What Will Ice-Free Arctic Summers Bring?

On Sunday, September 16, the sun did not rise above the horizon in the Arctic. Nevertheless enough of the sun's heat had poured over the North Pole during the summer months to cause the largest loss of Arctic sea ice cover since satellite records began in the 1970s. The record low 3.41 million square kilometers of ice shattered the previous low—4.17 million square kilometers—set in 2007. All told, since 1979, the Arctic sea ice minimum extent has shrunk by more than 50 percent—and even greater amounts of ice have been lost in the corresponding thinning of the ice, according to the U.S. National Snow and Ice Data Center (NSIDC).

"There is much more open ocean than there used to be," says NSIDC research scientist Walt Meier. "The volume is decreasing even faster than the extent [of surface area] as best as we can tell," based on new satellite measurements and thickness estimates provided by submarines. Once sea ice becomes thin enough, most or all of it may melt in a single summer.

Some ice scientists have begun to think that the Arctic might be ice-free in summer as soon as the end of this decade—leaving darker, heat-absorbing ocean waters to replace the bright white heat-reflecting sea ice. The question is: Then what happens? Although the nature and extent of these rapid changes are not yet fully understood by researchers, the impacts could range from regional weather-pattern changes to global climate feedbacks that exacerbate overall warming. As Meier says: "We expect there will be some effect…but we can't say exactly what the impacts have been or will be in future."

On thin ice

Arctic ice influences atmospheric circulation and, hence, weather and climate. Take away the ice and impacts seem sure to follow. There's more warming to come, as well, particularly in the Arctic, which is warming faster than the rest of the globe. Given cumulative greenhouse gas emissions, there's likely at least as much warming to come as has occurred to date—a rise of 0.8 degree Celsius in global average temperatures, most of that in the past 30 years.

The warmer Arctic waters and land have also begun to release methane, a short-lived but potent greenhouse gas that is also the primary hydrocarbon in natural gas fuel. The Arctic Ocean alone contains more methane than the rest of the world's oceans combined—though when and even if such a thawing would contribute a massive methane release remains a "known unknown" in the words of former Defense Secretary Donald Rumsfeld and oceanographer Wieslaw Maslowski of the Naval Postgraduate School in Monterey. "If we release that methane, we will amplify global warming by an unknown amount," Maslowski says. "We have no idea."

by David Biello, Scientific American |  Read more:

Image: Courtesy of NASA