New research suggests past predictions have overestimated the rate of Antarctic sea ice expansion. The error could be due to a processing error in satellite data.
Arctic sea ice is dramatically receding while satellite observations have suggested Antarctic ice is expanding and has even reached record highs, the European Geosciences Union reported. Researchers haven't been able to figure out what is causing ice in the Southern Hemisphere to expand as global temperatures rise.
"This implies that the Antarctic sea ice trends reported in the IPCC's AR4 and AR5 [the 2007 and 2013 assessment reports from the Intergovernmental Panel on Climate Change] can't both be correct: our findings show that the data used in one of the reports contains a significant error. But we have not yet been able to identify which one contains the error," said lead-author Ian Eisenman of the Scripps Institution of Oceanography at University of California San Diego.
Scientific literature from the time and the AR4 showed between the years of 1979 and 2005 sea ice cover remained relatively constant; but the AR5 and other current literature has suggested it actually expanded at a rate of 16.5 thousand square kilometers between 1979 and 2012. At first the scientists thought the change was a result of the added years.
"But when we looked at how the numbers reported for the trend had changed, and we looked at the time series of Antarctic sea ice extent, it didn't look right," Eisenman said.
Data used to measure sea ice comes from observations from multiple instruments. Researchers use an algorithm (usually the Bootstrap algorithm) to process estimates consistent with this data. To make their findings researchers compared two datasets for sea ice measurements and found the difference may be related to a transition in satellite sensors and the way the data 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 influence on the long-term trend," Eisenman said.
"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," he explained.
The study was published in the The Cryosphere.
