What is a Polar Vortex? And Other Cold Weather Climate Questions

    February 16, 2021, a post-freeze neighborhood in Austin, Texas, without electricity.  (Tamir Kalifa/The New York Times)

February 16, 2021, a post-freeze neighborhood in Austin, Texas, without electricity. (Tamir Kalifa/The New York Times)

The polar vortex is descending into the central United States, bringing bitterly cold air from the Arctic and causing temperatures to drop rapidly in many regions. The deep freeze will be accompanied by a massive blizzard that is expected to cause travel chaos.

A vortex is a large, swirling area of ​​cold air that usually surrounds the North Pole, but sometimes shifts southward from the pole. Vortex-related colds occur regularly in the United States. One of the most damaging occurred in February 2021, when cold air reached deep into Texas and temperatures dropped as low as 40 degrees Fahrenheit below normal.

This freeze killed at least 250 people and caused extensive damage to the state’s electrical infrastructure.

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As global heat-trapping carbon dioxide emissions continue, the Arctic is warming about four times faster than other parts of the planet, according to recent analysis, and the region’s sea ice coverage is shrinking. As the vortex bends southward, two fundamental questions arise. If yes, what is the role of climate change? And will extreme frosts increase as warming continues?

Short answer: Scientists aren’t sure yet. There are tips, but there is much more to learn.

“I wish I had a clear answer,” said climate scientist Steve Vavrus of the University of Wisconsin. Along with Jennifer Francis, now at the Woodwell Climate Research Center in Massachusetts, Vavrus wrote a seminal 2012 paper presenting the idea that Arctic warming is affecting the polar vortex. Unfortunately, the situation is still unclear,” he said.

What exactly is a polar vortex?

A vortex, as the term suggests, is a swirling air mass at high altitude that occurs in the Arctic region. (There are actually two vortices, one in the North Pole and the other in Antarctica, but only the one in the north affects the weather in the Northern Hemisphere.)

In winter, the vortex gets stronger and much colder because at that time of year, as the Northern Hemisphere tilts away from the sun, little or no sunlight reaches the North Pole to warm it.

If you were looking at the North Pole, the air would appear to rotate counterclockwise. Some scientists have compared it to a spinning top. The vortex is surrounded by the polar jet stream, a band of winds blowing around the planet from west to east.

What happens during deep freezing?

Under normal conditions, the vortex is constant and limited to the North Pole. However, when a top hits something, it may start to sway and drift, and the vortex may be disrupted. This is accompanied by changes in the jet stream that develops an undulating, snake-like pattern as it circles the globe.

Sometimes the vortex splits into several parts that move southward. Sometimes, like this week, it stretches like a rubber band. Either way, the outage can have several significant effects.

Temperatures in the atmosphere above the Arctic can sometimes rise dramatically. At the same time, cold Arctic air moves south.

If the movement is fast enough, temperatures in areas exposed to cold air masses can drop by tens of degrees within hours, and remain extremely low for days or even weeks until the vortex stabilizes again in the Arctic region.

How does the vortex break?

For climate scientists, this is the crux of the debate.

Some scientists say Arctic warming is causing disturbances in the vortex through changes in polar jet flow. Others say that modeling inherently variable factors triggered the outages, and that the increase in eddy disturbances that had occurred before — including a noticeable increase in the 2000s — did not continue.

Judah Cohen, a climate scientist at Atmospheric and Environmental Research, a weather risk assessment firm in Lexington, Massachusetts, is the author of a paper this year linking the 2021 Texas freeze to Arctic warming. He now sees the same thing happening.

The basic idea, he said, is that warmer conditions create larger and more energetic atmospheric waves that make the jet stream choppy, larger crests and troughs. This affects the polar eddy circulation.

“Like it started hitting something,” he said, to use the spinning ball analogy. “It loses its beautiful circular shape, and in this case it stretches even more.” A lobe stretches across Canada and the United States, bringing in an epidemic of cold weather.

Cohen said he has been studying the issue since 2005 and is more confident than ever about the link to changes in the Arctic. “The evidence is only increasing,” he said.

Other scientists are not so sure. In a brief article published in the journal Nature Climate Change in 2020, two researchers from the University of Exeter in England found that, despite continued Arctic warming and sea ice loss, extreme cold, jet stream surge and climate change in the 1990s and 2000s Other related measurements “have not continued over the past decade”, which weakens the argument that rising temperatures in the Arctic are to blame.

Some experts suggest that other naturally variable elements of Earth’s climate, rather than warming, may be affecting the vortex. Ted Shepherd, a climate scientist at the University of Reading in England, said among them, sea surface temperatures in the tropical Pacific Ocean could trigger changes in air masses in the Arctic that disrupt jet streams and vortices.

Will this debate be resolved?

Scientists say questions about how Arctic warming might play a role in extreme cold are an example of the healthy climate change debate taking place right now. The question isn’t whether climate change is real – that question has been answered – but what kind of effects does it have, how severe, and will it get worse as warming continues?

Most scholars see this debate as an important debate that is still ongoing. Some aspects are “on pretty solid physical foundations,” Vavrus said. Among them, he said, is the idea that Arctic warming weakens jet stream winds by reducing the temperature difference between the Arctic and the tropics. But other considerations, including whether and where warming makes the jet stream choppy, are “things we’re really wrestling with and remain unclear,” he said.

“In the early days, there was a lot of black and white thinking about this question, including people like me,” Vavrus added. “As more and more evidence comes in, it’s clear that there are many shades of gray.”

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