Is climate change behind the week’s extreme winter weather? Experts are divided – San Antonio Report
Blizzard-like blasts slammed Texas over the past week, barreling across an underprepared infrastructure and leaving millions across the state without electricity or water.
While the past week’s weather seemed extreme and out of character for Texas’ typically mild winters, scientists around the state and country disagree about exactly how unusual it was and what role climate change played in it – if any.
Across the state, the harsh weather broke a number of winter weather records, while in other areas the low temperatures didn’t approach records, said Paul Yura, warning coordination meteorologist at the National Weather Service Austin-San Antonio. San Antonio experienced its coldest Valentine’s Day on record Sunday, followed by two snow days in the same week – a definite “oddity,” Yura said, but not unheard of.
“Historic weather events have always happened,” Yura said. “We really only have about 100 years worth of data, which, in the capture of time, that’s not very long. We know there were big-time weather events in San Antonio probably in the 1600s and 1700s, but they just weren’t documented very well.”
Yura said while these events have always occurred, they’re rare. The most recent weather events that were similar to last week’s onslaught happened in the 1980s, he said.
Stretches of freezing weather in Texas due to blasts of Arctic air escaping the north and moving south were similarly documented in ’83 and ’89.
“Back in December of 1983 and of 1989 … both of those [events] were pretty darn close to the kind of outbreak that we basically [were] dealing with [last week],” he said.
Climate scientist Andrew Dessler, a professor of atmospheric sciences at Texas A&M University, has a similar view.
“Sometimes it’s just that the weather gods roll the dice, and that’s what you end up with,” Dessler said. He added that he doesn’t think there’s a single reason for this week’s event other than “that’s the way it worked out.”
The weather’s effects on Texas infrastructure definitely highlight a need for the state to be better prepared for natural disasters and extreme conditions, Dessler said, especially as other weather events like stronger hurricanes, which he said are undisputedly tied to climate change, start occurring more frequently.
“This shows that the government has a key role to play in preparing us,” Dessler said. “And the people in Austin have to recognize that.”
How the deep freeze developed
The weather Texans experienced this past week began in January far away from the state. The blast of arctic air actually began at the North Pole, where ultracold air typically is contained in a polar vortex high above the ground.
This vortex spins like a top, moving the cold air in a tight counterclockwise spiral. During the summer, the polar vortex tends to weaken. During the winter, the vortex expands and colder air moves south with the jet stream, typically across the northern and eastern United States.
On occasion, something called sudden stratospheric warming occurs. Scientists aren’t exactly sure why this happens, but it allows the cold air usually kept in the polar vortex to escape and head south.
“There’s evidence that that sort of disruption may be becoming more common with global warming,” said Texas State Climatologist John Nielsen-Gammon, a meteorology professor at Texas A&M. “That’s about the only aspect of this event that is likely to be enhanced by global warming, in my opinion.”
The polar jet stream is typically very strong. The air current maintains the difference between the extreme cold in the Arctic and the warmer air in the mid-latitudes, where we live, said Avery Tomasco, meteorologist for Austin’s KEYE-TV.
“[Occasionally] that warm air fights back and gets pushed up towards the north,” Tomasco said. “That can create that sudden stratospheric warming event. This year’s event would be an extremely strong example of that.”
When large atmospheric waves – waves of energy that cause specific weather patterns, similarly to how ocean waves cause undercurrents – slam against the polar vortex, they can cause this escape of cold air and push it along, explained climate scientist Kerry Cook, a University of Texas professor of geological sciences.
These waves hit the polar vortex in increments. The first strike happened in early January, then again in mid-January. At the end of January came the latest wave, which pushed cold air into the jet stream and down through the U.S.
Sometimes, the cold air that escapes splits into smaller waves that can cause large snowstorms across the U.S. Other times, the cold air mass stays together but moves to a new location. This time it did both, with the U.S. storms giving a large cold air mass enough power to push down deep into Texas.
“The same storm that brought the snow and ice gave it the final push southward to get the entire state extremely cold,” Nielsen-Gammon said.
The role of a warm Arctic region
While scientists have come to mostly agree that global warming is behind the increased frequency and severity of extreme summer weather such as hurricanes, heat waves, wildfires, droughts, and floods, there’s no consensus on its effects on winter weather.
“There are people working on this, and there are theories about it, but we are not sure yet,” Cook said. “It’s important to be really cautious about that.”
One person studying the relationship between climate change and more extreme winter weather is Massachusetts Institute of Technology climatologist Judah Cohen. In 2018, Cohen co-published a paper explaining how warm Arctic episodes – which are being caused by global warming – appear linked to an increased frequency of extreme winter weather in the U.S., especially in the eastern region.
“As the Arctic gets warmer than [it normally is] – the risk of severe winter weather increases very linearly,” Cohen told the San Antonio Report on Friday. “When the Arctic is at its warmest, it’s a huge jump in the likelihood or the probability of getting severe winter weather to many eastern U.S. cities.”
When the Arctic is warm, both cold temperatures and heavy snowfall are more frequent elsewhere than when the Arctic is cold, Cohen said.
More studies are needed to confirm causation, and that will likely not happen until decades of more data is collected, Yura said.
“Ask me that question in 50 years, and we can see if there’s a new pattern of cold snaps or a new pattern of record cold outbreaks. … We won’t know until you have a big set of data,” Yura said.