"Considering the relatively small number and size of the weapons, the effects are surprisingly large," said Richard Turco, a researcher from the University of California, Los Angeles. "The potential devastation would be catastrophic and long term."
According to the report presented yesterday at the annual meeting of the American Geophysical Union, the initial effects of a Hiroshima-sized detonation could be as many fatalities as all of World War II, and then the environment could be affected in ways never considered. The scientists said that large areas of the planet could drastically drop in temperature if a nuclear detonation occurred.
"It would be the largest climate change in recorded human history," said team member Alan Robock, associate director of the Center for Environmental Prediction at Rutgers' Cook College.
A team from the University of Colorado, Boulder focused their attention on the black smoke that would be created by a nuclear detonation, and the subsequent firestorms, basing their research on current population densities in large cities worldwide and current nuclear weapon inventories. They found that each country would sustain fatalities ranging from 2.6 million to 16.7 million people.
"A small country is likely to direct its weapons against population centers to maximize damage and achieve the greatest advantage," said lead researcher Owen "Brian" Toon.
Robock and his team used computer simulations of a conflict between India and Pakistan, for example, to analyze potential climate changes caused by a regional nuclear war. In the simulations, each combatant used 50 nuclear weapons on the other country. The smoke caused by such a battle would settle in the Earth's upper atmosphere -- where some rays from the sun are usually absorbed -- and greatly diffuse the sunlight before it hits the surface. The shroud would cause lower temperatures, darkness, reduced precipitation, and ozone depletion.
The team said, in the Pakistan/India example, the smoke could drop average temperatures by 2 degrees Fahrenheit as far away as North America and Eurasia. Ten years later, the simulated climate had not recovered from the war. Previous studies had analyzed what would happen if countries fired their entire nuclear arsenals at each other, but the recent study accounts for three-hundredths of a percent of that global arsenal.
The scientists said they were hopeful that positive change would come from their conclusion.
"We certainly hope there will be a political response because nuclear weapons are the most dangerous potential environmental danger to the planet." Robock said. "They're much more dangerous than global warming."