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

(CNN) — After seeing unprecedented levels of summer heat, large swathes of the United States are now facing record-low temperatures as brutal Arctic cold unleashes potentially deadly blasts of snow, ice and icy winds.

As record heat gives way to cold, it could provide fuel for climate change deniers who point to colder temperatures as evidence that global warming is an outsized problem.

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

World records for heat surpass records for cold: 2023 was the warmest year on record by a wide margin. Moreover, even as the United States struggles to cope with intense ice flows, in the long term, the man-made climate crisis has led to an alarming trend of ice disappearance in the Northern Hemisphere.

Some scientists say climate change may also play a role in these cold snaps, as warming in the Arctic increases the likelihood of frozen, polar air moving south.

How do you explain this cold?

Weather is closely related to the jet stream, a fast-moving, high-flowing river of air in the air at which airplanes fly.

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

Another factor must also be considered: the Arctic polar vortex.

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

The Arctic polar vortex is like a spinning top. In its normal state, it spins very quickly, keeping the cold air close to the center, like an ice skater spinning fast on the ground, with its arms crossed stiffly over its chest.

But there are interruptions from time to time. The Arctic polar vortex oscillates, stretches and distorts, carrying cold air and influencing the path of the jet stream.

The devastating cold snap in Texas in 2021 that left much of the state without power and killed more than 250 people was caused by one of these events, as was the historic cold snap that hit the United States in late December.

How does climate change fit in?

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 warming in the Arctic, which is warming about four times faster than the rest of the planet.

The idea gained traction after the publication of a 2012 study co-authored by scientist Jennifer Francis of the Woodwell Climate Research Center in Massachusetts. It suggests that Arctic warming is reducing the difference between cold temperatures in the north and warm temperatures in the south, resulting in a weak, undulating jet stream that pushes very cold air south.

Francis’s paper sparked debate, and many other scientists have since looked into the theory.

In 2021, climatologist Judah Cohen of the Massachusetts Institute of Technology published research that found that rapid warming in parts of the Arctic, along with heavy snowfall in Siberia, was making the jet stream wavier and causing the polar vortex to deviate from its course.

“We’re not arguing that winters are getting colder overall,” Cohen told CNN last year. But the idea that climate change means fewer swings between extreme temperatures “is an oversimplification,” he said.

How unified is science?

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

James Screen, a professor of climatology at the University of Exeter, explained to CNN that the United States and Asia have many cold winters that coincide with warm winters in the Arctic. “The challenge we face is determining the cause of the effect.”

Screen co-authored research using climate models to predict what will happen as Arctic sea ice shrinks further. According to the study, sea ice loss has very little effect on the jet stream and there is no real indication that it affects the polar vortex.

Although the research pointed to warmer winters in the Arctic and colder bursts further south, Screen said this “could be explained by general climate variability.”

In other words, even if the winter gets warmer, there will still be extreme cold, because that’s how winter works.

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

“If we look more closely at the data from climate models, we don’t see these kinds of links or they are very weak,” Dim Koumo, a climate professor at the Free University of Amsterdam, told CNN.

What scientists do agree on is the need to continue studying these extremely cold waves.

“We haven’t done enough research yet,” Daniela Domisen, professor of climate at ETH in Zurich, Switzerland, explained to CNN. “Eventually we’ll figure this out and really understand the mechanism, but I think we’re not there yet.”

— CNN’s Nooran Salahih and Alison Chincher contributed to this report.