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What is a polar vortex? And other cold weather climate questions

What is a polar vortex? And other cold weather climate questions

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The basic idea, he said, is that warmer conditions create larger and more energetic atmospheric waves, which make the jet stream more wavy, with larger peaks and troughs. This affects the circulation of the polar vortex.

To use the spinning top analogy, “it kind of started bumping into things,” he said. “It loses its nice round shape and becomes more stretched out in that case.” One lobe extends down into Canada and the United States, bringing a burst of cold weather.

Dr. Cohen said he has been studying the topic since 2005 and is more confident than ever about the connection to changes in the Arctic. “The evidence is only growing,” he said.

Other scientists aren’t so sure. In a short article in the journal Nature Climate Change in 2020, two researchers from the University of Exeter in England wrote that although Arctic warming and sea ice loss continue, short-term trends in cold extremes, jet waviness and other climate-related measurements over the 90- they and the 2000s “have not continued over the past decade,” weakening the argument that rising Arctic temperatures are to blame.

Some experts suggest that instead of warming, other naturally variable elements of Earth’s climate may be influencing the vortex. Among them, said Ted Shepard, a climate scientist at the University of Reading in England, are sea surface temperatures in the tropical Pacific that can cause changes in Arctic air masses that disrupt the jet stream and eddies.

Scientists say questions about what role Arctic warming might play in a cold snap are an example of the kind of healthy debates about climate change now taking place. It is not a question of whether climate change is real—that question has been answered—but what effects it has, how severe they are, and whether they will worsen with continued warming.

Most scholars consider this debate an important one that is still ongoing. Dr. Vavrus said some aspects “are on a pretty solid physical basis.” Among them, he said, is the idea that Arctic warming, by reducing the temperature difference between the Arctic and the tropics, has weakened the jet stream. But other aspects, including whether and where warming makes the jet stream more wavy, “are the things we’re really struggling with and remain uncertain,” he said.

“In the early days, there was a lot of black-and-white thinking, including among people like myself, about this,” added Dr Vavrus. “As more and more evidence comes in, it’s clear that there are many shades of gray.”

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