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Human Activity Tied to Deadly Heat Waves

Study finds influence could raise risk fourfold

WEDNESDAY, Dec. 1, 2004 (HealthDayNews) -- While human activity probably isn't directly responsible for the 2003 heat wave that caused thousands of deaths in Europe, British researchers say human influence on the Earth's climate has at least doubled the risk that such protracted hot spells can occur.

In fact, the scientists said, greenhouse gases and other pollutants may have caused up to a fourfold increase in the risk of serious heat waves.

"Our research shows a clear link between human influence on climate and the damaging heat wave of 2003 that led to between 22,000 and 35,000 extra deaths," said study co-author Peter Stott, a climate scientist at the Hadley Centre for Climate Prediction and Research. "We estimate the risk is increasing rapidly such that by the middle of this century, every other summer will be hotter than 2003 if no serious efforts are made to reduce greenhouse emissions."

Their findings are reported in the Dec. 2 issue of Nature.

The summer of 2003 may have been the hottest on record in Europe in about 500 years, according to the study. As many as 35,000 heat-related deaths were reported that summer, according to an editorial accompanying the article. Economic costs from crop losses and forest fires caused nearly $14 billion worth of damage, according to the editorial.

Using climate models, Stott and his colleagues statistically evaluated weather patterns with and without greenhouse gas emissions. They found that such emissions have at least doubled the risk of heat waves, and could perhaps increase the odds substantially higher.

"We've shown that greenhouse gas emissions, resulting mainly from fossil fuel burning, have increased the risk of heat waves in Europe, such as we saw last year," said Stott.

"We think it is very likely that the risk has more than doubled, and our best estimate is that the risk has already quadrupled. Greenhouse gas emissions have loaded the weather dice, making heat waves much more likely," he concluded.

Does this mean sweltering summers might become inevitable? Stott said it could mean just that, at least for a while.

"Because of the inertia of the climate system, we are already committed to heat waves becoming more common over the next few decades. But if we reduce greenhouse gas emissions, we can prevent further increases and avoid the more serious consequence of very large rates of warming in Europe and other regions of the world," Stott said.

The study "is the first successful attempt to link climate change to a specific extreme event, and to quantify the role of man-made greenhouse gas emissions on such heat wave[s]," said Christoph Schär, chairman of the Institute for Atmospheric and Climate Science in Switzerland and a co-author of the editorial.

But he also said there are many "uncertainties in applying this model to an extreme event such as the European heat wave," and added, "further studies will be needed to corroborate the paper's conclusions.

However, Schär added that this study brings up an interesting issue: Who's to blame?

"The quantification of the man-made contribution in extreme events might ultimately lead to climate liability claims," said Schär.

A second paper accompanying the Stott study specifically addressed potential liability issues. "A substantial fraction of our current elevated level of carbon dioxide might be traced to products produced and sold or used by only a few dozen major companies," wrote Myles Allen, a physicist at the University of Oxford, and Richard Lord, a London-based negligence attorney.

And, while there's no way to prove that greenhouse emissions directly caused damage today, in the future, the authors said, "We could one day see Californian farmers suing member states of the European Union for authorizing emissions that threatened the security of their water supplies."

Liability issues aside, both Stott and Schär said it's vital that steps be taken to reduce greenhouse gas emissions.

"Man-made emissions of greenhouse gases are considered the main driver behind global warming observed during the last 30 to 50 years. These emissions primarily result from the burning of fossil fuels -- oil, gas, coal. Reducing the emissions would ultimately slow down the warming," said Schär.

In the meantime, he recommended that humans try to adapt to the climate change.

"Governments should take actions to implement early warning systems, and to raise the awareness in the population about how to cope with such heat wave events. This could help reduce the negative health and societal implications," said Schär.

More information

To learn more about the European heat wave and other weather phenomena from the summer of 2003, visit the National Climactic Data Center.

SOURCES: Peter Stott, Ph.D., climate scientist, Hadley Centre for Climate Prediction and Research, Reading, England; Christoph Schär, Ph.D., professor and chairman, Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland; Dec. 2, 2004, Nature
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