Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Different Strengths of the Bipolar See-saw During Glacial and Interglacial times

Carrie Morrill, Katherine Pingree, Esther C. Brady, Bette L. Otto-Bliesner

We present results from two experiments using the National Center for Atmospheric Research (NCAR) coupled Community Climate System Model, version 3. In these experiments, we applied a 1 Sverdrup freshwater addition over the North Atlantic between 50 and 70 degrees N for 100 years. The two experiments used boundary conditions relevant for 8.5 ka and 21 ka (Last Glacial Maximum). The climate response in the Southern Hemisphere was significantly different between the two simulations. Mean annual 2-meter air temperature increased about 1.5 degrees C in the 21 ka simulation, while no change occurred in the 8.5 ka simulation. Temperature increases in the 21 ka simulation were even greater during the austral winter, with regional warming of up to 4 degrees C. The difference between the two simulations cannot be explained by differences in ocean heat transport; in each simulation there is an increase in southward ocean heat transport in the Atlantic at 29S of about 0.55 petawatts. Instead, sea ice feedbacks play a major role in determining the climate response. In the 21 ka simulation, there is enhanced insolation during austral summer due to orbital forcing and a more equatorward location of sea ice. These factors lead to stronger positive sea-ice feedbacks that amplify the initial warming caused by the increase in southward heat transport.