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Messages - AbruptSLR

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1
The findings of the linked research indicate that with continued global warming more of the increased heat will be advected by the atmosphere and proportionately less will be advected by the ocean.  This clearly implies that the relatively rapid poleward advection of heat energy through the atmosphere from the tropical oceans, will bring about more rapid climate change than expected by consensus climate science.  Furthermore, the disproportional concentration of ocean heat in the Southern Ocean, serves to destabilize Antarctic marine glaciers faster than assumed by consensus climate science:

Title: "Study: Climate change reshaping how heat moves around globe"

https://phys.org/news/2019-01-climate-reshaping-globe.html

Extract: " This is the first study to examine current changes in heat transfer and to conclude that warming temperatures are driving increased heat transfer in the atmosphere, which is compensated by a reduced heat transfer in the ocean. Additionally, the researchers concluded that the excess oceanic heat is trapped in the Southern Ocean around the Antarctic."

Chengfei He et al. The transient response of atmospheric and oceanic heat transports to anthropogenic warming, Nature Climate Change (2019). DOI: 10.1038/s41558-018-0387-3

https://www.nature.com/articles/s41558-018-0387-3


2
The paleo findings cited in the linked article confirms that Arctic Sea Ice loss can lead to abrupt increases in Arctic Amplification:

Title: "Arctic sea ice loss in the past linked to abrupt climate events"

https://www.sciencedaily.com/releases/2019/02/190211164033.htm

Extract: "A new study on ice cores shows that reductions in sea ice in the Arctic in the period between 30-100,000 years ago led to major climate events. During this period, Greenland temperatures rose by as much as 16 degrees Celsius.
...
"The summer time sea ice in the Arctic has experienced a 40% decline in the last few decades, but we know that about two thirds of that reduction is caused by human-induced climate change. What we now need to determine is, what can be learnt from these past sea ice losses to enable us to understand what might happen next to our climate.""

See also:

Louise C. Sime, Peter O. Hopcroft, Rachael H. Rhodes (February 13, 2019), "Impact of abrupt sea ice loss on Greenland water isotopes during the last glacial period", PNAS,   https://doi.org/10.1073/pnas.1807261116

https://www.pnas.org/content/early/2019/02/12/1807261116

Abstract: "Greenland ice cores provide excellent evidence of past abrupt climate changes. However, there is no universally accepted theory of how and why these Dansgaard–Oeschger (DO) events occur. Several mechanisms have been proposed to explain DO events, including sea ice, ice shelf buildup, ice sheets, atmospheric circulation, and meltwater changes. DO event temperature reconstructions depend on the stable water isotope (δ18O) and nitrogen isotope measurements from Greenland ice cores: interpretation of these measurements holds the key to understanding the nature of DO events. Here, we demonstrate the primary importance of sea ice as a control on Greenland ice core δ18O: 95% of the variability in δ18O in southern Greenland is explained by DO event sea ice changes. Our suite of DO events, simulated using a general circulation model, accurately captures the amplitude of δ18O enrichment during the abrupt DO event onsets. Simulated geographical variability is broadly consistent with available ice core evidence. We find an hitherto unknown sensitivity of the δ18O paleothermometer to the magnitude of DO event temperature increase: the change in δ18O per Kelvin temperature increase reduces with DO event amplitude. We show that this effect is controlled by precipitation seasonality.

Significance

The Dansgaard–Oeschger events contained in Greenland ice cores constitute the archetypal record of abrupt climate change. An accurate understanding of these events hinges on interpretation of Greenland records of oxygen and nitrogen isotopes. We present here the important results from a suite of modeled Dansgaard–Oeschger events. These simulations show that the change in oxygen isotope per degree of warming becomes smaller during larger events. Abrupt reductions in sea ice also emerge as a strong control on ice core oxygen isotopes because of the influence on both the moisture source and the regional temperature increase. This work confirms the significance of sea ice for past abrupt warming events

3
The linked references indicate that at a global scale permafrost is degrading fasters than previously assumed by consensus climate science; which could accelerate the rate of climate change this century:

Title: "Some Arctic ground no longer freezing—even in winter"

https://www.nationalgeographic.com/environment/2018/08/news-arctic-permafrost-may-thaw-faster-than-expected/

Extract: "On January 16, 2019, a new global study published in Nature Communications confirmed that permafrost is thawing quickly across much of the world. Between 2007 and 2016, permafrost temperature increased by 0.29 ± 0.12 °C globally. The greatest warming was seen in parts of Siberia, up to 0.93 °C. Significant warming was also seen in Antarctica, and less in mountain regions. In much of the Arctic ground temperature increased because of rising average air temperatures, while increased snow thickness in some areas also contributed to warming the ground underneath."
&

Biskaborn et al. (2019), "Permafrost is warming at a global scale", Nature Communications 10, No. 264, https://doi.org/10.1038/s41467-018-08240-4

https://www.nature.com/articles/s41467-018-08240-4#Fig6

4
As I have been (/will be) traveling, the following are some random considerations as to why the WAIS may collapse sooner than even DeConto & Pollard estimate (see the first image, and I note that the second image indicates that SSP5-Baseline results in a faster rate of global warming than computed by DeConto & Pollard):

1. Finer mesh resolution typically result in faster ice mass loss projections from ice sheet models, and this is particularly true for models of the Thwaites Gateway, and I note that DeConto & Pollards mesh could be finer if they had access to more computational power.

2.  If I am correct that once the residual Thwaites Ice Tongue is cleared away (maybe within 5 to 20 years), that ice cliff calved icebergs will be able to float-out by traveling along the seafloor trench at the base of the Thwaites Ice Tongue, then an MICI mechanism should be able to develop for the Thwaites Glacier prior to the development of hydrofracturing in this area.

3. As climate change is currently increasing the frequency of cyclones in the Amundsen-Bellingshausen Sea Sector, increased storm surge activity will likely accelerate ice mass loss from this area.

4. The recently observed trend of accelerating ice flow velocities for both the Thwaites, and Pine Island, Glaciers (partially attributable to the loss of buttressing on the SW Tributary Glacier in 2018), results in increased friction-induced ice melting within the body of these glaciers; and such ice meltwater drips/rains down to create increased subglacial meltwater; which serves to accelerate the destabilization of such key marine glaciers.

5. The glacial beds for the WAIS marine glaciers are all more worn/scoured than was the case for all paleo-cases.  Thus, any ice mass models calibrated using paleo-data will consequently err on the side of least drama.

6. It is likely that glacial isostatic rebound will increase geothermal heat flux through the beds of key WAIS marine glaciers; which would serve to accelerate the destabilization of such glaciers.

7. Projections of increased snowfall in the coastal regions of the WAIS (with continued global warming), will increase the gravitational driving force associated with MICI and MISI ice mass loss in coming decades.

8. Projections of increased El Nino activity (with continued global warming) will increase the volume of warm CDW advected to the grounding lines of key WAIS marine glaciers, and will also increase the likelihood of hydrofracturing of key WAIS ice shelves in the coming decades.

9. DeConto & Pollard (& Hansen) used consensus values of ECS in their model projections; which indicates that their projections of ice mass loss err on the side of least drama.

10. The Eastern Thwaites Ice Shelf and the Pine Island Ice Shelf, both appear to be degrading faster than projected by DeConto & Pollard; which indicates that their ice mass loss projections err on the side of least drama.

11. The freshening of much of the surface waters of the Southern Ocean, due to both early ice mass loss from Antarctic ice shelves and increase precipitation onto the surface of the Southern Ocean, is accelerating the projected increased upwelling of warm CDW.

12. The early ice mass loss from the Greenland Ice Sheet is accelerating the bipolar seesaw mechanism, which is compounding the influence of the decadal slow down of the MOC.

13. At some point, sufficient ice mass loss from the WAIS will trigger increased seismic and volcanic activity, not evaluated by DeConto & Pollard.

14. Recent evidence indicates that the negative forcing associated with anthropogenic aerosols has been/is greater than previously assumed by consensus climate science; which implies that GMSTA will increase faster than projected as anthropogenic aerosol emissions are reduced and/or redistributed around the globe.

5
One cannot understand Hansen's ice-climate feedback mechanism, without understanding the bipolar seesaw mechanism:

Joel Pedro, Markus Jochum, Christo Buizert, Feng He, Stephen Barker, and Sune Rasmussen (2018), "Beyond the bipolar seesaw: toward a process understanding of interhemispheric coupling", Geophysical Research Abstracts, Vol. 20, EGU2018-2551, EGU General Assembly 2018

https://meetingorganizer.copernicus.org/EGU2018/EGU2018-2551.pdf

Abstract: "The thermal bipolar ocean seesaw hypothesis was advanced by Stocker and Johnsen (2003) as the ‘simplest possible thermodynamic model’ to explain the time relationship between Dansgaard Oeschger (DO) and Antarctic Isotope Maxima (AIM) events. Here, we combine palaeoclimate observations, theory and general circulation model experiments to advance from the conceptual model toward a process understanding of interhemispheric coupling and the forcing of AIM events. We present four main results:  (1) Changes in Atlantic heat transport invoked by the thermal seesaw are partially compensated by opposing changes in heat transport by the global atmosphere and Pacific Ocean. This compensation is an integral part of interhemispheric coupling, with a major influence on the global pattern of climate anomalies.  (2) A change in cross-equatorial heat advection is commonly assumed to explain Atlantic Ocean temperature anomalies in the thermal seesaw.  We suggest that wind driven deepening of the South Atlantic thermocline contributes, in addition to the change in advection, to explain the speed and spatial pattern of the temperature changes in the South Atlantic and the storage of heat at depth.  (3) We support the role of a heat reservoir in interhemispheric coupling but argue that its location is the global interior ocean north of the Antarctic Circumpolar Current (ACC), not the commonly assumed Southern Ocean.  (4) Energy budget analysis indicates that the process driving Antarctic warming during AIM events is an increase in poleward atmospheric heat and moisture transport following sea-ice retreat and surface warming over the Southern Ocean. Sea-ice retreat is itself driven by eddy-heat fluxes from the global ocean heat reservoir across the ACC, amplified by sea-ice–albedo feedbacks. Our results underline the coupled role of the ocean and atmosphere in signal propagation linking DO and AIM events."

6
Here is an opinion piece (& related linked references) that supports the underlying tenets of this thread:

Title: "Are We Headed Toward the Worst-Case Climate Change Scenario?"

https://psmag.com/environment/are-we-headed-toward-the-worst-case-climate-change-scenario

Extract: "A series of recent studies and reports suggest that, without immediate and drastic action, the worst-case climate scenario will become the rule rather than the exception."

See also:

Title: "Accelerating changes in ice mass within Greenland, and the ice sheet’s sensitivity to atmospheric forcing"

https://www.pnas.org/content/116/6/1934
&

Title: "Melting Ice Sheets Could Worsen Extreme Weather"

https://www.scientificamerican.com/article/melting-ice-sheets-could-worsen-extreme-weather/


7
As it is my belief that potential future increases in ECS (this century) will be related to increases in El Nino event frequency, and to increasing Polar Amplification (both of which should be accelerated by ice-climate interactions), I provide the following three linked references which discuss modeling issues related to ENSO events and Polar Amplification, which are not fully addresses by current consensus model projections; but which do not themselves consider possible future ice-climate feedback mechanism:

Lorenzo M. Polvani & Katinka Bellomo (2019), "The Key Role of Ozone-Depleting Substances in Weakening the Walker Circulation in the Second Half of the Twentieth Century", Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0906.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0906.1

Abstract: "It is widely appreciated that ozone-depleting substances (ODS), which have led to the formation of the Antarctic ozone hole, are also powerful greenhouse gases. In this study, we explore the consequence of the surface warming caused by ODS in the second half of the twentieth century over the Indo-Pacific Ocean, using the Whole Atmosphere Chemistry Climate Model (version 4). By contrasting two ensembles of chemistry–climate model integrations (with and without ODS forcing) over the period 1955–2005, we show that the additional greenhouse effect of ODS is crucial to producing a statistically significant weakening of the Walker circulation in our model over that period. When ODS concentrations are held fixed at 1955 levels, the forcing of the other well-mixed greenhouse gases alone leads to a strengthening—rather than weakening—of the Walker circulation because their warming effect is not sufficiently strong. Without increasing ODS, a surface warming delay in the eastern tropical Pacific Ocean leads to an increase in the sea surface temperature gradient between the eastern and western Pacific, with an associated strengthening of the Walker circulation. When increasing ODS are added, the considerably larger total radiative forcing produces a much faster warming in the eastern Pacific, causing the sign of the trend to reverse and the Walker circulation to weaken. Our modeling result suggests that ODS may have been key players in the observed weakening of the Walker circulation over the second half of the twentieth century."
&

J. Ono et al. (2019), "Mechanisms for and Predictability of a Drastic Reduction in the Arctic Sea Ice: APPOSITE Data with Climate Model MIROC', Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0195.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0195.1

Abstract: "The mechanisms for and predictability of a drastic reduction in the Arctic sea ice extent (SIE) are investigated using the Model for Interdisciplinary Research on Climate (MIROC) version 5.2. Here, a control (CTRL) with forcing fixed at year 2000 levels and perfect-model ensemble prediction (PRED) experiments are conducted. In CTRL, three (model years 51, 56, and 57) drastic SIE reductions occur during a 200-yr-long integration. In year 56, the sea ice moves offshore in association with a positive phase of the summer Arctic dipole anomaly (ADA) index and melts due to heat input through the increased open water area, and the SIE drastically decreases. This provides the preconditioning for the lowest SIE in year 57 when the Arctic Ocean interior is in a warm state and the spring sea ice volume has a large negative anomaly due to drastic ice reduction in the previous year. Although the ADA is one of the key mechanisms behind sea ice reduction, it does not always cause a drastic reduction. Our analysis suggests that wind direction favoring offshore ice motion is a more important factor for drastic ice reduction events. In years experiencing drastic ice reduction events, the September SIE can be skillfully predicted in PRED started from July, but not from April. This is because the forecast errors for the July sea level pressure and those for the sea ice concentration and sea ice thickness along the ice edge are large in PRED started from April."
&

Xiaofan Li et al. (2019), "Contributions of Atmosphere–Ocean Interaction and Low-Frequency Variation to Intensity of Strong El Niño Events since 1979, Journal of Science, https://doi.org/10.1175/JCLI-D-18-0209.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0209.1

Abstract: "Evolutions of oceanic and atmospheric anomalies in the equatorial Pacific during four strong El Niños (1982/83, 1991/92, 1997/98, and 2015/16) since 1979 are compared. The contributions of the atmosphere–ocean coupling to El Niño–associated sea surface temperature anomalies (SSTA) are identified and their association with low-level winds as well as different time-scale variations is examined. Although overall SSTA in the central and eastern equatorial Pacific is strongest and comparable in the 1997/98 and 2015/16 El Niños, the associated subsurface ocean temperature as well as deep convection and surface wind stress anomalies in the central and eastern equatorial Pacific are weaker during 2015/16 than that during 1997/98. That may be associated with a variation of the wind–SST and wind–thermocline interactions. Both the wind–SST and wind–thermocline interactions play a less important role during 2015/16 than during 1997/98. Such differences are associated with the differences of the low-level westerly wind as well as the contribution of different time-scale variations in different events. Similar to the interannual time-scale variation, the intraseasonal–interseasonal time-scale component always has positive contributions to the intensity of all four strong El Niños. Interestingly, the role of the interdecadal-trend time-scale component varies with event. The contribution is negligible during the 1982/83 El Niño, negative during the 1997/98 El Niño, and positive during the 1991/92 and 2015/16 El Niños. Thus, in addition to the atmosphere–ocean coupling at intraseasonal to interannual time scales, interdecadal and longer time-scale variations may play an important and sometimes crucial role in determining the intensity of El Niño."


