Rapid Arctic warming likely drives extreme winter weather events in the US
Amid debate about the influence of changes in the Arctic on extreme weather elsewhere, a new study reports that rapid warming in the Arctic is a likely driver of the recent extreme winter weather in the United States. The findings, based on both observational and modeling data, establish a physical link between anthropogenic climate change and a phenomenon called the stratospheric polar vortex (SPV) disruption. While climate warming is anticipated to lead to increases in some weather extremes, including heat waves and precipitation events, it’s not widely considered to drive severe winter weather events. However, contrary to climate model predictions, winter weather extremes across the Northern Hemisphere – intense snowfall events and anomalous cold snaps – have reportedly become more frequent. One notable example of this is the U.S. Southern Plains cold wave of February 2021, which resulted in the collapse of the Texas energy grid and record damages estimated at nearly USD 200 billion, a cost substantially higher than recent high-impact hurricanes. It’s hypothesized that accelerated warming in the Arctic, or Arctic amplification (AA), is driving these events by disrupting the Arctic SPV – an atmospheric feature defined by the strong westerly winds that encircle the Arctic and, under normal conditions, keep its cold air contained. Whether AA and its impact on the SPV variability are physically linked to recent winter weather extremes has been unclear; observations and model predictions lack agreement. Building on previous work concerning SPV variability, Judah Cohen and colleagues combine observational analyses of the SPV over the last forty years with new climate model experiments. They reveal a physical link that implicates rapid Arctic warming and its effects, namely sea ice loss and increased Eurasian snow cover, with SPV disruption and the increased frequency of extreme mid-latitude winter weather. The results could be used to extend the warning lead time of cold extremes in Asia, Canada, and the United States, the authors say. “Future work should aim at further disentangling causal Arctic teleconnections for the cold and warm seasons in the mid-latitude regions, paying specific attention to high-impact extremes,” writes Dim Coumou in a related Perspective.
JOURNAL
Science
ARTICLE TITLE
Linking Arctic variability and change with extreme winter weather in the US
ARTICLE PUBLICATION DATE
3-Sep-2021
AER leads study to reveal extreme winter weather is related to arctic change
Peer-Reviewed PublicationLexington, Mass., September 2, 2021 — A new study shows that the frequency of polar vortex disruptions that is most favorable for extreme winter weather in the United States is increasing, and that Arctic change is likely contributing to the increasing trend. Led by Atmospheric and Environmental Research (AER), University Massachusetts Lowell and the Hebrew University of Jerusalem, the study is published in the September 3 issue of Science. AER is a Verisk (Nasdaq:VRSK) business.
The analysis demonstrates that a relatively obscure weak or disrupted state of the stratospheric polar vortex, where it takes on a stretched appearance rather than the more typical circular appearance, has been increasing over the satellite era (post 1979). Extreme winter weather in the US is more common when the polar vortex is stretched. Both observational analysis and numerical modeling experiments demonstrate that changes in the Arctic, including accelerated warming, melting sea ice and increasing Siberian snowfall, are favorable for stretching the polar vortex followed by extreme winter weather in North America east of the Rockies. Such a chain of events occurred in February 2021, when a stretched polar vortex preceded the destructive and deadly Texas cold wave.
During the past three decades, the Arctic has experienced the greatest climate change 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. The extent to which these rapid changes in the Arctic are influencing midlatitude weather has become a topic of vigorous debate by climate scientists and popular in the press.
“The publication of the paper is especially timely given the extreme winter of 2020/21: record warm Arctic, low Arctic sea ice, deep Siberian snows, a protracted and complex polar vortex disruption, record-breaking cold in the US, Europe and Asia, disruptive snowfalls in Europe and the US and most notably the record breaking and possibly unprecedented combination of cold and snow in Texas,” said Dr. Judah Cohen, director of seasonal forecasting at AER and lead author of the study.
Cohen adds, “Last winter the severe cold wave across Texas heated up the debate as to whether climate change can contribute to more severe winter weather with those arguing for and against. However, studies supporting or refuting the physical connection between climate change and the Texas cold wave and other recent US severe winter weather events don’t exist, until now. The study also provides cautionary evidence that a warming planet will not necessarily protect us from the devastating impacts of severe winter weather.”
The paper presents a physical mechanism of how climate change in general and Arctic change in particular are contributing to more severe winter weather despite an overall warming climate that has not been previously considered. Most theories on the connection between Arctic amplification and mid-latitude winter weather argue that the pathway is either through a wavier Jet Stream or sudden stratospheric warmings, which are the largest and most often studied disruptions to the polar vortex. This study provides compelling evidence that the strongest connection between the Arctic and mid-latitude weather, at least in the US, may be through this lesser known and weaker “stretched” disruption of the polar vortex.
These extreme winter weather events begin when a wave of high pressure between Northern Europe and the Urals and low pressure over East Asia undergoes amplification. Such an amplification can be forced by observed Arctic change during the fall season, and specifically by melting sea ice in the Barents-Kara Seas and heavier snowfall across Siberia. The excess energy from the Eurasian wave bounces or reflects off the polar vortex and is absorbed in a similar North American wave with high pressure over Alaska and the North Pacific and low pressure over eastern North America, causing rapid wave amplification. When atmospheric waves amplify, extreme weather is more likely.
UMass Lowell Environmental, Earth and Atmospheric Sciences Prof. Mathew Barlow, a co-author on the study, added, “The synthesis of both observational analysis and computer model experiments is a particular strength of this study and greatly increases our confidence in the results. The dynamical pathway explored here – from surface climate change in the Arctic up to the polar stratosphere and then back down to the surface in the US – highlights one example of the wide range of impacts that climate change can have.”
Israeli collaborator Prof. Chaim Garfinkel, the Hebrew University of Jerusalem, concludes “There has been a long-standing contradiction between an apparent increase in cold extremes in winter in midlatitudes even as temperatures globally are warming. This study helps resolve this contradiction and highlights that an apparent increase in such midlatitude cold extremes in winter should not be used as an excuse to delay taking urgently needed action to reduce greenhouse gas emissions.”
AER President Dr. Guy Seeley said: “We are very pleased to see this publication which reflects AER’s long term commitment to innovative scientific research on topics of vital interest to our customers and society at large.”
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The research is funded by the US National Science Foundation Office of Polar Programs and the European Research Council.
The study can be viewed here: https://science.sciencemag.org/lookup/doi/10.1126/science.abi9167
About Atmospheric and Environmental Research (AER)
Atmospheric and Environmental Research (AER) provides science-based solutions to global environmental challenges. AER’s internationally renowned scientists and software engineers collaborate to transform state-of-the-art predictive science and analytical tools into practical systems that address both civilian government and defense needs for geophysical understanding, computer simulation, and forecasting. AER customers include government agencies and national laboratories, aerospace and defense contractors, and academia. Areas of expertise comprise atmospheric and environmental science, air quality, remote sensing, meteorology, oceanography, space science, climate change, and software engineering. A Verisk (Nasdaq:VRSK) business, AER was established in 1977 and is headquartered in Lexington, Massachusetts. Visit www.aer.com.
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Ali Krueger Herbert
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