The hypothesis of a "nuclear winter" following a major nuclear exchange has been confirmed in comprehensive scientific assessments by the United Nations, the International Council of Scientific Unions, the World Meteorological Organization and the World Health Organization, as well as by the National Academy of Sciences of the United States and the Royal Society of Canada. The nuclear-winter theory forecasts worldwide human casualties one to two orders of magnitude larger than previous estimates based on the prompt effects or nuclear detonations alone. The catastrophic and now well-established prospect of nuclear winter suggests the following fundamental policy changes: Joint establishment by the superpowers of Canonical Deterrent Forces (CDFs) of 100-300 single-warkead hardened and/or mobile delivery systems on each side; dismantling of most existing strategic nuclear systems including all MIRVed land-based and submarine forces and nuclear-armed bomber fleets wherever possible, using appropriate elements of the existing forces to construct the CDFs; dismantling of all tactical nuclear weapons and reduction and balancing of conventional military forces in Europe, with emphasis on defensive postures; and abandonment of space-based strategic defense, and firm institutionalization of the existing ABM Treaty. These actions are highly stabilizing with respect to the deterrence of international conflict, and are far more affordable than the customary arms race.