To continue my series of posts listing various ice-climate feedback mechanisms (see Reply #1889):
16. An abrupt slowdown of the MOC due to an abrupt (MICI-type) collapse of the WAIS in coming decades would trigger an abrupt increase of rainfall in rainfall in both the Arctic (see that linked references and the first image) and the Antarctic (although the Arctic is more sensitive to this feedback), including due to atmospheric river events. When such rainfall is added to the volume of surface water in meltwater ponds on: snow, marine glaciers, ice shelves and/or sea ice resulting degradation can be much more rapid than what is currently being observed in these snow/ice features:
R. Bintanja (2018), "The impact of Arctic warming on increased rainfall", Scientific Reports, 8, Article number: 16001, DOI:
https://doi.org/10.1038/s41598-018-34450-3https://www.nature.com/articles/s41598-018-34450-3Abstract: "The Arctic region is warming two to three times faster than the global mean, intensifying the hydrological cycle in the high north. Both enhanced regional evaporation and poleward moisture transport contribute to a 50–60% increase in Arctic precipitation over the 21st century. The additional precipitation is diagnosed to fall primarily as rain, but the physical and dynamical constraints governing the transition to a rain-dominated Arctic are unknown. Here we use actual precipitation, snowfall, rainfall output of 37 global climate models in standardised 21st-century simulations to demonstrate that, on average, the main contributor to additional Arctic (70–90°N) rainfall is local warming (~70%), whereas non-local (thermo)dynamical processes associated with precipitation changes contribute only 30%. Surprisingly, the effect of local warming peaks in the frigid high Arctic, where modest summer temperature changes exert a much larger effect on rainfall changes than strong wintertime warming. This counterintuitive seasonality exhibits steep geographical gradients, however, governed by non-linear changes in the temperature-dependent snowfall fraction, thereby obscuring regional-scale attribution of enhanced Arctic rainfall to climate warming. Detailed knowledge of the underlying causes behind Arctic snow/rainfall changes will contribute to more accurate assessments of the (possibly irreversible) impacts on hydrology/run-off, permafrost thawing, ecosystems, sea ice retreat, and glacier melt."
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E.C. Massoud et al. (12 October 2019), "Global Climate Model Ensemble Approaches for Future Projections of Atmospheric Rivers", Earth's Future,
https://doi.org/10.1029/2019EF001249https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019EF001249?af=RAbstractAtmospheric rivers (ARs) are narrow jets of integrated water vapor transport that are important for the global water cycle, and also have large impacts on local weather and regional hydrology. Uniformly‐weighted multi‐model averages have been used to describe how ARs will change in the future, but this type of estimate does not consider skill or independence of the climate models of interest. Here, we utilize information from various model averaging approaches, such as Bayesian Model Averaging (BMA), to evaluate 21 global climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Model ensemble weighting strategies are based on model independence and atmospheric river performance skill relative to ERA‐Interim reanalysis data, and result in higher accuracy for the historic period, e.g. RMSE for AR frequency (in % of timesteps) of 0.69 for BMA vs 0.94 for the multi‐model ensemble mean. Model weighting strategies also result in lower uncertainties in the future estimates, e.g. only 20‐25% of the total uncertainties seen in the equal weighting strategy. These model averaging methods show, with high certainty, that globally the frequency of ARs are expected to have average relative increases of ~50% (and ~25% in AR intensity) by the end of the century.
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B. Teufel & L. Sushama (2019),"Abrupt changes across the Arctic permafrost region endanger northern development", Nature Climate Change, volume 9, pages858–862, DOI:
https://doi.org/10.1038/s41558-019-0614-6https://www.nature.com/articles/s41558-019-0614-6Abstract: "Extensive degradation of near-surface permafrost is projected during the twenty-first century, which will have detrimental effects on northern communities, ecosystems and engineering systems. This degradation is predicted to have consequences for many processes, which previous modelling studies have suggested would occur gradually. Here we project that soil moisture will decrease abruptly (within a few months) in response to permafrost degradation over large areas of the present-day permafrost region, based on analysis of transient climate change simulations performed using a state-of-the-art regional climate model. This regime shift is reflected in abrupt increases in summer near-surface temperature and convective precipitation, and decreases in relative humidity and surface runoff. Of particular relevance to northern systems are changes to the bearing capacity of the soil due to increased drainage, increases in the potential for intense rainfall events and increases in lightning frequency. Combined with increases in forest fuel combustibility, these are projected to abruptly and substantially increase the severity of wildfires, which constitute one of the greatest risks to northern ecosystems, communities and infrastructures. The fact that these changes are projected to occur abruptly further increases the challenges associated with climate change adaptation and potential retrofitting measures."
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Rebecca B. Neumann, Colby J. Moorberg, Jessica D. Lundquist, Jesse C. Turner, Mark P. Waldrop, Jack W. McFarland, Eugenie S. Euskirchen, Colin W. Edgar & Merritt R. Turetsky (03 January 2019), "Warming Effects of Spring Rainfall Increase Methane Emissions From Thawing Permafrost" Geophysical Research Letters,
https://doi.org/10.1029/2018GL081274https://agupubs.onlinelibrary.wiley.com/doi/pdf/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.