After two straight miserably cold winters in the East, the trendy explanation has been that climate change made them more extreme. But two new studies say not so fast, we should expect a warming climate to lead to a marked decrease in cold weather as time wears on.
The idea that winters are leading to increased extreme cold and big temperature swings is tied to the hypothesis that the jet stream is slowing down and becoming more erratic. Faster warming in the Arctic compared to regions to the south, a phenomenon known as “Arctic amplification”, is thought to be altering the jet stream’s behavior. Some have dubbed this the “drunk Arctic” hypothesis.
“When the Arctic is so warm, the west winds of the jet stream weaken, and this favors the highly wavy pattern to the jet stream responsible for this winter chill in the eastern U.S as well as the continued drought and heat in California,” explained Rutgers meteorology professor Jennifer Francis earlier this winter.
But the authors of two new studies, published in the Journal of Climate and the Bulletin of the American Meteorological Society (BAMS), ran computer model simulations and found winter temperatures should become less extreme and less variable as the Arctic heats up. They also say theory back up their findings.
“The results indicate that Arctic amplification of global warming leads to even less frequent cold outbreaks in Northern Hemisphere winter than a shift toward a warmer mean climate implies by itself,” the Journal of Climate study concludes.
The BAMS study makes the unusual move (for an academic paper) of citing and then refuting the remarks of a political figure, White House science advisor John Holdren. Holdren, following the vicious January 7, 2014 “polar vortex” blast in the eastern U.S., stated in a video: “…the kind of extreme cold being experienced by much of the United States as we speak is a pattern that we can expect to see with increasing frequency as global warming continues.”
But a cold wave as powerful as the January 7, 2014 event will cease to exist by the end of the century, the BAMS study concludes.
“Continued Arctic sea ice loss is a major drive of decreased – not increased – North America cold extremes,” the study says. “Projected Arctic sea ice loss alone reduces the odds of such an event to one third by the mid twenty-first century, and to zero (or near-zero) by the late twenty-first century.”
The authors of both the Journal of Climate and BAMS studies express skepticism that Arctic amplification will meaningfully reconfigure the jet stream.
“The waviness of the jet stream that makes our day-to-day weather does not change much,” said the Journal of Climate study lead author Tapio Schneider.
Schneider’s statement is supported by another study published in the Journal of Climate this March, which concludes: “[O]ur analysis leads us to conclude that the net circulation response in the future is unlikely to be determined solely– or even primarily – by Arctic warming.”
But even as these new studies push back against the idea the jet stream is changing and making winter weather more extreme, several other studies – published in the past year – argue the opposite. Rutgers’ Jennifer Francis, who has written several research papers on this subject, told the Post’s Chris Mooney there is increasing support for the “drunk Arctic” hypothesis:
Francis argues … that the evidence in her favor is mounting — she cites no fewer than five (1, 2, 3, 4, 5) scientific papers published in the last year or so that she considers supportive, and hints that more are coming. “We’ve got 5 papers that all look at that particular mechanism in different ways — different analysis, different data sets, observation and models — and they all come to the same conclusion and they all identify this mechanism independently,” she says.
The varying results in this recent flurry of studies on Arctic climate change, the jet stream, and extreme cold in the mid-latitudes are part and parcel of the scientific process. Only time will tell whose ideas are correct.