Extended Abstract (64K)7.4
Assessing model sensitivity to North Atlantic freshwater perturbations using past abrupt climate events
Carrie Morrill, CIRES/Univ. of Colorado and NOAA/NESDIS/NCDC, Boulder, CO; and A. Wagner, B. L. Otto-Bliesner, and N. Rosenbloom
One part of the coupled ocean-atmosphere system that could change considerably in the future is the Atlantic Meridional Overturning Circulation (AMOC). Based on results from comprehensive coupled climate models, a recent CCSP assessment found that it is very likely that the strength of the AMOC will decrease over the 21st century in response to increasing greenhouse gases, with a best estimate decrease of 25-30%. Representations of the AMOC in these models are imperfect, but we have limited observational data for model-data comparisons that could help to improve the models. The paleoclimate record, with its longer-term perspective on climate variability, may help to fill this gap.
We will present results from a series of experiments using a state-of-the-art coupled climate model, the NCAR CCSM3, to test its sensitivity to a known freshwater perturbation in the North Atlantic that occurred 8,200 years ago in a climate state not too different from present-day. This “8.2 ka” event occurred when a large lake drained into the Labrador Sea, decreasing the strength of the AMOC. Climate impacts, including cooling over large parts of the North Hemisphere and a southward shift of the Intertropical Convergence Zone, are documented and quantified in a variety of marine and terrestrial paleoclimate records. Our initial results indicate a model sensitivity that is potentially less than that observed in the records. We will discuss possible reasons for this and their implications.
Session 7, Special session on long-term climate variability and change emphasizing paleoclimatic observations and modeling
Tuesday, 19 January 2010, 3:30 PM-5:45 PM, B215
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