Regional nuclear war would trigger mass death, devastating climate change

December 11, 2006

Even a small-scale regional nuclear war could produce as many fatalities as all of World War II, disrupt the global climate for a decade or more and impact nearly every person on Earth, according to two new studies by University of Colorado at Boulder, Rutgers University and University of California, Los Angeles researchers.

Presented at the fall meeting of the American Geophysical Union in San Francisco Dec. 11 and published Nov. 22 in the online journal Atmospheric Chemistry and Physics Discussions, the two studies represent the first quantitative assessment of the consequences of a nuclear conflict between small or emerging nuclear powers, said CU-Boulder Professor Owen "Brian" Toon. Toon led the studies, working with UCLA Professor Richard Turco, Rutgers professors Alan Robock and Georgiy Stenchikov, CU-Boulder doctoral student Charles Bardeen and former Rutgers student Luke Oman, now a postdoctoral researcher at Johns Hopkins University.

"Considering the relatively small number and yields of the weapons, the potential devastation would be catastrophic and long term," said Toon, chair of CU-Boulder's atmospheric and oceanic sciences department.

Toon, chief author of one of the two studies titled "Atmospheric Effects and Societal Consequences of Regional Scale Nuclear Conflicts and Acts of Individual Terrorism," said fatality estimates for such a regional conflict ranged from 2.6 million to 16.7 million per country. The estimates were based on current nuclear weapons inventories and population densities in large urban regions and took into account scenarios of smoke emissions that urban firestorms could produce, he said.

The results represent the first comprehensive analysis of the consequences of a nuclear conflict between smaller nuclear states, said Toon, who noted even the smallest nuclear powers today likely have 50 or more Hiroshima-sized weapons. In addition, about 40 countries possess enough plutonium, uranium or a combination of both to construct substantial nuclear arsenals. "A small country is likely to direct its weapons against population centers to maximize damage and achieve the greatest advantage," Toon said.

"While there is a perception that a nuclear 'build-down' by the world's major powers in recent decades has somehow resolved the global nuclear threat, a more accurate portrayal is that we are at a perilous crossroads," said Toon. "Nations like Pakistan, India and North Korea, which have the potential of detonating 50 relatively small nuclear weapons, are as dangerous as the Soviet Union used to be. I think the world's politicians need to pay closer attention to the path we all are headed down."

The study also revealed smoke emissions from firestorms in such a conflict could exceed 5 million metric tons, which would have a huge potential impact on climate, Toon said. Since societies tend to gather in the largest cities, the quantity of black smoke per kiloton of explosives in a limited nuclear exchange would be far higher that that generated during a full-scale superpower nuclear exchange, he said.

The second paper, titled "Climatic Consequences of Regional Nuclear Conflicts," looks at the effects of the smoke produced in a regional war between two opposing nations in the subtropics, said lead author Robock. The researchers modeled the effects on each country using 50 Hiroshima-sized nuclear weapons to attack the most populated urban areas of an enemy nation.

Using computer tools originally developed to assess volcano-induced climate change, the researchers generated simulations depicting potential climatic conditions that a small-scale nuclear war could bring about. "Considering the relatively small number and size of the weapons, the effects are surprisingly large," said Turco, a co-author on both papers who formerly headed a research team that included Toon and Carl Sagan and which developed the original concept of "nuclear winter."

The bottom line, according to the researchers, is that while a regional nuclear confrontation among emerging third-world nuclear powers might be geographically constrained, the environmental impacts likely would be worldwide.

A cooling of several degrees, for example, would occur over large areas of North America and Eurasia, including most of the grain-growing regions, Robock said. "Like earlier nuclear winter calculations, large climatic effects would occur in regions far removed from target areas or countries involved in the conflict."

The 1815 eruption of the Tambora volcano in Indonesia -- the largest eruption in the past 500 years -- triggered what has become known as the "The Year Without a Summer" and could foreshadow the kind of climate disruptions that would follow such a regional nuclear conflict, according to the research team. The Year Without a Summer in 1816 included killing frosts and crop losses in New England as well as crop failures, food shortages and famines in Europe from wet and cold weather.

Unlike the climatic disruption resulting from Tambora, which lasted only for one year, the new simulations show a limited nuclear conflict would be much more severe, according to the authors. In a nuclear exchange involving 100 15-kiloton weapons -- just 0.03 percent of the total explosive power of the world's nuclear arsenal -- the resulting smoke would cause large amounts of carbon particles to remain in the stratosphere for up to 10 years, triggering unprecedented climate change, they said.

The current combination of nuclear proliferation, political instability and urban demographics "forms perhaps the greatest danger to the stability of human society since the dawn of man," said Toon. "The current buildup of nuclear weapons in a growing number of states points to scenarios in the next few decades that are even more extreme than those considered in this analysis."

Because of the complexity of the problem and limited amount of data available, the research team assessed uncertainty factors at each step in their analysis and emphasized further research is needed to improve the paper's predictions. The papers can be accessed on the Web at http://www.cosis.net/members/journals/df/recent.php"j%20id=1.
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University of Colorado at Boulder

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