The bombing of Hiroshima, Japan. New research indicates that even a small nuclear war could devastate the world's climate.

Credit: Wikimedia

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SYDNEY: Even a small-scale, regional nuclear war could produce as many fatalities as all of World War II and disrupt the global climate for a decade or more, U.S. researchers have found.

"With the exchange of 100 [hiroshima-sized] weapons as posed in this scenario, the estimated quantities of smoke generated could lead to global climate anomalies exceeding any changes experienced in recorded history," said co-author Alan Robock, of Rutgers Univeristy in New Jersey. "And that's just 0.03 per cent of the total explosive power of the current world nuclear arsenal."

While a nuclear confrontation among emerging third-world nuclear powers might be constrained to one global region, the research team concluded that the environmental impacts could be worldwide.

"We examined the climatic effects of the smoke produced in a regional conflict in the subtropics between two opposing nations, each using 50 Hiroshima-size nuclear weapons to attack the other's most populated urban areas," said Robock. The researchers carried out their simulations using a modern climate model coupled with estimates of smoke emissions from the resulting firestorm, which amounted to as much as five million metric tonnes of 'soot' particles.

"Considering the relatively small number and size of the weapons, the effects are surprisingly large. The potential devastation would be catastrophic and long term," said co-author Richard Turco, professor of atmospheric and oceanic sciences at the University of California, Los Angeles.

The authors of the study, presented at the annual conference of the American Geophysical Union and in two papers in the online journal Atmospheric Chemistry and Physics Discussions, point out that even the smallest nuclear powers today and in the near future may have as many as 50 or more Hiroshima-size (15 kilotonne) weapons in their arsenals; all told, about 40 countries possess enough plutonium and/or uranium to construct substantial nuclear arsenals.

The team generated a series of computer simulations depicting potential climatic anomalies that a small-scale nuclear war could bring about.

"[Our findings] represent the first comprehensive quantitative study of the consequences of a nuclear conflict between smaller nuclear states," said the authors. "A small country is likely to direct its weapons against population centres to maximise damage and achieve the greatest advantage."

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

Robock and his team calibrate their models using the smoke produced by the well documented 1912 eruptions of Katmai volcano in Alaska. They found that observed temperature anomalies were accurately reproduced by their model.

According to Robock, the 1815 eruption of Tambora in Indonesia - the largest in the last 500 years - hints at what a nuclear winter could be like. The eruption was followed by killing frosts throughout New England in 1816, during what has become known as "the year without a summer." The weather in Europe was reported to be so cold and wet that the harvest failed and people starved.

But the climatic disruption resulting from Tambora lasted for only about one year, the authors note. In their most recent computer simulation, in which carbon particles remain in the stratosphere for up to 10 years, the climatic effects are greater and last longer than those associated with the Tambora eruption.