nui) as models, a study conducted in 2018 posited that climate change induced by "energy intensive" civilizations may prevent sustainability within such civilizations, thus explaining the paradoxical lack of evidence for intelligent extraterrestrial life."

See also:

Title: "Drake equation"

https://en.wikipedia.org/wiki/Drake_equation

Extract: "The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.
…
Lifetime of such a civilization wherein it communicates its signals into space, L
…
The astronomer Carl Sagan speculated that all of the terms, except for the lifetime of a civilization, are relatively high and the determining factor in whether there are large or small numbers of civilizations in the universe is the civilization lifetime, or in other words, the ability of technological civilizations to avoid self-destruction. In Sagan's case, the Drake equation was a strong motivating factor for his interest in environmental issues and his efforts to warn against the dangers of nuclear warfare.
…
Fermi paradox
The pessimists' most telling argument in the SETI debate stems not from theory or conjecture but from an actual observation: the presumed lack of extraterrestrial contact. A civilization lasting for tens of millions of years might be able to travel anywhere in the galaxy, even at the slow speeds foreseeable with our own kind of technology. Furthermore, no confirmed signs of intelligence elsewhere have been recognized as such, either in our galaxy or in the observable universe of 2 trillion galaxies.  According to this line of thinking, the tendency to fill up all available territory seems to be a universal trait of living things, so the Earth should have already been colonized, or at least visited, but no evidence of this exists. Hence Fermi's question "Where is everybody?".
A large number of explanations have been proposed to explain this lack of contact; a book published in 2015 elaborated on 75 different explanations. In terms of the Drake Equation, the explanations can be divided into three classes:

•   …
•   The lifetime of intelligent, communicative civilizations is short, meaning the value of L is small. Drake suggested that a large number of extraterrestrial civilizations would form, and he further speculated that the lack of evidence of such civilizations may be because technological civilizations tend to disappear rather quickly. Typical explanations include it is the nature of intelligent life to destroy itself, it is the nature of intelligent life to destroy others, they tend to be destroyed by natural events, and others.

These lines of reasoning lead to the Great Filter hypothesis, which states that since there are no observed extraterrestrial civilizations, despite the vast number of stars, then some step in the process must be acting as a filter to reduce the final value. According to this view, either it is very difficult for intelligent life to arise, or the lifetime of such civilizations, or the period of time they reveal their existence, must be relatively short."

[blumenkraft]

Well, i could spontaneously come up with 10 or more answers to the Fermi Paradox, but climate change wasn't one of them until now. Added to the list! Thanks, AbruptSLR.

[AbruptSLR]

Well, i could spontaneously come up with 10 or more answers to the Fermi Paradox, but climate change wasn't one of them until now. Added to the list! Thanks, AbruptSLR.

The linked 2019 article published in the Bulletin of the Atomic Scientists discusses the Fermi Paradox and concludes by asking the question of whether mankind will rise-up to meet the multiple changes currently facing it (including climate change), or whether it will wind-up being "… just another flash in the cosmic pan?"

Title: "Did climate change destroy the aliens?"

https://thebulletin.org/2019/07/did-climate-change-destroy-the-aliens/

Extract: "There are many conceivable answers to the Fermi Paradox.
…
Self-inflicted climate change has frequently been identified as a possible Great Filter. According to this theory, any intelligent lifeform will consume vast amounts of energy as it develops technologies. Since harnessing energy always results in some kind of pollution, the planet’s ecosystem will eventually be degraded to the point where it imperils the polluting species.
…
Our universe might generously allow for the possibility of life, yet ruthlessly cull it as soon as it emerges—again, and again, and again. There is no single Great Filter, just the merciless statistical odds against long-term survival.

The human species is presently faced with several possible survival filters. Some, such as asteroid impacts, arise randomly; others are self-inflicted, such as nuclear weapons, anthropogenic climate change and, perhaps quite soon, runaway artificial intelligence.
…
We know that human beings have the capacity for intelligent foresight and large-scale cooperation. It cannot be pure luck that our species has survived as long as it has.

But now, we need to raise our game. Are we an exceptional species, or just another flash in the cosmic pan?"

[nanning]

If the 'aliens' were smarter than us and didn't pursue the high technology & growth (con)quest, they may all be living happily and sustainably but we'll never hear from them.

[kassy]

A puzzling past sea level rise might have its missing piece

About 14,650 years ago, sea level jumped 12 meters in just a few centuries.

...

 About 14,650 years ago, as the thawing of the last ice began to hit its stride, sea level made a remarkable jump of 12 meters or more—and did so in less than 400 years. It's an event known to scientists as Meltwater Pulse 1A.

Figuring out where all that water came from hasn’t been easy. ... , but models of past ice sheet change haven’t quite added up.

A new study led by Jo Brendryen at the University of Bergen takes an interesting route to discover that the melting of the Eurasian Ice Sheet, which has largely been overlooked, might just explain things.

...

Back to the ice sheets. During the last glacial period, an ice sheet once stretched across Scandinavia and the Barents Sea. The record of its shrinking is based on carbon dating of seafloor sediment cores, pinpointing times that ice retreated and life returned to a location. The reconstructions have indicated that the ice here had basically melted before the start of Meltwater Pulse 1A, giving it a clear alibi. But the carbon-dated ages assumed that the deep ocean carbon-14 delay in that region was constant over time, matching the modern pattern.

In this new study, the researchers looked carefully at that assumption. They turned to a seemingly unlikely source—a cave in China. There is actually a pretty good correlation between ocean circulation, the temperatures in the North Atlantic, and the Asian Monsoon rains, linked by a series of climatic dominoes. Cave records have excellent timelines, with annual layers and uranium radiometric dating.

By lining up the wiggles in the cave record and Norwegian Sea sediment records, the researchers avoid having to guess the unknown deep ocean carbon-14 delay. Instead, they can calculate that delay and its changes, providing a new calibration for seafloor paleoclimate records in this region.

With that done, the reconstructed timing of Eurasian Ice Sheet melt shifts. Rather than showing that the local ice melted before Meltwater Pulse 1A even started, they see a major loss of ice during this event. Previous reconstructions gave the Eurasian Ice Sheet credit for perhaps one meter of the 12 or more meters of sea level rise that occurred then. This study pushes that contribution up to about five meters—plus another meter or so in the century following.

There are obvious challenges to working out which giant block of ice melted thousands of years ago. But there are valuable clues. When an ice sheet melts, sea level rise doesn’t rise equally all around the world. The gravitational attraction of a massive ice sheet actually pulls seawater to it, raising sea levels near the sheet a bit. As the ice sheet shrinks, its gravitational pull relaxes, so sea level can actually fall right next to the ice sheet, even as it rises elsewhere. And the records of sea level change in various places are actually consistent with the Eurasian Ice Sheet being a big source: sites around Norway and Finland show a drop in sea level during this period of high-speed global sea level rise.

