What is the polar vortex? And other questions about cold weather

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

To use the peolla analogy, “it’s like it starts hitting things,” he said. “It loses its nice circular shape and in this case it stretches more.” A lobe extends into Canada and the United States, causing a burst of cold weather.

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

Other scientists aren’t so sure. In a short paper in the journal Nature Climate Change in 2020, two researchers from the University of Exeter in England wrote that while Arctic warming and sea ice loss continued, trends in short-term cold extremes, the jet stream ripple and other climate-related measures in the 1990s and 2000s “have not continued over the past decade,” undermining the argument that rising temperatures in the Arctic it was the culprit.

Some experts suggest that rather than warming, other naturally varying elements of Earth’s climate may be affecting the vortex. Among these, said Ted Shepherd, a climate scientist at the University of Reading in England, are sea surface temperatures in the tropical Pacific Ocean, which can lead to changes in Arctic air masses that they disrupt the jet stream and the vortex.

Scientists say questions about what role Arctic warming might play in times of extreme cold are an example of the kind of healthy debates about climate change happening now. It’s not whether climate change is real, that question has been answered, but what kinds of effects it has, how severe they are, and whether they will get worse as warming continues.

Most scientists see this debate as an important debate that is still ongoing. Dr. Vavrus said some aspects “are on a pretty solid physical basis.” Among these, he said, is the idea that Arctic warming, by reducing the temperature difference between the Arctic and the tropics, has weakened the jet stream winds. But other aspects, including whether and where warming makes the jet stream more wavy, “are the things we’ve really been struggling with and don’t know yet,” he said.

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

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