- The polar vortex is a normal, natural pattern that is stronger in the winter and tends to keep the coldest weather bottled up near the North Pole.
- The six years from 2015 to 2020 were Earth’s warmest six years in recorded history.
- “It’s been unusual for a few weeks now – very, very crazy … Totally topsy-turvy.”
The U.S. has endured a wild stretch of harsh winter weather lately thanks to an invasion of the infamous polar vortex. It may be counterintuitive, but could global warming have caused this?
First, an explainer: The polar vortex is a gigantic circular upper-air weather pattern in the Arctic that envelops the North Pole. It’s a normal, natural pattern that is stronger in the winter and tends to keep the coldest weather bottled up near the North Pole. The jet stream usually pens the polar vortex in and keeps it there, but at times, some of the vortex can break off or move south, bringing extremely cold weather down into the U.S., Europe, and Asia.
Some scientists – but not all – say there could be a connection between global warming and the wandering polar vortex: The theory is that when weird warmth invades the Arctic, some of the cold that’s supposed to stay up there – including the vortex – sloshes down south into North America and Europe.
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“There is evidence that climate change can weaken the polar vortex, which allows more chances for frigid Arctic air to ooze into the Lower 48,” University of Georgia meteorology professor Marshall Shepherd said.
While the vortex is a natural phenomenon, and polar vortex breakdowns happen naturally, there is likely an element of climate change at work.
Woodwell Climate Research Center climate scientist Jennifer Francis, who has published a study on the phenomenon, said in 2019 that “warm temperatures in the Arctic cause the jet stream to take these wild swings, and when it swings farther south, that causes cold air to reach farther south.”
‘Major breakdown’ in the vortex in recent weeks
The jet stream is the river of air up in the atmosphere that steers weather around. A study in 2015 in the journal Science reported that the rapid warming of the Arctic makes for a more wavy jet stream, with waves that move more slowly across the globe. When that happens, cold, Arctic air sometimes pours down over the U.S.
A study in 2018 in the Bulletin of the American Meteorological Society, co-written by Atmospheric Environmental Research meteorologist Judah Cohen, found that “over recent decades, the stratospheric polar vortex has shifted toward more frequent weak states,” allowing it to stray from its home above the North Pole.
Warming in the Arctic, with shrinking sea ice, is goosing the atmospheric wave in two places, giving it more energy when it strikes the polar vortex, making it more likely to disrupt the vortex, Cohen said.
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Human-caused global warming happens when fossil fuels such as coal, oil and gas are burned, releasing greenhouse gases such as carbon dioxide into Earth’s atmosphere and oceans. This has caused the planet to warm to levels that cannot be explained by natural factors, the National Climate Assessment said.
What’s happened to the vortex in the past few weeks has been remarkable: Francis said “it’s been a major breakdown. It really is the cause of all of these crazy weather events in the Northern Hemisphere.”
“It’s been unusual for a few weeks now – very, very crazy,” Francis said. “Totally topsy-turvy.”
Are February tornadoes unusual?
And as for the deadly tornadoes in the South this week, scientists say there is no clear connection between that type of severe weather and human-caused climate change. While climate change does have a documented effect on many extreme weather events, it has no clear connection to severe thunderstorms nor the tornadoes they produce.
In fact, a 2016 report from the National Academy of Sciences found that of all weather phenomenons, severe storms (and tornadoes) have the least connection to human-caused climate change.
On average, there are 29 tornadoes in February of each year across the nation, the National Oceanic and Atmospheric Administration (NOAA) said.
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And overall, global warming remains real, despite this week’s chill: The six years from 2015 to 2020 were Earth’s warmest six years in recorded history, according to NOAA. Global temperatures have also been above average for 433 consecutive months.
Indeed, though temperatures in the central U.S. neared all-time record lows this week, the U.S. as a whole covers only about 2% of the Earth’s surface.
Contributing: The Associated Press