Shrinking Arctic Ice Could Produce a Wayward Winter

By Lauren Morello, E&E reporter
9/13/2012 10:03:37 AM

This year's record-breaking thaw of Arctic sea ice could spell weird winter weather throughout the Northern Hemisphere.

Arctic glacier. Photo courtesy of Polar Cruises

Several recent studies suggest that the long-term decline of sea ice has had far-reaching effects on atmospheric circulation, altering the behavior of the jet stream and with it weather hundreds and thousands of miles away from polar ice.

Researchers suspect that Arctic warming intensified by sea ice's shrinking footprint had a hand in unusual weather over the past few years, including the powerful snowstorms that buried the U.S. East Coast in 2009-2010 and 2010-2011.

The key is the shrinking difference between temperatures in the Arctic -- which is warming twice as fast as the global average -- and areas farther south, said Jennifer Francis, a climate scientist at Rutgers University.

"The stronger the temperature difference between the Arctic and the mid-latitudes, the stronger the jet stream tends to be," she said. "As we warm the Arctic faster than areas to the south, the temperature difference gets weaker and the jet stream is weakening in the west-to-east direction."

The fast-flowing river of air also becomes wavier, as north-south wiggles within the jet stream become larger. The end result, Francis said, is that weather patterns "stick around longer."

Beware of 'polar amplification'

"Think back to the previous two winters before this past one on the East Coast of the U.S.," she said. "We had cold, snowy winters that occurred because of a dip in the jet stream right over the East Coast that wouldn't leave."

A similar bulge in the jet stream -- pointed in the opposite direction -- produced the unseasonably warm, dry East Coast winter last year.

Researchers believe sea ice plays a central role in the conditions that are reshaping the jet stream, contributing to a powerful feedback loop scientists call "polar amplification."

Warmer Arctic springs and summers increase the amount of ice that melts each summer, replacing highly reflective ice with huge swaths of dark ocean that trap heat. That warmth cycles back into the atmosphere each fall, when the amount of sunlight dips and sea ice re-forms.

And it is that vicious cycle of Arctic warming that is reducing the temperature difference between the Arctic and the middle latitudes of the Northern Hemisphere, the shift that scientists believe is altering the jet stream and spurring more extreme weather.

"It's a bit of a paradox," said James Overland, an oceanographer with the National Oceanic and Atmospheric Administration. "It's one thing to think of global warming as a small amount of warming everywhere, but because of the rotation of the Earth, we get these changes in wind patterns that affect extreme weather, both snowstorms and droughts at mid-latitudes."

How low will it go?

But predicting what will happen this year, in the wake of this summer's historic Arctic thaw, is difficult, researchers said.

Arctic sea ice extent now stands well under 4 million square kilometers, roughly 20 percent below the previous record low set in September 2007 (ClimateWire, Sept. 4).

Sea ice experts are watching the ice closely for signs of the annual minimum that normally occurs in mid- to late September, waiting to see just how low sea ice extent will go this year.

"Given the amazing loss of ice this year and energy that is going to have to be released into the atmosphere as the ocean cools and the ice reforms, I can only say I expect it will be a very interesting winter," Francis said.

"But it's pretty tough to pinpoint who's going to be in the snowy, cold place and who's going to be the mild winter," he added.

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500. E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.

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