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2 reasons the U.S. and U.K. are having extremely cold winters

Scientists now agree: warmer weather in the Arctic and a wavy jet stream are influencing winter weather in the UK and US.

The findings, published in Nature Climate Change, represent consensus between two schools of thought.

One group thought natural variability in the jet stream’s position caused the recent severe cold winter weather seen in places such as the Eastern United States and the UK.

The other camp found possible connections between the warming of the Arctic—such as melting sea ice, warming air temperatures, and rising sea surface temperatures—and the emerging pattern of severe cold winter weather.

Extreme ‘warm West, cold East’ winters now the norm?

Scientists now say they’re in agreement: The recent pattern of cold winters is primarily caused by natural changes to the jet stream’s position; however, the warming of the Arctic appears to be exerting an influence on cold spells, but the location of these can vary from year to year.

Previous studies have shown that when the jet stream is wavy there are more episodes of severe cold weather plunging south from the Arctic into the mid-latitudes, which persist for weeks at a time. But when the jet stream is flowing strongly from west to east and not very wavy, we tend to see more normal winter weather in countries within the mid-latitudes.

“We’ve always had years with wavy and not so wavy jet stream winds, but in the last one to two decades the warming Arctic could well have been amplifying the effects of the wavy patterns,” says Edward Hanna, a geography professor at the University of Sheffield. “This may have contributed to some recent extreme cold winter spells along the eastern seaboard of the United States, in eastern Asia, and at times over the UK.

“Improving our ability to predict how climate change is affecting the jet stream will help to improve our long-term prediction of winter weather in some of the most highly populated regions of the world.

The International Arctic Science Committee and the Climate and Cryosphere project of the World Climate Research Programme supported the work.

Source: University of Sheffield

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