This chapter looks at the nuclear winter project, an outcome of global modeling. The idea that the Earth could be plunged into a “nuclear winter” as the catastrophic outcome of a nuclear war was announced by a group of leading climate and environment scientists from the United States, Western Europe, and the Soviet Union shortly after Ronald Reagan delivered his “Star Wars” speech in March 1983. Drawing on experiments with data-based computer models, these scholars claimed that a nuclear war, unlike the two world wars, would be not simply a regional, but a truly global disaster. Nuclear missiles, detonated over urban areas, would ignite massive fire storms, which in turn would propel soot particles and aerosols into high levels of the atmosphere. As a result, the computer models predicted, a dust shield would emerge that would be transported by air currents to both the Northern and Southern hemispheres.