Re-aligning the Eurasian Ice Sheet history would make it significantly easier to understand where 12 meters of sea level came from, but it also raises some interesting questions. For example, such a massive flow of freshwater into the Norwegian Sea could be expected to gum up the critically important south-to-north conveyor belt current in the Atlantic Ocean, but records indicate it was actually quite strong during this time.  And how, exactly, did this portion of the Eurasian Ice Sheet collapse so quickly?

That question about the past is of interest to our future. The portion of the Eurasian Ice Sheet in question straddled topographic lows in contact with the ocean, making it vulnerable to rapid collapse. The same is true of the West Antarctic Ice Sheet today—the biggest wildcard for future sea level rise. Every ice sheet is different and the local details matter, but an equally rapid collapse of ice in Antarctica would be a worst-case scenario.

Nature Geoscience, 2020. DOI: 10.1038/s41561-020-0567-4 (About DOIs).

https://arstechnica.com/science/2020/04/a-puzzling-past-sea-level-rise-might-have-its-missing-piece/

[AbruptSLR]

The linked reference looks a meridional heat transport due to a quadrupling of CO2 in a model of the LGM and they found that the poleward atmospheric heat transport (AHT) component dominated the ocean heat transport (OHT) both associated with changes in the meridional overturning circulation (MOC).  As AHT heat transport occurs more rapidly than does OHT transport; this raises the prospect that GMSTA in our current situation may increase faster than previously expected due to poleward increases in AHT associated with freshwater hosing induced slowing of the MOC:

Aaron Donohoe et al. (2020), "The Partitioning of Meridional Heat Transport from the Last Glacial Maximum to CO2 Quadrupling in Coupled Climate Models", Journal of Climate, https://doi.org/10.1175/JCLI-D-19-0797.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0797.1

Abstract
Meridional heat transport (MHT) is analyzed in ensembles of coupled climate models simulating climate states ranging from the Last Glacial Maximum (LGM) to quadrupled CO2. MHT is partitioned here into atmospheric (AHT) and implied oceanic (OHT) heat transports. In turn, AHT is partitioned into dry and moist energy transport by the meridional overturning circulation (MOC), transient eddy energy transport (TE), and stationary eddy energy transport (SE) using only monthly averaged model output that is typically archived. In all climate models examined, the maximum total MHT (AHT + OHT) is nearly climate-state invariant, except for a modest (4%, 0.3 PW) enhancement of MHT in the Northern Hemisphere (NH) during the LGM. However, the partitioning of MHT depends markedly on the climate state, and the changes in partitioning differ considerably among different climate models. In response to CO2 quadrupling, poleward implied OHT decreases, while AHT increases by a nearly compensating amount. The increase in annual-mean AHT is a smooth function of latitude but is due to a spatially inhomogeneous blend of changes in SE and TE that vary by season. During the LGM, the increase in wintertime SE transport in the NH midlatitudes exceeds the decrease in TE resulting in enhanced total AHT. Total AHT changes in the Southern Hemisphere (SH) are not significant. These results suggest that the net top-of-atmosphere radiative constraints on total MHT are relatively invariant to climate forcing due to nearly compensating changes in absorbed solar radiation and outgoing longwave radiation. However, the partitioning of MHT depends on detailed regional and seasonal factors.

[AbruptSLR]

The findings (subject to verification) of the linked reference suggest that the local increases in surface air temperature above Arctic sea ice has contributed significantly to Arctic Amplification:

Allison B. Marquardt (2020), "Recent Arctic Ocean Surface Air Temperatures in Atmospheric Reanalyses and Numerical Simulations", Journal of Climate, https://doi.org/10.1175/JCLI-D-19-0703.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0703.1

Abstract
Surface air temperatures have recently increased more rapidly in the Arctic than elsewhere in the world, but large uncertainty remains in the time series and trend. Over the data-sparse sea ice zone, the retrospective assimilation of observations in numerical reanalyses has been thought to offer a possible, but challenging, avenue for adequately reproducing the historical time series. Focusing on the central Arctic Ocean, output is analyzed from 12 reanalyses with a specific consideration of two widely used products: the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), and the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim, hereafter ERA-I). Among the reanalyses considered, a trend of 0.9 K decade−1 is indicated but with an uncertainty of 6%, and a large spread in mean values. There is a partitioning among those reanalyses that use fractional sea ice cover and those that employ a threshold, which are colder in winter by an average of 2 K but agree more closely with in situ observations. For reanalyses using fractional sea ice cover, discrepancies in the ice fraction in autumn and winter explain most of the differences in air temperature values. A set of experiments using the MERRA-2 background model using MERRA-2 and ERA-I sea ice and sea surface temperature indicates significant effects of boundary condition differences on air temperatures, and a preferential warm bias inherent in the MERRA-2 model sea ice representation. Differences between experiments and reanalyses suggest the available observations apply a significant constraint on reanalysis mean temperatures.

[P-maker]

Kassy,

that was about time the giny got out of the bottle. I always had a hint that a major part of the 12 meter sea level rise could have come from a catstrophic emptying of the Baltic Ice Lake. Most of this fresh water could have made it's way to the Barents Sea - giving rise to the remote signals observed in Chinese caves.

[AbruptSLR]

Kassy,

that was about time the giny got out of the bottle. I always had a hint that a major part of the 12 meter sea level rise could have come from a catstrophic emptying of the Baltic Ice Lake. Most of this fresh water could have made it's way to the Barents Sea - giving rise to the remote signals observed in Chinese caves.

While the emptying of the Baltic Ice Lake may have made a contribution, it certainly could not have contributed 5m of SLR over the cited 400-year period.  Therefore, I remind readers of the first linked reference (& images) from Andreassen et al. (2017) indicates that the Barents Sea Ice Sheet was largely a marine glacier and thus subject to a MICI-type of failure and that the associated rapid glacier collapse could account for the massive blow-craters formed by hydrate-controlled methane expulsions from the Arctic seafloor.

K. Andreassen, A. Hubbard, M. Winsborrow, H. Patton, S. Vadakkepuliyambatta, A. Plaza-Faverola, E. Gudlaugsson, P. Serov, A. Deryabin, R. Mattingsdal, J. Mienert & S. Bünz (02 Jun 2017), "Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor", Science, Vol. 356, Issue 6341, pp. 948-953

DOI: 10.1126/science.aal4500

Furthermore, the second linked reference Deschamps et al. (2012) reminds us that during this same 400-year (MWP-1A) period findings from Tahiti indicate that a significant portion of the 12m SLR during this period was contributed by the Southern Hemisphere, possibly by marine glaciers on the current Antarctic continental shelf that might have be triggered by a bipolar seesaw effect from the collapse of the Barents Sea Ice Sheet.