8
Perhaps the largest obstruction blocking societies willingness/ability to face the true risks of abrupt climate change (likely to be triggered by ice-climate feedback mechanisms not adequately addressed by consensus climate science reports), can be characterized by what Sir Francis Bacon described as the 'four idols' of the mind (see the first linked article).  Consensus science (as well as other populist movements) get(s) bogged down by various preconceptions of the human mind, and per the extract below philosopher Dale Jamieson indicates that individual mindfulness (and the scientific integrity that goes with it) is fundamental to over-coming such misguided preconceptions that inhibit society from effectively facing the true risks of abrupt climate change.  In this regards, consensus climate science is used by society to create, and then promote, preconceptions/dogmas in order to absolve leaders (& societies as a whole) from the effort to remain mindful of the world (& Earth Systems) around them with compassion for that world (e.g.: empathy for sustainability).  Such scientific mindfulness would enable scientist to consider/address issues beyond the preconceived specialist silos that they typically work within, so as to better address the many 'fat-tailed' risks of abrupt climate change:

Title: "The 17th-century philosopher whose scientific ideas could tackle climate change today"

https://www.weforum.org/agenda/2019/02/francis-bacon-the-17th-century-philosopher-whose-scientific-ideas-could-tackle-climate-change-today

Extract: "In his key work Novum Organum, Bacon identified “four idols” of the mind – false notions, or “empty ideas” – that don’t just “occupy men’s minds so that truth can hardly get in, but also when a truth is allowed in they will push back against it”. A true science, he said, should “solemnly and firmly resolve to deny and reject them all, cleansing our intellect by freeing it from them”.

Bacon was referring to our understanding of the world around us. But his point applies to our morality too. As the philosopher Dale Jamieson has argued, our natural moral understanding is too limited to grasp the moral consequences and responsibility that comes with a problem like climate change, in which diffuse groups of people cause a diffuse set of harms to another diffuse set of people, over a diffuse range of time and space.
Since the “idols of the tribe” are natural and innate, they are tricky to shift. As Jamieson argued, one way to combat them is for individuals to mindfully cultivate green virtues, such as rejecting materialism, humility about your own importance, and a broad empathy with your ecosystem."

For one example of more holistic thinking on climate risks, see also:

Title: "Climate change, water and the spread of diseases: Connecting the dots differently"

https://phys.org/news/2018-09-climate-diseases-dots-differently.html

9
As Shared Humanity has encouraged me to provide additional explanatory discussion for many/most of my posts, I return to the topic of the Manhattan-sized subglacial cavity at the base of the Thwaites Ice Tongue in Reply #552, where I provided the first image from Milillo et al. (2019).  Among other things, Panel C of this image shows a 2011.5 grounding line, a 2017.91 grounding line and the color shading shows the change in surface elevation between 2011.5 and 2017.51.

P. Milillo et al. (30 Jan 2019), "Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica", Science Advances, Vol. 5, no. 1, eaau3433, DOI: 10.1126/sciadv.aau3433

http://advances.sciencemag.org/content/5/1/eaau3433

The extension of the grounding line from 2011.5 to 2017.91 occurs along the subglacial trench shown in the second image, and the change in surface elevation creates crevasses that eventually produce floating icebergs as shown in the third image.  The fourth image shows a Sentinel image for this area for January 7 2019; which shows plenty of crevasse in the ice immediately downstream of the 2017.91 grounding line; which in turn implies that icebergs could float out from this subglacial trench area as soon as the downstream mélange of icebergs float away within a decade or so.  If this is the case, then Panel A and B of the first image clearly show that any ice cliffs near the T2 or T4 areas of the subglacial trench would have sufficiently high ice faces above sea level to induce local ice cliff failures.  If so the local grounding line could rapidly down the negative bed slope into the Byrd Subglacial Basin anytime after about 2035.  Such failure mechanisms are not considered by consensus climate scientists.

10
The UK's Met Office has projected that most likely, sometime in the next five years, GMSTA will at least temporarily exceed the IPCC's aspirational 1.5C target:

Title: "Met Office: World has 10% chance of ‘overshooting’ 1.5C within five years"

https://www.carbonbrief.org/met-office-world-has-10-per-cent-chance-overshooting-1-point-5-c-within-five-years

Extract: "The results find that, over a five-year period from November 2018 to October 2023, the global average temperature rise is likely to be between 1.03C and 1.57C. This is shown on the chart below, where blue shading represents the range of expected temperature rise for this period, when compared to temperatures in the “pre-industrial period” (1850-1990)."

Caption: "Expected rise in global temperature from November 2018 to October 2023 (blue), relative to “pre-industrial” temperatures (1850-1900). Actual temperature rise from 1960 to October 2018 is shown in black, the results of previous Met Office decadal projections are shown in red (hindcast) and results from the “Coupled Model Intercomparison Project” (CMIP5) are shown in green. There is a gap between the black line and blue shading because the observational data finishes in October 2018 and the projections start in November 2018. Shading shows range of confidence. Source: Met Office."

See also:

https://www.metoffice.gov.uk/news/releases/2019/forecast-suggests-earths-warmest-period


11
As both the Meridional Overturning Circulation, MOC, and associated ocean circulation patterns in the Southern Ocean, play a major role in ice-climate feedback mechanisms (including Agulhaus current leakage, CO2 venting, etc), I thought that I would post the two attached images to provide unfamiliar readers with a better frame of context:

Edit:  The caption for the third attached image (showing the sources of AABW formation) is as follows:

Caption for the third image: "The amount of Antarctic bottom water generated governs the relative strength of global deep ocean circulation. The Weddell and Ross Seas are well known regions of Antarctic bottom water formation, but in recent years it has emerged that the waters off Adelie Land in the vicinity of East 140 degrees Longitude is also an important region for bottom water generation"

Edit2: The fourth image shows that path that icebergs from the ASE would follow; westward along the Antarctic Coastal Current to the Weddell Sea, where the Antarctic Peninsula would kick the icebergs northward into the ACC (Antarctic Circumpolar Current), where-after they would circulate eastward around Antarctica.

12
The linked reference indicates that Permafrost carbon feedback (PCF) will be stronger than currently assumed by consensus climate change models:

Katey Walter Anthony, Thomas Schneider von Deimling, Ingmar Nitze, Steve Frolking, Abraham Emond, Ronald Daanen, Peter Anthony, Prajna Lindgren, Benjamin Jones, Guido Grosse. 21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05738-9

http://www.nature.com/articles/s41467-018-05738-9

Extract: "These finding demonstrate the need to incorporate abrupt thaw processes in earth system models for more comprehensive projection of the PCF this century."

See also:

Title: "'Abrupt thaw' of permafrost beneath lakes could significantly affect climate change models"

https://www.sciencedaily.com/releases/2018/08/180816143035.htm

13
The linked reference provides additional evidence that with continued anthropogenic radiative forcing, global soil moisture (SM) drying will act as a positive feedback mechanism, indicating higher values of ECS than currently assumed by consensus climate science:

Xihui Gu et al (31 January 2019), "Attribution of global soil moisture drying to human activities: a quantitative viewpoint", Geophysical Research Letters, https://doi.org/10.1029/2018GL080768

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL080768

Abstract
Anthropogenic impacts on widespread global soil moisture (SM) drying in the root zone layer during 1948‐2005 were evaluated based on the Global Land Data Assimilation System version 2 (GLDAS‐2) and Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) using trend analysis and optimal fingerprint methods. Both methods show agreement that natural forcing alone cannot drive significant SM drying. There is a high probability (≥90%) that the anthropogenic climate change signal is detectable in global SM drying. Specifically, anthropogenic greenhouse gas forcing can lead to global SM drying by 2.1×10‐3 m3/m3, which is comparable to the drying trend seen in GLDAS‐2 (2.4×10‐3 m3/m3) over the past 58 years. Global SM drying is expected to continue in the future, given continuous greenhouse gas emissions.

Plain Language Summary
Satellite observations and model simulations indicated widespread soil moisture (SM) drying in the root zone layer. Global‐scale SM drying has also been corroborated by meteorological drought indices. SM drying can accentuate the intensity of heat waves under global warming. Recent record‐breaking heat waves were amplified by SM drying, such as the 2003 European heat waves and 2010 Russia heat waves. the contributions of human activities to global‐scale SM changes have not been comprehensively evaluated. There is a high probability (≧90%) that the anthropogenic climate change signal in global SM drying is detectable. Specifically, anthropogenic greenhouse gas forcing can lead to global SM drying by 2.1×10‐3 m3/m3, which is comparable to the drying trend seen in GLDAS‐2 (2.4×10‐3 m3/m3) over the past 58 years. Global SM drying is expected to continue in the future, given continuous greenhouse gas emissions.

14
The linked reference suggests that it may be better to report GMSTA projection from ESMs that do a better job of projection such multi-decadal parameters as the IPO and the AMV, over multi-decadal periods.  If the IPCC adopted such a practice they would likely give more weight to ESM projections that also have high ECS values:

Jules B. Kajtar et al. (2019), "Global mean surface temperature response to large‐scale patterns of variability in observations and CMIP5", Geophysical Research Letters, https://doi.org/10.1029/2018GL081462

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081462

Abstract
Global mean surface temperature (GMST) fluctuates over decadal to multidecadal time‐scales. Patterns of internal variability are partly responsible, but the relationships can be conflated by anthropogenically‐forced signals. Here we adopt a physically‐based method of separating internal variability from forced responses to examine how trends in large‐scale patterns, specifically the Interdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Variability (AMV), influence GMST. After removing the forced responses, observed variability of GMST is close to the central estimates of Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations, but models tend to underestimate IPO variability at time‐scales >10 years, and AMV at time‐scales >20 years. Correlations between GMST trends and these patterns are also underrepresented, most strongly at 10‐ and 35‐year time‐scales, for IPO and AMV respectively. Strikingly, models that simulate stronger variability of IPO and AMV also exhibit stronger relationships between these patterns and GMST, predominately at the 10‐ and 35‐year time‐scales, respectively.

Plain Language Summary
Despite the smooth and steady increase of greenhouse gas concentrations, the rate of global warming has not been as stable over the past century. There are periods of stronger warming, or even slight cooling, in the global mean temperature record, which can persist for several years or longer. These changes have been linked to regional climate patterns, most notably within the Pacific and Atlantic Ocean climate systems. Climate models do not exhibit the same level of variations in these Pacific and Atlantic oscillations as compared to the observed record, and the connections between these oscillations and the global temperature are also diminished. However, there is a tendency for those models that show stronger Pacific and Atlantic oscillations to also exhibit stronger relationships between these patterns and global temperature changes.

15
The linked reference contains the cited extract regarding potential climate change surprises which gives a very high confidence that future changes outside the consensus projections cannot be ruled out; and give a medium confidence that consensus climate model projections are more likely to underestimate rather than to overestimate long-term future climate change:

USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp.

Title: "Chapter 15: Potential Surprises: Compound Extremes and Tipping Elements"

https://science2017.globalchange.gov/chapter/15/

Extract: "While climate models incorporate important climate processes that can be well quantified, they do not include all of the processes that can contribute to feedbacks, compound extreme events, and abrupt and/or irreversible changes. For this reason, future changes outside the range projected by climate models cannot be ruled out (very high confidence). Moreover, the systematic tendency of climate models to underestimate temperature change during warm paleoclimates suggests that climate models are more likely to underestimate than to overestimate the amount of long-term future change (medium confidence)."

Also, I note that USGCRP (2017) Chapter 15: Potential Surprises provides the following supporting evidence for their medium confidence assertion that consensus climate models underestimate paleo reconstructions of climate sensitivity

Extract: "The second half of this key finding is based upon the tendency of global climate models to underestimate, relative to geological reconstructions, the magnitude of both long-term global mean warming and the amplification of warming at high latitudes in past warm climates (e.g., Salzmann et al. 2013; Goldner et al. 2014; Caballeo and Huber 2013; Lunt et al. 2012)."

Note USGCRP (2017) classifies Medium Confidence as: "Suggestive evidence (a few sources, limited consistency, models incomplete, methods emerging, etc.), competing schools of thought"

Furthermore, the guide to USGCRP (2017) classifies these "Potential Surprises" as 'potential low probability/high consequence "surprises" resulting from climate change' and as 'high-risk tails and bounding scenarios'; and acknowledge that 'knowledge gaps' exist that limit their ability to precisely define the probability/risks associated with these "surprises".

https://science2017.globalchange.gov/chapter/front-matter-guide/

Extract: "Complementing this use of risk-focused language and presentation around specific scientific findings in the report, Chapter 15: Potential Surprises provides an overview of potential low probability/high consequence “surprises” resulting from climate change. This includes its analyses of thresholds, also called tipping points, in the climate system and the compounding effects of multiple, interacting climate change impacts whose consequences may be much greater than the sum of the individual impacts. Chapter 15 also highlights critical knowledge gaps that determine the degree to which such high-risk tails and bounding scenarios can be precisely defined, including missing processes and feedbacks."

16
As an indication of how concerned climate scientists are about the stability of the WAIS (and the Antarctic Peninsula), I provide the following two linked news articles from the British Antarctic Survey website"

Title: "Scientists drill to record depths in West Antarctica", 24 January, 2019 Press releases

https://www.bas.ac.uk/media-post/scientists-drill-to-record-depths-in-west-antarctica/

Extract: "A team of scientists and engineers has for the first time successfully drilled over two kilometres through the ice sheet in West Antarctica using hot water. This research will help understand how the region will respond to a warming climate.

The 11-person team has been working on the Rutford Ice Stream for the last 12 weeks in freezing temperatures at low as minus 30 degrees Celsius. On Tuesday 8 January, following a 63 hour continuous round-the-clock drilling operation, the team broke through to the sediment 2152 metres below the surface.

The team has now drilled two holes (with the second completed on 22 January) and plan to be working on the ice until mid-February 2018. Further work will now continue at a second site a few kilometres away."

