Warming of the Arctic caused by climate change has increased the number of polar vortex outbreaks, when frigid air from the far north bathes the central and eastern United States in killer cold, a study finds.
A study published in the journal Science Thursday is the first to show the connections between changes in the polar region and February’s Valentine’s Week freeze that triggered widespread power outages in Texas, killing more than 170 people and causing at least $20 billion in damage.
The Arctic polar vortex is a band of strong westerly winds that form in the stratosphere between about 10 and 30 miles above the North Pole every winter. The winds enclose a large pool of extremely cold air.
The stronger the westerly winds, the more the air inside is isolated from warmer latitudes, and the colder it gets. The polar vortex doesn’t always influence winter weather in the mid-latitudes. When it does, however, the effects can be extreme.
And according to CBC Canada, the study’s lead author, Judah Cohen, a winter storm expert for Atmospheric Environmental Research, a commercial firm outside of Boston, says the number of times the polar vortex has weakened per year has more than doubled since the early 1980s
“It is counterintuitive that a rapidly warming Arctic can lead to an increase in extreme cold in a place as far south as Texas, but the lesson from our analysis is to expect the unexpected with climate change,” Cohen said.
According to NOAA stratosphere expert Amy Butler, not only is it reasonable to suppose that the polar vortex played a role in the extreme winter event in Texas in February, but there is plenty of research linking disruptions of the stratospheric polar vortex to extremely cold air outbreaks in the mid-latitudes of the United States or Eurasia a few weeks later.
But the question remains – could scientists blame the weakening polar vortex solely for the event in Texas? Climate scientists know that anthropogenic global warming is reducing the overall number of cold days, but they are still trying to understand if it leads to deeper cold snaps.
The lesser-known stratospheric polar vortex (SPV) disruption
The stratospheric polar vortex (SPV) is a rotating vortex of cold air high up in the stratosphere over polar regions. It forms every winter in the Northern Hemisphere and the strength of the Northern Hemisphere SPV has a great deal of influence on our weather patterns.
As long as the SPV is in a strong symmetrical state, it actually helps in maintaining a westerly momentum in the Troposphere, leading to our typical winter pattern of a strong west to east North Atlantic jetstream.
However, when the SPV is in a weakened state, it can go through further disruptions, leading to what is known as a Sudden Stratospheric Warming (SSW) event.
Cohen’s study is the first to use measurements of changes in the atmosphere to help explain a phenomenon that climate models had struggled to account for, reports France 24.
According to the study, the observational analysis showed that an SPV disruption that involves wave reflection and stretching of the SPV is linked with extreme cold across parts of Asia and North America, including the recent February 2021 Texas cold wave, and has been increasing over the satellite era.
Cohen was able to show how there have been dramatic differences in warming inside the Arctic itself, which drives how the polar vortex can stretch and weaken.
“The Texas cold blast of February 2021 is a poster child” for the link between the changing Arctic and cold blasts in lower latitudes, said climate scientist Jennifer Francis of the Woodwell Climate Research Center on Cape Cod.
She helped pioneer the Arctic link theory but wasn’t part of Cohen’s research. “The study takes this controversial hypothesized linkage and moves it solidly toward accepted science,” she said.
