Error Discovered in Antarctic Sea-Ice Record
A misalignment in data between satellites went undetected for years before being addressed

7-22-2014 | Mark Zastrow and Nature magazine

Rising temperatures have caused the amount of Arctic sea ice to shrink dramatically since global observations began in the 1970s. But on the other side of the world, sea ice in Antarctica was at first steady — and then began to slowly expand in the mid-2000s.

Some researchers now say that the Antarctic trend may have been inflated by an error in the decades-long record of satellite observations of Southern Hemisphere sea ice. Scientists process data from microwave-sensing satellites using one of two standard algorithms to distinguish bright sea ice from dark open water.

Researchers led by Ian Eisenman, a climatologist at the Scripps Institution of Oceanography in San Diego, California, discovered a mismatch between an older and a newer version of the same NASA sea-ice data set that occurred when a satellite sensor was replaced in December 1991. Such “jumps” in data are caused by slight differences in the satellites’ sensitivity, and are usually corrected when scientists process the data collected by the probes.

But the error that Eisenman identified — reported July 22 in The Cryosphere — wasn’t obvious. He found it only by comparing an old version of the data set with a 2008 version, and says that the data were too noisy to tell which version had been mishandled.

This article is reproduced with permission and was first published on July 22, 2014

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