Deschamps, P. et al. (2012), "Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago", Nature 483, 559–564, doi: 10.1038/nature10902

https://www.nature.com/articles/nature10902

Abstract: "Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the Bølling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A."

[AbruptSLR]

The linked reference finds that because both the means and variability of future (this century) Arctic precipitation will increase, particularly summer seasons with excessive precipitation will occur more often.  When one considers that in coming decades such excessive summertime precipitation will general take the form of rainfall in such places as Siberia, Alaska, Northern Canada and Greenland; it is clear that this means that not only will there be for ice mass loss into the oceans but also less coastal sea ice and more permafrost degradation due to the increased future rainfall.

R. Bintanja et al. (12 Feb 2020), "Strong future increases in Arctic precipitation variability linked to poleward moisture transport", Science Advances, Vol. 6, no. 7, eaax6869, DOI: 10.1126/sciadv.aax6869

https://advances.sciencemag.org/content/6/7/eaax6869

Abstract
The Arctic region is projected to experience amplified warming as well as strongly increasing precipitation rates. Equally important to trends in the mean climate are changes in interannual variability, but changes in precipitation fluctuations are highly uncertain and the associated processes are unknown. Here, we use various state-of-the-art global climate model simulations to show that interannual variability of Arctic precipitation will likely increase markedly (up to 40% over the 21st century), especially in summer. This can be attributed to increased poleward atmospheric moisture transport variability associated with enhanced moisture content, possibly modulated by atmospheric dynamics. Because both the means and variability of Arctic precipitation will increase, years/seasons with excessive precipitation will occur more often, as will the associated impacts.

[AbruptSLR]

The linked article discusses research published in 'The Cryosphere' that indicates that current consensus climate models may be missing about half of the likely future ice melting from Greenland in the coming decades.  If/when this additional ice mass loss into the North Atlantic combines with the eventual freshwater hosing event from the Beaufort Gyre the MOC will likely slow down abruptly and TCR will increase abruptly.

Title: "Climate models ‘missing half of the melting’ in Greenland ice"

https://www.sciencefocus.com/news/climate-models-missing-half-of-the-melting-in-greenland-ice/

Extract: "Climate models may be vastly underestimating how much ice will melt in Greenland in the future, a group of scientists believe.

Their analysis is based on the record loss of Greenland ice in 2019, which researchers believe was caused not just by warm temperatures but also unusual atmospheric conditions that led to clear skies in the summer."

According to Dr Marco Tedesco, from Columbia University’s Lamont-Doherty Earth Observatory, current global climate models are not able to capture the effects of a “wavier jet stream” – a phenomenon that can lead to extreme weather conditions."

[AbruptSLR]

I do not believe that the linked reference considers the increasingly frequent clear sky effect (due to more frequent high-pressure systems over Greenland) discussed in my last post; nevertheless, it finds that much of the future projected ice mass loss from the GIS will be irreversible:

Gregory, J. M., George, S. E., and Smith, R. S.: Large and irreversible future decline of the Greenland ice-sheet, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-89, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2020-89/

Abstract. We have studied the evolution of the Greenland ice-sheet under a range of constant climates typical of those projected for the end of the present century, using a dynamical ice-sheet model (Glimmer) coupled to an atmospheric general circulation model (FAMOUS-ice AGCM). The ice-sheet surface mass balance (SMB) is simulated by the AGCM, including its dependence on altitude within AGCM gridboxes. Over millennia under a warmer climate, the ice-sheet reaches a new steady state, whose mass is correlated with the initial perturbation in SMB, and hence with the magnitude of global climate change imposed. For the largest global warming considered (about +5 K), the contribution to global-mean sea-level rise (GMSLR) is initially 2.7 mm yr−1, and the ice-sheet is eventually practically eliminated (giving over 7 m of GMSLR). For all RCP8.5 climates, final GMSLR exceeds 4 m. If recent climate were maintained, GMSLR would reach 1.5–2.5 m. Contrary to expectation from earlier work, we find no evidence for a threshold warming that divides scenarios in which the ice-sheet suffers little reduction from those which it is mostly lost. This is because the dominant effect is reduction of area, not reduction of surface altitude, and the geographical variation of SMB must be taken into account. The final steady state is achieved by withdrawal from the coast in some places, and a tendency for increasing SMB due to enhancement of cloudiness and snowfall over the remaining ice-sheet, through the effects of topographic change on atmospheric circulation. If late twentieth-century climate is restored, the ice-sheet will not regrow to its present extent, owing to such effects, once its mass has fallen below a threshold of about 4 m of sea-level equivalent. In that case, about 2 m of GMSLR would become irreversible. In order to avoid this outcome, anthropogenic climate change must be reversed before the ice-sheet has declined to the threshold mass, which would be reached in about 600 years at the highest rate of mass-loss within the likely range of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

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The linked reference confirms that as:

"The future long-term increase in Atlantic heat transport is carried by warmer water as the current itself is found to weaken."

Thus generally as the MOC slows the North Atlantic OHT will penetrate deeper into the Arctic Basin; subject to local ocean and atmospheric variability.

Marius Årthun et al (2019), "The Role of Atlantic Heat Transport in Future Arctic Winter Sea Ice Loss", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0750.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0750.1

Abstract
During recent decades Arctic sea ice variability and retreat during winter have largely been a result of variable ocean heat transport (OHT). Here we use the Community Earth System Model (CESM) large ensemble simulation to disentangle internally and externally forced winter Arctic sea ice variability, and to assess to what extent future winter sea ice variability and trends are driven by Atlantic heat transport. We find that OHT into the Barents Sea has been, and is at present, a major source of internal Arctic winter sea ice variability and predictability. In a warming world (RCP8.5), OHT remains a good predictor of winter sea ice variability, although the relation weakens as the sea ice retreats beyond the Barents Sea. Warm Atlantic water gradually spreads downstream from the Barents Sea and farther into the Arctic Ocean, leading to a reduced sea ice cover and substantial changes in sea ice thickness. The future long-term increase in Atlantic heat transport is carried by warmer water as the current itself is found to weaken. The externally forced weakening of the Atlantic inflow to the Barents Sea is in contrast to a strengthening of the Nordic Seas circulation, and is thus not directly related to a slowdown of the Atlantic meridional overturning circulation (AMOC). The weakened Barents Sea inflow rather results from regional atmospheric circulation trends acting to change the relative strength of Atlantic water pathways into the Arctic. Internal OHT variability is associated with both upstream ocean circulation changes, including AMOC, and large-scale atmospheric circulation anomalies reminiscent of the Arctic Oscillation.

