What is the Polar Vortex?

The Polar Vortex, the climate phenomenon responsible for the occasional, bitterly cold temperatures in the Northern and Midwestern United States, explained—and why climate change will make it worse.

Every several years, the United States suffers a sudden, unpredictable blast of arctic air that can turn some locations in the Midwestern US into some of the coldest places on Earth. In 1985, a polar vortex event forced Ronal Reagan, newly re-elected President in 1984, to cancel his outdoor parade and celebration commemorating his second inaugural. In 2019, it set record low temperatures not seen in over 100 years. But what is the polar vortex, exactly?

We’ve known about this naturally occurring phenomenon since at least the 1850s, but thanks to social media, the term has become much more widely known though few of us know much about it—or that scientists fear that climate change will make its occasional blasts of arctic air even more regular.

What is the Polar Vortex?

Chicago Polar Vortex
Source: edward stojakovic / Flickr

If we’re being technical, its "what is a polar vortex", since there are actually two polar vortices, one for each pole. Since the polar vortex over Antarctica does not usually create weather events that we experience, the polar vortex over the Arctic is always the one people are concerned with. This vortex exists year-round, with a second one forming as the pole enters its winter season.

The cold air at the north pole creates sustained, high winds as it interacts with warmer air from the southIn the winter months, the temperature at the north pole gets seriously cold, dropping close to -110 degrees Fahrenheit (-79 degrees Celsius) and the temperature difference with the southern latitudes grows, creating stronger winds. It’s this frigid air that the polar vortex helps keep locked in place.

About 7 miles above the Earth, the counterclockwise movement of air driven by the temperature differences between the Arctic and southern latitudes creates what's known as the jet stream, which is a more or less circular current of westerly wind that surrounds the Arctic. You might recognize this from weather reports if you live in the Northern Hemisphere, since the jet stream is what creates and drives the high and low-pressure systems that give the more southern latitudes their weather, both clear blue skies and snowstorms, and its what brings warmer, more tropical air into northern Europe, allowing the United Kingdom, whose latitude is about the same as Nova Scotia, Canada, to have a relatively temperate.

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Further up, there is another vortex known as the stratospheric polar vortex, which forms during the winter months when the North Pole is plunged into its months-long night. According to NASA, it is a “large-scale region of air that is contained by a strong west-to-east jet stream that circles the polar region. This jet stream is usually referred to as the polar night jet.” This second vortex is smaller than the lower vortex creating

This upper vortex of extremely cold air is kept locked in place by the force of the lower jet stream, which is driven by the temperature difference between the arctic and southern latitudes. What this essentially creates is a gigantic eddy at the north pole that keeps arctic air twisting in a tight spiral above the pole.

When the Jet Stream Wobbles

If this all sounds like a well-ordered climate system, you’re partially right. This phenomenon usually keeps the worst of the arctic air contained so that New York City doesn’t regularly get as cold as Minneapolis, MN, and Minneapolis, MN is actually habitable year-round.

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Like any atmospheric system, however, there are going to be irregularities. The jet stream is driven by the temperature difference between the arctic polar region and the warmer lower latitudes, so when this difference becomes less extreme, these winds slow down.

The same way a fast moving river runs straight but a slow-moving one meanders, the jet stream begins to lose its circular shape the slower its winds move. This causes the jet stream to form ridges and troughs that bring high-pressure systems further north towards the pole, disrupting the upper vortex in the winter.

This has the effect of pushing the upper vortex off of the pole, and even splitting the vortex into smaller, but no less frigid, vortices that are pulled down off the poles by the meandering jet stream.

Vortex Diagram
Source: NOAA

As a result, according to the US National Weather Service, “the polar vortex will expand, sending cold air southward with the jet stream. This occurs fairly regularly during wintertime and is often associated with large outbreaks of Arctic air in the United States.”

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In 2014, just such an event occurred when “the polar vortex suddenly weakened, and a huge high-pressure system formed over Greenland,” according to the US National Oceanic and Atmospheric Administration. “The high-pressure system blocked the escape of all that cold air in the jet stream, and allowed part of the polar vortex to break off and move southward.”

“Places as far south as Tampa, Florida experienced the wrath of this wandering polar vortex. Most of Canada and parts of the Midwestern United States had temperatures colder than Alaska at the height of this cold snap.”

How Are Climate Change And The Polar Vortex Related?

Hurricane Florence
Source: Ricky Arnold / Twitter

If the difference between the temperatures in the Arctic and the temperature in the southern latitudes drives the jet stream and the closing of that difference creates opportunities for polar air to slip south, then future climate models indicate that these outbreaks of arctic air from the poles will become more frequent, demonstrating how closely climate change and the polar vortex are related.

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The problem is that the poles are warming much faster than the rest of the planet. As the planet heats up, colder, polar regions absorb the additional heat faster than regions that are already naturally warm. So, even as southern latitudes see temperature increases as a result of climate change, the rate of that change will be faster at the poles, leading to more frequent weakenings of the jet stream as the temperature difference between the two shrinks.

If the wobbling of the jet stream leads to the intrusion of the polar vortex further south, then the relationship between climate change and the polar vortex will lead to more frequent cold snaps like the one we're seeing this month.

This disruption of the jet stream has larger implications than just the increased frequency of the polar vortex dumping cold air on the American Midwest. It is also expected to create all kinds of extreme weather conditions year-round, from heat waves to increased flooding, more extreme storms, and persistent droughts throughout the Northern Hemisphere.

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Get Ready To Bundle Up

While many like to point to the polar vortex as evidence that climate change and the subsequent warming that accompany it must be wrong, it is both exactly in line with what we should expect and frightening evidence that the effects of climate change aren’t exclusively a future concern, but are being felt even as you read this.

Our current emission levels are already locked in, so some consequences of climate change are now unavoidable, but there is still much that we can do to prevent situations like 2019’s polar vortex event from becoming an even more regular occurrence than they already are.

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