Symptoms and causes of Antarctic climate change

Connected processes link thinning Antarctic ice shelves, regions of advancing and retreating sea ice, and trends in air temperature to changes in the atmospheric circulation. I discuss the changes that have occurred in sea level pressure, near-surface and zonal-mean winds, and surface wind stress. To investigate their origins, I compare observed trends (1979-present) with atmospheric circulation trends simulated by two sets of experiments with the Community Atmosphere Model. The first set is forced by observed SSTs and sea ice concentrations with constant radiative forcing; the second set prescribes the same SST forcing plus time-varying radiative forcings. SST forcing alone accounts for the essentially all of the spatial patterns of atmospheric circulation changes around Antarctica and the Southern Ocean, and most of the magnitude of the changes. These atmosphere-only experiments capture observed circulation trends much better than does the corresponding coupled experiment with CCSM4. A common feature among all experiments is the simulated poleward shift of the jet in austral summer. I argue that multiple factors, including internal variability (associated with ENSO) and warming of the tropical middle and upper troposphere (driven by rising SSTs) have contributed to this shift. Future work will seek to quantify the importance of internally generated and externally forced SST trends relative to stratospheric ozone depletion.

About the presenter
David Schneider

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Main Seminar Room

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Date and time: 
Tuesday, May 7, 2013 - 3:30pm