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Some of the scientists who advanced the controversial "nuclear winter" theory more than two decades ago have come up with another bleak forecast: even a regional nuclear war would devastate the environment.
Using modern climate and population models, researchers estimated that a small-scale nuclear conflict between two warring nations would cause three million to 17 million immediate casualties and lead to a dramatic cooldown of the planet that could bring crop failures and further misery.
As dire as the predictions seem, they fall short of nuclear winter. That theory says smoke and dust from an atomic war between the superpowers would blot out the sun, plunge the Earth into deep freeze and cause mass starvation, wiping out 90 per cent of the Earth's population, or billions of people.
The new scenario offers no estimate of the deaths from the environmental effects of a regional nuclear war. Still, scientists said the scenario points to the danger of small nuclear states obtaining atomic warheads.
The studies, presented at an American Geophysical Union meeting in San Francisco, were described as the first to document in detail the climatic effects of a nuclear war on a regional scale.
Some climate experts not connected with the research questioned some of its assumptions. For example, the studies assume smoke is made up mostly of soot. But other organic particles could cause smoke to scatter, lessening the impact, said scientist Steve Ghan of the Pacific Northwest National Laboratory.
The late astronomer Carl Sagan and four colleagues developed the nuclear winter theory, calculating in 1983 the possible effects of an all-out nuclear attack between the United States and the former Soviet Union.
Other scientists have disputed the degree of damage to the Earth.
The superpowers' nuclear stockpiles have shrunk considerably since the end of the Cold War. But some of the scientists behind the nuclear winter theory - including Brian Toon of the University of Colorado at Boulder and Richard Turco of the University of California, Los Angeles - decided to revisit the topic in light of more recent world tensions.
The new studies looked at the consequences if two nations dropped 50 Hiroshima-size bombs on each other's big cities. By analysing population data and distance from the blast, scientists predicted a regional nuclear war would kill three million people in Israel and up to 17 million in China. The US would see four million blast deaths.
But the researchers say soot from the fires would linger in the atmosphere, blocking the sun's rays and causing average global surface temperatures to drop about 1.11C in the first three years. Although the planet would see a gradual warming within a decade, it would still be colder than it was before the war, the scientists said.
The cooldown would shorten the growing season by about a month in parts of North America, Europe and Asia. Normal rainfall patterns such as summer monsoons in Africa and Southeast Asia would be disrupted, possibly causing huge crop failures.
And the ozone layer, which keeps out harmful ultraviolet radiation, would shrink more than 20 per cent, with the poles seeing a 70 per cent reduction.
- AFP
