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It was the coldest February Texas had seen in more than four decades, and the sustained blast of arctic air knocked out much of the state’s power grid for several days, causing hundreds of deaths and billions of dollars in damage.
Scientists still have much to learn about the links between climate change and extreme winter weather. There are many factors that can cause localized cold snaps. Evidence suggests that climate change may be affecting long-standing patterns of climate.
“The way those kinds of events occur involve a lot more complicated atmospheric processes,” said Jennifer Francis, a senior scientist and acting deputy director for Woodwell Climate Research Center in Falmouth, Massachusetts.
Francis and other scientists said there’s a significant body of research that can help explain why Texas — and other areas of the U.S. — may still experience extreme cold from time to time amid an overall warming of the planet.
“Maybe there was some nuance that was missed when people started talking about winters disappearing and how we’re never going to see snow again,” said Judah Cohen, a leading scholar on winter weather and climate change and the director of seasonal forecasting at the climate analytics company Atmospheric and Environmental Research. “People say, ‘I was told one thing and I’m experiencing something else.’”
Several factors impact the frequency and severity of cold spells in Texas, from the strength of the polar vortex — a seasonal, swirling mass of cold air that circles high above the Arctic — to whether we’re in an El Niño or a La Niña yearTexas’s wetness is determined by Dry winterTo the natural patterns that affect the strength and position of the jet stream, which can influence the course and duration of weather system.
Here’s what factors scientists say can cause an extreme cold snap to hit Texas — and how such storms may be influenced by climate change.
Are we likely to see another major winter freeze in Texas?
Scientists say it’s unlikely that another cold spell like the one that swept across the state in February will happen this winter. The National Oceanic and Atmospheric Administration forecasts a warmer-than-normal winter for Texas due to continued dry La Niña conditions — although last winter was also during a La Niña year.
“We’ve got these other differences that are happening that, all combined, probably create a very different winter this year from the winter last year,” Francis said. “I think it’s unlikely that we’re going to see a big cold air outbreak like we saw last year.”
How the polar vortex creates cold spells
The stratospheric polar vortex, high above in the Earth’s stratosphere, forms in the fall, when the northern hemisphere gets dark and cold.
After the polar vortex had broken down, very cold air was sent southwards. This caused the February storm.
A strong polar vortex keeps the cold air in the northern region of the planet spinning fast and tightly, just like ice skaters do by pulling in their arms.
“That keeps a lot of the Lower 48 at least fairly mild,” said Jason Furtado, an associate professor in the School of Meteorology at the University of Oklahoma. “It’s locking up the cold air at the high latitudes because it’s encased in this circulation.”
But when the polar vortex is weak, it’s like an ice skater losing their balance: It begins to wobble, and that can push arctic air onto the jet stream, or what’s called the tropospheric polar vortex, a mass of fast-moving winds that flow 5-9 miles above the Earth’s surface in a wavy path around the Northern Hemisphere.
That’s precisely what happened in February: The stratospheric polar vortex January: Weakened and divided, contributing to the jet stream’s big swing south. A few weeks later it brought a lot of cold air down to the Central, and South United States.
Arctic Climate Change and Arctic
There are many factors that influence the strength or weakness of the polar vortex. For example, the winds’ strength can be affected by a pattern called The arctic oscillation.
“When the arctic oscillation is positive, it strengthens the jet stream, which can reduce the likelihood of getting cooler air outbreaks,” said Deepti Singh, a climate change researcher and an assistant professor at Washington State University Vancouver. “When it’s negative, the jet stream is weaker and more wavy, and that allows the arctic air to flow to the lower latitudes.”
New science suggests that climate change could also play a part.
Cohen, the director for seasonal forecasting at Atmospheric and Environmental Research, published an article. Study in Science, SeptemberThe study found that the polar vortex is fracturing more often in recent decades than in the past. This has created patterns that could bring big blasts of colder air into the United States.
The Arctic has been impacted by climate change more than any other region: Arctic temperatures have increased since 2000. They have increased by about twice as fastAs global temperatures. Global warming is causing more of the Arctic’s sea ice to melt than in the past, leaving open water that absorbs more of the sun’s heat, accelerating warming in the Arctic.
Research is ongoing on whether a warmer Arctic is related to a weaker polar vortex. Cohen’s research suggests that one “hot spot” of sea ice melt in the Barents-Kara Sea, northwest of Russia, could be to blame: The heating there is so far north that the added heat can cause the jet stream to bulge north and interfere with the polar vortex.
“My argument is that arctic change [from global warming] is forcing the jet stream in a configuration that, at least partially, favors a weaker polar vortex,” said Cohen, who is also a visiting scientist at MIT.
Francis’ research has suggested that when the Arctic is abnormally warm and has seen significant ice loss, the the jet stream tends to weaken. Certain extreme weather events — droughts, heat waves, cold spells and heavy precipitation — are often associated with “persistent” weather patterns brought by the jet stream’s weakened state, Francis wrote in a Geophysical Research Magazines publishes 2012 study.
“There’s so many pieces to the puzzle, and there’s still a lot of research going on to understand how they’re all connected,” said Francis, a leading researcher on how the dramatic warming of the Arctic may be linked to extreme weather patterns in the U.S. and Europe.
Still, she added, “The Arctic is warming unbelievably fast, and it’s a tremendous change in a really important part of the climate system.”
Disclosure: Washington State University has been an financial supporter to The Texas Tribune. The Texas Tribune is a nonpartisan, nonprofit news organization that relies on donations from corporate sponsors and foundations. Financial supporters have no role in The Tribune’s journalism. Get a complete guide to journalism. Here is a list of them.