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This is just a quick note to remind readers that most consensus climate science model projections are dominated by Frequentist Probability/Inference assumptions.  Unfortunately, climate change is so complex that there is no why to run sufficient trials/experiments of all of the various cascades of relevant feedback mechanisms and forcing combinations in order to ensure that these models are appropriately simulating our current climate risks.  Thus, as noted by the links below, mankind is acting like a gambler who is only estimating odds without appropriate trails/experiments:


Title: "Frequentist probability"

https://en.wikipedia.org/wiki/Frequentist_probability

Extract: "Frequentist probability or frequentism is an interpretation of probability; it defines an event's probability as the limit of its relative frequency in many trials. Probabilities can be found (in principle) by a repeatable objective process (and are thus ideally devoid of opinion). This interpretation supports the statistical needs of many experimental scientists and pollsters. It does not support all needs, however; gamblers typically require estimates of the odds without experiments."

&

Title: "Frequentist inference"

https://en.wikipedia.org/wiki/Frequentist_inference

Extract: "Frequentist inference is a type of statistical inference that draws conclusions from sample data by emphasizing the frequency or proportion of the data. An alternative name is frequentist statistics. This is the inference framework in which the well-established methodologies of statistical hypothesis testing and confidence intervals are based. Other than frequentistic inference, the main alternative approach to statistical inference is Bayesian inference, while another is fiducial inference."

[AbruptSLR]

The following is a repost of gerontocrat's post today in the Consequences folder:

"It ain't half hot, mum"

https://www.theguardian.com/environment/2020/apr/27/meteorologists-say-2020-on-course-to-be-hottest-year-since-records-began
Meteorologists say 2020 on course to be hottest year since records began

Quote
Heat records have been broken from the Antarctic to Greenland since January, which has surprised many scientists because this is not an El Niño year, the phenomenon usually associated with high temperatures.

The US National Oceanic and Atmospheric Administration calculates there is a 75% chance that 2020 will be the hottest year since measurements began. The US agency said trends were closely tracking the current record of 2016, when temperatures soared early in the year due to an unusually intense El Niño and then came down.

The US agency said there was a 99.9% likelihood that 2020 will be one of the top five years for temperatures on record.

A separate calculation by Gavin Schmidt, the director of the Nasa Goddard Institute for Space Studies in New York, found a 60% chance this year will set a record.

The Met Office is more cautious, estimating a 50% likelihood that 2020 will set a new record, though the UK institution says this year will extend the run of warm years since 2015, which is the hottest period on record."

[AbruptSLR]

Previously I have noted that as the Tropical Pacific Ocean warms it will telecommunicate (through the atmosphere) more heat to West Antarctica.  Now, I note that the linked reference indicates that as Arctic and Antarctic sea-ice is sharply reduced in coming decades, this will trigger a feedback loop that will warm the SSTA of the tropical oceans and particularly of the eastern equatorial Pacific by an average of 0.5C (by 2100).  This feedback loop is bad news and was not previously recognized by consensus climate science:

England, M.R., Polvani, L.M., Sun, L. et al. Tropical climate responses to projected Arctic and Antarctic sea-ice loss. Nat. Geosci. 13, 275–281 (2020). https://doi.org/10.1038/s41561-020-0546-9

https://www.nature.com/articles/s41561-020-0546-9

Abstract
Arctic and Antarctic sea-ice extent are both projected to dramatically decline over the coming century. The effects of Arctic sea-ice loss are not limited to the northern high latitudes, and reach deep into the tropics. Yet little is known about the effects of future Antarctic sea-ice loss outside of the southern high latitudes. Here, using a fully coupled climate model, we investigate the tropical response to Antarctic sea-ice loss and compare it with the response to Arctic sea-ice loss. We show that Antarctic sea-ice loss, similar to Arctic sea-ice loss, causes enhanced warming in the eastern equatorial Pacific and an equatorward intensification of the Intertropical Convergence Zone. We demonstrate that Antarctic sea-ice loss causes a mini global warming signal comparable to the one caused by Arctic sea-ice loss, and reminiscent of the response to greenhouse gases. We also show that ocean dynamics are key to capturing the tropical response to sea-ice loss. In short, we find that future Antarctic sea-ice loss will exert a profound influence on the tropics. Combined Arctic and Antarctic sea-ice losses will account for 20–30% of the projected tropical warming and precipitation changes under the high-emissions scenario Representative Concentration Pathway 8.5.

See also:

Title: "New research first to relate Antarctic sea ice melt to weather change in tropics"

https://www.sciencedaily.com/releases/2020/03/200316141508.htm

Extract: "The years 2017 and 2018 set records for minimum sea ice extent in Antarctica. England and colleagues from Columbia University's School of Engineering, Colorado State University, and the National Center for Atmospheric Research in Colorado used computer simulations to see what scenarios play out near the equator if that decline continues through the end of the century. They found that Antarctic sea ice loss combines with Arctic sea ice loss to create unusual wind patterns in the Pacific Ocean that will suppress the upward movement of deep cold ocean water. This will trigger surface ocean warming, especially in the eastern equatorial Pacific Ocean. Warming there is a well-known hallmark of the El Niño climate pattern that often brings intense rains to North and South America and droughts to Australia and other western Pacific countries.

As that surface ocean water warms, it will also create more precipitation. Overall, the researchers believe the ice loss at both poles will translate to a warming of the surface ocean of 0.5℃ (0.9℉) at the equator and add more than 0.3 millimeters (0.01 inches) of rain per day in the same region."

