Over the past several decades, scientists have proven beyond a shadow of a doubt that global temperatures are rising due to human consumption of fossil fuels, a trend that is intensifying disasters associated with hot weather, such as heatwaves, hurricanes, and wildfires.
Now, a team has provided some of the most comprehensive and unusual evidence to date that climate change is also amplifying winter weather disasters, including the cold wave that devastated Texas and other southern states in February, killing hundreds and costing as much as $200 billion in damages.
Scientists led by Judah Cohen, a climatologist at the Massachusetts Institute of Technology (MIT) and director of seasonal forecasting at the company Atmospheric and Environmental Research (AER), linked dangerous cold snaps to a largely overlooked disruption of the stratospheric polar vortex, a cycle of westerly winds that forms above the North Pole in winter.
The team used both observational data and climate models to expose “stretching events” in the polar vortex that cause its circular shape to become elongated across the Arctic. This phenomenon “is linked with extreme cold across parts of Asia and North America” and could “potentially extend the warning lead time of cold extremes in Asia, Canada, and the United States,” according to a study published in the journal Science on Thursday.
“This is the only paper on Arctic change with this link” to stretching events, said Cohen in a call. “We had an observational component and a modeling component and they agree, which obviously helps lend credibility to our idea.”
“It should help with predicting these events, independent of Arctic change,” he added. “I think we should be able to recognize them fairly easily within two or maybe three weeks before the start” of a potential cold spell, enabling people to be “on the alert, or at least keep in their mind, that we could be setting up for an extreme winter weather event.“
Scientists have been examining possible connections between anthropogenic Arctic warming and anomalous cold spells for years, but most studies have focused on the role of sudden stratospheric warmings. Characterized by a rapid spike in polar temperatures that slows and reverses the polar vortex, these events have also been linked to dangerous conditions such as the February 2021 Texas cold snap.
Meanwhile, Cohen has been studying the lesser-known vortex stretching events, which are preceded by specific autumn seasonal effects such as heavy snowfall in Siberia and melting sea ice off the northern Eurasian coast. Those conditions provide more energy to atmospheric waves over Eurasia, which is reflected off of the polar vortex and subsequently absorbed into analogous North American waves. The amplification and transfer of this wave energy from Eurasia to North America, via the polar vortex, may be driving extreme winter weather in Canada, the United States, and Mexico.
Cohen was already teasing out these connections between stretching events and cold spells when the February 2021 disaster hit North America and crippled the Texan energy grid. It was an “aha moment,” he said, because the conditions were very similar to another cold spell in 2014 that he described as the “poster child” for stretching events.
“I had just been working on this  event and then the Texas cold wave happened,” he recalled. “If the two hadn’t coincided, the paper wouldn’t have come together.”
To get a better sense of the relationship between the stretching events and cold spells, Cohen and co-authors at the University of Massachusetts Lowell and the Hebrew University of Jerusalem used machine learning to scan through more than 40 years of Arctic satellite observations. The results revealed that this phenomenon may be the strongest indicator of cold spells in the United States, a finding that was backed up by modeling analyses conducted by the team.
“We have a dynamical explanation from start to finish and there are no large gaps,” Cohen said. “We know the signal of the energy and we can follow it through the whole process: it starts in Eurasia, bounces off the vortex, and ends up across North America.”
Because these stretching events are still poorly understood, the team hopes that their paper will encourage scientists around the world to start unraveling mysteries about their underlying mechanisms and effects on winter weather.
The new study adds to a compelling body of evidence that links global warming to all kinds of extreme weather, including winter disasters. This emerging consensus refutes a common refrain from climate change deniers that points to unusually cold weather as proof that global warming either isn’t happening, or is not a serious problem.
The most infamous example of this misconception may well be Oklahoma Senator Jim Inhofe’s argument that a snowball he brought to the Senate floor disproved the existence of climate change. More recently, an extreme cold spell in the US Northeast around New Year 2018 prompted former President Donald Trump to mock the reality of global warming on Twitter.
Interestingly, Cohen pointed out that the 2018 cold snap was also associated with a stretching event, and that it came close to imperiling people in the Northeast.
“That one reflective event almost caused a complete depletion of gas,” he said. “I'm a scientist, not a decision maker, but we can’t just say we'll just build resiliency to hurricanes and wildfires, and then ignore winter weather.”