Published: 11:10 EDT, 6 August 2012 | Updated: 03:03 EDT, 7 August 2012>
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” has become so loaded that the effect of greenhouse gas emissions is clear for anyone to see, say US experts.
New Yorkers taking in the sun on a beach at Coney Island on August. Scientists now blame global warming for this years record breaking temperatures
Scientists compared June, July and August temperature data from a “base period” of 1951 to 1980 with more recent 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 only experienced in 10% of years.
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.
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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 heat wave, 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 US space agency 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,' they said.
Commenting on the research, Met Office scientist Dr Peter Stott said: 'As far as how climate change is changing the statistics of extreme weather around the world, this new paper is broadly in line with previous work including work that we published in 2008 showing that hot summers which were infrequent 20-40 years ago are now much more common and that our projections indicate that the current sharp rise in incidence of hot summers is likely to continue.'
New Yorkers taking in the sun on Manhattan rooftops. Researchers believe the current heatwaves could be linked to global warming
But he is wary of tying specific heatwave events such as those in Moscow and Texas to man-made global warming.
'While we can provide evidence that the risk of heatwaves has increased, we cannot say that the chances of such heatwaves were negligible before global warming set in,' he said.
Both the Moscow and Texas heatwaves were associated with 'unusual circulation characteristics', he said.
'Further research is needed to understand how climate change could be affecting such aspects of climate variability as the position of the jet stream.
'It is the interplay of variability and climate change that counts,' said Dr Stott.
Source : http://www.dailymail.co.uk/sciencetech/article-2184474/Heatwaves-scoring-summers-Global-warming-blame-say-leading-scientists.html