climate change - extreme events narrow the doubts
PARIS, Aug 22, 2012 (AFP) - Heatwaves, drought and floods that have struck the northern hemisphere for the third summer running are narrowing doubts that man-made warming is disrupting Earth's climate system, say some scientists. [Over the last billion years, how many northern hemisphere summers have not included heatwaves, drought and floods?]
Weather, they argue, has to be assessed over far longer periods to confirm a shift in the climate and whether natural factors or fossil-fuel emissions are the cause. But for some, such caution is easing. A lengthening string of brutal weather events is going hand in hand with record-breaking rises in temperatures and greenhouse-gas levels, an association so stark that it can no longer be dismissed as statistical coincidence, they say. "We prefer to look at average annual temperatures on a global scale, rather than extreme temperatures," said Jean Jouzel, vice chairman of the UN's Nobel-winning scientists, the Intergovernmental Panel on Climate Change (IPCC). Even so, according to computer models, "over the medium and long term, one of the clearest signs of climate change is a rise in the frequency of heatwaves", he said. "Over the last 50 years, we have seen that as warming progresses, heatwaves are becoming more and more frequent," Jouzel said. "If we don't do anything, the risk of a heatwave occurring will be 10 times higher by 2100 compared with the start of the century."