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If global warming reaches record levels, why are there extreme cold snaps?

(CNN) — After an unprecedentedly hot summer, large swaths of the U.S. are now facing record low temperatures as an Arctic blast brings potentially deadly snow, ice and icy winds.

As record-breaking heat gives way to cold, it could provide fuel for climate change deniers who point to frigid temperatures as evidence that the global warming problem is exaggerated.

But scientists are clear: Even with generally warm winters, we will continue to experience extreme cold.

Hot world records surpass cold ones: 2023 leads by a wide margin as the hottest year on record. Additionally, while the United States is grappling with heavy snowfall, the man-made climate crisis has led to a worrying trend in the disappearance of snowpack in the Northern Hemisphere in the long term.

Some scientists say climate change may even play a role in these cold snaps, as a warming Arctic increases the likelihood that frozen polar air will move southward.

How to explain this cold?

The weather is closely related to the jet stream, a fast-moving, undulating river of air high in the atmosphere, about the same height an airplane flies.

When the jet stream turns south, it can push cold Arctic air toward North America, Europe and Asia. As it retreats to the north, the warm air will move further north. Large swings in high pressure over Europe last January led to record winter temperatures.

Another factor must be considered: the Arctic polar vortex.

This is a band of strong winds surrounding the frozen Arctic air that is high in the stratosphere around the North Pole, above the level of the jet stream.

The Arctic polar vortex is like a spinning top. Normally, it spins very quickly, keeping cool air close to the center, like a skater spinning quickly on the ground with arms tightly crossed over their chest.

But from time to time there will be interruptions. The Arctic vortex swings, stretches and twists, carrying cold air and affecting the path of the jet stream.

The devastating cold snap that hit Texas in 2021, knocking out power across much of the state and killing more than 250 people, was one of those events, as was the historic cold snap that hit the U.S. in late December.

How to adapt to climate change?

This is where the link to climate change comes into play. Some scientists believe that disruptions in the polar vortex and changes in the jet stream are caused by a warming Arctic, which is warming four times faster than the rest of the planet.

The idea gained traction in 2012 after the publication of a study co-authored by Jennifer Francis, a scientist at the Woodwell Climate Research Center in Massachusetts. It suggests that Arctic warming is narrowing the difference between colder temperatures in the north and warmer temperatures in the south, causing a weaker, fluctuating jet stream to push very cold air southward.

Francis’ paper sparked debate, and many other scientists have since investigated the theory.

In 2021, MIT climatologist Judah Cohen published research that found rapid warming in parts of the Arctic, coupled with heavy snowfall in Siberia, was making the jet stream more volatile and pushing the polar vortex off course.

“We’re not saying winters are getting colder overall,” Cohen told CNN last year. But he said the idea that climate change would mean fewer swings between temperature extremes was “overly simplistic”.

Extremely cold Texas

An ice warning sign appears on Interstate 35 on February 18, 2021, in Killeen, Texas. Photo credit: Joe Raedle/Getty Images North America/Getty Images

How solid is the science?

Absolutely. This is a very complex area of ​​research, and other scientists are much more cautious.

James Slater, a professor of climatology at the University of Exeter, explained to CNN that the United States and Asia have experienced several cold winters, while the Arctic has experienced warm winters. “The challenge is to determine the cause of the impact.”

The study Screen co-authored uses climate models to predict what will happen as Arctic sea ice shrinks further. Research shows that the loss of sea ice has very little impact on the jet stream, with no real indication that it affects the polar vortex.

While research points to warmer winters in the Arctic and cold snaps in the south, Slater said this could be “explained by normal meteorological changes.”

In other words, even if winter gets warmer, extreme cold will still happen because that’s just how winter is.

extremely cold

A frozen street in Yakutsk, eastern Russia.Photo credit: Alewxei Vasilyev/AP

One of the main criticisms of studies linking Arctic changes to extreme winter weather is that they are based on historical data.

“If we looked more at the data from climate models, we wouldn’t see these types of connections, or they would be very weak,” Dim Coumou, a climate professor at Vrije Universiteit Amsterdam, told CNN.

Scientists agree there is a need to continue studying these extreme cold snaps.

“We haven’t done enough research yet,” Daniela Domeisen, a professor of climatology at the Swiss Federal Institute of Technology in Zurich, explained to CNN. “Eventually we will find solutions and really understand the mechanisms, but I don’t think we’re there yet.”

——CNN’s Nouran Salahieh and Allison Chinchar contributed to this report.

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