See also:

Title: "BEAMISH: Bed Access, Monitoring and Ice Sheet History"

https://www.bas.ac.uk/project/bed-access-monitoring-and-ice-sheet-history-beamish/

Extract: "BEAMISH: Basal conditions on Rutford Ice Stream: Bed Access, Monitoring and Ice Sheet History"
&

Title: "International research expedition heads to West Antarctica

https://www.bas.ac.uk/media-post/international-research-expedition-heads-to-west-antarctica/

Extract: "An international team of scientists is travelling to the Amundsen Sea – one of the most vulnerable sectors of the Antarctic Ice Sheet – to answer vital scientific questions about the history of the West Antarctic Ice Sheet (WAIS).

As part of the International Ocean Discovery Program (IODP), researchers will spend 8 weeks working on board the JOIDES Resolution – a scientific drill ship. During the research cruise, the multinational team aim to recover sediment cores from the seabed on the fringes of the continent. These will be the first drill cores deeper than 35 metres obtained in the region, with target depths ranging from 700 to 1200 metres."

17
SH, Stephan, HapHazard,

Thank you for the thoughtful words.  So in the way of general education, I note that Pollard & DeConto (2016) estimates that Totten Glacier is the most susceptible for of the Antarctic Ice Sheet, AIS, to collapse after the WAIS glaciers, so I note that the linked reference helps to quantify the recent ice mass loss of the Totten and Moscow University Glaciers:

Yara Mohajerani et al. (25 July 2018), "Mass Loss of Totten and Moscow University Glaciers, East Antarctica, Using Regionally Optimized GRACE Mascons", Geophysical Research Letters, https://doi.org/10.1029/2018GL078173

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL078173

Abstract: "Totten and Moscow University glaciers, in the marine‐based sector of East Antarctica, contain enough ice to raise sea level by 5 m. Obtaining precise measurements of their mass balance is challenging owing to large area of the basins and the small mass balance signal compared to West Antarctic glaciers. Here we employ a locally optimized processing of Gravity Recovery and Climate Experiment (GRACE) harmonics to evaluate their mass balance at the sub‐basin scale and compare the results with mass budget method (MBM) estimates using regional atmospheric climate model version 2.3 (RACMO2.3) or Modèle Atmosphérique Régional version 3.6.4 (MAR3.6.4). The sub‐basin mass loss estimate for April 2002 to November 2015 is 14.8 ± 4.3 Gt/yr, which is weakly affected by glacial isostatic adjustment uncertainties (±1.4 Gt/yr). This result agrees with MBM/RACMO2.3 (15.8 ± 2.0 Gt/yr), whereas MBM/MAR3.6.4 underestimates the loss (6.6 ± 1.6 Gt/yr). For the entire drainage, the mass loss for April 2002 to August 2016 is 18.5 ± 6.6 Gt/yr, or 15 ± 4% of its ice flux. These results provide unequivocal evidence for mass loss in this East Antarctic sector."

Edit:  In the attached image from DeConto & Pollard (2016), the 'T' stands for Totten.  Also, note that the timescale on the image assumes a consensus science climate model, thus it is possible (probable) that the indicated dates are conservative.

18
For those who still do not understand how tropical oceanic energy, via evaporated water into the atmosphere, is telecommunicated (within weeks to months) poleward.......

Ooooh....me, me, me.....

SH,

Feel free to ask questions, as everyone knows that long-tail climate change is a complex and somewhat confusing topic.

ASLR

19
As a brief follow-on to my last post about a potential ice-climate domino-wave feedback mechanism scenario, I provide the following points:

1. Special initial conditions that may contribute to a ice-climate domino wave include:
a) The oceans, and particularly the Southern Ocean, have accumulated unexpectedly high Ocean Heat Contents, OHCs, in recent decades;
b) The Beaufort Gyre has accumulated unexpectedly high amounts of both freshwater and OHC in recent decades;
c) The grounding lines for several key Greenland marine terminating glaciers (like Jakobshavn) have retreated to retrograde zones of the bedslope in recent years;
d) Key ice shelves in the Amundsen Sea Embayment, ASE, have degraded significantly in recent years, and this year the ice shelf in-front of the Southwest Tributary Glacier has disappeared entirely;

2. The following ice-climate feedback mechanisms are all primed to reinforce each other, via:
a) The bipolar seesaw mechanism ice mass loss from Greenland is promoting future ice mass loss from Antarctica;
b) Telecommunication of heat energy from the Tropical Pacific and Atlantic to both polar regions.
c) Increasing MICI.
d) Increasing polar amplification.
e) Continued slowing of the MOC.
f) Telecommunication of heat energy from the Tropical Atlantic to the Pacific Basin.
g) The terrestrial biosphere will degrade with continuing climate change.
h) The permafrost will degrade with continuing climate change.
i) The ocean's ability to absorb carbon will degrade with continuing climate change.
j) Methane hydrates will degrade with continuing climate change.
k) The Hadley atmospheric cell will continue to expand poleward with continued climate change.

3. Assuming:
a) BAU radiative forcing through at least 2030.
b) Anthropogenic radiative forcing is more negative than assumed by AR5 (which implies that ECS is also higher than assumed by AR5).
c) Deforestation (& forest degradation) will continue with continuing climate change.
d) Climate sensitivity increases with continued warming.

20
At the risk of over simplifying matters, I am concerned that when I mention a cascade of tipping points contributing to the composite ice-climate feedback mechanism that many people may imagine a cascade such as that shown in the first image.  However, due to the mutually reinforcing nature of most of the contributing feedback mechanisms an actual cascade of ice-climate feedback mechanism would look more like the domino wave shown in the second image, with a response amplitude operator looking something like that when moving from right to left, with time, in the third image.

21
The linked article (and following linked reference) indicates that the terrestrial biosphere currently absorbs about 25% of all anthropogenic carbon dioxide emissions, but that changes in moisture patterns, together with depletion of nitrogen & phosphorus from the soil, will likely change the terrestrial biosphere from a carbon sink to a carbon source in the second half of this century.  If so, this would likely put Earth on a road toward 'Hothouse' conditions:

Title: "Climate change’s impact on soil moisture could push land past ‘tipping point’"

https://www.carbonbrief.org/climate-changes-impact-on-soil-moisture-could-push-land-past-tipping-point

Extract: "The research, published in Nature, shows that levels of soil moisture – which are impacted by rising temperatures and extreme events such as droughts – can have a “large negative influence” on the land’s ability to store carbon.

It finds that the rate at which land absorbs carbon is likely to increase until the second half of this century as a result of the “CO2 fertilisation effect” – a phenomenon where increased CO2 levels in the atmosphere bolsters the growth and, therefore, carbon uptake of plants.

However, after this point, the fertilisation is expected to “reach a peak”, the lead author tells Carbon Brief. This peak – combined with the negative impact of soil moisture changes – could turn the land “from a carbon sink to a carbon source, greatly accelerating climate change”, she says.

The projected impact of climate change on the land carbon sink is an example of a “tipping point” – a positive feedback mechanism within the Earth’s system that could cause runaway climate change, Green says:

“Unfortunately, many of the climate changes that we are currently witnessing – such as the melting of ice sheets and permafrost – have feedbacks associated with them which can further accelerate global warming. It is very difficult to assess all of the feedbacks that are occurring. I would just stress that we need to start to curb our emissions now.”

However, the models used in study are likely to have “overestimated” the extent to which the CO2 fertilisation effect would boost land carbon uptake, she says. This is because the models do not consider how plant growth could be limited by a lack of essential nutrients, such as nitrogen and phosphorous. She tells Carbon Brief:

“This effect in the models is, in my opinion, strongly over-estimated. Of all the [four] models, only one considers nitrogen limitation – but they do not at all consider phosphorus limitation. This is very important in the tropics, which is where the researchers expect the CO2 fertilisation effect to be the strongest.

“I think if this were corrected, we would see a much stronger effect from soil moisture. The soil moisture feedback would be much stronger.”

This would mean that the rate at which land uptakes carbon could reach a peak before 2060, she notes."

See also:

Green, J. K. et al. (2019) Large influence of soil moisture on long-term terrestrial carbon uptake, Nature, https://doi.org/10.1038/s41586-018-0848-x

https://www.nature.com/articles/s41586-018-0848-x


22
The linked article cites new PNAS findings that ice mass loss from the GIS is accelerating faster than consensus climate science previously assumed:

Title: "Greenland's ice melting faster than scientists previously thought – study"

https://www.theguardian.com/world/2019/jan/21/greenland-ice-melting-faster-than-scientists-previously-thought-study

Extract: "Greenland is melting faster than scientists previously thought, with the pace of ice loss increasing four-fold since 2003, new research has found."

23
For those who do not care to scroll back to Reply #42, I provide the following updated extracts:

The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm; which assuming the current rate of annual increase in CO2e of about 3.5ppm indicates that early in 2019 CO2e will exceed 537ppm (when including the radiative forcing from stratospheric ozone when computing CO2e):

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


Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html



Next, I provide links to Jagniecki et al. (2015) (and an associated article); indicating that early Eocene climatic optimum (EECO) conditions (with an equable climate) may have occurred with atmospheric CO₂ concentrations between 680ppm and 1260ppm (see the attached image); and that under such conditions the effective climate sensitivity (ESS) may have been twice that previously assumed by Royer et al (2012) …

Jagniecki,Elliot A. et al. (2015), "Eocene atmospheric CO2from the nahcolite proxy", Geology, http://dx.doi.org/10.1130/G36886.1


http://geology.gsapubs.org/content/early/2015/10/23/G36886.1

ftp://rock.geosociety.org/pub/reposit/2015/2015357.pdf

Abstract: "Estimates of the atmospheric concentration of CO2, [CO2]atm, for the "hothouse" climate of the early Eocene climatic optimum (EECO) vary for different proxies. Extensive beds of the mineral nahcolite (NaHCO3) in evaporite deposits of the Green River Formation, Piceance Creek Basin, Colorado, USA, previously established [CO2]atm for the EECO to be >1125 ppm by volume (ppm). Here, we present experimental data that revise the sodium carbonate mineral equilibria as a function of [CO2] and temperature. Co-precipitation of nahcolite and halite (NaCl) now establishes a well-constrained lower [CO2]atm limit of 680 ppm for the EECO. Paleotemperature estimates from leaf fossils and fluid inclusions in halite suggest an upper limit for [CO2]atm in the EECO from the nahcolite proxy of ∼1260 ppm. These data support a causal connection between elevated [CO2]atm and early Eocene global warmth, but at significantly lower [CO2]atm than previously thought, which suggests that ancient climates on Earth may have been more sensitive to a doubling of [CO2]atm than is currently assumed."

Extract: "These results show that [CO₂]atm may not have been as high as previously thought during the warmest interval of the Cenozoic, implying a climate sensitivity for CO₂ that is roughly twice as high as is currently assumed (Royer et al., 2012)."

24
the current high rate of anthropogenic radiative forcing (at least 100 times faster than during the PETM)

This may well happen later this century, but currently it seems more like 10x faster than during the PETM, according to Diffenbaugh & Field 2013 (see attachments below):
http://denning.atmos.colostate.edu/readings/Impacts/Ecosystems.Science-2013-Diffenbaugh-486-92.pdf

Such fast warming may indeed cause ECS to increase to levels that are higher than the natural ECS at the same temperature in the past, as far as I know (I would have to look for specific references).

Lennart,

Thanks for the catch (sometimes I type too fast), as indeed the current rate of CO₂ emissions is somewhere to 10 to 15 time the rate during the PETM (depending on which part of the PETM we compare to and whether we consider CO₂-equiv emission rates), see the attached image & associated linked article).

Title: "PETM: Global Warming, Naturally"

https://www.wunderground.com/climate/PETM

As to ECS increasing with continued warming, I believe that this is dynamically dependent on both radiative forcing path and rate.

Best,
ASLR

25
It is frustrating (to me at least) that the current generation of Earth System Models, ESMs (e. g. CMIP5), do not adequately address dynamical climate sensitivity.  Hopefully, CMIP6 and future phases of E3SM, will improve upon the accuracy of our current projections.

In this regards, the first linked reference (and associated image) calibrated an effective/specific equilibrium climate sensitivity (S) based on warming cycles during the past 784,000 years.  There findings for the upper end risk (e.g. RCP 8.5) indicated that the projected GMSTA range could be between 4.78C to 7.36C by 2100, based on one set of calculations.

Tobias Friedrich, Axel Timmermann, Michelle Tigchelaar, Oliver Elison Timm and Andrey Ganopolski (09 Nov 2016), "Nonlinear climate sensitivity and its implications for future greenhouse warming", Science Advances, Vol. 2, no. 11, e1501923, DOI: 10.1126/sciadv.1501923

http://advances.sciencemag.org/content/2/11/e1501923

Extract: "Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing—referred to as specific equilibrium climate sensitivity (S)—is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth’s future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections."

While Friedrich et. al. (2016) is a useful starting point, its use of an effective/specific equilibrium climate sensitivity (S) calibrated to the last 784,000 years of warming cycles, means that it is missing the aperiodic dynamical climate sensitivity illustrated in the third image, the risk of Hansen's ice-climate feedback mechanism and the risk that we may well exceed the value of S calibrated to the last 784,000 years, as the fourth attached image shows that S increases in value with increasing values of GMST.

In regards S increasing with GMST, per the following linked NOAA article is entitled: "Global Climate Report - Annual 2016"

https://www.ncdc.noaa.gov/sotc/global/201613#gtemp

Extract: "The average global temperature across land and ocean surface areas for 2016 was 0.94°C (1.69°F) above the 20th century average of 13.9°C (57.0°F), surpassing the previous record warmth of 2015 by 0.04°C (0.07°F)."


The immediate following linked reference clarifies the relationship of ECS and the dynamical sensitivity of climate models.:

Kevin M. Grise & Lorenzo M. Polvani (28 April 2016), "Is climate sensitivity related to dynamical sensitivity?", Journal of Geophysical Research Atmospheres, DOI: 10.1002/2015JD024687


http://onlinelibrary.wiley.com/doi/10.1002/2015JD024687/abstract

Abstract: "The atmospheric response to increasing CO2 concentrations is often described in terms of the equilibrium climate sensitivity (ECS). Yet, the response to CO2 forcing in global climate models is not limited to an increase in global-mean surface temperature: for example, the mid-latitude jets shift poleward, the Hadley circulation expands, and the subtropical dry zones are altered. These changes, which are referred to here as “dynamical sensitivity,” may be more important in practice than the global-mean surface temperature.

This study examines to what degree the inter-model spread in the dynamical sensitivity of 23 CMIP5 models is captured by ECS. In the Southern Hemisphere, inter-model differences in the value of ECS explain ~60% of the inter-model variance in the annual-mean Hadley cell expansion, but just ~20% of the variance in the annual-mean mid-latitude jet response. In the Northern Hemisphere (NH), models with larger values of ECS significantly expand the Hadley circulation more during winter months, but contract the Hadley circulation more during summer months. Inter-model differences in ECS provide little significant information about the behavior of the Northern Hemisphere subtropical dry zones or mid-latitude jets.

