The data is clear: Rising global temperatures mean winters are getting milder, on average, and the sort of record-setting cold that spanned the country Friday is becoming rarer. But at the same time, global warming may be altering atmospheric patterns and pushing harsh outbreaks of polar air to normally moderate climates, according to scientists who are actively debating the link.
Drastic changes in the Arctic, which is warming faster than anywhere else on Earth, are at the center of the discussion. Shifts in Arctic ice and snow cover are triggering atmospheric patterns that allow polar air to spread southward more often, according to recent research.
“We’ve seen the same situation basically the last three years in a row,” said Jennifer Francis, senior scientist at the Woodwell Climate Research Center in Massachusetts. “Here we go again.”
But understanding any link between planetary warming and extreme cold remains a work in progress. Many climate scientists still emphasize that even if frigid air escapes the Arctic more often, that air will nonetheless become milder over time.
The debate started with a research paper Francis co-authored in 2012. It gets revived whenever an extreme-cold event creates headlines, such as in 2021, when Texas’s energy grid was overwhelmed by a storm that killed 246 people.
Francis’s research hypothesized that Arctic warming was reducing the contrast between polar and tropical temperatures, weakening the jet stream, a band of strong winds in the upper atmosphere that helps guide weather patterns. A weaker jet stream would allow weather systems to more easily swing from the Arctic down into mid-latitude regions that typically have temperate climates.
Since then, observations of jet stream patterns have not confirmed the hypothesis, said Daniel Swain, a climate scientist at UCLA. But the research inspired a flurry of follow-up studies that Swain expects will eventually clarify a link between climate change and cold-weather outbreaks.
“We’re 10 years into this conversation and there’s still a lot of mixed feelings in the scientific community, though there is some tantalizing evidence that there is some ‘there’ there,” said Swain, who works at UCLA’s Institute of the Environment and Sustainability.
A 2021 study published in the journal Science is one new point of debate. The research explains what author Judah Cohen called “a physical foundation” linking Arctic warming and changes in atmospheric patterns.
It focuses on the polar vortex, an area of low pressure typically parked over the North Pole and surrounded by a band of fast-flowing air. Cohen likens it to a spinning top — when the polar vortex is strong, that band of air spins in a tight circle.
Increasingly often, Cohen found, the polar vortex weakens like a wobbling top. That gives the circulating air a more oblong, extended shape and encourages bursts of Arctic air to spread southward.
While the polar vortex took on that stretched shape for about 10 days a year in 1980, in recent years, it has been occurring more than twice as often, said Cohen, director of seasonal forecasting at Atmospheric and Environmental Research.
The research links that to changes in the climate around the Arctic: In the Barents and Kara seas north of Russia and Scandinavia, the waters have warmed and ice has melted, whereas in Siberia, there’s been a cooling trend from increases in snowfall induced by climate change.
Some scientists say that a longer and more thorough record of data is needed to back up Cohen’s research and that there isn’t enough evidence to blame Arctic warming for cold outbreaks at lower latitudes.
Swain predicted that scientists will make sense of the atmospheric dynamics but that it could take years.
“It’s one of the most complicated topics in climate science,” Swain said.
In the meantime, researchers are confident that cold extremes will follow larger global trends and gradually get warmer, though they still will have significant impacts on places unaccustomed to the cold.
“We’re going to break a lot of records this week, for sure,” Francis said. “The likelihood of breaking cold records is decreasing, and we see that in the data.”
And Cohen said data suggests that relief from the cold across the United States is near: Weather models agree that the polar vortex is going to snap back from its oblong shape by early January, trapping the most frigid air around the North Pole once again.