Published online 12 December 2006 | Nature | doi:10.1038/news061211-5

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A regional nuclear war would have long-lasting effects on the planet.

100 Hiroshima-sized bombs would have an unprecedented effect on global climate. Punchstock

More than 20 years ago, it was theorized that "a nuclear winter" would occur in the event of a superpower war using nuclear weapons. Now new computers, better climate-modeling techniques, and comparisons to natural disasters such as volcanic eruptions, shows that even a regional conflict would throw the planet into turmoil.

Global climate and the environment would be drastically altered for decades by two nations hitting each other with a total of just 100 Hiroshima-sized (15 kilotonnes) nuclear bombs, according to an analysis of such a conflict.

Millions of tonnes of soot would be blasted at least 12 kilometres high, circulating and completely covering the globe within a month.

"The global climate change would be unprecedented in the record of human history," says Alan Robock, an atmospheric scientist at Rutgers University in New Jersey.

And that's using less than 0.03% of the explosive yield of the planet's current total nuclear arsenal.

"Instantaneously, it would be colder than the little Ice Age," says Robock.

A regional attack would shrink crop-growing periods in the middle latitudes by 30 days, they add, drastically impacting available food supplies. And a global ozone hole would be created by the blasts, exposing the Earth to more damaging radiation.

Small war, big impact

A panel of US atmospheric scientists, including Robock, announced their results at a meeting of the American Geophysical Union in San Francisco on 11 December.

Beyond the horrific loss of millions of lives from such a nuclear exchange, the team is seeking to highlight the long-term global impact from a war between nations that could manufacture bombs. Such nations cited included Argentina, Mexico, Pakistan, India, Taiwan and Japan.

To build their model, the team hypothesized that the bombs would be targeted at major population areas. Burning material — such as plastics, fossil fuels and buildings — would generate heat capable of carrying soot high into the stratosphere, where mechanisms to remove the particles from the air are very slow. Older models didn't properly account for this effect, says Robock, and so did not realise how long-lived the climate impacts would be.

The team's results are also published online in Atmospheric Chemistry and Physics Discussusions1.

Growing threat

The public generally believes that the threat of nuclear war is decreasing because of the easing of tensions among superpowers, says the team. But in reality, the scientists warn, threats from regional conflicts are actually higher and increasing.

"We are at a perilous crossroads," says Brian Toon, a team member from the University of Colorado at Boulder.

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In the Middle East, the Korean peninsula and the Asian subcontinent, where nations are seeking to join the bomb club, they say there is great potential for calamity. Japan alone could make from its fissionable material 20,000 Hiroshima-sized weapons.

Rick Turco, a team member from the University of California at Los Angeles, noted that a regional war — such as between India and Pakistan — could generate soot levels of millions of metric tonnes.

"Human society is extremely vulnerable at this point in time," says Turco.

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