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February 8, 2025
Can climate change bring more severe winter weather?
The polar dance that caused snow to fall across the South in January has been studied for decades, but scientists still hope to answer many remaining questions.
Miles above the Earth, two bands of fast-moving air – the polar jet stream and the stratospheric polar vortex – sometimes tango together to influence weather in the northern hemisphere.
As the Arctic continues warming up to three times faster than the rest of the planet, some researchers say the two atmospheric patterns are working together to bring about bone-chilling cold air outbreaks more often.
But questions about the interaction aren’t fully settled and remain a subject of scientific debate.
When multiple things are all happening at the same time, “it’s difficult to disentangle the cause,” said Isla Simpson, a scientist with the National Center for Atmospheric Research.
One thing is sure, the phrase “polar vortex” has captured public attention and is now often misused to describe short-term bouts of frigid weather, experts told USA TODAY. Polar vortex is not a synonym for “cold snap,” according to the Polar Vortex Blog at Climate.gov, and it’s not the only weather pattern to blame for blasts of cold air.
“Weather can happen regardless of what the stratosphere is doing,” Simpson said.
What are the polar jet stream and the stratospheric polar vortex?
The high-speed polar jet stream typically spins at a height of 5 to 9 miles above the Earth’s surface, in the lower layer of the atmosphere known as the troposphere.
The jet undulates up and down in ridges and troughs that help steer weather systems around in the northern hemisphere, from cold fronts to hurricanes. When hot, dry conditions occur in one peak or valley of the jet, another may experience colder, wetter conditions.
The polar vortex might be considered the jet stream’s upstairs neighbor in the wintertime. It appears in September, when a seasonal lack of sunlight begins to make it cooler inside the Arctic region than outside, said Laura Ciasto, a meteorologist and co-author of the Polar Vortex Blog. The vortex usually disappears in April.
The polar vortex circles above the Arctic in a higher layer of atmosphere, known as the stratosphere, between 10 to 30 miles above the surface.
Like some human neighbors, the polar jet stream and vortex generally keep to themselves, but sometimes one neighbor or the other gets off kilter or bent out of shape and can disrupt the other band of fast-moving air.
How do the polar vortex and the jet stream affect our weather?
When the polar vortex is strong and circular, it acts as a barrier between the cold air over the pole and warmer air to the south and can speed up the westerly flow of the jet stream, helping it to be less wavy and more confined.
That tends to make the weather milder over the Eastern U.S. and Northern Europe, said Judah Cohen, director of seasonal forecasts at Atmospheric and Environmental Research.
When the vortex gets disrupted, and weakens or stretches, undulations in the jet stream can become steeper or “wavier.”
That’s when the hemisphere tends to get “a risk of a higher outbreak of severe weather,” said Cohen, one of more than a dozen international co-authors of a peer-reviewed paper on the stratospheric vortex published in December in the IOP Science journal Environmental Research: Climate.
That’s the stage that “really has a big impact on the U.S.,” Cohen said, with the kind of severe weather and rare snowstorms that blanketed beaches in Florida’s western Panhandle in January.
However, the vortex isn’t the only thing that influences the jet stream. Other factors include atmospheric waves around the globe, El Niño and even ocean temperatures. When something blocks the jet stream’s westerly flow, it forces pockets of Arctic air southward.
How might climate change affect these weather patterns?
Scientists compare the wind strength of the vortex to a spinning top or ice skater.
A strong, stable vortex is like a skater spinning with their arms tucked closely in, holding in an area of cold air over the Arctic. But when there’s a wobble in the rotation, winds in the vortex can slow or change by interactions with the jet stream or sudden changes in temperature. When that happens, it can stretch or become elongated.
The study published by Cohen and his co-authors suggested warming Arctic temperatures have been disrupting the polar vortex more often since 1990 and sending more frequent cold blasts into the U.S. The researchers surmise that might be why U.S. winters aren’t warming as fast as predicted, even though winter is still the season warming the fastest.
Other researchers aren’t convinced the phenomenon happens more often than it used to.
Over the last 65 years, “there is no significant trend in the strength of the stratospheric polar vortex or in the frequency of extreme breakdowns in the vortex that can lead to cold air outbreaks, Amy Butler, a research scientist with the National Oceanic and Atmospheric Administration’s Chemical Sciences Laboratory, previously told USA TODAY. Butler co-authors the blog on the vortex with Ciasto.
In a mid-January post, Butler and Ciasto agreed the jet stream and the polar vortex may have interacted to help bring about the wild weather.
The vortex – stretched over Canada and Hudson Bay – may have been associated with a southward shift in the jet stream, but that doesn’t mean it directly delivered the Arctic blast, according to the post. A building ridge of high pressure over Alaska may have helped force the jet stream’s southward dive.
Even though scientists don’t fully agree on the frequency of cold air outbreaks, together they say the questions over the powerful influence of these patterns and their potential changes in a warming world make additional research crucially important.
What may happen in a warmer future?
Scientists aren’t sure what all of this means for the future.
Competing factors are at work and the models are split when it comes to forecasting what could happen. Various factors such as melting sea ice and shifts in the subtropical jet stream over the mid-latitudes in the U.S. may counteract each other.
“We have big uncertainty about what’s going to happen with the stratospheric polar vortex,” Simpson said.
Whether it could become more likely that sudden warming in the stratosphere could break down the polar vortex more frequently and push the jet stream southward remains “very much an open question,” she said.
Cohen and his co-authors suggest Arctic change favors more polar vortex disruptions, which can trigger more severe winter weather for weeks. Looking ahead several decades, the picture is more uncertain, he said. For now, “the disruptions are putting a cap on our winter temperatures.”
That could all change and accelerate warmer winter temperatures in the U.S., he said, depending on where the ice melt takes place, or if the majority of the ice melts.
The models do generally agree that when extreme cold events do take place, they’ll be warmer than they are now, said Butler and Simpson.
“What we know for sure is the Arctic is warming faster than anywhere in the world,” Simpson said. “Even if these events happen, the air they’re going to be bringing down is going to be warmer.”
Until temperatures reach a point that it’s too warm to snow, a warmer winter atmosphere will hold more moisture, Simpson said. That means that locations where it’s still cold enough could see more snow.
