We wish to acknowledge the work of Larry Marx and Dan Paolino in executing the large number of GCM simulations. The insightful comments of the anonymous reviewers and the editor have helped to improve the manuscript. This work was supported by the National Science Foundation under Grant ATM-03-32910, the National Aeronautics and Space Administration under Grant NNG-04-GG46G, and the National Oceanic and Atmospheric Administration under Grant NA04-OAR-4310034.
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