Global warming has doubled risk of harsh winters in Eurasia, research finds

Severe winters are more likely over the next few decades due to climate change melting Arctic ice and sending freezing air south, according to new research

by Damian Carrington, The Guardian, October 26, 2014

New research shows that the increased risk of icy winters will persist for the next few decades. Photograph: Jeff J Mitchell/Getty Images

The risk of severe winters in Europe and northern Asia has been doubled by global warming, according to new research. The counter-intuitive finding is the result of climate change melting the Arctic ice cap and causing new wind patterns that push freezing air and snow southwards.

Severe winters over the last decade have been associated with those years in which the melting of Arctic sea ice was greatest. But the new work is the most comprehensive computer modelling study to date and indicates the frozen winters are being caused by climate change, not simply by natural variations in weather.

“The origin of frequent Eurasian severe winters is global warming,” said Prof Masato Mori, at the University of Tokyo, who led the new research. Climate change is heating the Arctic much faster than lower latitudes and the discovery that the chances of severe winters has already doubled shows that the impacts of global warming are not only a future threat. Melting Arctic ice has also been implicated in recent wet summers in the UK.

The new research, published in Nature Geoscience, shows that the increased risk of icy winters will persist for the next few decades. But beyond that continued global warming overwhelms the colder winter weather. The Arctic is expected to be ice-free in late summer by the 2030s, halting the changes to wind patterns, while climate change will continue to increase average temperatures.

“The agreement between observations in the real world and these computer models is very important in giving us more confidence that this [doubled risk of severe winters] is a real effect,” said Prof Adam Scaife, a climate change expert at the UK Met Office and not part of the research team. “The balance of evidence suggests this is real.”

Dr Colin Summerhayes, at the Scott Polar Research Institute in Cambridge, UK, said: “This counterintuitive effect of the global warming that led to the sea ice decline in the first place makes some people think that global warming has stopped. It has not. Although average surface warming has been slower since 2000, the Arctic has gone on warming rapidly throughout this time.”

The melting of sea ice influences Eurasian winters because the open ocean is darker than ice and absorbs more heat. This in turn warms the air above and weakens the high-level winds called the polar vortex. This causes meanders in the jet stream to become stuck in place. This “blocking” pattern pulls freezing air southwards out of the Arctic and, because it is stuck, the resulting severe weather can last for long periods.

Climate scientists have warned for many years that global warming is not simply leading to a slow, gradual rise in temperature. Instead, it is putting more energy into the climate system which drives more frequent extreme events.

Deadly heatwaves in Europe and Australia have already been shown to be many times more likely because of global warming, while some floods were made twice as likely by climate change as long ago as 2000.

“Annual average global temperatures continue to rise, but the distribution of temperature through the year is giving us more extremes, which is highly damaging to food production,” said Prof Peter Wadhams at the University of Cambridge. “As ice continues to retreat, we can expect these weather extremes to continue to occur and maybe worsen.”

http://www.theguardian.com/environment/2014/oct/26/global-warming-has-doubled-risk-harsh-winters-eurasia-research-finds