The components of dynamical sensitivity correlated with ECS appear to be driven largely by increasing sea surface temperatures, whereas the components of dynamical sensitivity independent of ECS are related in part to changes in surface temperature gradients. These results suggest that efforts to narrow the spread in dynamical sensitivity across global climate models must also consider factors that are independent of global-mean surface temperature."

Finally, I provide the following reference related to the calibration of dynamical sensitivity of climate models using paleodata.

The first following four linked references and I note that der Heydt et. al. 2016 concludes: "Such perturbations (illustrated in Fig. 1b,d) are not normally applied in climate models used for climate predictions [IPCC, 2013], where climate sensitivity is derived from model simulations considering prescribed, non-dynamic atmospheric CO2. In our conceptual model, we have derived climate sensitivities from both types of perturbations and find that the classical climate model approach (section 2.2, Fig. 4f) leads to significantly lower values of the climate sensitivity than the perturbations away from the attractor with dynamic CO2 (section 2.3, Fig. 11a). This emphasises the importance of including dynamic carbon cycle processes into climate prediction models. Moreover, it supports the idea that the real observed climate response may indeed be larger than the model predicted one, because those models never will include all feedback processes in the climate system.“

Anna S. von der Heydt, Peter Ashwin (Submitted on 12 Apr 2016), "State-dependence of climate sensitivity: attractor constraints and palaeoclimate regimes",    arXiv:1604.03311

http://arxiv.org/abs/1604.03311
&
http://arxiv.org/pdf/1604.03311v1.pdf

The second linked reference on the application of "dynamical systems theory" supports the position that the current effective ECS may be as high as 4.35C (but is masked both by lag times and by aerosol impacts):

Egbert H. van Nes, Marten Scheffer, Victor Brovkin, Timothy M. Lenton, Hao Ye, Ethan Deyle and George Sugihara (2015), "Causal feedbacks in climate change", Nature Climate Change, doi:10.1038/nclimate2568

http://www.nature.com/nclimate/journal/v5/n5/full/nclimate2568.html


The third linked reference examines the state dependency of ECS using paledata from the past 5 millions years and similarly finds that the effective ECS is higher than more CMIP5 models assume.

Köhler, P., de Boer, B., von der Heydt, A. S., Stap, L. B., and van de Wal, R. S. W. (2015), "On the state dependency of the equilibrium climate sensitivity during the last 5 million years", Clim. Past, 11, 1801-1823, doi:10.5194/cp-11-1801-2015.


http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.html
http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.pdf


The fourth linked reference could not make it more clear that paleo-evidence from inter-glacial periods indicates that ECS is meaningfully higher than 3C and that climate models are commonly under predicting the magnitude of coming climate change.  Furthermore, these finding concur with those of Köhler et al (2015) which indicates that inter-glacial values for specific ECS was about 45% higher than during glacial periods.

Dana L. Royer (2016), "Climate Sensitivity in the Geologic Past", Annual Review of Earth and Planetary Sciences, Vol. 44

http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-100815-024150?src=recsys


26
The linked article confirms that 2018 was the warmest year on record for ocean heat content (which is most important for the pending collapse of the WAIS, see the attached image) and that CO₂, methane and nitrous oxide concentrations all reached record levels in the atmosphere:

Title: "State of the climate: How the world warmed in 2018"

https://www.carbonbrief.org/state-of-the-climate-how-world-warmed-2018

Extract: "A number of records for the Earth’s climate were set in 2018:

•   It was the warmest year on record for ocean heat content, which increased markedly between 2017 and 2018.
•   …
•   Greenhouse gas concentrations reached record levels for CO2, methane, and nitrous oxide."

27
The fact that the Western Pacific warm pool has predominant influence on ECS, is bad news for those who believe in the ice-climate feedback mechanisms, as a slowing of the MOC (due to increasing ice mass loss) will directly increase the temperature of the Western Pacific, and thus will increase the frequency of El Nino events and the associated telecommunication of Tropical Pacific heat energy poleward:

Yue Dong, Cristian Proistosescu, Kyle Armour & David S. Battisti (Dec 19, 2018), "Attributing Historical and Future Evolution of Radiative Feedbacks to Regional Warming Patterns using a Green’s Function Approach: The Preeminence of the Western Pacific"

https://eartharxiv.org/tdrmx/

Abstract: "Global radiative feedbacks have been found to vary in global climate model (GCM) simulations. Atmospheric GCMS (AGCMs) driven with historical patterns of sea-surface temperatures (SST) and sea-ice concentrations produce radiative feedbacks that trend toward more negative values, implying low climate sensitivity, over recent decades.  Freely-evolving coupled GCMs driven by increasing CO₂ produce radiative feedbacks that trend toward more positive values, implying increasing climate sensitivity, in the future.  While this time-variation in feedbacks has been linked to evolving SST patterns, the role of particular regions has not been quantified.  Here, a Green's function is derived from a suite of simulations within an AGCM (NCAR's CAM4), allowing an attribution of global feedback changes to surface warming in each regions.

The results highlight the radiative response to surface warming in ascent regions of the western tropical Pacific as the dominant control on global radiative feedback changes.  Historical warming from the 1950s to 2000s preferentially occurred in the western Pacific, yielding a strong global outgoing radiative response at the TOA and producing a strongly negative global feedback.  Long-term warming in coupled GCMs occurs preferentially in tropical descent regions and in high latitudes, where surface warming yields small global TOA radiation changes, and thus a less-negative global feedback.  These results illuminate the importance of determining mechanism of warm pool warming for understanding how feedbacks have varied historically and will evolve in the future."

28
The linked reference indicates that Antarctica is currently losing ice mass at a rate six times that during the 1980s; which should not surprise anyone following this thread:

Eric Rignot, Jérémie Mouginot, Bernd Scheuchl, Michiel van den Broeke, Melchior J. van Wessem, and Mathieu Morlighem (January 14, 2019), "Four decades of Antarctic Ice Sheet mass balance from 1979–2017", PNAS https://doi.org/10.1073/pnas.1812883116

https://www.pnas.org/content/early/2019/01/08/1812883116

Abstract: "We use updated drainage inventory, ice thickness, and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the Antarctic Ice Sheet from 1979 to 2017. We compare the results with a surface mass balance model to deduce the ice sheet mass balance. The total mass loss increased from 40 ± 9 Gt/y in 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017. In 2009–2017, the mass loss was dominated by the Amundsen/Bellingshausen Sea sectors, in West Antarctica (159 ± 8 Gt/y), Wilkes Land, in East Antarctica (51 ± 13 Gt/y), and West and Northeast Peninsula (42 ± 5 Gt/y). The contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade with a cumulative 14.0 ± 2.0 mm since 1979, including 6.9 ± 0.6 mm from West Antarctica, 4.4 ± 0.9 mm from East Antarctica, and 2.5 ± 0.4 mm from the Peninsula (i.e., East Antarctica is a major participant in the mass loss). During the entire period, the mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), that is, consistent with enhanced polar westerlies pushing CDW toward Antarctica to melt its floating ice shelves, destabilize the glaciers, and raise sea level."

Significance Statement

We evaluate the state of the mass balance of the Antarctic Ice Sheet over the last four decades using a comprehensive, precise satellite record and output products from a regional atmospheric climate model to document its impact on sea-level rise. The mass loss is dominated by enhanced glacier flow in areas closest to warm, salty, subsurface circumpolar deep water, including East Antarctica, which has been a major contributor over the entire period. The same sectors are likely to dominate sea-level rise from Antarctica in decades to come as enhanced polar westerlies push more circumpolar deep water toward the glaciers.

See also the following related article:

Title: "Antarctica is losing ice six times faster than in 1980s"

https://www.axios.com/antarctica-ice-loss-has-grown-sixfold-in-past-4-decades-ad1ed0e1-ef89-4b80-9b14-242c847ac863.html


29
The two linked articles indicate that the Northwestern portion of the Ross Ice Shelf, RIS, is currently being destabilized by a previously unverified mechanism, i.e. local basal ice melting induced by '… seasonal masses of warm water near the ocean surface in front of the ice shelf.'  The attached image (which shows ice velocities from 2009) shows that a local weakening of buttressing action in the Northwestern portion of the RIS would likely lead to an acceleration of ice stream velocities for the important Byrd Glacier:

Title: "Antarctica's Largest Ice Shelf Could Be at Risk of Melting"

https://www.insidescience.org/news/antarcticas-largest-ice-shelf-could-be-risk-melting

Extract: "The ROSETTA-Ice researchers have built a computer model of the interconnected factors that control the Ross Ice Shelf, including seasonal conditions, ocean currents, and the structure of ice and bedrock on the adjacent continent. The model is based on data collected by the ROSETTA-Ice team using instruments mounted on aircraft and on undersea robots.

The findings suggest that a spot on the northwestern side of the ice shelf is melting in a way researchers have not seen before -- neither hydrofracture nor deep currents at the grounding line. Instead, the Ross's problem is seasonal masses of warm water near the ocean surface in front of the ice shelf.

The lost ice is currently being replaced by ice flowing down from the continent, so the shelf is not yet getting thinner. But it could easily start to thin as the climate continues to warm, and current projections don't take the processes the ROSETTA-Ice team observed into account, said Padman.
Most of the grounded glacier ice that is being held back by the Ross Ice Shelf is unlikely to melt anytime soon, in part because it is also held in place by the shape of underlying mountains and valleys, said Padman. But the melting corner of the Ross happens to be located right in front of a particularly vulnerable swathe of ice on the continent."

See also the associated presentation abstract:

Title: "C11A-04: Ice Shelf Vulnerability to Increased Seasonal Upper Ocean Warming" by Padman et al. (2018).

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/446984

Abstract: "Ice shelf vulnerability to climate change is strongly controlled by the interactions between ice, ocean and atmosphere. Most studies of ice shelves have focused on changes in melt rates near the deep grounding lines, driven by deep intrusions of warm water. Increased melting at the grounding line leads to mass imbalance and grounding line retreat, with potentially long-lasting consequences for ice dynamics. However, mass loss from anywhere on the ice shelf can alter the back-stress acting on the grounded ice. For Ross Ice Shelf, basal melting near the grounding line is governed by deep circulation of cold, dense water that is formed by winter convection in polynyas near the ice front. Circulation of this dense water is primarily controlled by seafloor bathymetry and is resistant to change. In contrast, melt rates close to the ice front are known to vary on seasonal and interannual time scales, and ice-sheet models indicate that grounded ice flow into the ice shelf is sensitive to changes in ice thickness near the ice front.

We use data from new radar surveys of Ross Ice Shelf to measure multi-decadal averaged basal melt rates within a key region of the ice shelf near Ross Island. These rates are comparable to estimates from satellite altimetry, suggesting that ocean processes governing melt near the ice front have been stable for several decades. However, ocean models suggest that melt in this region is caused by warm surface waters in summer intruding beneath the ice shelf where ice draft is shallow. These results indicate that the common assumption of Ross Ice Shelf stability during the next century may be incorrect, if the summer upper ocean temperature in the western Ross Sea increases significantly in response to a longer period free of sea ice or a decrease in summertime cloudiness. Our findings emphasize the importance of processes beyond the grounding line and call for a rethinking of the vulnerability of ice shelves in large-scale models of future ice sheet behavior."

30
The linked reference uses machine learning to demonstrate the consensus climate science underestimate the risk of carbon emissions that may occur from coastal temperate rainforests, with continued warming:

Gavin McNicol, Chuck Bulmer, David D'Amore, Paul Sanborn, Sari Saunders, Ian Giesbrecht, Santiago Gonzalez Arriola, Allison Bidlack, David Butman and Brian Buma (3 January 2019), "Large, climate-sensitive soil carbon stocks mapped with pedology-informed machine learning in the North Pacific coastal temperate rainforest", Environmental Research Letters, Volume 14, Number 1, https://doi.org/10.1088/1748-9326/aaed52

http://iopscience.iop.org/article/10.1088/1748-9326/aaed52/meta

Abstract
Accurate soil organic carbon (SOC) maps are needed to predict the terrestrial SOC feedback to climate change, one of the largest remaining uncertainties in Earth system modeling. Over the last decade, global scale models have produced varied predictions of the size and distribution of SOC stocks, ranging from 1000 to >3000 Pg of C within the top 1 m. Regional assessments may help validate or improve global maps because they can examine landscape controls on SOC stocks and offer a tractable means to retain regionally-specific information, such as soil taxonomy, during database creation and modeling. We compile a new transboundary SOC stock database for coastal watersheds of the North Pacific coastal temperate rainforest, using soil classification data to guide gap-filling and machine learning approaches to explore spatial controls on SOC and predict regional stocks. Precipitation and topographic attributes controlling soil wetness were found to be the dominant controls of SOC, underscoring the dependence of C accumulation on high soil moisture. The random forest model predicted stocks of 4.5 Pg C (to 1 m) for the study region, 22% of which was stored in organic soil layers. Calculated stocks of 228 ± 111 Mg C ha−1 fell within ranges of several past regional studies and indicate 11–33 Pg C may be stored across temperate rainforest soils globally. Predictions compared very favorably to regionalized estimates from two spatially-explicit global products (Pearson's correlation: ρ = 0.73 versus 0.34). Notably, SoilGrids 250 m was an outlier for estimates of total SOC, predicting 4-fold higher stocks (18 Pg C) and indicating bias in this global product for the soils of the temperate rainforest. In sum our study demonstrates that CTR ecosystems represent a moisture-dependent hotspot for SOC storage at mid-latitudes.

31
The linked reference indicates that projected increases of rainfall in Arctic permafrost regions will result in an increase in methane, that will "… increase near‐term global warming associated with permafrost thaw …", which is currently not considered in consensus science projections:

R. B. Neumann et al. (03 January 2019), "Warming effects of spring rainfall increase methane emissions from thawing permafrost", Geophysical Research Letters, https://doi.org/10.1029/2018GL081274

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081274

Abstract
Methane emissions regulate the near‐term global warming potential of permafrost thaw, particularly where loss of ice‐rich permafrost converts forest and tundra into wetlands. Northern latitudes are expected to get warmer and wetter, and while there is consensus that warming will increase thaw and methane emissions, effects of increased precipitation are uncertain. At a thawing wetland complex in Interior Alaska, we found that interactions between rain and deep soil temperatures controlled methane emissions. In rainy years, recharge from the watershed rapidly altered wetland soil temperatures, warming the top ~80 cm of soil in spring and summer, and cooling it in autumn. When soils were warmed by spring rainfall, methane emissions increased by ~30%. The warm, deep soils early in the growing season likely supported both microbial and plant processes that enhanced emissions. Our study identifies an important and unconsidered role of rain in governing the radiative forcing of thawing permafrost landscapes.

