It is generally agreed that the world would be better off with an international agreement to control greenhouse gas emissions. But it is not entirely clear that the leading emitters—the United States and China—would be better off with the agreement that would be in the world’s interest. The first problem is that as the largest emitters, the United States and China would probably have to bear a disproportionate cost of any significant emissions reduction effort. The second problem is that on prominent projections, the United States and China are unlikely to be the most serious losers from climate change. According to some analyses, the two nations are thus anticipated to bear disproportionately high costs from emissions controls and to gain disproportionately little from such controls. There are two ways to eliminate the resulting obstacle to an international agreement. The first is through altering the perceived cost-benefit analysis for both countries. The second is through an understanding that both nations, and the United States in particular, are under a moral obligation not to inflict serious harm on the highly vulnerable citizens of Africa, India, and elsewhere. Existing proposals for unilateral action on the part of the United States seem to stem from an unruly mixture of confusion, hope, and a sense of moral obligation.