The world is warming, including in winter. However, the United States has experienced severe winter storms in recent years, and experts are investigating the link between this extreme cold weather and climate change. While the link between global warming and heat waves is very direct, the behavior of winter storms is governed by complex atmospheric dynamics that are more difficult to study.

“There are certain aspects of winter storms for which the climate change link is quite strong and robust,” Michael Mann, a climatologist at the University of Pennsylvania, told AFP. For example, warming of water bodies – lakes or oceans – affects the amount of snowfall. In the United States, a mechanism called “lake-effect snow” operates around the Great Lakes region on the Canadian border. The city of Buffalo, located on the shore of one of the Great Lakes, was hit hard by a deadly snowstorm over the Christmas weekend.

The collision of cold air from the north with the warmer waters of these lakes causes convection, which results in snowfall.

“The higher the lake temperature, the more moisture in the air, and the more likely lake-effect snow,” Michael Mann wrote in a 2018 article. “It’s not surprising that we’ve seen a long-term increase in lake effect snowfall as temperatures have risen over the past century.”

polar vortex

However, there is no consensus on other mechanisms, such as the effects of climate change on the polar eddy and jet streams. A polar vortex is an air mass above the North Pole located high in the stratosphere. Man lives in the troposphere and the stratosphere is located slightly higher.

It is surrounded by a rotating band of air that acts as a barrier between the cold air in the north and the warmer air in the south. As the polar vortex weakens, this band of air begins to fluctuate and take on a more oval shape, bringing more cold air to the south.

According to a 2021 study, this type of disturbance is occurring more frequently and will be reflected at a lower level in the atmosphere of the jet stream for the next two weeks. Blowing from the west to the east, this airflow again follows the boundary between cold and warm air, then bends to allow cold air from the north to penetrate lower latitudes, particularly over the eastern United States.

“Everyone agrees that when the polar vortex is disrupted or disrupted, the likelihood of severe winter weather increases,” Judah Cohen, the study’s lead author and a climate expert in the Atmospheric and Environmental Research (AER) branch, told AFP.

And this “stretched” polar vortex is what was observed just before the storm that hit the United States this December, he said. The same phenomenon was seen during a cold snap that hit Texas in February 2021, causing massive power outages.

“Active discussion”

But the point of the discussion is something else: What is the cause of these increased disturbances in the polar vortex?

According to Cohen, these are about changes accelerated by climate change in the Arctic. On the one hand, the rapid melting of sea ice, on the other hand, the increase of snow cover in Siberia.

“This is something I’ve been working on for over 15 years and today I’m more confident than ever about connectivity,” he told AFP.

But Mann said that last point remains “an active debate in the scientific community.”

“Climate models do not yet capture all the fundamental physics that may be relevant to how climate change affects the behavior of the jet stream.”

More research will be needed in the coming years to unravel the mystery of these complex chain reactions.