Study links polar vortex disruption with extreme winter weather

Several studies have revealed a link between global warming and extreme weather, but it's not just hurricanes, heatwaves and droughts that are growing in strength and severity.

According to a new study, published Thursday in the journal Science, rising temperatures in the Arctic and subsequent disruptions to the polar vortex have increased the risk of extreme winter weather and prolonged cold-spells in North America.

Typically, the stratospheric polar vortex holds a tight circular pattern, keeping cold air trapped above the Arctic. The vortex's structure is stabilized by the temperature difference between polar air and the more temperate air to the south.

The Arctic is warming faster than the rest of the planet, and according to satellite imaging, the shape of the stratospheric polar vortex has become less stable over the last 40 years.

With its structure destabilized by the northern hemisphere's diminished temperature gradient, the vortex has become more easily disrupted and stretched, allowing cold air move southward across the eastern North America.

Last winter, a warming Arctic and stretched vortex allowed frigid air to stall atop Texas, leading to a deadly cold-spell.

While Texas was registering record lows, the Arctic winter was warmer than any previous winter on record. Additionally, Arctic sea ice extent hit a record low. Many parts of Europe and Asia also experienced record cold temperatures.

"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," lead study author Judah Cohen said in a press release.

"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," said Cohen, director of seasonal forecasting at Atmospheric and Environmental Research.

Previous studies have mostly blamed extreme winter weather on a waiver in the jet stream, but the latest research suggests a stretched polar vortex is more closely linked with extreme weather.

When the polar vortex becomes stretched, the contrast between high pressure air above Northern Europe and the Ural Mountains and low pressure air masses atop East Asia becomes amplified.

When atmospheric waves fueled by this contrast bounce off the polar vortex, they get absorbed by the atmosphere above eastern North America, increasing the odds of extreme winter weather.

"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," said study co-author Mathew Barlow.

"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," said Barlow, a professor of atmospheric sciences at the University of Massachusetts, Lowell.

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