Global warming probably to blame for killer heatwaves says Nasa scientist

Recent heatwaves and scorching summers are most probably the direct result of global warming, scientists claim.

Until now, experts have not been able to say whether extreme hot spells really are linked to climate change or merely the result of locally varying conditions.

But since 1980 the “climate dice” have become so loaded that the effect of greenhouse gas emissions is clear for anyone to see, say US experts.

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Scientists compared June, July and August temperature data from a “base period” of 1951 to 1980 with records from the past several years.

They found that recent summer heatwaves occurred far more often than would be expected as a result of normal variability.

Hot summers affected about a third of years during the base period compared with three quarters today.

Conversely, unusually cold summers occurred about a third of the time between 1951 and 1980 but were now experienced in only 10 per cent of years.

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The biggest sign of dice loading was the appearance of a “new category” of unusual and extremely hot summers, said the researchers writing in the journal Proceedings of the National Academy of Science. Once these were rarer than one in 300 but now the odds are closer to one in 10. Three of these events produced the 2003 European heatwave, blamed for tens of thousands of deaths, blistering temperatures in Moscow in 2010 and a devastating drought in Texas last year.

The study was led by top climate scientist Dr James Hansen, from Nasa’s Goddard Institute for Space Studies in New York. More than 20 years ago Dr Hansen first warned the world about the dangers of global warming as he sat before a US Senate panel.

In his latest paper, he and his team conclude: “The climate dice are now loaded to a degree that a perceptive person old enough to remember the climate of 1951-1980 should recognise the existence of climate change, especially in summer.”

Commenting on the research, Met Office scientist Dr Peter Stott said: “While we can provide evidence the risk of heatwaves has increased, we cannot say the chances of such heatwaves were negligible before global warming set in.”