Cold snap caused by climate-change-weakened jet stream, scientists suggest

Arctic conditions in the eastern United States this week may have been the result of climate-change-induced effects on the jet stream that regulates weather over the Northern Hemisphere, according to meteorologists.

Residents in a swath of the country's east have been met with subfreezing temperatures over the past week. And overnight Wednesday, more than 5 feet of snow descended on parts of western New York state. Media have referred to the strange weather pattern as the polar vortex and the Arctic blast. 

Ironically, though, it was warmer-than-usual temperatures that likely sent the cold weather southward. Climate-change-induced ocean warming in the Pacific turned Typhoon Nuri into a supertyphoon that punched the jet stream off its course, bringing the North Pole's weather down over the eastern U.S., according to experts.

Scientists have said that warmer ocean temperatures contribute to more frequent and intense extreme weather, making it likely that climate change strengthened Nuri.

“Eleven days ago, we saw Super Typhoon Nuri, one of the most intense storms ever seen in the Pacific, go north to the waters west of Alaska,” Jeff Masters, the director of meteorology at Weather Underground, told Al Jazeera.

As Nuri tracked north along the coast of Japan, it effectively ran headfirst into the jet stream — like an “800-pound gorilla,” Masters said. The jet stream is the fast-moving river of air high in the atmosphere that affects most of the weather seen in North America. The impact forced the normally fairly straight, eastward-moving jet stream — which acts as the barrier between frigid Arctic temperatures and warmer weather in the south — to bulge, creating large waves.

“If you think of the jet stream as a rope and you take that rope and whip it, that’s what [Nuri did]. It gave it a big whip,” said Jennifer Frances, a research professor at Rutgers University and the author of “Rapid Arctic Warming and Wacky Weather: Are They Linked?”

Waves in the jet stream are described as having ridges, with high and low points. When Nuri hit the jet stream, it created a trough that dipped far south over the eastern U.S., essentially lowering the border of where Arctic air can travel and allowing polar blasts to penetrate far south.

Meanwhile, the ridge hung over the west coast of the U.S., extending all the way to Alaska, bringing warm dry weather to those areas and making it possible for areas of Alaska to be hotter than Texas.

Those warm temperatures are expected to track east along the jet stream over the weekend, Masters said. "That warmer air is going to push eastwards (on the jet stream), and by Sunday or Monday the east coast will be about 10 degrees F warmer than average."

Meteorologists said Nuri’s effect on the waviness of the jet stream would not have been so pronounced on the jet stream had it not already been weakened by another effect of climate change — the fast-disappearing summer Arctic sea ice.

“We know that the Arctic is warming much faster than everywhere else on the planet,” Francis said. That's important because the speed of the jet stream as it moves eastwards is driven by the temperature differential between the Arctic and areas to the south.

“Because the warming is so fast, it’s causing that temperature differential to become smaller, and as a result the winds, west-east winds, are getting weaker,” Francis said.

When the jet stream weakens, it tends to wander more north and south — instead of its usually straight circle around the Northern Hemisphere. Francis said that scientists measuring the “waviness” of the jet stream have found that it becomes wavier as the Arctic melts. Masters echoed Francis, saying, “We’ve experienced record loss of Arctic sea ice and … when that happens it can influence the jet stream to allow more frequent plunges over the eastern part of the U.S.”

“We’ve had record breaking Arctic sea ice loss over the last 15 years, and we’ve seen a lot more of these Arctic plunges over the eastern two-thirds of the U.S., starting around 2000,” Masters added.

The other effect of a weaker jet stream is that weather patterns often get “stuck” in place, Francis said.

“When those waves get really big, they tend to get stuck and stay in place for a long time — we’re seeing it now,” Francis said. The phenomenon has also been blamed for the series of extreme snowstorms that pummeled the east coast of the U.S. last winter.

Masters said he didn’t expect that the east coast would see a winter like that of last year, but said isolated, extreme snowstorms were likely. He warned against letting the extreme cold detract from the reality of global warming.

“We’re having a cold spell here in the U.S., but that shouldn’t detract attention from the fact that we just had the third consecutive month of the warmest global temperatures on record,” Masters said. “And we’re headed for the warmest year on record.”

James Screen, a NERC research fellow at the University of Exeter, believes the cold weather bout in the U.S. this week was “normal” and the result of natural weather variability. Screen argued that the jet stream discussion was a “distraction" from two more important factors that would determine the frequency of extreme hot and cold in the future.

“The U.S. (like the rest of the globe) is warming and is expected to continue to do so in the long-term (with short-term fluctuations due to natural variability),” Screen told Al Jazeera via email. “The second factor is that disproportionately large warming in the Arctic compared to the mid-latitudes (e.g. U.S.) reduces the average temperature gradient between the two regions. Both of these factors reduce the risk of extreme cold.” 

But Screen admitted that there is “some evidence” that Arctic sea ice loss could increase the risk of extreme cold in other parts of the world, including central Asia.

The upside to such “weird weather,” according to Frances at Rutgers,  is that the general public is beginning to pay closer attention to the weather.

“People are starting to become more educated in some of these very complicated interactions that scientists are studying that connect climate change with changing weather patterns that affect individuals today,” Francis said.