For the first time since 2014, the polar vortex is descending on North America.
In parts of the Midwest and New England, about 25 million Americans are about to experience temperatures of minus 20 degrees Fahrenheit. Some areas in Minnesota and the Dakotas are facing temperatures 50 degrees below average — that’s life-threatening cold.
The National Weather Service’s Chicago office said windchill of minus 30 to minus 55 degrees Fahrenheit would hit the city between Tuesday and Thursday, with “record-breaking cold (potentially all-time)” on Wednesday.
The term polar vortex describes the mass of low-pressure cold air that circulates in the stratosphere above the Arctic and Antarctic regions. Sometimes the circulation of the polar vortex weakens during the winter, 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.
This polar air mass has always been present, but scientists first dubbed it the “polar vortex” in 2014, when a cold snap hit a majority of the continental US.
North America, Europe, and Asia can all experience polar-vortex events, which bring temperatures that are simply too cold for people to safely be outside.
“You’re talking about frostbite and hypothermia issues very quickly, like in a matter of minutes, maybe seconds,” Brian Hurley, a meteorologist with the Weather Prediction Center, told the Huffington Post.
Hypothermia occurs when your body loses heat faster than you can produce it. Frostbite arises when skin and the tissues below freeze, or, in extreme cases, die.
Chicago’s National Weather Service office said “dangerously cold wind chills could cause frostbite on exposed skin in as little as 5 minutes.” The office suggests covering any exposed skin and bringing pets indoors.
At least two deaths have already been linked to the recent cold wave, CNN reported.
Schools were closed in Chicago and parts of eastern Iowa, in addition to closures in Michigan, Wisconsin, and Minnesota. Nearly 2,300 flights have been canceled, and another 11,800 were delayed, according to Reuters.
We might start seeing polar-vortex events more often
Despite President Donald Trump’s assertions to the contrary on Twitter, the emergence of a polar vortex does not invalidate the scientific consensus on global warming.
The polar vortex creates weather events that take place regionally on dayslong or weeklong timescales. The latter is a planetwide phenomenon caused by increased concentrations of certain gases in Earth’s atmosphere. Global average temperatures are still the highest ever recorded, and oceans are the warmest they’ve been since we started keeping records.
In fact, recent research shows that the frequency of winter polar-vortex events has increased over the past four decades, perhaps because of climate change.
Although many questions remain, scientists have started to connect extreme cold waves to the warming Arctic, as Inside Climate News reported. Because temperatures are rising in the Arctic twice as fast as the rest of the globe, the difference between temperatures at the North Pole and continents at lower latitudes is decreasing, according to The Conversation. 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.
Kevin Loria contributed to a past version of this story.