Washington DC.- The world is getting warmer, including the winters.
However, the United States has experienced severe winter storms in recent years, and experts are taking a closer look at the link between these bouts of extreme cold and climate change.
Unlike the relationship between global warming and heat waves, which is very direct, the behavior of winter storms is governed by complex atmospheric dynamics that are more difficult to study.
Still, “there are certain aspects of winter storms … where the links to climate change are pretty clear,” said Michael Mann, a climatologist at the University of Pennsylvania.
For example, the warming of bodies of water, such as lakes or oceans, influences the amount of snow that falls.
In the United States, “lake effect snowfall” occurs around the Great Lakes region, on the border with Canada.
The city of Buffalo, which sits on the shores of one of the Great Lakes, was hit hard by a deadly snowstorm over Christmas weekend.
Cold air from the north colliding with warmer water from these lakes causes convection, which causes snowfall.
“The warmer the lake temperatures, the more moisture (there is) in the air and the greater potential for lake-effect snowfall,” Mann wrote in a 2018 article.
“As expected, we see a long-term increase in lake-effect snowfall as temperatures have been increasing over the last century,” he explained.
Polar vortex
There is, however, no consensus on other mechanisms, such as the effect of climate change on the polar vortex and jet streams.
The polar vortex is an air mass above the North Pole, located high in the stratosphere. Human beings inhabit the troposphere, and the stratosphere lies just above it.
This vortex is surrounded by a rotating band of air, which acts as a barrier between cold air from the north and warmer air from the south. As the polar vortex weakens, this band of air begins to ripple and become more oval in shape, bringing more cold air to the south.
According to a 2021 study, this type of disturbance is occurring more frequently, and when it does occur, it reverberates for the next two weeks further down in the atmosphere, where the jet stream is located.
This air current, which blows from west to east, again following the boundary between cold and warm air, then meanders in such a way as to allow cold air from the north to descend to lower latitudes, particularly over the eastern United States. .
“Everyone agrees that when the polar vortex is disturbed, the likelihood of severe winter weather increases,” said Judah Cohen, lead author of the study and a climatologist at Atmospheric and Environmental Research (AER).
And this “stretched” polar vortex is exactly what was observed just before the storm that hit the United States this December, he noted.
The same phenomenon was observed in February 2021, when a severe cold snap hit Texas, causing massive power outages.
“Ongoing Discussion”
But the center of the debate is on a key question: What is causing these increasing disturbances in the polar vortex?
According to Cohen, these alterations are linked to changes in the Arctic, accelerated by climate change. On the one hand, the rapid melting of sea ice, and on the other, the increase in snow cover in Siberia.
“This is a subject that I have been studying for more than 15 years and today I am more certain than ever of that link,” he told AFP.
However, this last point is still an “ongoing debate” within the scientific community.
“Climate models still don’t capture all of the underlying physics that may be relevant to how climate change is affecting jet stream behavior,” he said.
Therefore, more studies will be needed in the coming years to unravel the mystery of these complex chain reactions.
