Ten years ago this summer, President Clinton’s Council of Economic Advisers, of which I was a Member, responded to requests from the Congress, which was then under Republican control, to explain in analytical terms what would be the economic effects of the Kyoto Protocol on climate change that had just been negotiated among the members of the UN Framework Convention on Climate Change. Our response was a document called the Administration Economic Analysis. It relied on some of the leading Integrated Assessment Models, and showed that the costs of Kyoto could be relatively low provided international trading of emission permits were freely allowed, and provided developing countries participated in the system. Not zero costs, as wishful thinking by some techno-optimists would have it. Not prohibitive costs, as some skeptics would have it. But moderate costs — relatively low if measures could be implemented sensibly.