WASHINGTON -- A nuclear conflict involving as few as 100 weapons could produce long-term damage to the ozone layer, enabling higher than "extreme" levels of ultraviolet radiation to reach the Earth's surface, new research indicates (see GSN, March 16, 2010).

Increased levels of UV radiation from the sun could persist for years, possibly with a drastic impact on humans and the environment, even thousands of miles from the area of the nuclear conflict.

“A regional nuclear exchange of 100 15-kiloton weapons … would produce unprecedented low-ozone columns over populated areas in conjunction with the coldest surface temperatures experienced in the last 1,000 years, and would likely result in a global nuclear famine,” according to a presentation delivered on Friday at a major science conference in Washington.

Today, there are five recognized nuclear powers -- China, France, Russia, the United Kingdom and the United States. India, Israel and Pakistan are all known or widely assumed to hold nuclear weapons, while North Korea has a deterrent of undetermined capability and there are concerns about the atomic intent of nations such as Iran.

The global nuclear stockpile is believed to exceed 20,000 weapons, most of which are in U.S. and Russian hands, according to the Federation of American Scientists.

While the potential for a Cold War-size nuclear war has receded in recent decades, tensions in regions such as South Asia and the Korean Peninsula suggest that the danger of an atomic detonation cannot be dismissed.

The threat of long-term effects of such an event beyond the immediate death and destruction -- including nuclear winter, the deep reduction in surface temperatures produced by the release of massive amounts of smoke into the atmosphere -- has been recognized for decades.

Research backed by computer models in the last few years has indicated that fires ignited by the exchange of 100 nuclear weapons similar in power to the bomb dropped on Hiroshima during World War II would release millions of metric tons of soot into the atmosphere. That would speed up the pace at which ozone is eliminated in the stratosphere, according to the National Center for Atmospheric Research.

Center scientist Michael Mills likened the effects of a nuclear strike to the firestorms touched off by the mass conventional bombings of Dresden and Tokyo during the war.

“They just start feeding and create their own weather system from the flames and turn the whole city into this black carbon smoke,” he told Global Security Newswire yesterday.

The research by Mills and colleagues was the first to address the possibility that a nuclear explosion could lead to increased ultraviolet radiation levels on Earth, according to a NCAR press release issued during the American Association for the Advancement of Science conference.

The ozone gas layer limits exposure to UV radiation that at elevated levels has been linked to vision impairment and skin cancer in humans. That radiation can also produce “far-reaching impacts” on plant and animal life, along with the agricultural and marine sectors, the release states.

The Environmental Protection Agency and the National Weather Service established a measurement system that ranks ultraviolet levels from zero to 11, with no radiation at the low end of the scale and extreme levels at the top. Higher levels require increasing levels of protection against exposure, including staying inside during the hottest afternoon hours.

Computer simulations indicate that following an attack 100 times the size of the Hiroshima bomb, the United States and nations near its latitude would experience UV levels between 15 and 20 on completely sunny days in June. The ozone loss would produce a similar phenomenon for Southern Hemisphere nations in December.

The estimate is based on a nuclear conflict between India and Pakistan, a possibility raised in previous research on the climatic effect of nuclear war, Mills said.

The level of ultraviolet radiation exposure would be “unprecedented,” the National Center for Atmospheric Research said. Today, 15-level ultraviolet is found only in high-altitude nations at the equator when the sun is straight overhead.

"These UV levels are literally off the charts," NCAR scientist Julia Lee-Taylor said in the release.

Past research has identified a number of repercussions from significant ozone loss and heightened ultraviolet radiation exposure, according to Mills’s presentation at the conference. These include “plant height reduction, decreased shoot mass, and reduction in foliage area” and long-term genetic instability to plants. Another risk is depletion of phytoplankton that feed sea life, which are in turn a crucial protein source for humans.

“It would be very difficult for us to grow the type of crops we grow today,” Mills said. “In addition to ecological damage, there would be a global nuclear famine.”

The scientist said he hopes the continued ozone research makes clear to decision-makers the danger of even a “regional” nuclear war. Progress made in the recently enacted U.S.-Russian New START nuclear arms control treaty is worth building on with future additional cuts around the world, he said.

“We still have many, many more than are needed to destroy the world many times over,” Mills said. “How many do you need to deter an enemy? Just 100 would produce an ecological catastrophe.”