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The first linked Vol 37 of Advances in Atmospheric Sciences is a special issue on past, present and future Antarctic meteorology and climate and includes eleven papers such as the second linked paper by Ding et al (2020). Selected key findings include that the ASL is deepening which will likely force more warm-CDW into the ASE and that while the Antarctic sea ice extent has been relatively high since the 1970s for the past two years it has dropped sharply.  Also, for what it is worth, I remind readers that if snow fall increases at high elevations in West Antarctica this will increase gravitational forcing on key marine glaciers; which will cause ice velocities to increase for such glaciers as Thwaites and PIG (which will increase the rate of calving, which increases the chances of triggering a MICI-type WAIS collapse):

Special Issue: Antarctic Meteorology and Climate: Past, Present and Future", Advances in Atmospheric Sciences, Volume 37, Issue 5, May 2020

https://link.springer.com/journal/376/37/5

&

Ding, M., Han, W., Zhang, T. et al. Towards More Snow Days in Summer since 2001 at the Great Wall Station, Antarctic Peninsula: The Role of the Amundsen Sea Low. Adv. Atmos. Sci. 37, 494–504 (2020). https://doi.org/10.1007/s00376-019-9196-5

https://link.springer.com/article/10.1007/s00376-019-9196-5

Abstract
The variation in the precipitation phase in polar regions represents an important indicator of climate change and variability. We studied the precipitation phase at the Great Wall Station and Antarctic Peninsula (AP) region, based on daily precipitation, synoptic records and ERA-Interim data during the austral summers of 1985–2014. Overall, there was no trend in the total precipitation amount or days, but the phase of summer precipitation (rainfall days versus snowfall days) showed opposite trends before and after 2001 at the AP. The total summer rain days/snow days increased/decreased during 1985–2001 and significantly decreased at a rate of −14.13 d (10 yr)−1/increased at a rate of 14.31 d (10 yr)−1 during 2001–2014, agreeing well with corresponding variations in the surface air temperature. Further, we found that the longitudinal location of the Amundsen Sea low (ASL) should account for the change in the precipitation phase since 2001, as it has shown a westward drift after 2001 [−41.1° (10 yr)−1], leading to stronger cold southerly winds, colder water vapor flux, and more snow over the AP region during summertime. This study points out a supplementary factor for the climate variation on the AP.

See also:

Title: "Latest findings from expanded research on Antarctic meteorology and climate"

https://www.eurekalert.org/pub_releases/2020-04/ioap-lff041920.php

Extract: "Signs of climate change in the Antarctic, added Liu, include a strong warming over the Antarctic Peninsula, a deepening of the Amundsen Sea low, rapid warming of the upper ocean north of the circumpolar current, an increase of sea ice since the late 1970s followed by a recent rapid decrease and accelerated ice loss from ice shelf/sheet during the same period."

[AbruptSLR]

I have used bold typeface in the passages in the linked reference that the GIS and the WAIS are of particular importance in potentially initiating a cascade of climate tipping point elements; which are not considering in current ESM projections:

Wunderling, N., Donges, J. F., Kurths, J., and Winkelmann, R.: Interacting tipping elements increase risk of climate domino effects under global warming, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2020-18, in review, 2020.

https://www.earth-syst-dynam-discuss.net/esd-2020-18/

Abstract. There exists a range of subsystems in the climate system exhibiting threshold behaviour which could be triggered under global warming within this century resulting in severe consequences for biosphere and human societies. While their individual tipping thresholds are fairly well understood, it is of yet unclear how their interactions might impact the overall stability of the Earth's climate system. This cannot be studied yet with state-of-the-art Earth system models due to computational constraints as well as missing and uncertain process representations of some tipping elements.

Here, we explicitly study the effects of known physical interactions between the Greenland and West Antarctic Ice Sheet, the Atlantic Meridional Overturning Circulation, the El-Nino Southern Oscillation and the Amazon rainforest using a conceptual network approach. We analyse the risk of domino effects being triggered by each of the individual tipping elements under global warming in equilibrium experiments, propagating uncertainties in critical temperature thresholds and interaction strengths via a Monte-Carlo approach.

Overall, we find that the interactions tend to destabilise the network. Furthermore, our analysis reveals the qualitative role of each of the five tipping elements showing that the polar ice sheets on Greenland and West Antarctica are oftentimes the initiators of tipping cascades, while the AMOC acts as a mediator, transmitting cascades.

This implies that the ice sheets, which are already at risk of transgressing their temperature thresholds within the Paris range of 1.5 to 2 °C, are of particular importance for the stability of the climate system as a whole.

[interstitial]

Something to think about: Given limited time and much to read in a particular science field I find reading the conclusion to be far more important than the abstract. The abstract tells why the were interested and what they looked at. The conclusion on the other hand explains what they found. Science journals distribute abstracts freely but conclusions are behind a paywall. Just a thought.

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While the following is a repost, here I add a long hyperlink to the whole paper (at the end of this post) for those who want to read the conclusions for themselves:

The linked reference presents research that the world's tropical rainforests have already reached their saturation point for their net ability to absorb CO2, and that currently their net uptake is declining.  Unfortunately, current ESM projections do not consider this behavior which amounts to a net positive feedback for more global warming:

Hubau, W., Lewis, S.L., Phillips, O.L. et al. Asynchronous carbon sink saturation in African and Amazonian tropical forests. Nature 579, 80–87 (2020). https://doi.org/10.1038/s41586-020-2035-0

https://www.nature.com/articles/s41586-020-2035-0

Abstract
Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions. Climate-driven vegetation models typically predict that this tropical forest ‘carbon sink’ will continue for decades. Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53–0.79), in contrast to the long-term decline in Amazonian forests. Therefore the carbon sink responses of Earth’s two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature. Despite the past stability of the African carbon sink, our most intensively monitored plots suggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth’s intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth’s climate.

For access to the entire reference click on the following long hyperlink:

https://www.nature.com/articles/s41586-020-2035-0.epdf?referrer_access_token=1JyC8Qk9bocUSjMvwF1ScNRgN0jAjWel9jnR3ZoTv0NOJ2x2BsrUNZyzCBuuL0UUqQjPW2euF71wbnss7bZVTypLc0eJu3wcwXkQBGokyA9HW2k-okTMHDdectG92AB7UCaAEYubgKcBIjfvWwAarBHNAQlggxcW6gKC8EBuatXyyNG4lsNoKGBuz6jwneDBL85C6ZibPhm8YlwdenuepVVP3nfandk-FdksbHp95BMzbOlkWsOdA_w-AgEHUgpR--O3YMfs5rGobLgW3dErAFzL2HiJnxMDdXmrUYWB9BmXvV6tOn6btzbsOf6thVTa&tracking_referrer=www.theguardian.com&utm_campaign=Hot%20News&utm_source=hs_email&utm_medium=email&utm_content=84317976&_hsenc=p2ANqtz-8UPQfxoelrSvfbdYQCIkzqlCfBROkJ5jKELKAq3Pgh1uafh2U1uOzeDyMDWDEuNhhanL130IV3OuvMP6uUTYnT4uig2Q&_hsmi=84317976

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Previously I have noted that as the Tropical Pacific Ocean warms it will telecommunicate (through the atmosphere) more heat to West Antarctica.  Now, I note that the linked reference indicates that as Arctic and Antarctic sea-ice is sharply reduced in coming decades, this will trigger a feedback loop that will warm the SSTA of the tropical oceans and particularly of the eastern equatorial Pacific by an average of 0.5C (by 2100).  This feedback loop is bad news and was not previously recognized by consensus climate science:

England, M.R., Polvani, L.M., Sun, L. et al. Tropical climate responses to projected Arctic and Antarctic sea-ice loss. Nat. Geosci. 13, 275–281 (2020). https://doi.org/10.1038/s41561-020-0546-9

https://www.nature.com/articles/s41561-020-0546-9

...

