Editors' Summary: Prof. Cass Sunstein compares the relative ease with which the United States adopted the Montreal Protocol against its rejection of the Kyoto Protocol to conclude that the perceived costs versus perceived benefits of climate change action will have to significantly improve before the United States adopts an international climate change treaty. Daniel Magraw suggests that the comparison between the problems of ozone depletion and climate change downplays the significant differences between the two problems and criticizes the use of cost-benefit analysis as a reliable analytical method. In addition, he writes that actual governmental decisions about climate may be motivated by considerations beyond relative costs and benefits. Peter Orszag and Terry Dinan, on the other hand, note that Professor Sunstein's recommendations to increase the benefits of an international climate change treaty would be unlikely to motivate the United States to enter into such an agreement because his approaches would serve to increase domestic costs while doing little to change perceptions of domestic benefits, that the difficulties in implementing a global system to address climate change are understated, and that an insurance perspective against catastrophic consequences of climate change may be more likely to spur U.S. action.