Abstract: Two of the most important sources of catastrophic risk are terrorism and climate change. The United States has responded aggressively to the risk of terrorism while doing very little about the risk of climate change. For the United States alone, the cost of the Iraq war is now in excess of the anticipated cost of the Kyoto Protocol. The divergence presents a puzzle; it also raises more general questions about both risk perception and the public demand for legislation. The best explanation for the divergence emphasizes bounded rationality. Americans believe that aggressive steps to reduce the risk of terrorism promise to deliver significant benefits in the near future at acceptable cost. By contrast, they believe that aggressive steps to reduce the risk of climate change will not greatly benefit American citizens in the near future - and they are not willing to pay a great deal to reduce that risk. This intuitive form of cost-benefit analysis is much influenced by behavioral factors, including the availability heuristic, probability neglect, outrage, and myopia. All of these contribute, after 9/11, to a willingness to support significant steps to respond to terrorism and to relative indifference to climate change. It follows that Americans are likely to support such steps in response to climate change only if one of two conditions is met: the costs of those steps can be shown to be acceptably low or new information, perhaps including a salient incident, indicates that Americans have much to gain from risk reduction in the relatively near future.