The linked reference confirms that neither CMIP5 nor CMIP6 did a very good job at matching the observed changes in Arctic and Antarctic sea ice extents, SIE (although CMIP6 was more precise than CMIP5).  Therefore, neither CMIP5 nor CMIP6 do a good job of projecting the positive feedback between future possible SIE declines and accelerated climate change identified by England et al. (2020).

Qi Shu et al. (23 April 2020), "Assessment of sea ice extent in CMIP6 with comparison to observations and CMIP5", Geophysical Research Letters, https://doi.org/10.1029/2020GL087965

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL087965?af=R

Abstract
Both the Arctic and Antarctic sea ice extents (SIE) from 44 coupled models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) are evaluated by comparing them with observations and CMIP5 results. The CMIP6 multi‐model mean can adequately reproduce the seasonal cycles of both the Arctic and Antarctic SIE. The observed Arctic September SIE declining trend (−0.82±0.18 million km2/decade) between 1979 and 2014 is slightly underestimated in CMIP6 models (−0.70±0.06 million km2/decade). The observed weak but significant upward trend of the Antarctic SIE is not captured, which was an issue already in the CMIP5 phase. Compared with CMIP5 models, CMIP6 models have lower inter‐model spreads in SIE mean values and trends, although their SIE biases are relatively larger. The CMIP6 models did not reproduce the new summer tendencies after 2000, including the faster decline of Arctic SIE and the larger interannual variability in Antarctic SIE.

[AbruptSLR]

While only presenting representative methane dynamics from one Siberian river, bay and lake, the findings of the linked reference confirm prior studies of methane emissions from thermokarst lakes in the Arctic permafrost and reminds us all that additional methane emissions (but lower than from thermokarst lakes) come from Arctic rivers and ocean bays:

Bussmann, I., Fedorova, I., Juhls, B., Overduin, P. P., and Winkel, M.: Seasonal methane dynamics in three different Siberian water bodies, Biogeosciences Discuss., https://doi.org/10.5194/bg-2020-106, in review, 2020.

https://www.biogeosciences-discuss.net/bg-2020-106/

Abstract. Arctic regions and their water bodies are being affected by the most rapid climate warming on Earth. Arctic lakes and small ponds are known to act as an important source of atmospheric methane. However, not much is known about other types of water bodies in permafrost regions, which include major rivers and coastal bays as a transition type between freshwater and marine environments. We monitored dissolved methane concentrations in three different water bodies (Lena River, Tiksi Bay and Lake Golzovoye, Siberia, Russia) over a period of two years. Sampling was carried out under ice cover (April) and in open water (July/August). The methane oxidation (MOX) rate in water and melted ice samples from the late winter of 2017 was also investigated. In the Lena River winter methane concentrations were a quarter of the summer concentrations (8 vs 31 nmol L−1) and mean winter MOX rate was low (0.023 nmol L−1 d−1). In contrast, Tiksi Bay winter methane concentrations were 10-times higher than in summer (103 vs 13 nmol L−1). Winter MOX rates showed a median of 0.305 nmol L−1 d−1. In Lake Golzovoye, median methane concentrations in winter were 40-times higher than in summer (1957 vs 49 nmol L−1). However, MOX was much higher in the lake (2.95 nmol L−1 d−1) than in either the river or bay. The temperature had a strong influence on the MOX, (Q10 = 2.72 ± 0.69) compared to temperate environments. In the ice cores a median methane concentration of 9 nM was observed, with no gradient between the ice surface and the bottom layer at the ice-water-interface. MOX in the (melted) ice cores was mostly below the detection limit. Comparing methane concentrations in the ice with the underlaying water column revealed 100 – 1000-times higher methane concentration in the water column. The winter situation seemed to favor a methane accumulation under ice, especially in the lake with a stagnant water body. While on the other hand, in the Lena River with its flowing water no methane accumulation under ice was observed. Methane oxidation rate was not able to counteract this winter time accumulation.

[AbruptSLR]

While the linked open access reference on the influence of past hydroxyl radical (OH) variability on global methane budgets is somewhat esoteric; it does discuss one more factor/uncertainty in evaluating the challenging to determine global methane budget.  While the linked reference primarily evaluates the variability of OH due to the ENSO cycle; I note that if future atmospheric concentrations of OH decrease (for whatever combination of reasons) then the lifetime of methane in the atmosphere will increase which would increase the GWP of potential future methane emissions.  This climate change risk is often underreported in consensus projections:

Zhao, Y., Saunois, M., Bousquet, P., Lin, X., Berchet, A., Hegglin, M. I., Canadell, J. G., Jackson, R. B., Deushi, M., Jöckel, P., Kinnison, D., Kirner, O., Strode, S., Tilmes, S., Dlugokencky, E. J., and Zheng, B.: On the role of trend and variability of hydroxyl radical (OH) in the global methane budget, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2020-308, in review, 2020.

https://www.atmos-chem-phys-discuss.net/acp-2020-308/

Abstract. Decadal trends and interannual variations in the hydroxyl radical (OH), while poorly constrained at present, are critical for understanding the observed evolution of atmospheric methane (CH4). Through analyzing the OH fields simulated by the model ensemble of the Chemistry–Climate Model Initiative (CCMI), we find (1) the negative OH anomalies during the El Niño years mainly corresponding to the enhanced carbon monoxide (CO) emissions from biomass burning and (2) a positive OH trend during 1980–2010 dominated by the elevated primary production and the reduced loss of OH due to decreasing CO after 2000. Both two-box model inversions and variational 4D inversions suggest that ignoring the negative anomaly of OH during the El Niño years leads to a large overestimation of the increase in global CH4 emissions by up to 10 Tg yr−1 to match the observed CH4 increase over these years. Not accounting for the increasing OH trends given by the CCMI models leads to an underestimation of the CH4 emission increase by ~ 23 Tg yr−1 from 1986 to 2010. The variational inversion estimated CH4 emissions show that the tropical regions contribute most to the uncertainties related to OH. This study highlights the significant impact of climate and chemical feedbacks related to OH on the top-down estimates of the global CH4 budget.

