Nuclear winter is a term used to describe a catastrophic atmospheric effect that might occur after a massive exchange of nuclear firepower between major powers as well as natural phenomena, particularly huge volcanic eruptions and asteroid impact, which would have much the same effect. The heat from the nuclear blasts and from resulting fires would cause powerful updrafts carrying sooty regions. This would result in several years of much lower combustion products to stratospheric summertime. There are several reasons for temperatures and freezing temperatures even during matter would absorb solar such an effect. First of all, the highly absorbe largely black p radiation high in the atmosphere so that it would not reach the earth's surface. Cooling would also occur from a phenomenon opposite to that of the greenhouse effect. That is because outgoing infrared radiation from particles high in the atmosphere would have to penetrate relatively much less i water vapor and the atmosphere and, therefore, would be exposed to much less infrared-absorbing carbon dioxide gas. This would deprive the lower atmosphere of the warming effect of outgoing infrared radiation and would mean that less infrared would be re-radiated from the atmosphere back to the earth's surface. The cooling would also inhibit the evaporation of water, thereby reducing the water vapor in the atmosphere and slowing the process by which amount of infrared-absorbing particulate matter is scavenged from the atmosphere by rain. In addition to the direct suffering caused. starvation of millions of people would result from crop failures accompanying years of nuclear winter.