A predicted drop in global temperature following a nuclear war due to dust in the upper atmosphere reducing sunlight reaching the ground
theoretical cool down of the Earth's climate that would occur following a nuclear war (as a result of dust and airborne particles blocking the Sun's heat and light)
Nuclear winter refers to the possible effects on the environment of a war in which large numbers of nuclear weapons are used. It is thought that there would be very low temperatures and very little light during a nuclear winter. A worldwide darkening and cooling of the atmosphere with consequent devastation of surviving life forms, believed by some scientists to be a probable outcome of large-scale nuclear war. Environmental devastation that some scientists contend would result from a nuclear war. The basic cause, as hypothesized, would be huge fireballs created by exploding nuclear warheads, which would ignite great fires (firestorms). Smoke, soot, and dust would be lifted to high altitudes and driven by winds to form a uniform belt encircling the Northern Hemisphere. The clouds could block out all but a fraction of the Sun's light, and surface temperatures would plunge for as much as several weeks. The semidarkness, killing frosts, and subfreezing temperatures, combined with high doses of radiation, would interrupt plant photosynthesis and could thus destroy much of the Earth's vegetation and animal life. Other scientists dispute the results of the original calculations, and, though such a nuclear war would undoubtedly be devastating, the degree of damage to life on the Earth remains controversial
a long period of darkness and extreme cold that scientists predict would follow a full-scale nuclear war; a layer of dust and smoke in the atmosphere would cover the earth and block the rays of the sun; most living organisms would perish