Plain Language Summary
Because the world is getting warmer, permanently frozen ground around the arctic, known as permafrost, is thawing. When permafrost thaws, the ground collapses and sinks. Often a wetland forms within the collapsed area. Conversion of permanently frozen landscapes to wetlands changes the exchange of greenhouse gases between the land and atmosphere, which impacts global temperatures. Wetlands release methane into the atmosphere. Methane is a potent greenhouse gas. The ability of methane to warm the Earth is 32‐times stronger than that of carbon dioxide over a period of 100 years. In our study, we found that methane release from a thaw wetland in Interior Alaska was greater in rainy years when rain fell in spring. When spring rainwater entered the wetland, it rapidly warmed wetland soils. Rain has roughly the same temperature as the air, and during springtime in northern regions, the air is warmer than the ground. The microbial and plant processes that generate methane increase with temperature. Therefore, wetland soils, warmed by spring rainfall, supported more methane production and release. Northern regions are expected to receive more rainfall in the future. By warming soils and increasing methane release, this rainfall could increase near‐term global warming associated with permafrost thaw.

32
The linked reference indicates that models of key Antarctic ice shelves currently underestimate observes ice melt rates, indicating that both more refined  local meshing needs to be employed as well as improved ice-ocean interaction, otherwise we are underestimating our associated risk levels:

D. N. Goldberg et al. (31 December 2018), "How Accurately Should We Model Ice Shelf Melt Rates?", Geophysical Research Letters, https://doi.org/10.1029/2018GL080383

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080383

Abstract
Assessment of ocean‐forced ice sheet loss requires that ocean models be able to represent sub‐ice shelf melt rates. However, spatial accuracy of modeled melt is not well investigated, and neither is the level of accuracy required to assess ice sheet loss. Focusing on a fast‐thinning region of West Antarctica, we calculate spatially resolved ice‐shelf melt from satellite altimetry and compare against results from an ocean model with varying representations of cavity geometry and ocean physics. Then, we use an ice‐flow model to assess the impact of the results on grounded ice. We find that a number of factors influence model‐data agreement of melt rates, with bathymetry being the leading factor; but this agreement is only important in isolated regions under the ice shelves, such as shear margins and grounding lines. To improve ice sheet forecasts, both modeling and observations of ice‐ocean interactions must be improved in these critical regions.

Plain Language Summary
The Antarctic coastline is fringed by large floating ice shelves, often the size of cities or larger. They play a crucial role as a stopgap against acceleration of the ice sheet, and their loss could lead to considerable sea level rise. Many of these ice shelves are exposed to warm waters from farther north, leading to considerable melting underneath. Scientists use models of the ice sheet and the ocean in order to understand the link between warming oceans and sea levels, and how this might change in the future. In our study we focus on one of these fast‐thinning ice shelves and determine through satellite imagery that melting is not uniform across the ice shelf but is highly focused in certain areas due to ocean currents. Using state‐of‐the‐art ice and ocean models, we investigate what information will be needed in order to predict how the Antarctic Ice Sheet will respond to climate change. Our findings suggest that improved knowledge of ocean depth under ice shelves, as well as improved understanding of ocean flow just below the ice bottom, will be vital in determining the effects of climate change on ice shelves and ice sheets.

33
I have previously speculated that when the Getz Ice Shelf eventually collapses, the associated regional changes in seawater temperatures and current flows could contribute to an acceleration of the degradation of the Ross Ice Shelf, RIS (see the Hazard Analysis for the FRIS/RIS in the 2012 to 2060 Timeframe).  In this regards, I provide the following linked reference that verifies the relationship of changes (climate change related) to the local winds that changed the local upwelling of warm CDW and consequent increasing in ice mass loss from the Getz Ice Shelf:

K. M. Assmann et al. (04 January 2019), "Warm Circumpolar Deep Water at the western Getz Ice Shelf Front, Antarctica", Geophysical Research Letters, https://doi.org/10.1029/2018GL081354

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081354

Abstract
The Getz Ice Shelf is one of the largest sources of fresh water from ice shelf basal melt in Antarctica. We present new observations from three moorings west of Siple Island 2016‐18. All moorings show a persistent flow of modified Circumpolar Deep Water towards the western Getz Ice Shelf. Unmodified Circumpolar Deep Water with temperatures up to 1.5° C reaches the ice shelf front in frequent episodes. These represent the warmest water observed at any ice shelf front in the Amundsen Sea. Mean currents within the warm bottom layer of 18‐20 cm s−1 imply an advection time scale of 7 days from shelf break to ice shelf front. Zonal wind stress at the shelf break affects heat content at the ice shelf front on weekly to monthly time scales. Our two‐year mooring records also evince that upwelling over the shelf break controls thermocline depth on sub‐annual to annual time scales.

Plain Language Summary
The recent retreat of the West Antarctic Ice Sheet has been linked to changes in the transport of warm ocean water up to 1.5C to the floating ice shelves in the Amundsen Sea. One of these is the Getz Ice Shelf that produces one of the largest amounts of ice shelf melt water in Antarctica. To measure how much ocean heat is transported towards this ice shelf, we deployed a series of temperature, salinity and current sensors at its western end from 2016‐2018. We find a constant flow of warm water towards the ice shelf cavity. Comparing our ocean observations with wind data from the area we found that stronger easterly winds in the area make it harder for the warm water to reach the ice shelf front by depressing the warm bottom layer over the shelf break. Climate projections indicate that these easterlies will weaken in future, making it easier for the warm water to reach the ice shelf base. Gradients in the wind field over the shelf break control the thickness of the warm layer on longer time scales. This provides the missing ocean evidence for previous studies that have linked this wind mechanism to ice sheet changes.

34
The linked reference indicates that as the Atlantic warm pool (AWP) continues to warm (& I note that a slowing of the AMOC acts to warm the AWP), enhance telecommunications from the AWP to the Pacific, increases the frequency of El Nino events; which increases ECS, and the telecommunication of heat energy from the Tropical Pacific to West Anarctica:

Park, JH., Li, T., Yeh, SW. et al. (2019), "Effect of recent Atlantic warming in strengthening Atlantic–Pacific teleconnection on interannual timescale via enhanced connection with the pacific meridional mode", Clim Dyn, https://doi.org/10.1007/s00382-018-4591-7

https://link.springer.com/article/10.1007%2Fs00382-018-4591-7

Abstract: "The Atlantic warm pool (AWP), which features the highest sea surface temperature (SST) in the western Hemisphere in boreal summer to early fall, has been known to have a significant influence on the climate in its surrounding regions. It is reported that the AWP has become warmer and warmer, so that AWP–SST during a couple of recent decades has been higher than any other period since the twentieth century. Under the increased mean AWP–SST, atmospheric responses to the anomalous AWP–SST are intensified, which corresponds to a higher possibility of deep convection formation. Through Rossby wave propagation induced by the deep convection, AWP signals are able to reach further west toward the central North Pacific. At this moment, anomalous northerly winds are introduced over the North Pacific, which advects negative moist static energy (MSE) into the subtropics and simultaneously contributes to a SST cooling by interacting with northerly mean trade winds. Owing to the Gill-type response to a negative heating anomaly associated with the anomalous SST cooling and the negative MSE, the anomalous northerly winds are further developed over the North Pacific. Such air–sea coupling persists throughout fall to winter, leading to Pacific meridional mode development in the following spring. Subsequently, the PMM acts to boost El Niño and Southern Oscillation events. Coupled model experiments were carried out to investigate the extent to which the mean AWP–SST warming strengthens the Atlantic–Pacific interbasin teleconnection on interannual timescales, and it is proven to support observational analysis."

35
...
Maybe this could contribute to an explanation:
http://advances.sciencemag.org/content/2/4/e1501693

“We analyze space geodetic and satellite gravimetric data for the period 2003–2015 to show that all of the main features of polar motion are explained by global-scale continent-ocean mass transport. The changes in terrestrial water storage (TWS) and global cryosphere together explain nearly the entire amplitude (83 ± 23%) and mean directional shift (within 5.9° ± 7.6°) of the observed motion. We also find that the TWS variability fully explains the decadal-like changes in polar motion observed during the study period, thus offering a clue to resolving the long-standing quest for determining the origins of decadal oscillations. This newly discovered link between polar motion and global-scale TWS variability has broad implications for the study of past and future climate.”

The Nature article doesn't seem to mention this possibility?

Lennart,

Thanks for the 2016 reference, while the following linked 2018 article (& associated image) about the findings of the GRACE satellite findings about changes in freshwater over the past 14 years, shows that water changes in aquifers, ice, lakes, rivers, snow and soil are all having significant gravitational impacts on the Earth:

Title: "NASA finds 'human fingerprint' in many areas of water-supply change worldwide"

https://www.usatoday.com/story/tech/nation-now/2018/05/16/nasa-global-water-supply-study/616431002/

Extract: "The researchers analyzed 14 years of data from NASA’s twin Gravity Recovery and Climate Experiment satellites, which the space agency has dubbed GRACE. They studied areas with large increases or decreases in freshwater — including water stored in aquifers, ice, lakes, rivers, snow and soil — to determine the most likely causes of these changes.

Changes in two-thirds of the 34 hot spots from California to China may be linked to climate change or human activities, such as excessive groundwater pumping for farming, according to their new study."

Best,
ASLR

36
The linked reference, and associate article, indicate that '… a geomagnetic pulse under South America in 2016 shifted the magnetic field unexpectedly …'; which may have triggered '… a high-speed jet of liquid iron beneath Canada…'; which may have weakened the magnetic field beneath Canada, allowing the high-strength magnetic field beneath Siberia to accelerate the migration of the magnetic north pole towards Siberia since 2016.  Whether the acceleration in magnetic polar wander shown in the first attached image (from Nature 2019) is related to the high magnetic anomaly in the South Atlantic, see the second image (and Replies #113, #115 & #117), and thus possibly to Antarctic ice mass loss, is a matter worth investigating.

Title: "Earth's magnetic field is acting up and geologists don't know why"

https://www.nature.com/articles/d41586-019-00007-1?utm_source=twt_nnc&utm_medium=social&utm_campaign=naturenews&sf205680051=1

Extract: "First, that 2016 geomagnetic pulse beneath South America came at the worst possible time, just after the 2015 update to the World Magnetic Model.

… scientist are working to understand why the magnetic field is changing so dramatically. Geomagnetic pulses, like the one that happened in 2016, might be traces back to 'hydromagnetic' waves arising from deep in the core.  And the fast motion of the north magnetic pole could be linked to a high-speed jet of liquid iron beneath Canada."

See also:

Earth's Magnetic Field has Moved Unexpectedly and Scientists Aren't Sure Why

https://www.newsweek.com/earth-magnetic-field-baffle-scientists-north-pole-siberia-canada-world-1286507

Extract: "Earth’s north magnetic pole is moving fast and in an unexpected way, baffling scientists involved in tracking its motions

"The error is increasing all the time,” Arnaud Chulliat, a geomagnetist at the University of Colorado Boulder and the National Oceanic and Atmospheric Administration (NOAA), told Nature. He said finding out the WMM had become inaccurate placed scientists in an “interesting situation” with experts wondering just what was going on.

According to Nature, a geomagnetic pulse under South America in 2016 shifted the magnetic field unexpectedly. This was exacerbated by the movement of the north magnetic pole. “The fact that the pole is going fast makes this region more prone to large errors,” Chulliat is quoted as saying.

Researchers are now trying to work out why the magnetic field is changing so quickly. They are studying the geomagnetic pulses, like the one that disrupted the WMM in 2016, which could, Nature reports, be the result of “hydromagnetic” waves emanating from Earth’s core.

To fix the World Magnetic Model, he and his colleagues fed it three years of recent data, which included the 2016 geomagnetic pulse. The new version should remain accurate, he says, until the next regularly scheduled update in 2020."

37
In this post I list three issues that I am not prepared to elaborate upon in separate individual posts:

1. As marine glaciers have collapsed numerous times in the past 35 million years, most of the key marine glaciers have previously dug troughs that should make them more susceptible to collapse in the near future, than during the Eemian/MIS 5.

2. The image shows an image from Skeptical Science showing the relative CO₂ velocity since 1850; which illustrates a sharp acceleration after 1950, and indicating that the current relative CO₂ velocity is several hundred times the velocity coming out of the last ice age.  First, due to the thermal inertia of the Earth's climate change systems, the sharp acceleration after 1950 can create a false sense of security that our current BAU pathway hasn't shown full, observable (as most of the observations have been collected after 1950) climate impact.  Second, our current high relative CO₂ velocity will not give terrestrial and oceanic biological ecologies adequate time to adapt; which will likely turn many associated carbon sinks into carbon sources. Finally, our current high relative CO₂ velocity makes it more likely that transient and phase related positive feedbacks (& forcings) will superimpose upon each other; which increases the risk that such a transient perturbation could push various Earth Systems beyond their tipping points.

3. While the IPCC reports cite a range of probably values for ECS, in reality only one value is applicable at any given time (noting that ECS can increase in value with increasing forcing).  Thus when policy makers, the public and/or the media focus on mean or mode values for ECS, they are eliminating your factor of safety against possible higher values of ECS.  This consideration has major significance for risk evaluations that use distributed values (PDFs) for ECS; which means that a worse case risk assessment for high values of ECS would indicate many times higher impacts on society that currently considered by the IPCC.

38
The linked reference indicates interhemispheric synchronization between the AO and the AAO, may be one factor contributing to the bipolar seesaw mechanism.

Y. Tachibana et al. (28 November 2018), "Interhemispheric Synchronization Between the AO and the AAO", Geophysical Research Letters, https://doi.org/10.1029/2018GL081002

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL081002

Abstract
Teleconnections between lower and higher latitude regions are widely known in both the Northern and Southern Hemispheres. To broaden our view of these teleconnections, we searched a reanalysis data set for evidence of a teleconnection between the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO), two widely separated circumpolar phenomena. Statistical analysis of the Japanese 55‐year reanalysis data set showed significant in‐phase synchronization between the AO and AAO, particularly in October and February, with a vertical structure extending from the troposphere to the stratosphere. This vertical structure may suggest a stratospheric control, and we did not find a significant signature indicating a tropical ocean control. We also observed decadal‐scale modulation of the synchronicity. Observational evidence implies that the stratospheric meridional circulation may be responsible for AO‐AAO synchronization.

Plain Language Summary
The Arctic Oscillation (AO) and the Antarctic Oscillation (AAO) are dominant atmospheric variability patterns in the Northern and Southern Hemispheres, respectively. Each is a pressure seesaw between the pole and the midlatitudes that remotely affects weather, climate, and environment around the world. We showed interhemispheric in‐phase synchronization between the AO and AAO in October and February, and we also found decadal‐scale variation of the synchronicity. Because the vertical structure of the AO‐AAO synchronization extends from the troposphere to the stratosphere, stratospheric variations may be responsible for the synchronization. This finding of AO‐AAO synchronization points the way to a better understanding of past, present, and future pole‐to‐pole climatic relationships and improvements in long‐term weather forecasts.

