Research Briefs

Nuclear war and ultraviolet radiation

Map of the world with colors indicating UV indices.

These plots (see large verison) show the potential UV indices that could result from a regional nuclear war, depending on the extent to which black carbon particles in the atmosphere filter the incoming radiation. On cloud-free days, many areas in the Northern Hemisphere in June would experience levels greater than 11 (left), which are considered extreme. Researchers have also created maps of UV levels in December (right), when regions in the Southern Hemisphere would be especially affected. (Image courtesy Michael Mills and Julia Lee-Taylor.)

New research indicates that a regional nuclear war would deplete Earth’s protective ozone layer so profoundly that levels of ultraviolet radiation (UV) across the world would exceed levels now considered extreme. NCAR scientist Michael Mills, who conducted the research with colleague Julia Lee-Taylor, presented the preliminary results in February at the annual conference of the American Association for the Advancement of Science.

The study builds on research into the potential impacts of nuclear weapons on the climate system and other aspects of the global environment. It draws on a 2008 paper by Mills and colleagues showing that a regional war involving 100 Hiroshima-sized bombs would lead to massive ozone loss. Fires ignited during the war would send several million metric tons of soot into the upper stratosphere, where the soot would absorb solar radiation and heat the atmosphere. The resulting higher temperatures would accelerate reactions that destroy ozone in the stratosphere.

To study the impact of the ozone loss on UV radiation, Mills and Lee-Taylor used a specialized computer model developed at NCAR. At present, UV levels typically range from 0 (none) to 11+ (extreme), according to a scale established by the World Health Organization and the World Meteorological Organization. However, the computer model results indicated that the United States and other midlatitude countries could face UV levels of up to 20 on cloud-free days in June, when sunshine is strongest in the Northern Hemisphere, with especially high levels in the Mountain West. The Southern Hemisphere, in turn, would face comparable UV levels in December.

Prolonged human exposure to high levels of UV radiation can result in vision loss and skin cancer. The radiation can have far-reaching impacts on animals and plants, as well as on agricultural productivity.

“The phrase ‘regional nuclear exchange’ is misleading because such an event would have global implications,” Mills says. “Even after such a war ended, it would affect the planet for at least a decade.”