for National Geographic News
Even a small nuclear conflict would cause long-lasting global devastation that could kill tens of millions, scientists warned this week.
Within a couple of decades, 40 countries could have arsenals large enough to cause such a disaster, the researchers added.
This means the threat of global catastrophe is higher now than it was during the Cold War—even though worldwide stocks of nuclear weapons have declined by a factor of three since the end of the four-decades-long conflict.
The dire predictions came from the first ever study of a regional nuclear exchange, unveiled Monday at the fall meeting of the American Geophysical Union in San Francisco.
Previous studies had looked only at the effects of all-out nuclear war between superpowers.
"This is the greatest danger to survival since the dawn of humanity," said study co-author Owen Toon of the University of Colorado, Boulder.
In an exchange in which each side uses only 50 Hiroshima-size bombs—just 0.3 percent of the world's arsenal—the initial explosions could kill more than 20 million people, the scientists calculate.
(See a National Geographic magazine feature on weapons of mass destruction.)
But more far-reaching would be the resulting fires, which would fill the upper atmosphere with soot—destroying the Earth's ozone layer, blocking sunlight, and reducing average global temperatures by 2 degrees Fahrenheit (1.25 degrees Celsius), said co-author Alan Robock of Rutgers University in New Jersey.
The effect would persist for several years and be stronger at mid-latitudes, including the U.S. and Europe.
"This would be a global climate change unprecedented in recorded history," Robock said.
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