Increased urbanization around the globe, combined with greater proliferation of nuclear materials and political instability, has increased the risks of nuclear war, said a panel of scientists at the American Geophysical Union, a conference taking place here this week.
An exchange of 100 15-kiloton weapons between India and Pakistan would kill approximately 20 million people, said Richard Turco, a professor of atmospheric and oceanic sciences at the University California, Los Angeles.
Fifty 15-kiloton weapons would kill about 4 million people in the U.S., if dropped on the biggest cities in the country. During the Cold War, defense analysts estimated that the U.S. would lose 4 million people in a massive attack from the Soviet Union involving thousands of weapons, he noted.
"We're seeing increased urbanization around the world. We are creating megacities around the world," Turco said. "Tehran has 10 million people. The obvious thing to attack if you don't have many weapons is a megacity."
And those are just the direct deaths. The smoke created by a 100-bomb exchange in the subtropical regions would loft in the stratosphere and stay for years, Turco said. This would cause global temperatures to decline by 1.25 degrees Celsius, thereby shortening growing seasons for several crops for years. In the early years, some crops would completely miss their growing seasons. Worldwide precipitation would decline by 10 percent.
Interestingly, Turco and other panelists noted that the energy released by the fires that would follow a nuclear exchange would likely be greater than the energy released by the explosions. The fires get accelerated by the thermal pulse, a huge burst of energy at the time of the explosion of a bomb.
"It's like bringing a piece of the sun down to Earth," he said.
One hundred 15-kiloton weapons represents only a fraction--three-hundredths of 1 percent, actually--of the world's arsenal of nuclear weapons. A 15-kiloton weapon is about the same size of the bomb that was dropped on Hiroshima, Japan. India and Pakistan are believed to have 50 weapons each. Around 40 nations have enough nuclear material to make a 15-kiloton bomb, said Owen Toon, a professor of atmospheric sciences at the University of Colorado.