Human Activity Raises Risk of Deadly European Heatwaves

EXETER, UK, December 2, 2004 (ENS) - Human burning of fossil fuels has increased greenhouse gases in the atmosphere and more than doubled the risk of recordbreaking hot European summers, like that of 2003, according to new research by a British team. Linked to more than 27,000 excess deaths across the continent, the summer temperatures of 2003 were the highest in Europe for over 500 years.

The new study, published today in the journal "Nature," is the work of a team led by Peter Stott from the Met Office's Hadley Centre for Climate Prediction and Research. They set out to estimate by how much human activities may have increased the risk of the occurrence of the 2003 heatwave.

The Hadley Centre for Climate Prediction and Research, which is part of the British Meteorological Office (Met Office), provides a focus in the United Kingdom for the scientific issues associated with climate change. Researchers employed a fast NEC SX-6 supercomputer, sophisticated climate models and new statistical techniques.

"We simulated 2003 summer temperatures over Europe - with and without the effect of man's activities - and compared these with observations," explains Stott.

"We found that although the high temperature experienced in 2003 was not impossible in a climate unaltered by man, it is very likely that greenhouse gases have at least doubled the risk and our best estimate is that such a heatwave is now four times more likely as a result of human influence on climate."

Fire spreads across the land during the early afternoon of July 21, 2003 near Freixiosa, Portugal. (Photo courtesy Global Fire Monitoring Center)

In London, trains were halted over fears that tracks would buckle in the heat, while in Scotland the high temperatures combined with falling water levels in rivers and streams threatened the spawning and survival of salmon.

Throughout France, Spain, Portugal, and Italy, the intense heat and dry conditions sparked deadly forest fires.

The researchers predict that the type of summer experienced in 2003 could be expected to occur as often as every other year by the middle of this century.

"We know that 2003 type hot summers and associated heatwaves won't happen every year, but continuing man-made global warming will increase the chance," Stott said. "According to our model, by the middle of this century every other summer could be even hotter than 2003."

Stott's co-author Myles Allen of the University of Oxford has also co-authored, with Richard Lord QC, a commentary on the legal implications of the research, which is published in the same edition of "Nature."

"Quantifying the costs of climate change requires being able to separate natural from man-made contributions to weather risk," said Allen.

This image shows the differences in day time land surface temperatures collected from July 2001 to July 2003 by the Moderate Resolution Imaging Spectroradiometer on NASA’s Terra satellite (Photo courtesy NASA)

Using a threshold for mean summer temperature that was exceeded in 2003, but in no other year since the start of the instrumental record in 1851, the research team estimates with a confidence level of greater than 90 percent that human influence has "at least doubled the risk of a heatwave exceeding this threshold magnitude."

Changes in the frequency of extremes are often the most sensitive aspects of climate change for ecosystems and societal responses.

Co-author Dáithí Stone, also of Oxford, said, "This research will help us understand how human influences on climate affect the increased risk of deaths, forest fires, and crop losses."