The US is suffering through a polar vortex. Paradoxically, we may have global warming to thank for that.
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- The US is in the midst of a polar-vortex event. About 84 million Americans are experiencing subzero temperatures.
- The polar vortex is an area of circulating cold air that rings the planet's North Pole. Sometimes that vortex destabilizes, sending surges of Arctic air south.
- Climate change - specifically melting Arctic ice - may impact how often countries in the Northern Hemisphere experience polar-vortex events and other extreme winter weather. Some research suggests these cold snaps might get more common.
The 2019 polar-vortex event continues to sweep the country.
Between the US Midwest and East Coast, 84 million Americans are contending with subzero temperatures, CNN reports. Wind chill advisories have impacted 140 million people.
Parts of Minnesota and Wisconsin saw windchill temperatures are as cold as minus 50 degrees Fahrenheit on Thursday - that's life-threatening. At those temperatures, frostbite can set in within five minutes, according to the Chicago National Weather Service office. At least eleven deaths in Midwest have been linked to the weather this week.
The cold snap has prompted some people - most notably President Donald Trump - to question how temperatures could get so low given that the Earth is warming.
Generally, polar-vortex events - which are short-term weather patterns - shouldn't be confused with long-term changes in Earth's climate. Global average temperatures are still among the highest ever recorded, and oceans are the warmest they've been since we started keeping records.
"Even in a warming world you can still have extreme cold," Judah Cohen, director of seasonal forecasting and atmospheric and environmental research at Verisk Business, told Business Insider.
However, global warming may actually play a role in the frequency of these cold snaps, according to a growing body of research.
The consequences of a warming Arctic
The term polar vortex describes the mass of low-pressure cold air that circulates in the stratosphere above the Arctic and Antarctic regions. A strong polar vortex stays where it belongs, swirling around the North Pole. But sometimes the circulation of the polar vortex weakens, causing surges of frigid air to splinter off and drift south.
The freezing air is carried by the jet stream, a current of wind that extends around the hemisphere and divides the air masses in the polar region from those farther south.
Although researchers have not yet reached a consensus, many are starting to link the weakening of the polar vortex to the warming Arctic, as Inside Climate News reported.
The logic goes like this: Because temperatures are rising in the Arctic at double the rate of the rest of the planet, the difference between temperatures at the North Pole and continents at lower latitudes is decreasing. Less disparity in temperatures means less difference between air pressure levels, which weakens the jet stream. That can lead the jet stream to take longer, less direct paths.
If the jet stream wanders enough, that can disrupt the natural flow of the polar vortex, weakening it. A weakened polar vortex sends freezing Arctic air south, towards North America, Europe, and Asia.
A 2017 study found that the frequency of winter polar-vortex events has increased by as much as 140% over the past four decades, perhaps because of climate change.
"Stronger polar-vortex states are decreasing and weak polar-vortex states and increasing," Cohen, a co-author on the study, explained.
He noted that Arctic warming and melting sea ice are amplifying conditions typically associated with a weakening polar vortex. In another study published last year, Cohen also found a connection between rising Arctic temperatures and severe winter weather in the eastern US.
"I see a direct connection to changes in the Arctic, that it's warming faster than the rest of globe," Cohen said. "But other people look at it and say, 'weather happens and it's not anything new.'"
The World Resources Institute (WRI) also reported that increasing sea ice melt, particularly in the Barents-Kara seas north of Russia, has been linked to colder winters and more cold snaps in Siberia.
Kelly Levin, a senior associate at WRI, told Business Insider that she believes "this is definitely something we need to pay attention to."
"Instead of seeing this as a disconnected set of events, we need to really explore links between broader patterns of warming climate and extreme weather," Levin said.