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It was the coldest February Texas had seen in more than four decades, and the sustained blast of arctic air destroyed much of the state’s power grid for several days, causing hundreds of deaths and billions of dollars in damage.
Scientists say they’re still working to understand the relationship between climate change and extreme winter weather. Many factors can influence localized cold spells, and evidence suggests that climate change is affecting long-standing climate models in new ways.
“The way these types of events occur involves much more complicated atmospheric processes,” said Jennifer Francis, senior scientist and acting deputy director of the Woodwell Climate Research Center in Falmouth, Massachusetts.
Francis and other scientists have said there’s a large body of research that can help explain why Texas – and other parts of the United States – can still experience extreme cold from time to time in the middle of a general warming of the planet.
âMaybe there was a nuance that was missed when people started talking about the end of winters and the fact that we will never see snow again,â said Judah Cohen, leading snow specialist. winter meteorology and climate change and director of seasonal forecasts at the climate analysis company Atmospheric and Environmental Research. “People say, ‘I’ve been told one thing and I’m living something else.'”
Several factors impact the frequency and severity of cold waves in Texas, from the strength of the polar vortex – a seasonal swirling cold air mass that revolves high above the Arctic – to the fact that we are in an El NiÃ±o or a La NiÃ±a year, which influences whether Texas has a wetland or dry winter, to natural models that influence the position and strength of the jet stream, which can determine the trajectory and duration of weather systems.
Here are what factors scientists believe can cause an extreme cold snap in Texas – and how those storms can be influenced by climate change.
Is Texas at risk of another major frost this winter?
Scientists say another cold snap like the one that swept through the state in February is unlikely to occur this winter. the National Oceanic and Atmospheric Administration forecasts a warmer than normal winter for Texas due to persistent dry conditions in La NiÃ±a – although last winter was also a La NiÃ±a year.
âWe have these other differences which, all combined, probably create a very different winter this year than the winter of last year,â Francis said. “I think it’s unlikely that we will see a big cold air epidemic like we saw last year.”
How the polar vortex causes cold waves
the stratospheric polar vortex, well above the Earth’s stratosphere, forms in the fall, when the northern hemisphere turns dark and cold.
The February storm occurred after the polar vortex collapsed, sending very cold air much further south than normal.
Just as ice skaters spin faster and harder when pulling in their arms, a powerful polar vortex keeps the cold air spinning fast and tight in the northern part of the planet.
âThis keeps a lot of the lower 48 at least soft enough,â said Jason Furtado, associate professor in the School of Meteorology at the University of Oklahoma. “It traps cold air at high latitudes because it’s locked in that circulation.”
But when the polar vortex is weak, it’s as if a skater is losing balance: it starts to wobble, and this can push arctic air over the jet stream, or what’s called the tropospheric polar vortex, a mass of rapid winds that flow 5 to 9 miles above the Earth’s surface in a wavy path around the northern hemisphere.
This is precisely what happened in February: the stratospheric polar vortex weakened and split in january, contributing to the large southerly oscillation of the jet stream. A few weeks later, it brought a large mass of cold air into the central and southern United States.
Climate change and the Arctic
Several factors influence whether the polar vortex is strong or weak. For example, the strength of the winds can be affected by a pattern called arctic oscillation.
“When the arctic oscillation is positive, it strengthens the jet stream, which can reduce the likelihood of outbreaks of fresher air,” said Deepti Singh, climate change researcher and assistant professor at the Washington State University Vancouver. “When negative, the jet stream is weaker and more wavy, allowing arctic air to flow to lower latitudes.”
Emerging science has suggested that climate change may also play a role.
Cohen, director of seasonal forecasts at Atmospheric and Environmental Research, published a study in the journal Science in September who discovered that the polar vortex collapses more frequently in recent decades than in the past, forming models that have the potential to bring these large blasts of cold air deeper into the United States
Climate change has also hit the Arctic harder than anywhere else: since 2000, Arctic temperatures grew about twice as fast than global temperatures. Global warming is causing more of the Arctic sea ice to melt than in the past, leaving free water that absorbs more of the sun’s heat, accelerating warming in the Arctic.
Whether a warmer Arctic is directly linked to a weakened polar vortex is still an active area of ââresearch. Cohen’s research suggests that a melting ice “hot spot” in the Barents-Kara Sea, northwest of Russia, could be to blame: with the polar vortex.
âMy argument is that the arctic change [from global warming] forces the jet stream into a configuration that, at least partially, favors a weaker polar vortex, âsaid Cohen, who is also a visiting researcher at MIT.
Francis’ research suggested that when the Arctic is unusually warm and has experienced significant ice loss, the jet stream tends to weaken. Certain extreme weather events – droughts, heat waves, cold spells and heavy precipitation – are often associated with “persistent” weather conditions brought on by the weakened state of the jet stream, Francis wrote in an article. 2012 study published in Geophysical Research Letters.
Corn other scientists have supported that the disturbances in the polar vortex might just be a natural variation. And emerging science on how the melting Arctic could bring harsh winter conditions to lower latitudes has not yet clearly reproduced in climate models, which would help make definitive connections by isolating and eliminating other potential causes.
“There are so many pieces to the puzzle, and there is still a lot of research going on to understand how they all are connected,” said Francis, a leading researcher on how the dramatic warming of the Arctic can. be linked to extreme weather conditions in the United States and Europe.
Yet, she added, âthe Arctic is warming incredibly fast, and it’s a huge change in a very important part of the climate system. “
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