The results of observations and numerical modeling showed that the main reason for the abnormally cold weather observed in the Northern Hemisphere in the winter of 2020–2021 was a disruption of the atmospheric circulation system in the polar region associated with ongoing warming in the Arctic. The article was published in the journal Science.

Scientists from the Department of Environmental, Earth and Atmospheric Sciences at the Massachusetts Institute of Technology, together with colleagues from the Hebrew University of Jerusalem, analyzed changes in the nature of the stratospheric polar vortex over the past forty years and compared the results with data from modern climate models.

The polar vortex is a cell of circulation of the earth's atmosphere in the subpolar Arctic region, the driving force of which is the difference in heating of the earth's surface at the poles and in temperate latitudes.

The authors found a direct physical link between rapid warming in the Arctic and its consequences—declining sea ice and increasing snow cover in Eurasia—with disruption of the polar vortex and an increase in extreme winter weather events in mid-latitudes.

In its classical form, the polar vortex looks like a circular circulation cell, but in recent years it has acquired an extended appearance. Researchers have reconstructed the entire chain of events associated with this change.

First, a high pressure wave forms between Northern Europe and the Urals, and an area of low pressure is established over East Asia. This picture appears at the end of autumn, when the area of polar ice in the basins of the Barents and Kara Seas is minimal, and heavy snowfalls begin in Siberia.

Excess energy from the Eurasian wave is reflected from the polar vortex and absorbed by a similar North American wave, with high pressure over Alaska and the North Pacific and low pressure over eastern North America.

During the winter, the energy from the two pressure waves from the merger intensifies and the likelihood of extreme weather events increases. This situation occurred, for example, in February 2021 in North America, when an extended polar vortex brought an unprecedented cold wave to Texas.

“Last winter, a severe cold wave in Texas sparked debate about whether climate change could be contributing to more severe winter weather.

However, there has been no research to confirm or refute a physical link between climate change and the Texas cold wave and other recent severe winter weather events in the United States, lead study author Jude Cohen said in a press release from the American Association for the Advancement of Science. Judah Cohen). “Our study provides compelling evidence of this connection and shows that a warming planet will not protect us from the devastating impacts of a harsh winter.”

“There is a long-standing tension between the apparent increase in winter extremes in mid-latitudes as global temperatures become warmer,” said study co-author Chaim Garfinkel of the Hebrew University of Jerusalem. “This study helps resolve this controversy and emphasizes that the apparent increase in winter extreme cold in mid-latitudes should not be used as an excuse to delay urgent action to reduce greenhouse gas emissions.”

Over the past three decades, the Arctic has experienced the most dramatic climate change of any region on Earth, including rapidly rising temperatures, melting sea ice, and decreasing spring snow cover and increasing fall snow cover.

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