Illustration courtesy SVS/NASA
Published August 28, 2012, corrected September 10
Arctic sea ice is thawing at a historic rate, scientists say. In fact, a recent analysis of satellite data "utterly obliterates" the previous record, set in 2007.
The chief culprit? Global warming. The potential upshot? Longer and more intense extreme-weather events such as heat waves, cold spells, and droughts. (Read more about extreme weather in National Geographic magazine.)
On Monday, researchers at the U.S. National Snow and Ice Data Center said the rate of Arctic sea ice decline is now the highest that has ever been observed for the month of August. In August of this year, the sea ice disappeared at an average rate of about 35,400 square miles (91,700 square kilometers) per day—or about twice as fast as normal, NSIDC scientists say.
Moreover, the area of Arctic sea ice around the North Pole had shrunk to 1.58 million square miles (4.1 million square kilometers)—the smallest measurement since 1979, when satellite observations began.
By comparison, said NSIDC's Julienne Stroeve, Arctic sea ice cover in the 1970s and '80s at this time of year was typically in excess of 2.7 million square miles (7 million square kilometers).
The worst news of all? The new record probably won't last long. With up to three more weeks of the melting season left, said Stroeve, the total is likely to shrink further.
"It will be below 4 million square kilometers (1.5 million square miles) before it's all said and done."
Sea Ice: Why Is This Year Different?
Scientists think the old record—1.61 million square miles (4.17 million square kilometers) on September 18, 2007—was made possible by a "perfect storm" of conditions that included an unusually persistent weather pattern known as an anticyclone, or high-pressure ridge, in the region that led to clear skies, which allowed more sunlight to reach the ice and melt it.
But weird weather doesn't seem to be a factor this time around.
"There's no persistent weather pattern that's emerged this summer," Stroeve said.
"The ice is just thinner than it used to be. So it doesn't really matter so much what the summer weather does anymore—the thin ice melts out easier during the summer melt season."
In a new study, detailed recently in the journal Geophysical Research Letters, Stroeve and her colleagues analyzed nearly two dozen computer climate models to determine the extent to which global warming is responsible for the increasing shrinkage of Arctic sea ice.
Her team determined that human activity can be blamed for some 60 percent of the observed rate of decline since 1979, with the rest due to natural climate variability.
"If you run these climate models and you don't put in the observed record of greenhouse gases, none of them show the ice declining," Stroeve said. "None of them are able to capture what's happening today without including greenhouse gases." (Learn about the greenhouse effect.)
Climate models used by the Intergovernmental Panel on Climate Change (IPCC) also predict that Arctic summers will be completely free of sea ice in the coming decades if global warming continues unabated.
In light of the new record low, said Jennifer Francis, a climate researcher at Rutgers University's Institute of Marine and Coastal Science, "I'm definitely thinking that we're going to see [ice-free Arctic summers] earlier than most people have suggested.
"I think it could happen anytime within the next 30 years," instead of 50 years or more that some models predict, said Francis, who was not involved in the study.
Sea Ice Loss Fuels Extreme Weather
Even though Arctic sea ice is melting faster than at any point on record, it's not causing global sea levels to rise, Stroeve explained.
That's because the space taken up by the melted sea ice is the same as the original ice cover—a process akin to what happens when ice cubes melt in a glass of water.
But how long will that be the case? Scientists say Arctic sea ice shrinkage may yet play a role in sea-level rise if it causes land glaciers—like those in Greenland—to melt. (Read "The Big Thaw" in National Geographic magazine.)
That could happen because as more sea ice melts, more open water is exposed, which in turn allows water vapor and heat that's been stored in the ocean to enter the atmosphere, where they can contribute to warmer temperatures and storm formation.
And that's not all. According to research by Francis's team, Arctic sea ice reduction can both raise temperatures in the northern hemisphere and influence the "meander," or flow, of atmospheric jet streams, which are like rivers of air that circulate the globe.
Already, said Francis, the Arctic melt has meant that "these meanders in the jet stream are both getting larger and moving more slowly."
Since jet streams generate and steer storms, she added, their slowing meander can prolong fall and winter weather patterns across the entire Northern Hemisphere.
"Many extreme weather events are associated with weather patterns that are stuck or moving very slowly ... including droughts, cold spells, heat waves," Francis said. (See a graphic of extreme-weather trends.)
"I would not be at all surprised to see another unusual winter around the Northern Hemisphere" this year or next.
"Everything is connected," added NSIDC's Stroeve. "Even though [Arctic sea ice melt] is happening thousands of miles away from us, it does impact our weather."
Corrected: The intial version of this story said the rate of Arctic sea ice decline is the highest on record, but this is true for only the month of August. Also, the story said the "sea ice disappeared at an average rate of about 39 square miles (a hundred square kilometers)" in August 2012.
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