(Washington) In February, a rare polar cold wave swept across Texas, causing dozens of deaths and power outages.
This extreme weather episode was also estimated at about $ 200 million and caused record damage.
Although it is now established that global warming causes severe heat waves, the question of its impact on such cold waves is still the subject of intense scientific debate.
For the first time, a major study was published in the journal Thursday Science Has been successful in showing a link between global warming in the Arctic and the winter solstice in the Northern Hemisphere, the United States, but also in Asia.
“This pronounced warming in the Arctic seems very counter-intuitive and unpredictable, and it causes cooling in other areas,” agrees AFP Matthew Barlow, one of the study’s co-authors.
Yet, despite this contradiction, the researchers are definite.
A professor of climate science at Lowell University in Massachusetts said: “Because the results were so clear, I was able to establish a direct link.
The fastest warming area on the Arctic.
But two phenomena actually work: on the one hand the rapid melting of sea ice, and on the other hand an increase in ice haze, especially in Siberia.
Melting ice causes a strong warming because the sea absorbs more heat, while the extra snow in Siberia reflects more of the sun’s rays, causing a slight cooling.
In an indirect and complex chain reaction, these two evolutions together lead to an upsurge in the atmospheric cycle.
The researchers focused on their impact on the polar vortex. These are the strongest winds that blow near the pole in winter, and are located at high altitudes in the stratosphere (the atmosphere is made up of the tropics we live in, followed by the stratosphere).
In general, the polar vortex forms a circle containing cold air.
“But under the influence of climate change in the Arctic, it is weakening and becoming oval,” says Matthew Barlow.
The most important atmospheric disturbances arising from the ground are then “jumping back” toward the surface when it reaches the polar rotation.
This change in the movement of depression “pushes Jet stream Towards the south, ”explains the researcher. The Jet stream It is a wind current that blows from west to east.
“When you push Jet stream In the south, it brings in cool air. ”
Good to expect
The strength of this study is that it combines two approaches. First, an analysis of direct observations made over the past forty years.
The researchers selected periods in which the polar vortex extended into an oval shape: thus before each of these chapters, they observed a significant change in temperature in the Arctic, for example snowfall. Strong or particularly pronounced ice melting. In the following weeks, it was colder in North America.
For the second approach, they used a climate model to verify the cause-and-effect link by varying the different parameters.
This finding will have many implications.
First, Matthew Barlow believes that identifying this mechanism will make possible the forecast of a severe cold, “perhaps even several weeks in advance.”
This work shows that it is necessary to better prepare for the possibility of severe cold waves, even if the globe is generally warming.
Second, researchers hope that this warning will help people understand the global impact of the climate crisis, so we need to combat it by reducing greenhouse gas emissions.
“Climate change in the Arctic is not the only thing polar bears have to worry about,” emphasizes Matthew Barlow. “It can really affect you.”
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