We thank Thomas Karl, Susan Solomon, Jochem Marotzke, Stefan Rahmstorf, Steve Lewandowsky, James Risbey and Naomi Oreskes for their comments on earlier drafts. We acknowledge the Program for Climate Model Diagnosis and Intercomparison and the World Climate Research Programme's Working Group on Coupled Modelling for their roles in making the WCRP CMIP multi-model datasets available. Portions of this study were supported by the Regional and Global Climate Modeling Program (RGCM) of the US Department of Energy's Office of Biological & Environmental Research (BER) Cooperative Agreement # DE-FC02-97ER62402, and the National Science Foundation.