The basic idea, he said, is that the warmer conditions create larger and more energetic atmospheric waves that make the jet stream more wavy, with larger peaks and valleys. This affects the polar vortex circulation.
To use the spinning top analogy, “It’s like it started hitting things,” he said. “It loses its nice rounded shape and in this case becomes more elongate.” A lobe extends to Canada and the United States, bringing with it a burst of cold weather.
DR Cohen said he has been studying the subject since 2005 and is more confident than ever about the link to changes in the Arctic. “The evidence only multiplies,” he said.
Other scientists are not 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 continued, short-term trends in extreme cold, jet stream ripple and other climate-related measurements in the 1990s and 2000s “have not continued for the past decade,” belying the argument that rising temperatures in the Arctic were the culprit.
Some experts suggest that instead of warming, other naturally variable elements in Earth’s climate could be affecting the vortex. These include, according to Ted Shepherd, a climate scientist at the University of Reading in England, sea surface temperatures in the tropical Pacific Ocean, which can lead to changes in air masses in the Arctic that disrupt jet streams and eddies.
Will this debate be resolved?
Scientists say asking what role Arctic warming might play in extreme cold snaps is an example of the kind of healthy debates about climate change that are happening now. The issue is not whether climate change is real – that question has been answered – but what its effects are, how severe they are and whether they will worsen as warming continues.
Most scholars regard this debate as an important one that is still ongoing. Dr. Vavrus said that some aspects “stand on pretty solid physical feet”. Among them, he said, is the idea that by reducing the temperature difference between the Arctic and the tropics, Arctic warming has weakened jet stream winds. But other aspects, including whether and where warming is making the jet stream more rippled, “are the things that we’ve really struggled with that remain uncertain,” he said.
“In the early days there was a lot of black and white thinking on this question, even among people like me,” says Dr. Added Vavrus. “As more and more evidence comes in, it’s clear there are many shades of gray.”