The global climate regime and the global trade policy regime are on a collision course. National efforts to reduce emissions of greenhouse gases (GHGs) instill among environmentalists fears of leakage and among businesspeople fears of lost competitiveness. Policy-makers respond to these fears. In 2008, legislative attempts in both Washington, DC, and Brussels to enact long-term targets for reduced emission of GHGs included provisions for possible penalties against imports from countries perceived as non-participating. Trade measures, if well designed, could in theory be WTO-compatible. But the actual provisions emerging from the political process are likely to violate the rules of the WTO, which poses the scenario of a WTO panel rejecting a major country's climate change legislation. That would be a nightmare for the supporters of the WTO and free trade as much as for the supporters of the Kyoto Protocol and environmental protection. The issue is just the latest and largest instance of fears among many environmentalists that the WTO is an obstacle to their goals in general. The first part of this paper discusses the broader issue of whether environmental goals in general are threatened by the global free trade system. The paper then focuses exclusively on the narrower question of trade measures in the effort to implement climate change policy and whether they are likely to be successful. It concludes with specific recommendations for how border measures could be designed so that they were more likely to be true to the goal of reducing leakage and yet consistent with the WTO.