If one understands intuitively that global warming increases the number and severity of heat waves, the link with cold waves seems less obvious. The intense cold such as the one that hit Texas in February 2021, could however be linked to a warming of the Arctic, which is stretching the polar vortex.
For a certain number of climate skeptics, the cold spells constitute an opportunity to question the. However, more and more studies (read our article below) show a clear link between global warming and atmospheric disturbances likely to reinforce the in L’ . The latest, published in September 3, explains that the warming of the Arctic, which occurs at a rate twice as fast as the average, induces a “stretch” of the , a circular atmospheric current that forms over the North Pole during . The latter normally isolates the cold in the Arctic, which preserves mean extreme temperatures.
The stretching of the polar vortex, a better indicator of a future cold snap
The team, led by Judah Cohen,to Massachusetts Institute of Technology (MIT) and director of seasonal forecasts at the company Atmospheric and Environmental Research (AER), combined observation data and to understand the extreme cold spells that have occurred in parts of Asia and North America. So far, the main hypotheses to explain are that the of ice in the Arctic causes a . This is because the ocean is darker than ice or snow and therefore absorbs more radiation. This sudden warming is likely to slow down and even reverse the which then no longer plays its role of protective shield.
The new study highlights another phenomenon: “stretching” of the, caused by seasonal events such as heavy snowfall in Siberia and melting ice in the Barents and Kara seas. According to the researchers, this stretch is the best predictor of cold snaps in the United States. ” Our model could thus make it possible to better predict and anticipate future cold spells. », Indicate the authors.
A cause and effect link that is difficult to establish
However, the link between global warming and cold snap remains rather tenuous. Aexplains that the frequency and size of snowstorms in North America will significantly decrease in a warmer world. According to , with an average temperature increase of 3.9 ° C by 2100, winter frosts will have almost disappeared in the west of the country and will be three times less frequent in the east and on the reliefs.
« Although changes in ice and snow cover certainly appear to play a role in thefrom over the arctic, the stretching of the polar vortex could simply be related to the natural variability of the climate “, Explain , climatologist at the Max Institute from from Hamburg, Germany [et qui n’a pas participé à l’étude]. « Climate change is not linear. What happens in a decade does not bode well for what will happen in the next. ».
Extreme cold events during a period of global warming
Article bypublished the 15/08/2021
Extreme temperature events are becoming more and more frequent. Intuitively, everyone understands that global warming can cause intense heat, but the connection with unusually freezing cold is harder to grasp. A team of researchers wanted to elucidate the mechanisms underlying these events by basing themselves on three of them.
During the winter of 2020-2021, several records for low temperatures were broken in East Asia and North America. Bursts of cold air swept across the surface of thecreating freezing temperatures and winds especially in China, Beijing and Tianjin; from struck parts of North America.
The frequency of these events motivated the researchers to look into their study. An article seeking to explain why these extremes occur more often in awas published on August 9 in . « The main fundamental problem is therefore whether the increase in the frequency of extreme cold episodes is the result of forced external warming or of natural variability in the climate system.. In order to understand the mechanisms underlying the anomalies, the scientists compared the observational data for the winter of 2020-2021 with those of the previous 42 years. They determined that maritime and atmospheric events can be the basis of extreme weather.
The explanation lies in the oceans and the atmosphere
The cause of these exceptional events lies in a coupling of(at the level of the North Atlantic and Pacific oceans, as well as at the level of the Barents and Kara seas where there was a significant retreat of ice) at For the three extreme colds this year, a striking expansion of polar cold air towards warmer areas to the south broke all records. In addition, they were all linked by the influence of an event of Sudden Stratospheric Warming (SSW) or , caused by the disruption of the polar vortex.
In fact, the sudden warming of a layer of the atmosphere disturbs the, which creates unusual weather. ” By studying these periods of record cold, we get an overview of extreme weather events », Says Zhe Han, scientist at the Institute of atmospheric at the Chinese Academy of Sciences, and study co-author. According to him, ” although the events may be different, they could share similar underlying mechanisms, linked to global warming. »
Need to learn more
Extreme weather events have a significant number of socio-economic costs, just thinkWhere which threaten many countries at this very moment. Whether it is a correlation or a causality that links them to global warming, their study is necessary to better understand the complex processes that govern them and to know how to predict them. “ Interactions between global warming and natural variability influence the occurrence, intensity and extreme events. »For the environment and As much as for human health, understanding the mechanisms behind these abnormalities is essential.