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The linked open access reference studies the Getz Ice Shelf to confirm that basal ice melting from beneath Antarctic ice shelves is increased both where warm CDW is advected beneath the ice shelves and where freshwater is discharged from the grounding line to beneath the ice shelves:
 
Wei, W., Blankenship, D. D., Greenbaum, J. S., Gourmelen, N., Dow, C. F., Richter, T. G., Greene, C. A., Young, D. A., Lee, S., Kim, T.-W., Lee, W. S., and Assmann, K. M.: Getz Ice Shelf melt enhanced by freshwater discharge from beneath the West Antarctic Ice Sheet, The Cryosphere, 14, 1399–1408, https://doi.org/10.5194/tc-14-1399-2020, 2020.

https://www.the-cryosphere.net/14/1399/2020/

Abstract
Antarctica's Getz Ice Shelf has been rapidly thinning in recent years, producing more meltwater than any other ice shelf in the world. The influx of fresh water is known to substantially influence ocean circulation and biological productivity, but relatively little is known about the factors controlling basal melt rate or how basal melt is spatially distributed beneath the ice shelf. Also unknown is the relative importance of subglacial discharge from the grounded ice sheet in contributing to the export of fresh water from the ice shelf cavity. Here we compare the observed spatial distribution of basal melt rate to a new sub-ice-shelf bathymetry map inferred from airborne gravity surveys and to locations of subglacial discharge from the grounded ice sheet. We find that melt rates are high where bathymetric troughs provide a pathway for warm Circumpolar Deep Water to enter the ice shelf cavity and that melting is enhanced where subglacial discharge fresh water flows across the grounding line. This is the first study to address the relative importance of meltwater production of the Getz Ice Shelf from both ocean and subglacial sources.

[AbruptSLR]

The linked article is a reprint of a Mother Jones article, which points out that chaos in the oil & gas sector (such as we are now experiencing worldwide) is not good news w.r.t. GHG emissions from this sector for reasons including:

1. When global economies start to recover oil/gas price will remain low for much of the recovery; which will spur oil/gas consumption during this period.

2. Chaos can lead to a sharp increase in abandoned oil/gas wells; which historically have been a major source of GHG emissions.

3. Chaos promotes increased flaring of natural gas; which is associated with increased GHG emissions.

4. Stimulus spending and political chaos is not leading to improved policies to limit either current, or future, GHG emissions.

Furthermore, I note that the current economic chaos is hitting the coal industry even harder than it is hitting the Oil & Gas sector; and abandoned coal mines are another significant source of coal gas (mostly methane) emissions into the atmosphere.

Title: "Chaos in the oil sector: Not really good news for climate emissions"

https://thebulletin.org/2020/04/chaos-in-the-oil-sector-not-really-good-news-for-climate-emissions/

Extract: "As the coronavirus cripples world economies, greenhouse gas emissions are plummeting: This year, they could drop by as much as 5.5 percent—the largest decrease ever recorded. On Monday, the price of oil went negative, meaning storing oil now costs more than the oil itself. Since we’re burning less gas and fuel, air pollution has dropped 30 percent in northeastern cities, and Los Angeles’ notorious smoggy skyline has cleared.

You might be thinking all this is great news for the environment. It’s a nice idea—but the real story is more complicated. “You don’t want companies collapsing like this,” says Andrew Logan, oil and gas director of Ceres, a think tank focused on sustainable investment. “Even the most ardent climate advocate shouldn’t wish for a chaotic transition in this sector. A chaotic transition brings all sort of pain to workers and also the environment.”
…
Environmentalists are worried about what comes next, because of the many unintended consequences of market chaos. For starters, when gas prices tank, Americans will likely start buying more cars and taking more road trips, driving up demand all over again.

Other environmental problems aren’t quite so obvious. Lorne Stockman, a senior research analyst with the climate advocacy group Oil Change International, worries that the coming bankruptcies this year “are an environmental nightmare in the making,” with “wells left to rot as bankruptcy proceedings are going through.”

As the industry contracts, some drilling operations will simply leave their wells, and many don’t have the funding set aside to take proper precautions to make sure greenhouse gases and other pollutants don’t leak out. Environmental advocates are especially worried about leaks of methane, a particularly potent greenhouse gas.

Abandoned wells are already a big problem.
…
Drilling operations that don’t shutter will have to find ways to cut costs. In boom times, methane is valuable to drillers because it can be captured and reused for fuel. But when oil and natural gas prices have crashed in the past, drillers have sought to get rid of excess methane in the cheapest way possible—by burning it (a process known as “flaring”) or simply letting it leak into the atmosphere (called “venting”). Both processes can contribute to climate change and contaminate surrounding communities. Flaring and venting worry many environmental advocates. The International Energy Agency notes that “low natural gas prices may lead to increases in flaring or venting, and regulatory oversight of oil and gas operations could be scaled back.”
…
So far, it looks like the short-term emissions drop won’t result in any lasting policy improvements, Stockman says. “We have seen the wrong kind of stimulus that isn’t aimed at changing our relationship to fossil fuels.”"

[AbruptSLR]

While the linked reference does not provide clear guidance on how to best model Earth Systems in our increasingly warm climate, I provide the following linked information that provides more paleo-reconstructions from the past 3.6 millions years as it might help some readers to better understand past ice-climate relationships:

Berends, C. J., de Boer, B., and van de Wal, R. S. W.: Reconstructing the Evolution of Ice Sheets, Sea Level and Atmospheric CO2 During the Past 3.6 Million Years, Clim. Past Discuss., https://doi.org/10.5194/cp-2020-52, in review, 2020.

https://www.clim-past-discuss.net/cp-2020-52/

Abstract. Understanding the evolution of, and the interactions between, ice sheets and the global climate over geological time is important for being able to constrain earth system sensitivity. However, direct observational evidence of past CO2 concentrations only exists for the past 800 000 years. Records of benthic δ18O date back millions of years, but contain signals from both land ice volume and ocean temperature. In recent years, inverse forward modelling has been developed as a method to disentangle these two signals, resulting in mutually consistent reconstructions of ice volume, temperature and CO2. We use this approach to force a hybrid ice-sheet – climate model with a benthic δ18O stack, reconstructing the evolution of the ice sheets, global mean sea level and atmospheric CO2 during the late Pliocene and the Pleistocene, from 3.6 million years (Myr) ago to the present day. During the warmer-than-present climates of the Late Pliocene, reconstructed CO2 varies widely, from 320–440 ppmv for warm periods such as Marine Isotope Stage (MIS) KM5c, to 235–250 ppmv for the MIS M2 glacial excursion. Sea level is relatively stable during this period, with a high stand of 6–14 m, and a drop of 12–26 m during MIS M2. Both CO2 and sea level are within the wide ranges of values covered by available proxy data for this period. Our results for the Pleistocene agree well with the ice-core CO2 record, as well as with different available sea-level proxy data. During the early Pleistocene, 2.6–1.2 Myr ago, we simulate 40 kyr glacial cycles, with interglacial CO2 decreasing from 280–300 ppmv at the beginning of the Pleistocene, to 250–280 ppmv just before the Mid-Pleistocene Transition (MPT). Peak glacial CO2 decreases from 220–250 ppmv to 205–225 ppmv during this period. After the MPT, when the glacial cycles change from 40 kyr to 80/120 kyr cyclicity, the glacial-interglacial contrast increases, with interglacial CO2 varying between 250–320 ppmv, and peak glacial values decreasing to 170–210 ppmv.

