The end of the cold war and ongoing arms-control efforts by the U.S., Russia and other countries have greatly reduced the threat of global nuclear annihilation. But rogue nations and continued tensions make a local exchange of nuclear firepower all too real.
A single detonation can cause horrible death in several ways. The Hiroshima blast—equal to about 15 kilotons of TNT—generated supersonic wind speeds that crushed concrete buildings near ground zero. Heat from the blast scorched to death anyone within one kilometer. People many kilometers away eventually succumbed to radiation poisoning and cancer.
Global effects, however, would not happen unless dozens of bombs exploded, as might occur in an exchange between Pakistan and India. In modeling the effects, scientists have assumed that those nations would unload their entire arsenals, so that about 100 Hiroshima-size bombs would go off [see “Local Nuclear War, Global Suffering,” by Alan Robock and Owen Brian Toon; Scientific American, January].
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Aside from 20 million killed in the war, many outside the conflict would perish over time. That is because the blasts would throw up five million metric tons of soot into the upper atmosphere. Driven by weather patterns, the particulates would encircle the globe in about a week; within two months they would blanket the planet. Darkened skies would rob plants of sunlight and disrupt the food chain for 10 years. The resulting famine could kill the one billion people who now survive on marginal food supplies.
The outcome is grim. But there is one bright spot: it is within humanity’s ability—and responsibility—to see that such a world-changing event never happens.