Global warming and airflow changes 'caused US and EU heatwaves'

The Guardian (UK) via Reuters: Global warming may have caused extreme events such as a 2011 drought in the United States and a 2003 heatwave in Europe by slowing vast, wave-like weather flows in the northern hemisphere, scientists said on Tuesday.

The study of meandering air systems that encircle the planet adds to understanding of extremes that have killed thousands of people and driven up food prices in the past decade.

Such planetary airflows, which suck warm air from the tropics when they swing north and draw cold air from the Arctic when they swing south, seem to be have slowed more often in recent summers and left some regions sweltering, they said.

"During several recent extreme weather events these planetary waves almost freeze in their tracks for weeks," wrote Vladimir Petoukhov, lead author of the study at the Potsdam Institute for Climate Impact Research in Germany.

"So instead of bringing in cool air after having brought warm air in before, the heat just stays," he said in a statement of the findings in the US journal Proceedings of the National Academy of Sciences. A difference in temperatures between the Arctic and areas to the south is usually the main driver of the wave flows, which typically stretch 2,500km- 4,000km (1,550-2,500 miles) from crest to crest....

The Loire River at Nevers, during the 2003 heat wave, shot by Cypris, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license