What is the link between winter storms and global warming?
The planet is warming, yet the United States has been experiencing severe winter storms for several years. Experts are increasingly looking into the phenomenon.
The city of Buffalo is particularly affected by the storm that hit the United States this year, in the middle of the Christmas weekend.
KEYSTONE/AP PHOTO/CRAIG RUTTLE
Even if such a comparison seems completely counter-intuitive, certain connections could clearly be identified. Others, on the other hand, are still much debated by the scientific community.
If the link between global warming and heat waves is very direct, the behavior of winter storms is governed by complex atmospheric dynamics, which are more difficult to study. Even so, “there are certain aspects of winter storms […] where the link with climate change is quite strong,” Michael Mann, a climatologist at the University of Pennsylvania, told AFP.
The warming of water bodies, such as lakes or oceans, influences, for example, the amount of snow that falls. In the United States, a mechanism called “lake effect” occurs especially around the Great Lakes region, at the Canadian border. It is also in this area that the city of Buffalo is located, particularly affected by the storm that hit the United States this year, in the middle of the Christmas weekend.
polar vortex
The collision between cold air coming from the north with the warmer water of these lakes, causes convection which leads to snowfall.
“The warmer the temperature of these lakes, the more moisture in the air and the greater the possibility of snow from a lake effect,” described Michael Mann in a text published in 2018. “ Unsurprisingly, we are seeing a long-term increase in lake-effect snowfall as temperatures warm over the past century.”
On the other hand, other mechanisms, such as the effect of climate change on the air currents that are the polar vortex and the jet stream, are not the subject of a consensus. The polar vortex is a mass of air above the North Pole, located high in the stratosphere (we live in the troposphere and the stratosphere is located just above it).
It is surrounded by a rotating band of air, which acts as a barrier between the cold northern air and the milder southern air. But as the polar vortex weakens, this band of air begins to undulate and take on a more oval shape, bringing more cold air south.
More and more frequent
According to a 2021 study, this type of disturbance is occurring more and more often, and reverberates in the following two weeks lower in the atmosphere, where the jet stream is located.
This air current, which blows from west to east, again following the border between cold and warm air, then meanders in such a way that it allows the cold air from the north to intrude at lower latitudes, in particular on eastern United States.
This type of disturbance occurs more and more often, and is reflected in the two weeks that follow lower in the atmosphere, where the jet stream is.
KEYSTONE/AP PHOTO/JEFFREY T. BARNES
“Everyone agrees that when the polar vortex is disrupted, there is an increased likelihood of severe winter storms,” Judah Cohen, lead author of the study and climatologist for the study, told AFP. 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 pointed out. This was also the case in February 2021, when freezing cold weather hit Texas, causing massive power outages.
“Active Debate”
But the heart of the debate lies elsewhere. The key question is, what is causing these increased polar vortex disturbances?
According to Judah Cohen, they are linked to changes in the Arctic, accelerated by climate change: on the one hand the rapid melting of the sea ice and, on the other hand, an increase in snow cover in Siberia. “It’s a subject that I have been studying for more than 15 years, and I am more convinced today by this link than I have ever been,” he told AFP.
This last point, however, remains “an active debate within the scientific community”, underlined Michael Mann. “Climate models do not yet capture all of the underlying physics that may be relevant to how climate change is impacting jet stream behavior.”
Future studies will therefore still be necessary in the years to come, in order to unravel the mystery of these complex chain reactions.
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