The mushroom cloud from Ivy Mike (a code name given to a test) rises above the Pacific Ocean over the Enewetak Atoll in the Marshall Islands in 1952.

(AP Photo/Los Alamos National Laboratory)

The idea of a "nuclear winter" first gained attention in 1983. A team of scientists, including Carl Sagan, theorized that a nightmarish, frigid climate would follow a nuclear war. In a short film, Sagan predicted "virtually all domesticated and wild sources of food would be destroyed. Most the human survivors would starve to death. The extinction of the human species would be a real possibility."

CU Boulder atmospheric scientist Brian Toon helped formulate those early theories. He's now part of a new team that aims to update predictions about the fate of the climate and humanity after a nuclear conflict. "If a dam is about to fail, it's the job of scientists to tell local politicians and dam makers they have to fix it," he tells Colorado Matters. "Nuclear winter is a hazard. I'm trying to tell people they need to do something about it."