Friday, November 14, 2014

What the Arctic Outbreak and Last Year’s ‘Polar Vortex’ Have in Common

The jet stream for November 14, 2014. (Credit: Click to Enlarge.
The Arctic Outbreak, an unseasonable bout of frigid air that’s sweeping across the U.S. this week, is not the same as last winter’s so-called “Polar Vortex” event.  Though both gave Americans the rare experience of breathing crisp, cold Arctic air, both were caused by different things:  last winter’s “Polar Vortex” event seemingly random, and the current Arctic Outbreak caused by Super Typhoon Nuri in the Western Pacific.

But the two events do have at least two things in common.  One is that that they’re both due to deep dips in the jet stream.  In both cases, Arctic air from the Polar Vortex has been displaced to the south by a wavy jet stream, which brings coldness down to the temperate United States and leaves Alaska and the Arctic relatively warm.  Sure enough, right now it’s warmer in Alaska than it is in Texas, and next week the National Weather Service predicts temperatures in Alaska will be 70 percent higher than average, with temperatures in Texas about 50 percent below average.

The second thing is that both events were unusual, catching Americans by relative surprise, and raising questions as to whether climate change played a role.

With both cases, the answer has been “maybe.”  Though it may seem contradictory that extreme cold events could be linked to global warming, it’s been shown time and again that bizarre and unpredictable things can happen to the weather when heat accumulates in the atmosphere and ocean.  A warmer atmosphere holds more water vapor, which in turn can make precipitation events — including snow — more extreme.  And some scientists think a warmer ocean can make tropical storms more intense, which can drive big dips in the jet stream.

The latter is why some scientists, like bioanthropologist Greg Laden, think that climate change helped make this year’s Arctic Outbreak more intense.

“We can’t rule out climate change here,” said Laden, who writes for National Geographic’s Scienceblog.  “[Super Typhoon Nuri] was in the top 2 or 3 hurricanes, maybe the top 2 of the year, in terms of overall strength.  That’s because the Pacific has been really warm, creating a lot of extra hurricanes and extra strong hurricanes.”

While no weather event, including hurricanes, can be attributed directly to climate change (it’s really the wrong question — “All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.”), Laden is correct that Nuri was one of the two most intense storms on Earth so far this year.  And Nuri, as Mashable’s Andrew Freedman explains, increased the chance of extreme weather across the U.S.

Read More at What the Arctic Outbreak and Last Year’s ‘Polar Vortex’ Have in Common

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