From: Bloomberg
Published February 24, 2009 10:06 AM

Arctic Sea Ice Underestimated for Weeks Due to Faulty Sensor

A glitch in satellite sensors caused scientists to underestimate the extent of Arctic sea ice by 500,000 square kilometers (193,000 square miles), a California- size area, the U.S. National Snow and Ice Data Center said.

The error, due to a problem called “sensor drift,” began in early January and caused a slowly growing underestimation of sea ice extent until mid-February. That’s when “puzzled readers” alerted the NSIDC about data showing ice-covered areas as stretches of open ocean, the Boulder, Colorado-based groupsaid on its Web site.

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“Sensor drift, although infrequent, does occasionally occur and it is one of the things that we account for during quality- control measures prior to archiving the data,” the center said. “Although we believe that data prior to early January are reliable, we will conduct a full quality check.’’

The extent of Arctic sea ice is seen as a key measure of how rising temperatures are affecting the Earth. The cap retreated in 2007 to its lowest extent ever and last year posted its second- lowest annual minimum at the end of the yearly melt season. The recent error doesn’t change findings that Arctic ice is retreating, the NSIDC said.

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