39
The linked reference provides further insights on the interaction (and timescales) between (of) Arctic sea ice loss and the bipolar seesaw mechanism:

Wei Liu et al, (26 December 2018), "Timescales and mechanisms of global climate impacts of Arctic sea ice loss mediated by the Atlantic meridional overturning circulation", Geophysical Research Letters, https://doi.org/10.1029/2018GL080602

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL080602

Abstract
We explore the global impacts of Arctic sea ice decline in climate model perturbation experiments focusing on the temporal evolution of induced changes. We find that climate response to a realistic reduction in sea ice cover varies dramatically between shorter decadal and longer multi‐decadal to centennial timescales. During the first two decades, when atmospheric processes dominate, sea ice decline induces a “bipolar seesaw” pattern in surface temperature with warming in the Northern and cooling in the Southern Hemisphere, leading to a northward displacement of the Intertropical Convergence Zone (ITCZ) and an expansion of Antarctic sea ice. In contrast, on multi‐decadal and longer timescales, the weakening of the Atlantic meridional overturning circulation, caused by upper‐ocean buoyancy anomalies spreading from the Arctic, mediates direct sea ice impacts and nearly reverses the original response pattern outside the Arctic. The Southern Hemisphere warms, a Warming Hole emerges in the North Atlantic, the ITCZ shifts southward, and Antarctic sea ice contracts.

Plain Language Summary
To understand how the recent Arctic sea ice decline may affect global climate, we conduct model experiments in which we modify the properties of Arctic sea ice, in order to simulate an Arctic sea ice loss similar to the observed. We find that climate response shows dramatically different patterns during different periods after the imposed sea ice decline. During the first one or two decades, Arctic sea ice decline allows more solar energy into the Northern Hemisphere (NH), altering the Earth's energy balance. As the NH warms while the Southern Hemisphere (SH) cools, the tropical rain belt moves northward and Antarctic sea ice expands. However, after several more decades to a century, the impacts from changes in the deep ocean become more important and eventually overwhelm the direct effects of sea ice loss on the atmosphere. The weakening of the Atlantic deep ocean circulation causes a cooling in the North Atlantic and a warming in the SH. Antarctic sea ice contracts and the tropical rain belt shifts back to it original position and further south.

40
In prior posts in this thread, I have noted several NH decadal-scale positive feedback mechanisms that individually will contribute to a slowing of the AMOC, which in turn will serve to slow the entire MOC, and which via the bipolar seesaw mechanism will in turn accelerate ice mass loss from the AIS.  The first linked reference adds the conversion of the Barents Sea into an arm of the North Atlantic to the list of decadal-scale feedback mechanisms, of which I provide bullet point summaries for the more significant mechanisms below:

•   The Greenland Atmospheric Blocking pressure (see Reply #433) will likely double the projected surface mass loss from the GIS in coming decades.  I note that this accelerated surface mass loss will initially come primarily from episodic weather related high surface temperature events, but with continued warming will increasingly include ice mass loss from weather related rainfall events.

•   Several key Southern Greenland marine terminating glaciers will almost certainly experience accelerated rates of iceberg calving, as their calving face retreats along retrograde bedslopes (see Reply #424).

•   The current and projected increased frequency of El Nino events will increase the ocean surface temperature in the Northern Pacific Ocean (via atmospheric telecommunication), and then in non-El Nino periods [see Dai & Tan (2017), cited below] the increased water vapor from the North Pacific is advected into the Arctic Basin where it contributes directly to Arctic Amplification and the associated flux of freshwater into the Arctic Ocean.

•   The Beaufort Gyre has been stockpiling increasing quantities of freshwater since 1997, and as the Arctic Sea Ice Area progressively decreases, this stockpile of freshwater becoming increasingly unstable and subject to advection into the North Atlantic (see Reply #431).

Lind, S., Ingvaldsen, R. B., & Furevik, T. (2018). Arctic warming hotspot in the northern Barents Sea linked to declining sea-ice import. Nature Climate Change, 8(7), 634–639. doi:10.1038/s41558-018-0205-y

https://www.nature.com/articles/s41558-018-0205-y

Abstract: "The Arctic has warmed dramatically in recent decades, with greatest temperature increases observed in the northern Barents Sea. The warming signatures are not constrained to the atmosphere, but extend throughout the water column. Here, using a compilation of hydrographic observations from 1970 to 2016, we investigate the link between changing sea-ice import and this Arctic warming hotspot. A sharp increase in ocean temperature and salinity is apparent from the mid-2000s, which we show can be linked to a recent decline in sea-ice import and a corresponding loss in freshwater, leading to weakened ocean stratification, enhanced vertical mixing and increased upward fluxes of heat and salt that prevent sea-ice formation and increase ocean heat content. Thus, the northern Barents Sea may soon complete the transition from a cold and stratified Arctic to a warm and well-mixed Atlantic-dominated climate regime. Such a shift would have unknown consequences for the Barents Sea ecosystem, including ice-associated marine mammals and commercial fish stocks."

See also:

Title: "Barents Sea seems to have crossed a climate tipping point"

https://arstechnica.com/science/2018/06/barents-sea-seems-to-have-crossed-a-climate-tipping-point/

Extract: "Now, a team of Norwegian scientists is suggesting it has watched the climate reach a tipping point: the loss of Arctic sea ice has flipped the Barents Sea from acting as a buffer between the Atlantic and Arctic oceans to something closer to an arm of the Atlantic.

The loss of ice also means that the surface water in this area is exchanging heat with the atmosphere and absorbing more sunlight during the long Arctic summer days. These two have combined to heat the top 100m of water dramatically. If the mean of its temperature from 1970-1999 is taken as a baseline, the temperatures from 2010-2016 are nearly four standard deviations higher. 2016—the most recent year we have validated data for—was 6.3 standard deviations higher.

This has the effect of heating the intermediate water from above. Meanwhile, the warm Atlantic water will heat it from below. As a result, the cold intermediate water has essentially vanished from the Barents Sea, turning the area into a basin dominated by Atlantic water. The entire water column, from surface to the sea floor, has both warmed and gotten saltier, all starting in the late-2000s.

But the general gist of the study is considerably more ominous: not only have we discovered a climate tipping point, but we've spotted it after the system has probably already flipped into a new regime. It also provides some sense of what to expect from the future. Rather than seeing the entire planet experience a few dramatic changes, we're likely to see lots of regional tipping points that have more of a local effect. The future will be the sum of these events and their interactions, making it a bit harder to predict which changes we should be planning for."
&

Panxi Dai and Benkui Tan (2017), "The Nature of the Arctic Oscillation and Diversity of the Extreme Surface Weather Anomalies It Generates", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0467.1

https://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0467.1

Abstract: "Through a cluster analysis of daily NCEP–NCAR reanalysis data, this study demonstrates that the Arctic Oscillation (AO), defined as the leading empirical orthogonal function (EOF) of 250-hPa geopotential height anomalies, is not a unique pattern but a continuum that can be well approximated by five discrete, representative AO-like patterns. These AO-like patterns grow simultaneously from disturbances in the North Pacific, the North Atlantic, and the Arctic, and both the feedback from the high-frequency eddies in the North Pacific and North Atlantic and propagation of the low-frequency wave trains from the North Pacific across North America into the North Atlantic play important roles in the pattern formation. Furthermore, it is shown that the structures and frequencies of occurrence of the five AO-like patterns are significantly modulated by El Niño–Southern Oscillation (ENSO). Warm (cold) ENSO enhances the negative (positive) AO phase, compared with ENSO neutral winters. Finally, the surface weather effects of these AO-like patterns and their implications for the AO-related weather prediction and the AO-North Atlantic Oscillation (NAO) relationship are discussed."

Readers should be aware that the caveats in AR5 relieves consensus scientists from any responsibility for accounts for the impacts of such regional and transient positive feedback mechanisms.

Edit: I forgot to note (reiterate) that the AMOC is currently in a natural slowing phase, and the decadal-scale freshwater inputs to the North Atlantic cited in this post, will serve to further decelerate the natural slowing of the AMOC (& the MOC), in the next few decades.

Edit2: For those who find this post too subtle, I am suggesting that a transient plus of freshwater into the North Atlantic (say from 2020 to say 2040) would likely accelerate the timing of the initiation of the collapse of the WAIS; which would likely then (via the bipolar seesaw mechanism) lead to an acceleration of Arctic Amplification (say from 2040 to say 2080); which would likely tip the world's ECS into Early Pliocene like conditions even if anthropogenic GHG emissions pathway follows say SSP1-Baseline.

41
The linked reference indicates that CMIP5 projections of ice mass loss from the Greenland Ice Sheet may be too low by a factor of two:

Edward Hanna et al, Recent changes in summer Greenland blocking captured by none of the CMIP5 models, The Cryosphere Discussions (2018). DOI: 10.5194/tc-2018-91

https://www.the-cryosphere.net/12/3287/2018/tc-12-3287-2018-discussion.html

Abstract: "Recent studies note a significant increase in high-pressure blocking over the Greenland region (Greenland Blocking Index, GBI) in summer since the 1990s. Such a general circulation change, indicated by a negative trend in the North Atlantic Oscillation (NAO) index, is generally highlighted as a major driver of recent surface melt records observed on the Greenland Ice Sheet (GrIS). Here we compare reanalysis-based GBI records with those from the Coupled Model Intercomparison Project 5 (CMIP5) suite of global climate models over 1950–2100. We find that the recent summer GBI increase lies well outside the range of modelled past reconstructions and future GBI projections (RCP4.5 and RCP8.5). The models consistently project a future decrease in GBI (linked to an increase in NAO), which highlights a likely key deficiency of current climate models if the recently observed circulation changes continue to persist. Given well-established connections between atmospheric pressure over the Greenland region and air temperature and precipitation extremes downstream, e.g. over northwest Europe, this brings into question the accuracy of simulated North Atlantic jet stream changes and resulting climatological anomalies over densely populated regions of northern Europe as well as of future projections of GrIS mass balance produced using global and regional climate models."

Extract: " The GCM-forced projections may also underestimate future GrIS surface mass balance decreases by a factor of 2, independently of the precise timing and amplitude of global warming, if the recent observed circulation changes continue to persist in summer (Delhasse et al., 2018). Model– observation discrepancies and thus model fidelity may, of course, be partly addressed in CMIP6 but clearly this is far from certain and meanwhile CMIP5 represents the current “state of the science”. Given the recent rapid changes in Arctic climate and Greenland Ice Sheet dynamics – which were not well predicted 15–20 years ago – it is therefore essential that future climate modelling efforts focus on improving their representation of blocking, as this is a key aspect of mid- to high-latitude cryosphere–climate dynamics and change."

See also:

Title: "Climate models fail to simulate recent air-pressure changes over Greenland"

https://phys.org/news/2018-10-climate-simulate-air-pressure-greenland.html

Extract: " Climatologists may be unable to accurately predict regional climate change over the North Atlantic because computer model simulations have failed to accurately include air pressure changes that have taken place in the Greenland region over the last three decades.

Researchers compared real data with simulation data over a 30 year period and found that the simulations on average showed slightly decreasing air pressure in the Greenland region, when in fact, the real data showed a significant increase in high air pressure—or so-called 'Greenland blocking' - during the summer months.

See also:

Title: "Climate change is more extensive and worse than once thought"

https://phys.org/news/2018-11-climate-extensive-worse-thought.html

Extract: "By nature, scientists said they are overly conservative.

In nearly every case, when scientists were off the mark on something, it was by underestimating a problem not overestimating, said Watson, the British climate scientist.

But there are ultimate worst cases. These are called tipping points, after which change accelerates and you can't go back. Ice sheet collapses. Massive changes in ocean circulation. Extinctions around the world.

"In the early 1990s we only had hints that we could drive the climate system over tipping points," said Jonathan Overpeck, environment dean at University of Michigan. "We now know we might actually be witnessing the start of a mass extinction that could lead to our wiping out as much as half the species on Earth." "

Also see:

Title: "What the past can tell us about the future of climate change"

https://pursuit.unimelb.edu.au/articles/what-the-past-can-tell-us-about-the-future-of-climate-change

42
For those who are interested in the details of the differences in the lapse rate feedbacks between the tropics and the poles, I provide the following linked reference:

Matthew Henry and Timothy M. Merlis (2018), "The Role of the Nonlinearity of the Stefan–Boltzmann Law on the Structure of Radiatively Forced Temperature Change", Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0603.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0603.1

Abstract: "The Stefan–Boltzmann law governs the temperature dependence of the blackbody emission of radiation:  . A consequence of this nonlinearity is that a cold object needs a greater increase in temperature than a hot object in order to reach the same increase in radiation emitted. Therefore, this nonlinearity potentially has an impact on the structure of radiatively forced atmospheric temperature change in both the horizontal and vertical directions. For example, it has previously been argued to be a cause of polar amplification (PA) of surface air warming. Here, the role of this nonlinearity is investigated by 1) assessing the magnitude of its effect on PA compared to spatial variations in CO2’s radiative forcing for Earth’s atmosphere and 2) linearizing  in a gray radiation atmospheric general circulation model (GCM) with an interactive hydrological cycle. Estimates for Earth’s atmosphere show that the combination of the Planck feedback and forcing from CO2 would produce a tropically amplified warming if they were the only means of changing the Earth’s energy balance. Contrary to expectations, climate change simulations with linearized radiation do not have reduced polar amplification of surface air warming relative to the standard GCM configuration. However, simulations with linearized radiation consistently show less warming in the upper troposphere and more warming in the lower troposphere across latitudes. The lapse rate feedbacks from pure radiative and radiative–convective configurations of the model are used to show that the “cold-altitudes-warm-more” effect of the  nonlinearity carries across this model hierarchy"

43
The linked reference indicates that the new generation (e.g. CMIP5) of ESMs include numerous feedback mechanisms that were not included in the past generation (e.g. CMIP5).  The uncertainties associated with these new feedbacks represent a risk to society (with continued warming).  Furthermore, I reiterate that CMIP6 does not include any feedback mechanisms associated with ice cliff, and hydrofracturing, failure mechanism; which means that society may very well be in for a rude awakening circa 2040 +/-5-years:

Heinze, C., Eyring, V., Friedlingstein, P., Jones, C., Balkanski, Y., Collins, W., Fichefet, T., Gao, S., Hall, A., Ivanova, D., Knorr, W., Knutti, R., Löw, A., Ponater, M., Schultz, M. G., Schulz, M., Siebesma, P., Teixeira, J., Tselioudis, G., and Vancoppenolle, M.: Climate feedbacks in the Earth system and prospects for their evaluation, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2018-84, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2018-84/

Abstract. Earth system models (ESMs) are key tools for providing climate projections under different scenarios of human-induced forcing. ESMs include a large number of additional processes and feedbacks such as biogeochemical cycles that traditional physical climate models do not consider. Yet, some processes such as cloud dynamics and ecosystem functional response still have fairly high uncertainties. In this article, we present an overview of climate feedbacks for Earth system components currently included in state-of-the-art ESMs and discuss the challenges to evaluate and quantify them. Uncertainties in feedback quantification arise from the interdependencies of biogeochemical matter fluxes and physical properties, the spatial and temporal heterogeneity of processes, and the lack of long-term continuous observational data to constrain them. We present an outlook for promising approaches that can help quantifying and constraining the large number of feedbacks in ESMs in the future. The target group for this article includes generalists with a background in natural sciences and an interest in climate change as well as experts working in interdisciplinary climate research (researchers, lecturers, and students). This study updates and significantly expands upon the last comprehensive overview of climate feedbacks in ESMs, which was produced 15 years ago (NRC, 2003).

