New European data indicate this summer’s loss of ice cover matches the 2007 record

By Janet Raloff

Web edition: October 6, 2011

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Ice Monitor

The ice breaker Polarstern — seen here in August — just returned from 16 weeks plying Arctic waters to measure the extent and depth of summer sea ice.

Credit: AWI

On October 4, the National Snow and Ice Data Center posted information on its website indicating that the summer melt of sea ice in the Arctic, this year, approached — but did not quite match — a record set four years ago. A team of European scientists now concludes NSIDC got it wrong. This year's loss was every bit as big.

“I know what NSIDC said,” says Marcel Nicolaus of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. “Nevertheless, we have just found that this year's ice [loss] was very comparable to the extent reported in 2007.”

The sea ice physicist had just returned that morning at daybreak (October 5) from a cruise aboard the research ice breaker Polarstern. Some 130 scientists from six countries participated in parts or all of the ship’s 16-week, 11,800-nautical-mile trek mapping Arctic sea ice. To gauge ice thickness, they collected measurements with a 4-meter-long sensor deployed from a helicopter above the ice and with a remotely piloted mini-sub under the ice. By mapping the sea surface, they were able to observe gaps between floes to gauge how completely ice covered the surface.

Their data now indicate that at its minimum, ice covered 4.3 million square kilometers of the sea surface, says Stefan Hendricks, another Alfred Wegener Institute sea ice physicist. And depth profiles show the ice cover “is exactly as thin as in the record year." Taken together, he says: This summer's sea-ice cover "appears to have melted to exactly the same degree as in 2007."

The good news, Nicolaus says: “We didn’t have — which some of us might have expected — a further thinning of sea ice [beyond the 2007 minimum].”

In the United States, another team of scientists has just completed analyzing 32 years worth of data from satellites and field measurements to build a composite picture of the volume of ice that exists at the end of each summer in the Arctic. Using a computer program, the researchers melded all of those disparate data into meaningful trends.

The analyses now point to a general continuing drop in sea ice throughout the period — losses that on average have been falling by 2,800 cubic kilometers per decade, notes climatologist Axel Schweiger of the University of Washington's Polar Science Center in Seattle. His team's findings appeared online September 27 in the Journal of Geophysical Research.

To Schweiger, identifying a new record minimum is "not exactly of great scientific value." He says "the real story is the decline over the past 30 years in both [ice] extent and thickness."

Still, he acknowledges that people continually ask whether his analyses affirm the 2007 record, "so we tried to answer it." And even using a very conservative estimate of the uncertainties associated with all of the data that were included in his analyses, at least in terms of sea ice volume "we believe that 2010 broke the previous record of 2007."

And this year? His team's preliminary analyses (not a part of the new paper) indicate the "ice volume was lower than in 2010." However, Schweiger cautions, the apparent drop from last year is well within the error bars associated with the computer model. So focus instead, he argues, on that steady and far more reliable long-term trend.