[AbruptSLR]

The linked reference finds that with lags of about a decade oscillations of the Southern Ocean Westerly winds (commonly associated with variations in SAM) can drive variations in the MOC.  This represents a climate risk as these variations in MOC might temporarily be super imposed on freshwater hosing events that tend to slow the MOC.

Woo Geun Cheon & Jong-Seong Kug (2020), "The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation", Journal of Climate, https://doi.org/10.1175/JCLI-D-19-0364.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0364.1

Abstract
In the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

Extract: "With lags of about a decade the Atlantic MOC variation is correlated with the oscillating SH westerly winds, which modulate the transport of salinity from the subtropics to the northern North Atlantic. In this regard, the SH westerly wind anomalies associated with the SAM can drive the Atlantic Ocean conveyor belt variations."

[AbruptSLR]

The linked article (& associated linked reference) indicate that the CESM2 simulations of the Early Eocene are not as precise as the prior CESM1.2 simulations; which had a mean ECS of 4.2C (which is much higher than the AR5 mean value of around 3C).  However, the Early Eocene had a much different climate than our current climate so it is difficult to say what this means other than to say that there will be a lot of work required for CMIP7 when it is initiated:

Title: "Some of the latest climate models provide unrealistically high projections of future warming"

https://www.eurekalert.org/pub_releases/2020-04/uom-sot042820.php

Extract: "The predecessor to CESM2, the CESM1.2 model, did a remarkably good job of simulating temperatures during the Early Eocene, according to the researchers. It has an equilibrium climate sensitivity of 4.2 C (7.6 F)."

See also:

Zhu, J., Poulsen, C.J. & Otto-Bliesner, B.L. High climate sensitivity in CMIP6 model not supported by paleoclimate. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0764-6

https://www.nature.com/articles/s41558-020-0764-6

[vox_mundi]

Catastrophic outburst floods carved Greenland's 'Grand Canyon'
https://phys.org/news/2020-04-catastrophic-outburst-greenland-grand-canyon.html

Buried a mile beneath Greenland's thick ice sheet is a network of canyons so deep and long that the largest of these has been called Greenland's "Grand Canyon." This megacanyon's shape suggests it was carved by running water prior to widespread glaciation, but exactly when and how the island's grandest canyon formed are topics of intense debate.

Now scientists from the U.S. and Denmark are proposing a surprising new hypothesis for the megacanyon's formation: catastrophic "outburst" floods that suddenly and repeatedly drained large meltwater-filled lakes. The findings, published this week in the journal Geology, also suggest that Greenland's subglacial canyon network has influenced the island's ice sheet since its inception.

Although repeated outburst floods have been suggested as the mechanism by which the Columbia River and other North America canyon networks formed, they had not previously been considered as the source of the remarkable landscape hidden beneath the Greenland Ice Sheet

"If the floods we propose occurred, they could have influenced ocean circulation, causing abrupt climate changes with regional and perhaps global significance," says Keisling, now a postdoctoral fellow at Lamont-Doherty Earth Observatory. "The megacanyon beneath northern Greenland also influences how ice and water flow in the subglacial environment today, which affects present-day ice-sheet stability," he says.


Modeled outburst flood during ice-sheet retreat, routed to the outlet of Petermann Glacier. The animation covers 22,000 simulated years, and pauses to highlight a large ice-dammed proglacial lake during the deglaciation.

The researchers used coupled ice-sheet and climate models to simulate the Greenland Ice Sheet's evolution over multiple glacial-interglacial cycles during the global cooling from the Pliocene into the Pleistocene, 2.58 million years ago. They found that following long periods with stable temperatures, an exceptionally warm period could cause the ice sheet to retreat rapidly. This melting led to the development of large, ice-dammed lakes in areas where the bedrock was still depressed due to the former ice sheet's weight.

The simulations eventually show the ice dams give way, leading to large outburst floods. "Over time," says Keisling, "it appears that the filling and draining of these lakes as the ice repeatedly retreated and advanced carved Greenland's megacanyons." Similar floods have been documented at the edge of other retreating ice sheets, he says

https://scx2.b-cdn.net/gfx/news/2020/1-catastrophic.gif
Modelled outburst flood during a deglaciation scenario routed to the outlets of the northeast Greenland ice stream (NEGIS). The animation covers 25,000 simulated years, and pauses to highlight a large ice-dammed proglacial lake during the deglaciation

Based on comparisons with modern outburst floods, the researchers estimate that it took tens to hundreds of these events to carve Greenland's largest canyon. According to Keisling, widespread sediment deposition in the water-filled basins may have also impacted the ice sheet's behavior each time it grew back.

Benjamin A. Keisling et al, Pliocene–Pleistocene megafloods as a mechanism for Greenlandic megacanyon formation, Geology (2020).
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G47253.1/584570/Pliocene-Pleistocene-megafloods-as-a-mechanism-for

[AbruptSLR]

Catastrophic outburst floods carved Greenland's 'Grand Canyon'
...

Now scientists from the U.S. and Denmark are proposing a surprising new hypothesis for the megacanyon's formation: catastrophic "outburst" floods that suddenly and repeatedly drained large meltwater-filled lakes. The findings, published this week in the journal Geology, also suggest that Greenland's subglacial canyon network has influenced the island's ice sheet since its inception.

...

This makes me wonder how fast the meltwater accumulated in the firn will drain when these reservoirs find a drainage path to the ocean.

[sidd]

The water in firn is not free water. It is held in place by van der Walls forces between water and ice as well as surface tension effects. That firn reservoir cannot escape untill the firn melts as we see it does in summer when it (together with direct ice melt) forms melt pools and drills its way down to the bed.

It is very far cry from firn reservoir to free water reservoir ...

sidd