Last winter, for the first time in many years, the Dutch were able to ski on the canals of Amsterdam. At the same time, Texas was hit by a severe cold snap that killed more than 100 people and destroyed nearly $200 billion in infrastructure. Elsewhere it has become unusually hot, such as Kalmar where the temperature was measured at 17 degrees in mid-February.
For several years, climate scientists have believed that extreme weather events in the Northern Hemisphere during winter may have something to do with the rapid rise in temperatures in the Arctic. In the past 30 years, the Arctic has warmed twice as fast as the planet as a whole.
The hypothesis was The abnormal winter weather is caused by a meteorological phenomenon with the polar jet stream. It is a belt of winds that moves circularly around the North Pole and traps icy air in the North.
When the air over the Arctic becomes unusually warm – during what’s called rapid stratospheric warming – the jet stream loses speed and expands in a two-clover shape. The cold arctic air then moves down over the northern hemisphere.
But among researchers, the relationship between winter weather, the polar jet stream and global warming has been debated.
But point now New study That rapid warming in the Arctic is likely to be the cause of sudden cold such as those in Texas. The study, which combines observational data with a climate model, shows that loss of Arctic sea ice and increased snowfall in Siberia – two effects of warming – are weakening polar currents and harsh winter weather in the northern hemisphere.
Jetströmmen February 15, 2021
On February 15, the jet stream went far south across the United States, all the way to Texas. Cold arctic air caused record low temperatures.
Source: NASA Earth Observatory / GMAO, Scott Duncan.
No previous studies have examined the relationship between change in the Arctic and severe winter weather. So this is the first time there has been data showing that these phenomena are associated, says Judah Cohen, a US climate researcher and lead author of the study, with DN.
The study’s observational data show that the polar jet stream has weakened and expanded more and more in recent decades. Between 1980 and 2020, the number of fall and winter days nearly doubled when the jet stream was at a weak point. On these occasions, it was also possible to see that it became statistically more common with a warm Arctic and a cold continent.
Judah Cohen Minar Their study is interesting not least in light of the climate debate in the United States regarding the sudden cold in Texas: did it have anything to do with climate change or is it just a random weather phenomenon?
We have observed that only Asia and eastern North America have the greatest temperature response to the extended polar jet stream. This is where the link is strong with severe winter weather, so I think in this regard our study is important, he says.
Michael Tegernström, professor of meteorology at Stockholm University, has read the study and believes it contains an interesting discussion about the dynamics of the polar jet stream.
—This isn’t a paradigm shift, but it’s a powerful study that adds a few pieces of puzzle to understanding how these extreme winter phenomena emerge, he says.
Is the study also appropriate for understanding the deviations in Swedish winter weather?
– Yes, these are the same mechanisms that apply to very cold winters in Europe and Sweden. There is a lot to suggest that the very cold Swedish winter of 2009-2011 had something to do with the weakening of the polar jet stream, says Michael Tegernström.
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