15/03/2018

Extreme Winter Weather Becoming More Common As Arctic Warms, Study Finds

The Guardian - 

Scientists found a strong link between high temperatures near the pole and unusually heavy snowfall and frigid weather farther south.
Freezing weather conditions dubbed the ‘Beast from the East’ brought snow and sub-zero temperatures to the UK. Photograph: Matt Cardy/Getty Images
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. Researchers compared daily temperatures from across the Arctic region with something called the accumulated winter season severity index, which grades winter weather based on temperature, snow fall and snow depth, across 12 US cities.
“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.
Two large winter storms recently swept the US east coast in less than a week, unloading up to three inches of snow per hour in places, resulting in several deaths, thousands of cancelled flights, closed schools and snarled traffic.
The cold front even reached Florida, contributing to a recent surge in manatee deaths. So far this year, 166 of the marine mammals have been found dead off the state’s coast, with stress from the cold the leading cause of mortality. “Manatees may join polar bears as one of the first iconic victims of extinction in the wild from climate change,” said Jeff Ruch, executive director of Public Employees for Environmental Responsibility.
The US storms follow freezing winds from Siberia – dubbed the ‘beast from the east’ – that battered parts of Europe, with the British army deployed to help liberate hundreds of stranded drivers on UK motorways.
“This winter is a great example of what we can expect from climate change,” said Cohen. “In the US we had the ‘bomb cyclone’ in January, followed by July-like warm weather in February that I’d never seen before. And now we’ve had a parade of powerful winter storms and the beast from the east. It’s mind boggling.”
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.
This nuanced picture of the consequences of climate change has been derided by Donald Trump, with the president using Twitter to mockingly reference cold weather during almost every winter in recent years. In December, Trump tweeted that “perhaps we could use a little bit of that good old Global Warming” amid plunging temperatures.
Scientists say this stance overlooks the complicated changes underway in the environment as the world warms due to human activity, by an average of around 1C over the past century. This temperature rise hasn’t been uniform across the globe and has fueled an array of conditions, from increased flood risk in some areas to drought conditions and heatwaves in others.
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.
“The broadest picture is that we are indeed warming the world’s climate, primarily from carbon dioxide release from fossil-fuel burning, and this will impact us and other living things,” said Alley.
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.
“There have always been cold outbreaks. The cold air has to go somewhere,” said Kevin Trenberth, senior scientist at the National Center for Atmospheric Research.
“The issue is whether the air stays put or gets loose. Some years it is contained, other years it breaks out. The question is where and what is the cause. This study reaffirms the relationship but not its cause. The Arctic likely plays a modest role in terms of feedbacks but it is unlikely it is a cause.”

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