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Study suggests climate change behind extreme weather events

The world has been on an extreme weather rollercoaster ride since the early 2000s. Researchers in Germany say the high incidence of extreme weather events is not by chance. Presented in the journal Nature Climate Change, their study highlights a pattern generated by a number o...

The world has been on an extreme weather rollercoaster ride since the early 2000s. Researchers in Germany say the high incidence of extreme weather events is not by chance. Presented in the journal Nature Climate Change, their study highlights a pattern generated by a number of single events. The findings point to an association between anthropogenic global warming and extreme rainfall and heat waves. The connection is not as evident between global warming and storms despite the rise in hurricane events. The Potsdam Institute for Climate Impact Research (PIK) researchers say 14 extreme weather events hit the United States in 2011 alone, and each event cost more than USD 1 billion. Japan also faced a number of extreme weather events, reporting record rainfalls. Western Russia was challenged with very hot summer temperatures, while Australia and Pakistan reported record-breaking rainfall levels. China, and specifically the Yangtze River basin, was hit by a record drought. Europe, meanwhile, was hit with the hottest summer season in 2003, accounting for the highest summer temperatures in at least half a millennium. 'The question is whether these weather extremes are coincidental or a result of climate change,' says PIK's Dr Dim Coumou, lead author of the article. 'Global warming can generally not be proven to cause individual extreme events - but in the sum of events the link to climate change becomes clear. It is not a question of yes or no, but a question of probabilities.' The PIK researcher goes on to say there is nothing normal about the recent high incidence of weather records. 'It's like a game with loaded dice,' explains Dr Coumou. 'A six can appear every now and then, and you never know when it happens. But now it appears much more often, because we have changed the dice.' The team focused on three pillars in their assessment: basic physics, statistical analysis and computer simulations. Basic physical principles suggest that a warming of the atmosphere results in more extreme events. They add that clear statistical trends can be found in temperature and precipitation data. Finally, detailed computer simulations substantiate the link between warming and records in both temperature and precipitation. The researchers estimate that the intensity of tropical storms, and not the actual number, will rise in various regions, triggered by the increase in ocean temperatures. It should be noted, however, that the dependencies are complex and more information is needed to better understand what is happening. The researchers identified how cold extremes drop with global warming. This does not compensate for the increase in heat extremes, they add. 'Single weather extremes are often related to regional processes, like a blocking high pressure system or natural phenomena like El Niño,' says Stefan Rahmstorf, co-author of the article and chair of the Earth System Analysis department at PIK. 'These are complex processes that we are investigating further. But now these processes unfold against the background of climatic warming. That can turn an extreme event into a record-breaking event.'For more information, please visit: Potsdam Institute for Climate Impact Research (PIK): http://www.pik-potsdam.de/ Nature Climate Change: http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1452.html

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