This spells out the odd weatherwe have has for two winters running. That the Arctic has remained warm is quite an anomaly and makes the workof the Navy’s PIPS program that shows increasing ice volume somewhat suspectwhen eyeballs fail to support it.
The other big anomaly is thateven with all this we come up short on the number of cold days as compared tothe normal weather of the fifties and the sixties.
If we have learned anything it isthat the jet stream is able to shift atmospheric heat and cold around way moredramatically than anticipated while actually changing nothing as far as the netresult. It certainly has happened beforeand is actually a normal state of affairs that also makes climate prediction areal fool’s game. Just look at the explanationhere of what happened.
I personally anticipated both ofthese winters but only because the early signals were in place as we enteredthe fall. I think it quite plausible topredict a couple of months ahead. Yet asfar as next year is concerned, we are simply too far out. All touted triggers are just playing withchance.
Cold Jumps Arctic ‘Fence,’ Stoking Winter’s Fury
A subway station in Brooklyn . Whilethe Northeast shivers, the Arctic has beenfreakishly warm.
Published: January 24, 2011
Judging by the weather, the world seems to have flipped upside down.
For two winters running, an Arctic chill has descended on Europe , burying that continent in snow and ice. Last yearin the United States Deep South has endured unusual snowstorms and severecold, and a frigid Northeast is bracing for what could shape into another majorsnowstorm this week.
Yet while people in Atlanta Canada and Greenland , temperatures in December ran asmuch as 15 to 20 degrees Fahrenheit above normal. Bays and lakes have been slowto freeze; ice fishing, hunting and trade routes have been disrupted.
Iqaluit, the capital of the remote Canadian territory of Nunavut, hadto cancel its New Year’s snowmobile parade. David Ell, the deputy mayor, saidthat people in the region had been looking with envy at snowbound American andEuropean cities. “People are saying, ‘That’s where all our snow isgoing!’ ” he said.
The immediate cause of the topsy-turvy weather is clear enough. Apattern of atmospheric circulation that tends to keep frigid air penned in theArctic has weakened during the last two winters, allowing big tongues of coldair to descend far to the south, while masses of warmer air have moved north.
The deeper issue is whether this pattern is linked to the rapid changesthat global warming iscausing in the Arctic , particularly thedrastic loss of sea ice. At least two prominent climate scientists have offeredtheories suggesting that it is. But others are doubtful, saying the recentevents are unexceptional, or that more evidence over a longer period would beneeded to establish a link.
Since satellites began tracking it in 1979, the ice on the Arctic Ocean ’s surface in the bellwether month ofSeptember has declined by more than 30 percent. It is the most striking changein the terrain of the planet in recent decades, and a major question is whetherit is starting to have an effect on broad weather patterns.
Ice reflects sunlight, and scientists say the loss of ice is causingthe Arctic Ocean to absorb more heat in thesummer. A handful of scientists point to that extra heat as a possible culpritin the recent harsh winters in Europe and the United States
Their theories involve a fast-moving river of air called the jet streamthat circles the Northern Hemisphere. Many winters, a strong pressuredifference between the polar region and the middle latitudes channels the jetstream into a tight circle, or vortex, around the North Pole, effectivelycontaining the frigid air at the top of the world.
“It’s like a fence,” said Michelle L’Heureux, a researcher in Camp Springs , Md.
When that pressure difference diminishes, however, the jet streamweakens and meanders southward, bringing warm air into the Arctic and cold air into the midlatitudes — exactly what has happened the last coupleof winters. The effect is sometimes compared to leaving a refrigerator dooropen, with cold air flooding the kitchen even as warm air enters therefrigerator.
This has happened intermittently for many decades. Still, it is unusualfor the polar vortex to weaken as much as it has lately. Last winter, one indexrelated to the vortex hit its lowest wintertime value since record-keepingbegan in 1865, and it was quite low again in December.
James E. Overland, a climate scientist with NOAA in Seattle, has proposed that the extrawarmth in the Arctic Ocean could be heating the atmosphere enough to make itless dense, causing the air pressure over the Arctic to be closer to that ofthe middle latitudes. “The added heat works against having a strong polarvortex,” he said.
But Dr. Overland acknowledges that his idea is tentative and needsfurther research. Many other climate scientists are not convinced, saying thata two-year span, however unusual, is not much on which to base a new theory.“We haven’t got sufficient insight to make definitive claims,” said KevinTrenberth, head of climate analysis at the NationalCenter for Atmospheric Research in Boulder , Colo.
Judah Cohen, director of seasonal forecasting at a company called Atmospheric andEnvironmental Research in Lexington, Mass., has spotted what hebelieves is a link between increasing snow in Siberia and the weakening of thepolar vortex. In his theory, the extra snow is creating a dense, cold air massover northern Asia in the late autumn, settingoff a complex chain of cause and effect that ultimately perturbs the vortex.
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