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Other scientists cautioned against putting too much focus on Arctic warming, saying other factors are contributing to changing weather patterns in the lower latitudes. Both sides agree that more research is needed into the connection between warming in the far north and weather elsewhere.
Temperatures in the Arctic have increased about twice as fast as they have in the rest of the globe over the past 25 years, an increase of seven degrees Fahrenheit, or more, in some areas. Less white ice on the Earth's surface means that less of the sun’s heat is reflected back into space. That exacerbates the warming pattern and, in a vicious cycle, melts even more ice.
The scientific consensus is that the higher temperatures all over Earth have created secondary effects, like rapid sea level rise, more intense heat waves and a shifting in the ranges of some animals. As much as one-quarter of the globe's warming has been linked to the loss of sea ice.
Researchers six years ago first suggested another profound impact: warming in the Arctic contributes to extreme weather events in the Northern Hemisphere. The theory goes like this: Warmer Arctic air is closer to the temperature in the lower latitudes, thereby weakening the atmospheric barrier that previously kept the jet stream flowing in a relatively straight line. The river of air that speeds west to east around the globe now meanders north and south. The peaks and troughs in this "wavier" path drive weather on Earth. And because the unleashed jet stream moves more slowly, weather systems tend to linger.
“There are some very clear signals emerging from the noise, and one of them is this tendency for warm west, cold east in North America and very cold winters recently,” said Jennifer Francis, a Rutgers University research professor who co-authored one of the first papers connecting Arctic warming to jet stream upheaval. “It’s all a very consistent story, and there is no reason to think it’s going to go back to normal, maybe ever.”
As weather systems linger, then move on, only to stall again, they create a kind of “weather whiplash,” said Francis, who noted that Boston had record high temperatures in late February before flipping to the string of Nor’easters that dominated the last month.
Many other scientists are looking at the possible effects of the altered jet stream. Researchers at Lawrence Livermore National Laboratory released a computer simulation late last year suggesting that median rainfall in California will decline 10 percent to 15 percent by the middle of the century solely because of the loss of ice and warming in the Arctic.
Other researchers caution that extreme weather events probably stem from a variety of causes, and suggest that some could be random anomalies, rather than signs of a fundamentally altered climate.
Michael Mann, a climate scientist at Pennsylvania State University, warned against oversimplification. He said via email, “Increased snowfalls in the northeastern U.S. and mid-Atlantic are in part reflective of warmer ocean temperatures and stronger coastal storms, which produce stronger Nor’easters like we’ve seen this season, with larger snowfall totals."
"This is an entirely separate mechanism from Arctic warming.”
On one thing Mann and Francis agree: more research will be needed on the connection between the Arctic and weather patterns. “We don’t understand all the mechanisms yet,” said Francis, “but it would be hard to say that moving so much ice ... has not had an impact on weather down here.”
Mann called the debate over the science "refreshing, because too often we’re subject to a fake debate about whether climate change is real or human-caused, something there is no debate about among real scientists."