Extract: "Within an Earth system context, many more climatically relevant feedbacks influence climate projections under given forcing scenarios than in previous generations of physical climate models. In addition to the classical physical climate feedbacks, biogeochemical feedbacks are also considered in more complex Earth system models."

Caption for image: "Table 1: Classification of specific feedbacks (left vertical column) with respect to general “archetypes” of feedbacks. Feedbacks can be summarised as thermodynamic and composition altering feedbacks. Aerosol feedbacks are among the most complex feedbacks.  The numbers in front of the specific feedbacks refer to the headers/sub-headers of the respective sections in the text."

44
It is worth pointing out (reiterating) that a short-term surge (decadal) of ice mass loss (due to an acceleration of calving as the calving front retreats down a retrograde bedslope) from key South Greenland marine terminating glaciers (including both Jakobshavn and Kangerdlugssuaq Glaciers), would almost certainly accelerate ice mass loss from key Antarctic marine glaciers due to the bipolar seesaw mechanism:

Bevan, S. L., Luckman, A. J., Benn, D. I., Cowton, T., and Todd, J.: Warming of SE Greenland shelf waters in 2016 primes large glacier for runaway retreat, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-260, in review, 2019.

https://www.the-cryosphere-discuss.net/tc-2018-260/

Abstract. Kangerdluqssuaq Glacier in south-east Greenland has now retreated further inland than at any time in the past 33 years and is fast approaching a region of retrograde bedslope, meaning that continued rapid retreat is likely. Here we show that the current retreat was driven by anomalously warm surface water on the continental shelf during 2016. The warm surface water likely penetrated the fjord and weakened the mixture of sea ice and icebergs known as mélange, which is normally rigid enough to inhibit calving in winter. As Kangerdlugssuaq Glacier continued to calve almost continuously throughout 2017 and 2018 it accelerated by 35% and thinned by 35m.

Caption for the first image: "Figure 7. Surface elevation profiles for advanced (red, 26/06/2016) and retreated (blue, 09/05/2018) front positions, corresponding to the same colour points plotted in Fig. 3c. The surface velocity profile is the result of feature tracking TanDEM-X data from 29/05/2014 to 09/06/2014"

Edit: The second image shows how close the calving face for the Jakobshavn Glacier is to entering a retrograde bedslope:

An, L., E. Rignot, S. Elieff, M. Morlighem, R. Millan, J. Mouginot, D. M. Holland, D. Holland, and J. Paden (2017), Bed elevation of Jakobshavn Isbræ, West Greenland, from high-resolution airborne gravity and other data, Geophys. Res. Lett., 44, 3728–3736, doi:10.1002/2017GL073245.

Caption for second image: "Figure 3. Profile A-A’ along the deepest bed of Jakobshavn Isbræ, West Greenland, showing the surface and bed elevations from the MC reconstruction (grey), the GBMF data in this study (black), Bamber et al. [2013] (dotted red), Joughin et al. [2014] (dotted purple), and CReSIS (dark blue) with corresponding error bars in shaded color (±1 sigma). The surface elevation is from year 2007 to 2008 (MC, B2013,C2009) and 2012 (GBMF). Red stars denote bathymetry data in the fjord. Colored triangles denote the positions of the glacier grounding lines at different epochs with the same color table as in Figure 1. Origin of distance is the 1996 grounding line position. Superimposed on that plot with a secondary vertical axis on the left-hand side is a comparison of the observed gravity anomaly (continuous blue) versus the calculated (dotted blue) gravity anomaly in mGal along profile A-A’."

45
I have generally made relatively few posts about the dynamics between climate change and food production, as this matter seems to cut to the core of mankind's aspirational nature in the face of a very complex issue.  Here I use the word aspirational in the sense that 'the road to hell is paved with good intentions', in what James Hansen has called mankind's Faustian Bargain with the Earth's many biosystems (both wild and managed).

As this topic is so complex and politically charged, I will only make a few bullet points for the readers consideration and then I will provide some links to a few articles that err on the side of least drama on this topic as I could not find any references that directly face issues like the following bullet points in their various evaluations of our potential circumstances circa 2050 +/- 10-years.  Selected food production related issues relevant to this thread include:

1. Circa 2050 the median population projection per the UN is about 10 billion people, and meat consumption is projected to increase at an even faster rate (food demands between 2013 and 2050 are projected to increase by 50%).  BECCS and hydropower production both have a negative impact on food security, and also transportation and distribution for food will require make major demands on both energy (including fossil fuels) and infrastructure (ships, ports, road & rail etc), including due to climate change impacts on farm distributions.  I further not that currently world hunger is increasing, most likely due to the relatively mild impacts of climate change that we are already experiencing.
2. Abrupt climate change and ice-climate feedbacks associated with multiple meters of SLR in the coming decades, would have severe impacts on food production, virtually none of which are seriously addressed in any food security projections that I have ever seen.  Relevant topics include abrupt increases in: a. extreme weather events, b. shifts in rainfall and surface temperature patterns, c. coastal flooding (see the attached image from Hansen [2018]) of croplands and associated salinity intrusion into neighboring groundwater, etc.
3. Agriculture, forestry and land use already contribute on fifth of anthropogenic GHG emissions, and on a BAU pathway this percentage is likely to increase by 2050.  Furthermore, climate change is decreasing the nutritional value of crops and is increasing the risks of foodborne diseases and of transboundary pests.  Also, following a BAU pathway will increase climate change related human migration, which will increase regional and global conflicts.  Vegetation losses associated with abrupt climate change, will not only reduce the negative feedback from carbon sinks, but will increase carbon emissions from decaying plant matter.

Title: "Climate change will reshape the world’s agricultural trade"

http://theconversation.com/climate-change-will-reshape-the-worlds-agricultural-trade-102721

Extract: "Even the United States, which has opted out of the Paris Agreement, acknowledged at last year’s G7 summit that climate change was one of a number of threats to “our capacity to feed a growing population and need[ed] to be taken into serious consideration”.

However, the most recent UN report on food security and nutrition shows that world hunger is on the rise again and scientists believe this is due to climate change."
&

Title: "The future of food production amid global change"

http://news.mit.edu/2018/mit-joint-program-workshop-explores-future-food-production-amid-global-change-1120

Extract: "When it comes to impacting global change, agriculture cuts both ways. Subject to the vicissitudes of global climate change, population, and economic growth, the cultivation of crops and livestock alters atmospheric concentrations of planet-warming greenhouse gases and contributes to pollution of freshwater and coastal areas. Assessing the risks to and from the agriculture sector — and identifying opportunities for the sector to thrive amid global change — is both urgent and essential.

The Outlook shows significant increases in food production driven by population and economic growth as well as transformation of the value chain, with more rapid growth in livestock than crops.

Observing that 70 percent of today’s freshwater withdrawals are for irrigation, and that by 2050 about 17 percent of all water now used in agriculture will be at risk from reallocation to nonagricultural economic growth, population and urban growth, and environmental protection, Strzepek highlighted several trends that pose a growing threat to such withdrawals, including the adoption of clean energy generation through hydropower at the expense of water for irrigation.

“You can get a lot of energy at the expense of water and food security,” said Strzepek, who co-authored a study indicating that agriculture has the lowest marginal value of all economic sectors. “We’re seeing rapid growth and urbanization in Africa, and increased hydropower, which increases water demands. Where do we invest in the future? Water for agriculture? Water for energy? Where do we put our values?”

Joint Program Deputy Director C. Adam Schlosser explored the extent to which land-use and land-cover change impact the local, regional, and global climate by absorbing or redirecting energy received from the sun. He noted that at the regional level, changes in land use and land cover lead to corresponding changes in albedo (reflectivity), soil moisture, canopy, and plant characteristics, which can collectively amplify or offset global warming from key atmospheric greenhouse gases."

See also:

"Climate Change in a Nutshell: The Gathering Storm", 18 December 2018, by James Hansen

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

Extract: "In reality CO2 is not only continuing to increase, its rate of growth is increasing.  The reason is that global population and energy demands continue to increase, and about 85 percent of global energy is provided by fossil fuels.

A case has been made (Ice Melt, 2016) that the doubling time for ice sheet mass loss, assuming continued growth of fossil fuel emissions, may be as short as 10-20 years, based on evidence from the combination of paleoclimate data, modern observations, and ocean-atmosphere modeling.   In that case, multi-meter sea level rise would occur on a time scale of 50-150 years."

46
I have been periodically encouraged to post again in other threads, but I have decided not to do so; nevertheless, while the following information could easily be posted in the "Adapting to the Anthropocene", the "Systemic Isolation" and/or other threads, I post it here because I feel that it may help some readers to better understand why mankind seems to be barreling towards an "Ice Apocalypse" when it is within our collective 'free feel' to stop proceeding on such a harmful path.

All of the following links lead to information about Karl Friston's various efforts to explain his 'free energy principle' which uses formulae (e.g. see the attached image) from physics to define the 'prediction error' of models (or 'inference engines') where by minimizing the 'free energy' one minimizes the 'prediction error' and thus minimizes surprises.  Friston go on beyond considering only traditional Bayesian 'inference engines' to define 'active inference' where active systems (say human minds) can use their free will to deal with surprises by either accepting the short-comings of the model (or 'inference engine' associated with a particular 'Markov Blanket') and make changes to the model, or by acting to make their predictions come true.

The 'free energy principle' can used to better understand how human society has made the collective decision that it has made to stay on a BAU pathway, and its mathematics can also be used to improve AI projections; that could possibly help society to better deal with abrupt climate change in the coming decades:

Title: "The Genius Neuroscientist Who Might Hold the Key to True AI"

https://www.wired.com/story/karl-friston-free-energy-principle-artificial-intelligence/

Extract: "Friston calls this his first scientific insight, a moment when “all these contrived, anthropomorphized explanations of purpose and survival and the like all seemed to just peel away,” he says. “And the thing you were observing just was. In the sense that it could be no other way.”

Hinton described a new technique he’d devised to allow computer programs to emulate human decisionmaking more efficiently—a process for integrating the input of many different probabilistic models, now known in machine learning as a “product of experts.”

Inspired by Hinton’s ideas, and in a spirit of intellectual reciprocity, Friston sent Hinton a set of notes about an idea he had for connecting several seemingly “unrelated anatomical, physiological, and psychophysical attributes of the brain.” Friston published those notes in 2005—the first of many dozens of papers he would go on to write about the free energy principle.

The psychologist Christopher Frith—who has an h-index on par with Friston’s—once described a Markov blanket as “a cognitive version of a cell membrane, shielding states inside the blanket from states outside.”

In Friston’s mind, the universe is made up of Markov blankets inside of Markov blankets. Each of us has a Markov blanket that keeps us apart from what is not us. And within us are blankets separating organs, which contain blankets separating cells, which contain blankets separating their organelles. The blankets define how biological things exist over time and behave distinctly from one another. Without them, we’re just hot gas dissipating into the ether.

The concept of free energy itself comes from physics, which means it’s difficult to explain precisely without wading into mathematical formulas. In a sense that’s what makes it powerful: It isn’t a merely rhetorical concept. It’s a measurable quantity that can be modeled, using much the same math that Friston has used to interpret brain images to such world-¬changing effect. But if you translate the concept from math into English, here’s roughly what you get: Free energy is the difference between the states you expect to be in and the states your sensors tell you that you are in. Or, to put it another way, when you are minimizing free energy, you are minimizing surprise.

So far, as you might have noticed, this sounds a lot like the Bayesian idea of the brain as an “inference engine” that Hinton told Friston about in the 1990s. And indeed, Friston regards the Bayesian model as a foundation of the free energy principle (“free energy” is even a rough synonym for “prediction error”). But the limitation of the Bayesian model, for Friston, is that it only accounts for the interaction between beliefs and perceptions; it has nothing to say about the body or action. It can’t get you out of your chair.

This isn’t enough for Friston, who uses the term “active inference” to describe the way organisms minimize surprise while moving about the world. When the brain makes a prediction that isn’t immediately borne out by what the senses relay back, Friston believes, it can minimize free energy in one of two ways: It can revise its prediction—absorb the surprise, concede the error, update its model of the world—or it can act to make the prediction true.

And in fact, this is how the free energy principle accounts for everything we do: perception, action, planning, problem solving. When I get into the car to run an errand, I am minimizing free energy by confirming my hypothesis—my fantasy—through action.

For Friston, folding action and movement into the equation is immensely important. Even perception itself, he says, is “enslaved by action”: To gather information, the eye darts, the diaphragm draws air into the nose, the fingers generate friction against a surface. And all of this fine motor movement exists on a continuum with bigger plans, explorations, and actions.

So what happens when our prophecies are not self-fulfilling? What does it look like for a system to be overwhelmed by surprise? The free energy principle, it turns out, isn’t just a unified theory of action, perception, and planning; it’s also a theory of mental illness."

See also:

Title: "Free energy principle"

https://en.wikipedia.org/wiki/Free_energy_principle
&

Title: "Free Energy Principle — Karl Friston"


&

Title: "Karl Friston: Active inference and artificial curiosity"


&

Title: "Markov blanket"

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

Extract: "In statistics and machine learning, the Markov blanket for a node in a graphical model contains all the variables that shield the node from the rest of the network. This means that the Markov blanket of a node is the only knowledge needed to predict the behavior of that node and its children. The term was coined by Judea Pearl in 1988."

47
The linked reference indicates that the warming of the North Pacific subpolar waters in likely the most important feedback for driving enhanced Arctic Amplification with continued global warming, and the attached image demonstrates how the North Pacific subpolar water can be warmed directly by atmospheric telecommunication of energy from the Tropical Pacific.  If show this indicates that the CMIP5 projections likely underestimate ECS, and as ice-climate feedback would likely accelerate warming the Tropical Pacific, it is likely that CMIP6 projections will also underestimate ECS as these models do not consider ice-cliff failures or hydrofracturing:

Summer Praetorius, Maria Rugenstein, Geeta Persad, Ken Caldeira. Global and Arctic climate sensitivity enhanced by changes in North Pacific heat flux. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05337-8

https://www.nature.com/articles/s41467-018-05337-8

Abstract: "Arctic amplification is a consequence of surface albedo, cloud, and temperature feedbacks, as well as poleward oceanic and atmospheric heat transport. However, the relative impact of changes in sea surface temperature (SST) patterns and ocean heat flux sourced from different regions on Arctic temperatures are not well constrained. We modify ocean-to-atmosphere heat fluxes in the North Pacific and North Atlantic in a climate model to determine the sensitivity of Arctic temperatures to zonal heterogeneities in northern hemisphere SST patterns. Both positive and negative ocean heat flux perturbations from the North Pacific result in greater global and Arctic surface air temperature anomalies than equivalent magnitude perturbations from the North Atlantic; a response we primarily attribute to greater moisture flux from the subpolar extratropics to Arctic. Enhanced poleward latent heat and moisture transport drive sea-ice retreat and low-cloud formation in the Arctic, amplifying Arctic surface warming through the ice-albedo feedback and infrared warming effect of low clouds. Our results imply that global climate sensitivity may be dependent on patterns of ocean heat flux in the northern hemisphere."

