Blisteringly hot summers similar to the one in 2003 when thousands of people in continental Europe died of heatstroke will become commonplace because of climate change, a study has found.
Scientists estimate global warming has already doubled the risk of similar hot summers, and if the climate continues to change, they will occur every couple of years.
It is estimated that between 22,000 and 35,000 people died heat-related deaths in Europe during the summer of 2003, when soaring temperatures and drought also caused widespread forest fires and crop failures in the Mediterranean area.
Until now it has not been possible to say with any accuracy how much of this extra heat was the result of man-made global warming and how much of it was the result of a naturally warm summer. But Peter Stott, of the Met Office's Hadley Center, and Daithi Stone and Myles Allen, of Oxford University, have found a way of teasing apart the human and natural influences on the temperatures measured across Europe in 2003. Using a computer model of the climate, they found the extra heat that made the summer of 2003 the hottest for at least 500 years was largely the result of human influences, such as the burning of fossil fuel which exacerbates the planet's greenhouse effect.
Dr Stott said: "We simulated 2003 summer temperatures over Europe, with and without the effect of man's activities, and compared these with observations."
"We found that although the high temperature experienced was not impossible in a climate unaltered by man, it is very likely that greenhouse gases have at least doubled the risk.
"Our best estimate is that such a heatwave is now four times more likely as a result of human influence on climate."
The study, published in the journal Nature, calculates that human influence is to blame for 75 per cent of the increased risk.
At the rate at which the climate is changing, the scientists estimate that by the 2040s more than half of the summers will be warmer than that of 2003, and by the end of the century a summer similar to 2003 will be classed as unusually cold.
"Anthropogenic [man-made] warming trends in Europe imply an increased probability of very hot summers," the scientists wrote. "Nevertheless, it seems likely that past human influence has more than doubled the risk of European mean summer temperatures as hot as 2003. And with the likelihood of such events projected to increase 100-fold over the next four decades, it is difficult to avoid the conclusion that potentially dangerous anthropogenic interference is already under way."
Lawyers wishing to pin blame on organizations or governments for exacerbating global warming may use scientific analysis as evidence in a court of law, said Dr Allen, who has co-authored a study into the legal implications of such research with Richard Lord, QC.
"Quantifying the costs of climate change requires being able to separate natural from man-made contributions to weather risk," Dr Stott said. Doug Parr of Greenpeace said: "This study could be a stepping stone to holding climate villains to account.
"Like the tobacco industry big polluters could face massive lawsuits. Polluters should know that if they ignore moral arguments for action, legal liability could hit them."
© 2004 lndependent Digital (UK) Ltd