Oliver Milman
Tue 13 Mar 2018 12.00 EDT
Last modified on Tue 13 Mar 2018 12.02 EDT
The sort of severe winter weather that has rattled parts of the US and UK is becoming more common as the Arctic warms, with scientists finding a strong link between high temperatures near the pole and unusually heavy snowfall and frigid weather further south.
A sharp increase in temperatures across the Arctic since the early 1990s has coincided with an uptick in abnormally cold snaps in winter, particularly in the eastern US, according to new research that analyzed temperature data from 1950 onwards.
Extreme cold winter weather is up to four times more likely when temperatures in the Arctic are unusually high, the study found.
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“There’s a remarkably strong correlation between a warm Arctic and cold winter weather further south,” said Judah Cohen, a climatologist at Atmospheric and Environmental Research. “It’s a complex story – global warming is contributing to milder temperatures but is also having unforeseen consequences such as this.”
The Arctic has just experienced its toastiest winter on record, with parts of the region 20C (68F) warmer than the long-term average, a situation scientists have variously described as “crazy,” “weird,” and “simply shocking”. The far north latitudes are warming around twice as quickly as the global average, diminishing glaciers and sea ice and imperiling creatures such as polar bears.
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The research didn’t look at the reasons behind the trend of see-sawing temperatures between the Arctic and areas to the south but Cohen said it was consistent with the theory that the polar vortex – which shot to public consciousness during a 2014 cold spell – is being disrupted as the earth heats up.
The polar vortex is a low pressure system that swirls around the polar region. Sometimes it can stray further south, bringing cold Arctic air with it. There is continuing conjecture over the impact climate change is having but some scientists believe warming temperatures could be weakening the polar vortex’s flow, allowing it to meander towards the equator.
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Richard Alley, a leading glacier and climate expert at Penn State who was not involved in Cohen’s research, said the study is “fascinating” and “important” but added the discrepancy between Arctic temperatures and winter weather elsewhere could have other drivers, such as a warm Gulf of Mexico feeding extra energy into storms along the US east coast.
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The Arctic’s role is seen quite differently by some other scientists, however, who point out that occasional outbursts of cold weather haven’t altered the trend that winters in the US northeast have been getting warmer, particularly since the 1970s.
[I don't see the basis for saying these scientists see things "quite differently". It is perfectly compatible to point out that on average winters have been getting warmer, while at the same time there are more frequent temporary bursts of polar incursions.]
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https://www.cbsnews.com/news/noreasters-arctic-warming-severe-weather-northeast-east-coast/
https://www.livescience.com/62006-arctic-warms-united-states-freezes.html
Get Used to Nor'easters — Arctic Warming May Mean More Severe Winters in the Northeast
By Mindy Weisberger, Senior Writer | March 13, 2018 12:52pm ET
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According to the study, data from past decades showed that fall snow cover in Siberia increased as the Arctic warmed, which cooled northeastern Eurasia. Meanwhile, melting sea ice fueled warmer temperatures in northwestern Eurasia.
These air-temperature changes close to the surface led to similar changes higher up in the atmosphere. This, in turn, affected the jet stream — a conveyer belt of wind that carries warm air and moisture around the globe — by increasing its "waviness," making jetstream waves dive farther south and stretch farther to the north. In turn, this extra amplification can alter the movement of cold air masses near the pole, otherwise known as the polar vortex, Cohen explained.
And this disturbance of the polar vortex could end up shaping conditions that worsen winter weather in the U.S.
"The cold air that's normally confined to the Arctic, it's kind of dammed in by the polar vortex itself — because winds normally blow from west to east inside the polar vortex, so it acts as barrier, keeps the cold air to the north and the mild air to the south," Cohen said. "When it breaks down, the cold air that's penned up in the Arctic spills to lower latitudes, and that's when you get those episodes of severe winter weather."
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