This dissertation examines the problem of radioactive fallout from nuclear weapons testing as a pioneering case of global environmental politics during the Cold War. It traces the fallout crisis from the radiological disaster of 1954 in the Pacific to the Partial Test Ban Treaty of 1963. Informed by sociological studies of risk, the dissertation explores why the mid-20 ^th century world came to interpret the risk of global fallout as unacceptable. It argues that this shift was an outcome of politics, which developed around the paradox that one must blend scientific facts and social values to conceive of risk but also demarcate them to be recognized as authoritative. This tension, arising from the trans-scientific nature of risk, shaped the respective courses of public debates, scientific research, and expert reviews. The dissertation focuses on the United States but emphasizes its interactions with Japan, where the fallout crisis first broke out, and also with the other two fallout polluters of the time, Great Britain and the Soviet Union.

The dissertation analyzes the politics of risk as unfolding at global and local levels. The global level revolved around the proposition that the biological effects of low-level radiation from global fallout were infinitesimal to the individual but loomed large on the scale of the whole population. This raised a serious question of whether the risk was acceptable to innocent bystanders in the world. The local level of risk politics centered at the interplay of fallout monitoring and radiation safety standards. The expanding surveillance of fallout revealed its rising levels and uneven distribution. The permissible dose, however, gradually declined in anticipation of the increase of radiation exposure. This dynamic created the alarming impression that a margin of safety was rapidly vanishing. The dissertation also investigates various impacts of the changing outlook of risk on the issue of a nuclear test ban among the three nuclear powers. It argues that the politics of risk stimulated not only a call for a test ban but also a pursuit of technological solutions, and that the partial ban was a joint product of these opposite approaches to the risk.