Talk by Eric Steig, University of Washington – Niels Bohr Institute - University of Copenhagen

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Talk by Eric Steig, University of Washington

Influence of natural (?) climate variability in the tropics on the likelihood of Antarctic Ice Sheet collapse

The large ice shelves in West Antarctica have experienced periods of
thinning and acceleration in the past few decades. The primary cause has
been increased delivery of warm circumpolar deep water (CDW) to the
underside of the shelves. Climate observations and results from
numerical modeling experiments show that the increased ocean heat
delivery is the consequence of changes in atmospheric circulation over
the Amundsen-Bellinghausen Seas, which have caused increased Ekman
pumping, bringing CDW nearer to the surface. The atmospheric circulation
changes over the Amundsen-Bellinghausen Seas are, in turn, due to trends
in the tropical Pacific sea surface temperature (SST): a localized
warming in the central Pacific in the 1990s caused a teleconnection
pattern that featured an anomalous high pressure in the Amundsen Sea
(Ding et al 2011; Steig et al 2012). Similarly, the strong La Nina event
in 2010-2012 significantly reduced the melting in West Antarctica
(Dutrieux et al. 2014). Ice core data from WAIS Divide and the US ITASE
cores provide a long term context for these changes, and suggest that
recent conditions in West Antarctica are unusual, but perhaps not
unprecedented: similar conditions prevailed in the 1940's. The ultimate
fate of the West Antarctic ice shelves depends on the future disposition
of the tropical Pacific atmosphere-ocean system. This raises important
issues concerning the causes of the observed decadal variability in the
tropical Pacific. These results also have implications for Greenland.