Antarctic Sea Ice May Not be Expanding as Much as Previously Thought

Could Antarctic sea ice not be expanding as fast as usual? Scientists have found that much of the increase measured for this sea ice could simply be due to a processing error in satellite data, which could have major implications for climate models.

While the Arctic sea ice is retreating at a rapid pace, the sea ice in the Antarctic is doing just the opposite. In fact, satellite observations seem to show that this ice is expanding at a moderate rate and that its extent has reached record highs in recent years. This phenomenon has puzzled scientists but now, it seems like the expansion may not be nearly as dramatic as once thought.

The AR4, which is the 2007 assessment report from the Intergovernmental Panel on Climate Change, reported that Antarctic sea ice remained more or less constant between 1979 and 2005. In contrast, the AR5, which is the report from 2013, seemed to show that between 1979 and 2012, the ice increased at a rate of about 16.5 thousand square kilometers per year. At first, scientists assumed this difference was due to adding several more years of data to the observational record. Yet they soon realized that the time series didn't quite fit.

The researchers re-examined the datasets and found a difference between the two related to a transition in satellite sensors in December 1991. In addition they found a difference in the way the data collected by the two instruments was calibrated.

"It appears that one of the records did this calibration incorrectly, introducing a step-like change in December 1991 that was big enough to have a large effect on the long-term trend," said Ian Eisenman, one of the researchers, in a news release. "You'd think it would be easy to see which record has this spurious jump in December 1991, but there's so much natural variability in the record-so much 'noise' from one month to the next-that it's not readily apparent which record contains the jump. When we subtract one record from the other, though, we remove most of this noise, and the step-like change in December 1991 becomes very clear."

The findings reveal that this error could actually explain why Antarctic sea ice appears to be expanding so much. While some expansion is happening, it's probably not occurring at the rate that data seems to indicate.

The findings are published in the journal The Cryosphere.