Arctic climate change may not be making winter jet stream ‘weird’ after all

arctic-sea-ice

Arctic sea ice [image credit: Geoscience Daily]

‘New research is pouring cold water on once-hot theory’ – WashPo. Researchers refer to ‘overestimation’. (Weird in this context at least tends to mean something like ‘not well understood’).
– – –
An influential, highly publicized theory — that a warming Arctic is causing more intense winter outbreaks of cold and snow in midlatitudes — is hitting resistance from an ongoing sequence of studies, including the most comprehensive polar modeling to date, says the Washington Post.

The idea, first put forth in a 2012 paper by Jennifer Francis, now at the Woodwell Climate Research Center, and Stephen Vavrus, at the University of Wisconsin at Madison, is that two well-established trends — Arctic amplification (intensified global warming at higher latitudes) and depleted sea ice — can force the polar jet stream to dip farther south, thus causing more intense bouts of winter weather than might have otherwise occurred.

Over the past decade, this hypothesis sparked widespread public interest and scientific debate, as various high-profile cold waves and snow onslaughts hit North America and Eurasia, including a deadly, prolonged cold wave in Texas last February.

Winter temperatures over the past three decades have shown cooling in some areas of the northern midlatitudes, especially eastern Asia.

But the cooling has been far from ubiquitous and the Arctic-midlatitude link has been difficult to detect in simulations by global computer models.

Instead, the models point more strongly toward the gradual, longer-term trend of milder midlatitude winters that one would expect in a human-warmed climate. [Talkshop comment – or any warmed climate].

(A separate line of research is addressing extremes during the summer, such as the unprecedented heat wave that struck the Pacific Northwest in June; see below.)

Some emerging work, not yet peer-reviewed, does reveal faint fingerprints of the Francis-Vavrus hypothesis in new simulations of Arctic and midlatitude winter climates, part of the Polar Amplification Model Intercomparison Project (PAMIP).

“It does look like there’s something there, but it looks fairly weak,” James Screen, a climate scientist at the University of Exeter, said in an interview. “That doesn’t mean it’s not one part of the overall jigsaw.”

“There’s genuine reason to be concerned about climate change and its effects,” Screen added, “but an increase in the frequency in cold events would not be at the top of my list.”

Screen has published several related studies with Russell Blackport, now at Environment and Climate Change Canada, over the past two years. The title of one of their latest, published in April in the Journal of Climate, is itself an assertion: “Observed Statistical Connections Overestimate the Causal Effects of Arctic Sea Ice Changes on Midlatitude Winter Climate.”

In this study and others, Screen and Blackport suggest that the connection between Arctic sea ice loss and extreme midlatitude events is real, but not necessarily causal. Instead, they argue, a third factor — most likely large-scale changes in atmospheric circulation that may not be permanent — is probably driving both the sea ice loss and the extreme winter events.

Full article here.

via Tallbloke’s Talkshop

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August 1, 2021 at 09:33AM

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