The fundamental idea, he said, is that the hotter conditions create larger and more energetic atmospheric waves that make the jet stream wavier, with greater peaks and troughs. That affects the polar vortex circulation.
To make use of the spinning top analogy, “it’s like if it began banging into things,” he said. “It loses its nice circular shape and on this case becomes more stretched out.” One lobe stretches down into Canada and the US, bringing an outbreak of cold weather.
Dr. Cohen said he’s been studying the topic since 2005, and is more confident than ever concerning the link to changes within the Arctic. “The evidence is barely growing,” he said.
Other scientists will not be as certain. In a temporary paper within the journal Nature Climate Change in 2020, two researchers on the University of Exeter in England wrote that, although Arctic warming and sea-ice loss were continuing, the short-term trends in cold extremes, jet-stream waviness and other climate-related measurements within the Nineties and 2000s “haven’t continued over the past decade,” weakening the argument that rising temperatures within the Arctic were the perpetrator.
Some experts suggest that fairly than warming, other naturally variable elements of the earth’s climate could also be affecting the vortex. Amongst these, said Ted Shepherd, a climate scientist on the University of Reading in England, are sea-surface temperatures within the tropical Pacific Ocean, which might drive changes to air masses within the Arctic that disrupt the jet stream and vortex.
Will this debate get resolved?
Scientists say that questions over what role Arctic warming may play in extreme cold snaps is an example of the type of healthy climate-change debates that occur now. It’s not about whether climate change is real — that query has been answered — but what sorts of effects it has, how severe they’re and whether they are going to worsen as warming continues.
Most scientists view this debate as a crucial one which remains to be underway. Dr. Vavrus said that some points “are on pretty solid physical footing.” Amongst these, he said, is the concept Arctic warming, by reducing the temperature difference between the Arctic and the tropics, has weakened the jet stream winds. But other points, including whether and where warming is making the jet stream wavier, “are the things that we’ve really been wrestling with and remain uncertain,” he said.
“Within the early days there was lots of black and white pondering, including amongst people like myself, on this query,” Dr. Vavrus added. “As increasingly more evidence has are available, it’s clear that there are lots of shades of gray.”