A nuclear exchange between India and Pakistan could globally harm the ozone layer, according to computer simulations. If those nations each launched 50 Hiroshima-level nuclear weapons—a total of 1.5 megatons, or just 0.03 percent of the total explosive power of the world's nuclear arsenal—smoke from burning cities would loft up as much as five million metric tons of soot. This ash would eventually rise to stratospheric heights of up to 80 kilometers, where it would trigger ozone-destroying reactions. As much as 70 percent of the ozone above the high northern latitudes would get lost, a depletion comparable to the Antarctic ozone hole. Up to 45 percent of the ozone above the earth's midlatitudes, where most of the world's population lives, would also vanish. As stratospheric ozone diminished, ultraviolet light–triggered cancer and other forms of serious damage would rise sharply. The analysis, which appeared online April 7 in the Proceedings of the National Academy of Sciences USA, suggests that the ozone would begin to recover only after five to eight years.