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SUMMARY:Sea ice stability and rapid retreat - Ian Eisenman (University of 
 California\, San Diego)
DTSTART:20170913T080000Z
DTEND:20170913T084500Z
UID:TALK79061@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Changes in the Arctic sea ice cover involve an amplifying feed
 back associated with the surface albedo\, which suggests the possibility o
 f unstable climate states and bifurcations\, or "tipping points". The firs
 t part of this talk will focus on the stability of the sea ice cover. Prev
 ious studies have identified sea ice bifurcations due to the ice-albedo fe
 edback occurring in a range of idealized models but not in comprehensive g
 lobal climate models (GCMs). We will propose a physical explanation for th
 is discrepancy\, drawing on a model that we developed to bridge the gap be
 tween low-order models and GCMs. The results support the finding from GCMs
 \, suggesting that such bifurcations should not be expected in nature. Non
 etheless\, Arctic sea ice has been observed to retreat abruptly during rec
 ent decades. The second part of the talk will address how well the observe
 d 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 o
 bserved\, a substantial minority of the simulations do capture the observe
 d rate of retreat. Hence a number of recent studies have suggested that th
 e GCMs and the observations are consistent. We will show that the observed
  rate of Arctic sea ice retreat actually occurs only in GCM simulations wi
 th substantially more global warming than observed. We will suggest an alt
 ernative metric for evaluating the GCMs that takes this factor into consid
 eration. The results suggest that the GCMs may be getting the right Arctic
  sea ice trends for the wrong reasons.
LOCATION:Seminar Room 1\, Newton Institute
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