Here is some evidence that Earth System Models, ESMs, need to be updated to include such dynamical sensitivity considerations as 'freshwater hosing' and warming induced rainfall on permafrost (particularly in Siberia):
The first linked reference studies ice-climate feedback calibrated to 'freshwater hosing' events in the North Atlantic over the past 720,000 years, in order to study state dependence of climatic instabilities within a CMIP class of climate model. Such research can help to calibrate models for such 'freshwater hosing' events such as the possible collapse of the WAIS this century:
Ayako Abe-Ouchi, et. al. (2017), "State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling", Science Advances, Vol. 3, no. 2, e1600446, DOI: 10.1126/sciadv.1600446
http://advances.sciencemag.org/content/3/2/e1600446&
http://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/218067/1/sciadv.1600446.pdfAbstract: "Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets."
The Last Glacial Termination, LGT, occurred from 18,000 to 11,650 kya, and the following reference, reconstructs the dynamic response of the Antarctic ice sheets to warming in this period in order to better evaluate Hansen's ice-climate feedback mechanisms. The abstract from the second linked reference concludes: "Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise."
Fogwill, et. al. (2017), "Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the last Glacial Termination", Scientific Reports 7, Article number 39979, doi:10.1038/srep39979
https://www.nature.com/articles/srep39979Finally (for this post), can you imagine how the timing of a rain-dominated Arctic will be affected by Hansen's ice-climate feedback mechanism driven by a WAIS collapse circa 2040-2060 (which almost all ESM projections currently ignore), and or pulses of methane emission from thermokarst lakes? I also note that the third linked reference assumes that ECS is only around 3C.
Richard Bintanja and Olivier Andry (2017), “Towards a rain-dominated Arctic”, Geophysical Research Abstracts Vol. 19, EGU2017-4402
http://meetingorganizer.copernicus.org/EGU2017/EGU2017-4402.pdfAbstract: “Current climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, very little is known about future changes in rain/snow distribution in the Arctic, notwithstanding the importance for hydrology and biology. Here we use 37 state-of-the-art climate models in standardised twenty-first century (2006–2100) simulations to show that 70◦ – 90◦N average annual Arctic snowfall will actually decrease, despite the strong increase in precipitation, and that most of the additional precipitation in the future (2091– 2100) will fall as rain. In fact, rain is even projected to become the dominant form of precipitation in the Arctic region. This is because Arctic atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rain/snowfall will heavily impact Arctic hydrology (e.g. river discharge, permafrost melt), climatology (e.g. snow, sea ice albedo and melt) and ecology (e.g. water and food availability).”
See also the fourth linked reference:
R. Bintanja et al. Towards a rain-dominated Arctic, Nature Climate Change (2017). DOI: 10.1038/nclimate3240
http://www.nature.com/nclimate/journal/v7/n4/full/nclimate3240.htmlExtract: "Rain causes more (extensive) permafrost melt, which most likely leads to enhanced emissions of terrestrial methane (a powerful greenhouse gas), more direct runoff (a smaller seasonal delay) and concurrent freshening of the Arctic Ocean. Rainfall also diminishes snow cover extent and considerably lowers the surface albedo of seasonal snow, ice sheets and sea ice, reinforcing surface warming and amplifying the retreat of ice and snow; in fact, enhanced rainfall will most likely accelerate sea-ice retreat by lowering its albedo (compared with that of fresh snowfall) "