In recent decades, extreme winter weather has become more strongly connected to disruptions in the polar vortex, according to a new study from Atmospheric and Environmental Research (AER), a Verisk business, and Rutgers University, published in Nature Communications. It revealed that the frequency of extreme winter weather in the United States is sensitive to Arctic temperatures.
The analysis demonstrates that in the eastern United States, severe winter weather-including both cold temperatures and heavy snowfalls-is two to four times more likely when the Arctic is abnormally warm compared with when the Arctic is abnormally cold. The study also shows that winters are colder across much of the Northern Hemisphere midlatitudes, including Europe and East Asia, when the Arctic is very warm.
In the western U.S., the relationship between severe winter weather is either weak or, in some cities, the opposite of the East, with colder Arctic temperatures related to increased severe winter weather. This research is timely given the recent severe winter weather experienced across the U.S. and may help explain how climate change in general and Arctic change in particular are contributing to more severe winter weather despite an overall warming climate.
During the past three decades, the Arctic has experienced the greatest climate changes of anywhere on Earth, including rapidly rising temperatures, melting sea ice, diminishing spring snow cover, and increasing autumn snow cover. Rapid Arctic warming relative to the rest of the globe is referred to as Arctic amplification. To what extent these rapid changes in the Arctic are influencing midlatitude weather has become a “hot topic” of research and debate by climate scientists.
The new study also separately analyzed whether Arctic amplification is contributing to more frequent severe cold and heavy snowfalls in the eastern U.S. While a robust connection to severe cold was not found, the analysis did show a statistically significant increase in heavy snowfalls related to Arctic amplification for many northeastern cities.
The study found that when Arctic warming occurred mainly near the surface, links to severe winter weather were weak. When the warming extended through a deep layer, however, disruptions of the stratospheric polar vortex were likely. These disruptions usually cause severe winter weather in mid- to late winter and affect large metropolitan centers of the northeastern U.S.
“The publication of the paper is especially timely given the extreme winter of 2017/2018, which has included a record-warm Arctic and record-low sea ice, record-breaking polar vortex disruption, record-breaking cold in both the U.S. and Europe, disruptive snowfalls in both the U.S. and Europe, severe ‘bomb cyclones,’ and costly nor’easters,” said Dr. Judah Cohen, director of seasonal forecasting at AER and lead author of the study. “This paper argues that the weather was cold not in spite of climate change but likely because of climate change. In fact, our statistical analysis shows that one is more likely to be struck by lightning, attacked by a shark, and win the Powerball all at the same time than the possibility of severe winter weather in the northeastern U.S. not being related to Arctic temperatures. That’s how robust our findings are.”
According to co-author Jennifer Francis, “Five of the past six winters have brought persistent cold to the eastern U.S. and warm, dry conditions to the West, while the Arctic has been off-the-charts warm. Our study suggests that this is no coincidence. Exactly how much the Arctic contributed to the severity or persistence of the pattern is still hard to pin down, but it’s becoming very difficult to believe they’re unrelated.”
The research is funded by the National Science Foundation’s Division of Atmospheric and Geospace Sciences and the Office of Polar Programs.
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