Nuclear winter is the term for a theory describing the climatic effects of nuclear war. Smoke from the fires started by nuclear weapons, especially the black, sooty smoke from cities and industrial facilities, would be heated by the Sun, lofted into the upper stratosphere, and spread globally, lasting for years. The resulting cool, dark, dry conditions at Earth's surface would prevent crop growth for at least one growing season, resulting in mass starvation over most of the world. In addition, there would be massive ozone depletion, allowing enhanced ultraviolet radiation. More people could die in the noncombatant countries than in those where the bombs were dropped, because of these indirect effects. Nuclear proliferation is now expanding the threat. A nuclear war between India and Pakistan could produce so much smoke that it would produce global environmental change unprecedented in recorded human history. Although the number of nuclear weapons in the world has fallen from 70,000 at its peak in the 1980s to less than 10,000 currently deployed, a nuclear war between the United States and Russia could still produce nuclear winter. This theory cannot be tested in the real world. However, analogs can inform us about parts of the theory, and there are many that give support to the theory. They include the seasonal cycle, the diurnal cycle, forest, fires, volcanic eruptions, and dust storms on Mars. The only way to be sure to prevent the climatic effects of nuclear war is to rid the world of nuclear weapons. Copyright © 2010 John Wiley & Sons, Ltd.

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