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Sea ice stability and rapid retreat

Presented by: 
Ian Eisenman University of California, San Diego
Wednesday 13th September 2017 - 09:00 to 09:45
INI Seminar Room 1
Changes in the Arctic sea ice cover involve an amplifying feedback associated with the surface albedo, which suggests the possibility of unstable climate states and bifurcations, or "tipping points". The first part of this talk will focus on the stability of the sea ice cover. Previous studies have identified sea ice bifurcations due to the ice-albedo feedback occurring in a range of idealized models but not in comprehensive global climate models (GCMs). We will propose a physical explanation for this discrepancy, drawing on a model that we developed to bridge the gap between low-order models and GCMs. The results support the finding from GCMs, suggesting that such bifurcations should not be expected in nature. Nonetheless, Arctic sea ice has been observed to retreat abruptly during recent decades. The second part of the talk will address how well the observed rate of Arctic sea ice retreat is simulated in the suite of current GCMs. Although the majority of these GCMs simulate less sea ice retreat than observed, a substantial minority of the simulations do capture the observed rate of retreat. Hence a number of recent studies have suggested that the GCMs and the observations are consistent. We will show that the observed rate of Arctic sea ice retreat actually occurs only in GCM simulations with substantially more global warming than observed. We will suggest an alternative metric for evaluating the GCMs that takes this factor into consideration. The results suggest that the GCMs may be getting the right Arctic sea ice trends for the wrong reasons.
University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons