(CNN) — Even as the world smashes through one all-time heat record after another and speeds towards critical warming thresholds, brutal waves of deadly cold can still arrive in bomb cyclones that bring icy weather and deep snow — and add fuel for those who deny the climate crisis is real or significant.

But some scientists say that climate change — and more specifically rapid warming in the Arctic — may actually be increasing the likelihood that frigid, polar air can dive south.

Look no further than the heavily populated US Northeast this weekend to see a real-time example of the long-term warming trend being interrupted by tremendous, record-setting cold.

Last month will be remembered for the winter-that-wasn't in the region — ranking as the warmest January on record for nearly all Northeast cities. It was the first month in New York City that temperatures ranked above-average every single day, and first time the month ended without measurable snowfall in the city.

But the weather pendulum swings hard to the other extreme this weekend when record warmth will become record cold, with dozens of low temperature milestones predicted. The wind chill is expected to plunge to dangerous levels of minus 30 degrees Fahrenheit (minus 34 Celsius) for millions on Saturday.

So what's going on?

Extreme cold

While winters are becoming warmer overall and warm records outpace cold, this January brought a brutal cold snap deep into parts of Asia.

Temperatures in the city of Mohe in northern China plummeted to minus 53 degrees Celsius (minus 63.4 degrees Fahrenheit), the lowest temperature the country has ever recorded.

Fierce cold and record amounts of heavy snow in Japan killed at least four people in what the country's Chief Cabinet Secretary Hirokazu Matsuno called a "once-in-a-decade cold snap."

Low temperature records also fell in several places in South Korea.

"Cold air from the North Pole has reached South Korea directly," after traveling through Russia and China, Korea Meteorological Administration spokesperson Woo Jin-kyu told CNN.

More than 150 people died in Afghanistan as temperatures reached lows of minus 28 degrees Celsius (minus 18 degrees Fahrenheit), in what has so far been one of the country's harshest winters.

And the world's coldest city, Yakutsk in eastern Siberia, saw temperatures reach minus 62.7 degrees Celsius (minus 80.9 degrees Fahrenheit) — the lowest in more than two decades according to meteorologists.

Extreme winter weather is now shifting to the US, with dangerously cold Arctic air pushing southwards, sweeping across many parts of the country and quickly dispensing with what had been a mild January.

What explains the cold?

Our weather is intimately connected with the jet stream, a wavy river of fast-moving air high in the atmosphere, around the level at which airplanes fly.

When the jet stream swings south, cold Arctic air can dive into the mid-latitudes along with it — the part of the Earth where the most people live in North America, Europe, and Asia.

That's what happened in Asia in January, Judah Cohen, a climatologist at Massachusetts Institute of Technology and director of seasonal forecasting at Atmospheric and Environmental Research, told CNN.

When the jet stream retreats north, warm air will also push further north. A big high-pressure swing over Europe in January led to record warm winter temperatures and and left some mountains bare of snow.

There is also another factor to consider: The polar vortex.

This is a belt of strong winds encircling blisteringly cold Arctic air, which sits extremely high in the stratosphere — above the level of the jet stream — around the North Pole.

The polar vortex is like a spinning top, Cohen said. In its normal state, it rotates very fast, keeping the cold air close to the center, like an ice skater spinning quickly on the spot, arms neatly across their chest.

But every now and then it gets disrupted. It's as if the ice skater hits a crack in the ice and flies off course, arms flailing. The polar vortex wobbles, becoming stretched and distorted, spilling out cold air and influencing the path of the jet stream.

The devastating cold spell that hit Texas in 2021, taking out power across much of the state and leading to more than 240 deaths, was caused by one of these stretching events, as was the historic cold that hit the US in late December.

Some scientists say minor disruptions in the polar vortex may help explain the recent extreme cold in Asia.

How does climate change fit in?

The theory centers on the Arctic, which is warming up to four times faster than the rest of the world as a result of heat-trapping pollution from burning fossil fuels.

Some scientists argue that this warming is triggering changes to the jet stream and polar vortex, causing more frequent winter extremes.

This idea gained traction following the publication of a 2012 study, co-authored by Jennifer Francis, a senior scientist at the Woodwell Climate Research Center in Massachusetts. It suggested that Arctic warming was reducing the difference between the cold temperatures in the north and warm temperatures in the south, leading to a weaker, wavier jet stream, which pushed very cold air southwards.

Francis' paper kicked off a debate and, in the decade since, many more scientists have looked at the theory.

One of the most prominent papers, co-authored by Cohen in 2021, said it found clear links between Arctic warming and disruptions to the polar vortex.

Cohen's argument is that particularly rapid heating in an area of the Arctic, north of western Russia, combined with increased snowfall in Siberia, amplifies the waviness of the jet stream and pushes energy upwards. This knocks the polar vortex off course, causing very cold air to spill out.

The paper linked Arctic warming to extreme winter weather across parts of Asia and North America, including the prolonged cold wave in Texas in 2021.

"We are not arguing that winters are getting colder overall," Cohen said. The world is smashing through many more heat records than it is cold records.

But the idea that climate change will mean fewer swings between extreme temperatures is "an oversimplification," he said.

"As we continue to dump greenhouse gasses into the atmosphere, and thicken this blanket of greenhouse gasses around the Earth, we will see more extreme events of all sorts, including these cold spells," Francis told CNN.

How settled is the science?

Not at all. This is a very complex area of research and other scientists are far more cautious.

There have been a number of cold winters in the US and Asia coinciding with warm winters in the Arctic, James Screen, professor in climate science at Exeter University, told CNN. "The challenge we face is determining cause from effect."

Screen co-authored research which used climate models to predict what will happen when Arctic sea ice reduces even further. It found sea ice loss had only a very small effect on the jet stream and there was no real sign of an effect on the polar vortex.

While the research pointed to warmer Arctic winters and bursts of cold further south, Screen said this can be "explained by normal weather variability."

In other words, even as winters warm, cold extremes will still occur — because that's just how winters work.

One key criticism of the research linking Arctic changes to severe winter weather is that it's based on historical data.

"If we look more at climate model data, we don't see these types of links or they're very weak," Dim Coumou, a climate professor at Vrije Universiteit Amsterdam, told CNN.

What scientists do agree on is the need to keep studying these extremely cold spells.

"We don't really have enough research yet," Daniela Domeisen, a climate professor at ETH Zurich, in Switzerland, told CNN. "Eventually we'll find a solution to this and actually understand the mechanism, but I just think we're not there yet."

The-CNN-Wire
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