Extract: "Systematic cold biases in North Pacific and North Atlantic SSTs in CMIP5 models48 may thus partly lead to an underestimation of Arctic warming and sea-ice decline in climate projections, with important ramifications for climate and ecological tipping points in the Arctic."

See also:

Title: "Pacific Ocean's effect on Arctic warming"

https://www.sciencedaily.com/releases/2018/08/180807095149.htm

Extract: "Paleoclimate records show that climate change in the Arctic can be very large and happen very rapidly. During the last deglaciation, as the planet was starting to warm from rising greenhouse gases, there were two episodes of accelerated warming in the Arctic -- with temperatures increasing by 15°C (27°F) in Greenland over the course of decades. Both events were accompanied by rapid warming in the mid-latitude North Pacific and North Atlantic oceans."

48
While in Reply #353 I provided the first attached image as one simple example of how AR5's ECS risk (probability of occurrence times consequences) could have been better conveyed to decision makers (including the public).  That said, in this post I would like to note that I do not agree with AR5's assessment of the PDF for ECS; nor do I believe that possible high values of ECS represents the only source of under-represented risk of abrupt climate change in the coming decades.

With regards to AR5's assessment of the PDF (probability density function) for ECS I note that:
1. The 1.5C value at the lower end of the likely range, was based on incorrect interpretations of observed data, which has subsequently been proven to be incorrect, so the lower value of the likely range should have been 2C as it was in AR4.

2. AR5 ECS range mixes different means of calculating ECS that result in different definitions of ECS, without any effort to normalize/standardize the values under condition.  AR5's sole bases for including different values of ECS for inclusion in the PDF is whether they fall with the 10% to 90% range of peer-reviewed references published before the cut-off date.  For example, AR5 combines inferred ECS values with true ECS values.

3. AR5 assumes values of ECS that are not 'state-dependent'; which means that AR5 does not consider possible increases in ECS due to either increasing temperature, nor due to ice-climate,  feedback mechanisms (see the second attached image from Hansen and Sato 2012).

With regard to consequences, high values of ECS will most likely cause a collapse of the WAIS (and other key marine glaciers) in the coming decades; which would cause multiple meters of sea level rise, the impacts of which are certainly not included in the first attached image.

49
Discovery of recent Antarctic ice sheet collapse raises fears of a new global flood

Quote
Some 125,000 years ago, during the last brief warm period between ice ages, Earth was awash. Temperatures during this time, called the Eemian, were barely higher than in today’s greenhouse-warmed world. Yet proxy records show sea levels were 6 to 9 meters higher than they are today, drowning huge swaths of what is now dry land.

Scientists have now identified the source of all that water: a collapse of the West Antarctic Ice Sheet. Glaciologists worry about the present-day stability of this formidable ice mass. Its base lies below sea level, at risk of being undermined by warming ocean waters, and glaciers fringing it are retreating fast. The discovery, teased out of a sediment core and reported last week at a meeting of the American Geophysical Union in Washington, D.C., validates those concerns, providing evidence that the ice sheet disappeared in the recent geological past under climate conditions similar to today’s. “We had an absence of evidence,” says Anders Carlson, a glacial geologist at Oregon State University in Corvallis, who led the work. “I think we have evidence of absence now.”

If it holds up, the finding would confirm that “the West Antarctic Ice Sheet might not need a huge nudge to budge,” says Jeremy Shakun, a paleoclimatologist at Boston College. That, in turn, suggests “the big uptick in mass loss observed there in the past decade or two is perhaps the start of that process rather than a short-term blip.” If so, the world may need to prepare for sea level to rise farther and faster than expected: Once the ancient ice sheet collapse got going, some records suggest, ocean waters rose as fast as some 2.5 meters per century.

http://www.sciencemag.org/news/2018/12/discovery-recent-antarctic-ice-sheet-collapse-raises-fears-new-global-flood
wdmn,

Thanks for your link to the new evidence about SLR during the Eemian Peak (MIS 5e); however, when I read the associated article it struck me that some people reading the article might believe that SLR during the Eemian might represent an upper-bound limit for the consequences of our current situation.  Furthermore, I am concerned that some readers of my prior posts in this thread may be confused by the dynamic nature of such matters as the 'state-dependence' of climate sensitivity and what it means to 'tip' from one climate state (say our current climate state) into another climate state (say the Early-Pliocene) in the context of oscillating/chaotic Earth Systems, such as indicated by the first 2D image [where panel a shows a normalized climate state (say GMSTA) on the y-axis and a generic climate driver (say GHG) on the x-axis; and panel b showing the time-evolution of the driver for two different scenarios, one leading to a climate state tipping event and one not leading to a climate state tipping event] from Bathiany et al. (2018), and/or the second 3D image (where the z-axis would be other controlling parameters such as the various feedback mechanisms) of abrupt shifts in climate state.

Bathiany, S., Scheffer, M., van Nes, E. H., Williamson, M. S., & Lenton, T. M. (2018). Abrupt Climate Change in an Oscillating World. Scientific Reports, 8(1). doi:10.1038/s41598-018-23377-4, https://doi.org/10.1038/s41598-018-23377-4

https://www.nature.com/articles/s41598-018-23377-4

Caption for the first image: "Figure 1. Stable states and trajectories in the example system (Eq. 1). (a) The equilibria of state x for constant driver D are shown as black lines (continuous: stable; dashed: unstable). The flow towards a stable state is shown as dashed orange arrows; B1 and B2 indicate the bifurcation points. (b) Time evolution of driver D for two pulses, the red one having a longer period than the blue one. The trajectories of the system that result from these forcings are shown as red and blue curves in (a). See Supplementary Information for details on the parameter choices."

Now, to take a larger paleo-overview, I have previous noted (see Replies #252 and #342) that climate sensitivity was higher during the Holsteinian Peak (MIS 11c) than during modern times, during the Holocene Peak and during the Eemian Peak; to the extent that the current ESM projections have not yet been able to match the observed climate sensitivity of the Holsteinian because they intentionally omit numerous possible feedback mechanisms (such as the ice-climate feedback and/or various methane feedback mechanisms).  Note that adding such feedback mechanisms into the ESM models would be the same as moving up the z-axis in the second image, which reduces the size of bifurcation gap between different climate states, thus making it easier for a perturbation (whether a pulse of GHG, or the collapse of the WAIS) to cause a transition into the higher climate state.

Reasons to believe that the MIS 11c is more relevant to our current/modern climate change risks include:

- MIS 11c occurred after a long period of relatively warm climatic conditions such as we have experienced to date during the Holocene.

- MIS 11c had comparable atmospheric greenhouse gas concentrations (considering only the period before the beginning of the Industrial Revolution, i.e. 1800 AD ca.),

- MIS 11c shows the highest-amplitude response to forcing for deglacial warming in the last 5 Myr,

- The period prior to MIS 11c, although cooler than the Holocene, is characterized by overall warm sea-surface temperatures in high latitudes, strong thermohaline circulation, unusual blooms of calcareous plankton in high latitudes, higher sea level than the present, coral reef expansion resulting in enlarged accumulation of neritic carbonates, and overall poor pelagic carbonate preservation and strong dissolution in certain areas. 

- Considering the variability in the astronomically-driven insolation, MIS 11 is the interval in which insolation is highly correlated with predicted near future situation.

Finally, I conclude by re-posting the Coletti et al. (2015) reference that elaborates on the fact that even the most advanced modern analysis of the MIS 11c event cannot yet full account for the exceptionally high Arctic Amplification during this period; which again raises the prospect that a rapid methane emission rate from the possible future collapse of the WAIS pushing warm water into the Arctic Ocean.

Coletti, A. J., DeConto, R. M., Brigham-Grette, J., and Melles, M.: A GCM comparison of Pleistocene super-interglacial periods in relation to Lake El'gygytgyn, NE Arctic Russia, Clim. Past, 11, 979-989, doi:10.5194/cp-11-979-2015, 2015.

http://www.clim-past.net/11/979/2015/cp-11-979-2015.pdf
http://www.clim-past.net/11/979/2015/cp-11-979-2015.html

Abstract: "Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stages (MISs) 1 (9 ka), 5e (127 ka), 11c (409 ka) and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the mean temperature of the warmest month (MTWM) indicate conditions up to 0.4, 2.1, 0.5 and 3.1 °C warmer than today during MIS 1, 5e, 11c and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer (JJA) orbital forcing, the extraordinary warmth of MIS 11c compared to the other interglacials in the Lake El'gygytgyn temperature proxy reconstructions remains difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice and circum-Arctic land ice feedbacks on the modeled climate of the Beringian interior. Simulations accounting for climate–vegetation–land-surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on northeast Asian temperature during the warmth of stages 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic Ocean does have some effect on Lake El'gygytgyn's regional climate, but the exceptional warmth of MIS 11c remains enigmatic compared to the modest orbital and greenhouse gas forcing during that interglacial."

Extract: "The timing of significant warming in the circum-Arctic can be linked to major deglaciation events in Antarctica, demonstrating possible interhemispheric linkages between the Arctic and Antarctic climate on glacial–interglacial timescales, which have yet to be explained."

Best,
ASLR

50
In CMIP5 (& AR5) many models did a poor job of matching the important behavior of the Southern Ocean.  Thus, the first linked reference provides key metrics to better calibrated CMIP6 (& AR6) ESM projections, in order to better account for the Southern Ocean's behavior.  The last two linked references discuss new finds regarding  sea ice and cloud modeling, respectively, that need to be better represented in CMIP6 (& AR5) as compared to CMIP5 (& AR5):

Joellen L. Russell et al. (16 February 2018), "Metrics for the Evaluation of the Southern Ocean in Coupled Climate Models and Earth System Models", JGR Oceans, https://doi.org/10.1002/2017JC013461

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JC013461

Abstract: "The Southern Ocean is central to the global climate and the global carbon cycle, and to the climate's response to increasing levels of atmospheric greenhouse gases, as it ventilates a large fraction of the global ocean volume. Global coupled climate models and earth system models, however, vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic trend. Due to the region's complex water‐mass structure and dynamics, Southern Ocean carbon and heat uptake depend on a combination of winds, eddies, mixing, buoyancy fluxes, and topography. Observationally based metrics are critical for discerning processes and mechanisms, and for validating and comparing climate and earth system models. New observations and understanding have allowed for progress in the creation of observationally based data/model metrics for the Southern Ocean. Metrics presented here provide a means to assess multiple simulations relative to the best available observations and observational products. Climate models that perform better according to these metrics also better simulate the uptake of heat and carbon by the Southern Ocean. This report is not strictly an intercomparison, but rather a distillation of key metrics that can reliably quantify the “accuracy” of a simulation against observed, or at least observable, quantities. One overall goal is to recommend standardization of observationally based benchmarks that the modeling community should aspire to meet in order to reduce uncertainties in climate projections, and especially uncertainties related to oceanic heat and carbon uptake."

Extract: "In order to ensure their inclusion in the various model intercomparison projects that are part of the upcoming CMIP6, we encourage all modeling centers to make their simulations available in standard, orthogonal grids (latitude versus longitude versus depth) and to calculate and report quantities with significant covariance (e.g., lateral heat fluxes) for better budget calculations. Toward this goal, the Earth System Model Evaluation Tool (ESMValTool; http://www.esmvaltool.org/, Eyring et al., 2016) is an invaluable resource for the climate modeling and assessment community that allows for routine comparison of single or multiple models against observations. Several of us are working on developing packages for the metrics discussed in this study to be included in the ESMValTool, and we strongly encourage other modeling groups to do the same."



See also:

Beaumet, J., Déqué, M., Krinner, G., Agosta, C., and Alias, A.: Effect of uncertainties of Southern Ocean surface temperature and sea-ice change on Antarctic climate projections, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-231, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-231/

Abstract. In this study, the atmospheric model ARPEGE is used with a stretched grid in order to reach a average horizontal resolution of 35 kilometers over Antarctica. Over the historical period (1981–2010), ARPEGE is forced by the historical sea surface conditions (SSC, i.e. sea surface temperature and sea-ice concentration) from MIROC and NorESM1-M CMIP5 historical runs and by observed SSC (AMIP-experiment). These three simulations are evaluated against ERA-Interim for atmospheric general circulation and against MAR regional climate model and in-situ observations for surface climate. As lower boundary conditions for simulations for the period 2071–2100, we use SSC from coupled climate model CMIP5 simulations of the same models following the RCP8.5 emission scenario. We use these output both directly and with an anomaly method based on quantile mapping. We assess the uncertainties linked to the choice of the coupled model and the impact of the method (direct output and anomalies). For the simulation using SSC from NorESM1-M, we do not find significant changes in climate change signals over Antarctica when using bias-corrected SSC. For the simulation using MIROC-ESM output, an additional increase of +185Gtyr−1 in precipitation and of +0.8K in winter temperatures for the grounded Antarctic ice-sheet was obtained when using bias-corrected SSC.
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Hyder, P., Edwards, J. M., Allan, R. P., Hewitt, H. T., Bracegirdle, T. J., Gregory, J. M., … Belcher, S. E. (2018). Critical Southern Ocean climate model biases traced to atmospheric model cloud errors. Nature Communications, 9(1). doi:10.1038/s41467-018-05634-2, https://doi.org/10.1038/s41467-018-05634-2

https://www.nature.com/articles/s41467-018-05634-2

Abstract: "The Southern Ocean is a pivotal component of the global climate system yet it is poorly represented in climate models, with significant biases in upper-ocean temperatures, clouds and winds. Combining Atmospheric and Coupled Model Inter-comparison Project (AMIP5/ CMIP5) simulations, with observations and equilibrium heat budget theory, we show that across the CMIP5 ensemble variations in sea surface temperature biases in the 40–60°S Southern Ocean are primarily caused by AMIP5 atmospheric model net surface flux bias variations, linked to cloud-related short-wave errors. Equilibration of the biases involves local coupled sea surface temperature bias feedbacks onto the surface heat flux components. In combination with wind feedbacks, these biases adversely modify upper-ocean thermal structure. Most AMIP5 atmospheric models that exhibit small net heat flux biases appear to achieve this through compensating errors. We demonstrate that targeted developments to cloud-related parameterisations provide a route to better represent the Southern Ocean in climate models and projections."

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