By Tom Balmforth
(Reuters) - The freak cold spell that has killed at least 21 Americans and shut down power for days in Texas has revived scientific discussion over whether climate change could be delivering this week's chill.
Scientists say global warming – specifically the rapid warming of the Arctic – is a possible, if not likely, culprit in the extreme weather.
Historically, frigid temperatures have typically been contained within the Arctic by a jet stream circling the polar region. In fact, along with the spinning of the planet, it's the contrast in temperatures and atmospheric pressures between the Arctic and lower latitudes that results in the winds.
But as the Arctic has warmed more than twice as fast as the global average over the last three decades, that contrast can be less pronounced, said Paul Beckwith, a climate system scientist in Ottawa. That could cause the polar jet stream to slow down and meander, so that it carries more warmer air toward the pole and frigid air further south, he said.
"What we're seeing this year is an extreme example of what happens when the jet stream trough goes really deep southward," Beckwith said.
"I think it's a rock-solid case," he said. But "it might take a bit of time for the science to catch up and find all the details" to prove it.
This polar vortex theory, first proposed in 2012, has some researchers like Beckwith worried about what future warming might mean for traditionally temperate lands further south.
Others caution that it's still too early to draw conclusions. The theory "remains speculative, and it is the reporting of it as fact that is not justified," climate scientist Geoffrey Vallis at the University of Exeter tweeted on Tuesday. "It may be true, but perhaps more likely not."
Cold weather is something to expect in winter, after all, and extreme cold could be a result of natural variability, some say.
However, scientists have found a strong correlation between extreme winter weather in 12 U.S. cities and warmer temperatures in the Arctic over the last 50 years, according to research published in 2018 in the Nature Communications journal.
The United States may not be the only country affected, either.
Temperatures fell to a bone-chilling minus 60 Celsius (minus 76 Fahrenheit) in Russia's Siberian region of Yakutia last month, according to the Roshydromet meteorological service. Much of Russian Siberian had one of its 15 coldest Januaries on record, it said.
Vladimir Semenov, a climate scientist at the Moscow-based Obukhov Institute of Atmospheric Physics, said the recent cold spell in Russia could be another likely consequence of a wobbly jet stream.
While Semenov acknowledges there is still not enough data to establish a firm climate link in the pattern, he said research pointing to the theory of a "wavier" polar jet stream due to Arctic warming was compelling.
Computer simulations of climate and weather patterns have resulted in contradictory findings on the issue though, he said. "Thus, the uncertainty still remains."
(Reporting by Tom Balmforth in Moscow; editing by Katy Daigle and Lisa Shumaker)