Rapid Arctic warming is linked to extreme US cold snaps, study argues

Scientists present compelling evidence that a phenomenon affecting the polar vortex is the missing link, Andy Gregory reports

Ice floes fill the Hudson River in 2014 during a cold snap caused by the stratospheric polar vortex (Afton Almaraz/Getty Images)

Rapid warming and melting sea ice in the Arctic is likely to be driving an increase in extreme winter weather events in the United States, a new study argues.

While climate breakdown has been linked to increases in some weather extremes, such as heatwaves and the hurricane that churned its way up the Gulf Coast this week, no concrete link has previously been made with severe winter weather events, according to the authors.

Yet, contrary to current climate modelling projections, extreme winter weather events have been increasing across the northern hemisphere since 1990, they argue – pointing notably to the cold snap in February which drove the collapse of the Texas energy grid and was blamed for at least 111 deaths.

In recent years, scientists have started to suggest that the previously missing link between Arctic heating and such extreme weather events could be an atmospheric feature known as the stratospheric polar vortex (SPV).

The SPV is defined as the strong westerly winds that encircle the Arctic during the winter season and, under normal conditions, keep its cold air tightly contained.

In a new study published in the journal Science, researchers build upon recent work suggesting that accelerated warming in the Arctic is disrupting the vortex.

Researchers previously suggested that rapid Arctic warming can result in the polar vortex becoming “stretched”. This causes it to weaken and for the patterns of the winds to deviate from their typical circular flow – instead blowing further south, over the American and Eurasian continents.

The new study – led by scientists from the Massachusetts Institute of Technology, University of Massachusetts Lowell and Hebrew University of Jerusalem – argues that the number of autumn and winter days during which the SPV has become “stretched” has nearly doubled in the past 40 years.

“Melting sea ice across northwestern Eurasia, coupled with increased snowfall in Siberia, leads to a strengthening of the temperature difference from west to east across the Eurasian continent,” Judah Cohen, one of the paper’s authors, told Bloomberg. “When that temperature difference increases, it leads to more disruptions in the polar vortex.”

Using new modelling and observational analysis, based on data of Arctic snow and sea ice and temperatures in North America, the scientists claim to have proven a physical link between disruption to the SPV and the increase in extreme winter weather events in the northern hemisphere.

They correlate these stretching events with past cold snaps such as the one suffered by Texas in February.

“I know it’s very counterintuitive, and I think that’s why there’s a lot of resistance and hesitancy to our idea, right?” Dr Cohen told The Guardian. “Because how could making the Earth warmer lead to more extreme cold? But that’s what we’re arguing.”

The authors hope that, by identifying the precursor to these stretching events, their findings can be used to extend the warning times ahead of cold snaps in Asia, Canada, and the US.

Furthermore, they hope policymakers will now plan for an increase in extreme winter weather, rather than the reverse. The study concludes: “Preparing for only a decrease in severe winter weather can compound the human and economic cost when severe winter weather does occur.”