THE extreme Russian heatwave of 2010 was made three times more likely because of man-made climate change, according to a study led by climate scientists. But the size of the event was mostly within natural limits, said the scientists, laying to rest a controversy last year over whether the extreme weather was natural or human-induced.

The 2010 heatwave broke all records for Russia — temperatures in the central region of the country, including Moscow, were around 10°C above what they should have been for the time of year. More than 50,000 people died from respiratory illnesses and heat stress during that time. The temperatures also had a substantial impact on that year’s Russian wheat harvest, leading to economic losses of more than $15bn.

Two studies published in 2011 looked at the causes of the extreme weather, but they disagreed on whether it was a natural event or whether it was a result of anthropogenic climate change.

An American team led by Randy Dole of the National Oceanographic and Atmospheric Administration (Noaa) suggested that the heatwave was mostly natural in origin. “They based that on the fact that there was no basis for anticipating the heatwave given the conditions which applied at that time in Russia,” said Myles Allen, a climate scientist at Oxford University.

“Heatwaves of that nature had happened in the past on a 100-year timescale and there wasn’t an obvious significant trend in temperatures in that region or in the statistics of hot temperatures in that region. They came to the conclusion this was an event that was mostly natural in origin. There was no need to induce climate change to explain this event.”

A separate study by Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research near Berlin suggested otherwise.

“What they [said] was that the risk of the heatwave occurring had gone up by a substantial factor, the odds of it occurring were 80 per cent due to the large-scale warming trend and, of course, most of that large-scale warming is attributed to human influences on climate,” said Allen. — The Guardian, London