The past decade has been one of unprecedented¹ weather extremes. Scientists of the Potsdam Institute for Climate Impact Research (PIK) in Germany argue that the high incidence of extremes is not merely accidental. From the many single events a pattern emerges. At least for extreme rainfall and heat waves the link with human-caused global warming is clear, the scientists show in a new analysis of scientific evidence in the journal Nature Climate Change. Less clear is the link between warming and storms, despite the observed increase in the intensity² of hurricanes. In 2011 alone, the US was hit by 14 extreme weather events which caused damages exceeding one billion dollars each -- in several states the months of January to October were the wettest ever recorded. Japan also registered record rainfalls, while the Yangtze river basin in China suffered a record drought. Similar record-breaking events occurred also in previous years. In 2010, Western Russia experienced the hottest summer in centuries, while in Pakistan and Australia record-breaking amounts of rain fell. 2003 saw Europe´s hottest summer in at least half a millennium³. And in 2002, the weather station of Zinnwald-Georgenfeld measured more rain in one day than ever before recorded anywhere in Germany -- what followed was the worst flooding of the Elbe river for centuries.

"The question is whether these weather extremes are coincidental or a result of climate change," says 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." This is what his analysis of data and published studies shows. "It is not a question of yes or no, but a question of probabilities," Coumou explains. The recent high incidence of weather records is no longer normal, he says.

"It´s like a game with loaded dice⁴（骰子） ," says 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 past week illustrates⁵ this: between March 13th and 19th alone, historical heat records were exceeded in more than a thousand places in North America.