‘It is not a question of yes or no, but a question of probabilities’
By Summit Voice
SUMMIT COUNTY —An unusual heat wave persisting across huge parts of the U.S. in early March, once again fueled discussions about possible links between long-term climate change and what appears to be more frequent extreme weather events.
Scientists with the Potsdam Institute for Climate Impact Research in Germany said the high incidence of extremes is not a coincidence.Through a statistical analysis, they said they’ve identified a pattern in the chain of extreme weather events, finding evidence that extreme rainfall and heatwaves can be traced to global warming.
“The question is whether these weather extremes are coincidental or a result of climate change,” said Dim Coumou, lead author of an article recently published in he journal Nature Climate Change. “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,” Coumou said.
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 millennium. 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.
“It´s like a game with loaded dice,” Coumou said. “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 scientists based their analysis on three pillars: basic physics, statistical analysis and computer simulations. Elementary physical principles already suggest that a warming of the atmosphere leads to more extremes. For example, warm air can hold more moisture until it rains out. Secondly, clear statistical trends can be found in temperature and precipitation data, the scientists explain. And thirdly, detailed computer simulations also confirm the relation between warming and records in both temperature and precipitation.
The researchers also concluded that global warming can turn extreme events into a record-breaking events.
“Single weather extremes are often related to regional processes, like a blocking high pressure system or natural phenomena like El Niño,” said Stefan Rahmstorf, co-author of the article and chair of the Earth System Analysis department at the Potsdam Climate Institute. “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.”