The United States is once again bracing itself for bitter cold, with the country enduring what is at least the eighth Arctic blast of the winter season. Despite winter warming faster than any other season in many parts of the US, this year has seen a resurgence of cold not experienced in years; January marked the coldest month in the Lower 48 since 1988. However, the US stands out as an anomaly, as January was the warmest on record globally, making the country seem out of place in a world of overall warmth.
Scientists attribute this phenomenon to a misbehaving polar vortex interacting with a persistent weather pattern. Some suggest that these factors, and the extreme cold witnessed this winter, could be indicative of how cold weather patterns are changing in a warming climate. Others argue that more research is necessary to fully understand the situation. What is clear, though, is that winters are becoming warmer as the planet heats up due to fossil fuel emissions, making this Arctic blast feel like a relic of the past.
Zeke Hausfather, a research scientist at the University of California, Berkeley, notes that the concept of a “normal” winter is evolving, with no region in the US experiencing colder temperatures on the coldest day of the year over the past five decades. The shifting weather patterns that have brought extreme cold to the US this winter can be attributed to a combination of factors, including the polar vortex and a persistent high-pressure system that has allowed cold air to flow southward through the jet stream.
This year’s recurring weather pattern could be a glimpse into the future as the Arctic region warms and weakens the jet stream, leading to more frequent incursions of cold air into lower latitudes. While some scientists see this as evidence of climate change impacts, others call for further research to better understand the complexities at play. Regardless of the underlying causes, the US is currently in the grip of a winter characterized by frigid temperatures and disruptive weather patterns.
According to Jennifer Francis, a senior scientist at the Woodwell Climate Research Center, the polar vortex does not cause cold air outbreaks in the US but actually intensifies them. The polar vortex refers to a region of fast-moving winds high above the Earth’s surface and the jet stream that encircles the Arctic during the coldest months of the Northern Hemisphere. A strong polar vortex keeps frigid air trapped in the Arctic, similar to a figure skater spinning with arms close to the body. Conversely, a weak polar vortex allows cold air to spill southward.
This year, the polar vortex has been notably stronger than usual, which should typically prevent record-breaking cold temperatures in the US. However, the polar vortex has been behaving unusually, stretching into irregular shapes, as explained by meteorologist Laura Ciasto from NOAA’s Climate Prediction Center.
When the polar vortex is circular and undisturbed, it resembles a rubber band at rest. External energy in the atmosphere can disrupt the polar vortex, causing it to stretch into an oblong shape, akin to pulling a rubber band apart. This altered polar vortex can then push the jet stream even farther south than what a blocking high pressure system could achieve on its own, leading to the influx of cold air into the US.
This fluctuation between a normal and stretched polar vortex state has occurred frequently this winter, resulting in multiple cold snaps. At least ten stretched polar vortex events have been observed, with four in December, four in January, and two in February. This rapid shift is attributed to the warming Arctic as demonstrated in a 2021 study co-authored by Cohen.
The impact of these stretched polar vortex events is significant. For instance, such an event contributed to the freezing temperatures that affected Texas in February 2021, resulting in over 200 fatalities. The interplay between the blocking pattern and the stretched polar vortex is a key area of research into the increasing occurrence of extreme cold outbreaks in a warming world.
While the influence of human-caused climate change on the jet stream is multifaceted, the complex interaction of various factors contributes to extreme weather events like the current cold spell. As temperatures continue to rise globally, extreme cold events may happen more frequently, albeit with less intensity over time. Yet, these events remain disruptive even amid a changing climate.
The above text was contributed to by Laura Paddison from CNN. For more CNN news and newsletters, you can sign up for an account at CNN.
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