Climate change is not only an environmental problem but also a foreign policy problem, for the United States and indeed any country. Our best scientific knowledge about the effects of global warming predicts negative changes, from precipitation to agriculture to disease vectors. As such, it is axiomatic that nations would want to mitigate this phenomenon as early as possible. However, our current system of international law places no involuntary obligations, such as compliance with a climate mitigation treaty, on any state. In the past, if a state refused to become party to a treaty, this refusal was assumed to be without prejudice. Not anymore. Because the effects of greenhouse gases (GHGs) emitted anywhere are felt everywhere, efforts to mitigate climate change must be coordinated across all nations, lest any one nation have the incentive to free ride on the efforts of others. Unfortunately, that is exactly what the United States has done over the past decade with its repudiation of the Kyoto Protocol. A new norm of compliance with agreements is becoming customary with

regard to the global environmental commons, particularly in the case of climate change, and this norm is being driven by improving climate science. This chapter will examine the development of this norm of compliance, why the United States has failed to comply with it, and what the consequences and implications of this norm for both international law and American foreign policy are. However, two key assumptions must be stated at the outset. First, the intellectual concepts behind the creation of customary norms of international law are valid regardless of the application of those norms. In other words, states are expected to comply with existing laws and norms, even if there is currently no real-world forum for their adjudication. Second,

treaty and a party that is out of compliance with that same treaty.1 In both cases, the desired end-state is that all nations are parties and that they comply with the treaty’s terms.