Behind the snow and ice storms that have hit the United States in recent days there would be a weakening of the polar vortex.
What does the climate crisis have to do with the epic snowfall, freezing rain and freezing winds that have hit the United States in recent days? There is a connection, or rather there could be, even if apparently counterintuitive.
The Arctic cold wave affecting the Midwest region, the southern and eastern United States, is a consequence of the weakening of the polar vortex, a vast circulation of cold winds that normally hovers over the Arctic. Let’s see how climate change may have affected the “resistance” of this weather system, and why this translates into a record cold grip on the United States.
Polar vortex: what it is and why it matters that it is stable
The polar vortex is a ring of strong winds blowing counterclockwise that forms every winter above the North Pole, at an altitude between 16 and 48 kilometers. It is an area of low pressure, where the pressure is lower than surrounding areas, and traps cold air above the Arctic region, isolating it from the warmer surrounding air.
When the polar vortex is stable, the belt of winds that confine it, known as the polar jet stream, moves northward and holds cold air in the Arctic region. However, when the polar vortex is no longer stable, it changes from a circular ring to a more elongated, wavy and sinuous band, which also touches regions further south and lets part of the previously retained cold flow towards the middle latitudes, in this case North America.
The journey of frost from north to south
This deformation of the polar vortex is believed to be at the origin of the lethal frost that paralyzed air and road traffic, closed schools, brought temperatures as low as -45°C and transformed squares into snowboard slopes in part of the United States. As he explained to BBC Brette Anderson, meteorologist at AccuWeather: «The cold wave at the beginning of January and the one that characterized January 16 are essentially fragments detached from the polar vortex: it is like a large piece of ice that breaks off from a glacier and floats southwards with the current, represented by the winds of the jet stream».
Why is the polar vortex weakening?
According to MIT climatologist Judah Cohen, there would be a strong relationship between polar vortex deformation events, extreme winter weather events like those recently seen in the United States, and climate change. For Cohen, who published an article on the topic in 2025 Sciencethe instability of the polar vortex would be partly linked to the loss of sea ice in the Arctic due to human-caused global warming.
The Arctic is also warming four times faster than the rest of the world, and melting ice, especially in the Barents Sea (north of the Scandinavian Peninsula) and Kara Sea (north of Siberia), has made the polar vortex more elongated and more variable, increasing the likelihood of record-breaking winter storms in mid-latitudes (including Europe).
So is the weakening of the polar vortex set to get worse? Not necessarily. For Amy Butler, an atmospheric scientist at the National Oceanic and Atmospheric Administration (NOAA), the models do not show agreement on this and it is therefore difficult to predict. “There are many factors that can alter the intensity of the polar vortex,” he explains. “Sea ice is one of them: some models suggest that melting sea ice could have a weakening effect on the gyre. However, warming of the upper atmosphere can potentially strengthen it. Regional changes in sea surface temperatures could also influence the gyre.”
