Arctic Ice Got Smaller, Thinner, Younger This Winter
for National Geographic News
|April 6, 2009|
Turns out there is such a thing as being too young and too thin.
Arctic ice continued its decline this winter, with hardy, thicker old ice increasingly being replaced with quick-to-melt, thinner young ice, according to a new report by NASA and the National Snow and Ice Data Center.
This winter's maximum Arctic sea ice extent was 5.85 million square miles (15,150,000 square kilometers)—about 278,000 square miles (720,000 square kilometers) less than the Arctic average between 1979 and 2000.
"That's a loss about the size of the state of Texas," said Walter Meier of the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.
"We used to have a winter ice maximum about twice the size of the lower 48 United States," Meier added.
This year's ice cover was not a record low, but it did continue a dubious streak. The past six years (2004-09) have seen the least Arctic ice at the time of maximum cover, in winter, since satellite records began in 1979.
Young and Thin
Ice a year or more old—thicker, hardier, and less prone to melting than younger ice—was at an all-time low at the end of this past winter, the new report says.
Ice older than two years once accounted for some 30 to 40 percent of the Arctic's wintertime cover and made up 25 percent as recently as 2007.
But last year it represented only 14 percent of the maximum. This year the figure fell to 10 percent.
The team did report one ray of hope. In winter 2008-09, more new ice (in this case from winter 2007-08) had survived the summer than in years past.
"From a record low last year of 5 percent or less [it was] back where it used to be, in the 10 to 15 percent range," Meier explained.
But he remains skeptical that enough of the younger ice could survive coming summers to make up for losses of older ice.
"This is not something that can be done in a couple of cold winters. We're way below where we used to be, and it would take many years to get back to where we were in the 1980s."
(Also see "Arctic Ice Isn't Refreezing in the Winter, Satellites Show.")
The Arctic's ice holds enough water to fill both Lake Michigan and Lake Superior. But since the ice floats atop ocean waters, its loss would not directly raise sea levels.
Even so, vanishing sea ice poses severe hardships to Arctic plants and animals—including humans—that have evolved to coexist with the ice.
The great Arctic melt may also worsen global warming.
In summertime Arctic ice reflects sunlight back into space. When the ice melts, newly exposed, dark ocean waters absorb that heat, with unpredictable consequences for wind and ocean circulatory systems worldwide.
The New Normal?
The new data are not surprising, said Sheldon Drobot of the National Center for Atmospheric Research in Boulder, Colorado.
"It's almost like the new normal is a time frame where we're setting records or near-records every year," said Drobot, who was not involved in the research.
Comprehensive Arctic satellite data stretches back some three decades, though some regions near Alaska and Siberia have been otherwise closely monitored since the 1950s.
Data from the rest of the 20th century, and previous centuries, are far less comprehensive. But scientists do have reports of ice cover from shipping records and other historic documents.
"It's been a long time since we've seen so much open water," said Ron Lindsay of the University of Washington's Polar Science Center.
"It really is unprecedented, what we've been seeing, for centuries and maybe thousands of years."
The new study comes on the heels of a report released last week by the U.S. National Oceanic and Atmospheric Administration (NOAA) and the Joint Institute for the Study of Atmosphere and Ocean.
That study used computer modeling and ice-level decline data to predict that most of the Arctic's summer ice could be gone in 30 years.
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