All the major regions of the polar ice sheets except one have been losing mass since 1992, according to a study that pulls together several independent measurement methods.
All told, mass loss from the polar ice sheets has contributed 11.1 +/- 3.8 millimeters to global sea level since 1992, researchers report in the 30 November issue of the journal Science. This is roughly 20% of the total global sea level rise during that period.
Estimates of change by the ice sheets of Greenland and Antarctica have differed greatly, making it difficult to project future sea level change. Some studies have even disagreed over whether the ice sheets are experiencing an overall mass loss or gain, also known as “mass balance.”
Andrew Shepherd of the University of Leeds in the United Kingdom and colleagues determined the rates of ice loss from the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula. East Antarctica is the only region where the mass balance is increasing, although this increase isn’t enough to compensate for the larger losses in the rest of Antarctica.
“What we can provide is a 20-year record and within that 20-year record there are two important takeaway points,” said co-author Erik Ivins of the Jet Propulsion Laboratory, in a 28 November press teleconference. “Antarctica is losing mass, but it’s not losing as much mass as many of the reports had suggested. Greenland, on the other hand, is losing more mass today than it was in 1990 by a factor of five.”
There have been variations in earlier mass balance estimates, partly because many satellite surveys cover relatively short time periods, and because various satellite methods have different strengths and weaknesses.
To address this, Shepherd and colleagues have now combined datasets produced by three independent, satellite-based methods to construct a more robust ice sheet mass balance for the period between 1992 and 2011. Their study included 47 scientists from 26 key labs involved in past ice sheet studies.
“We used data from 10 different satellite missions that have been in operation over different time periods since 1992,” Shepherd said at the teleconference. “In total, we’ve collected more than 50 overlapping years of satellite observations and these all went into our final assessment.”
After reprocessing the datasets to ensure they were comparing “apples to apples,”—that is, common geographical regions, time intervals, and models of ice sheet behavior—the researchers found that the different methods agreed well and that combining the data sets added certainty to their estimates.
“It’s really critical that these measurements are sustained,” said co-author Ian Joughin of the Polar Science Center’s Applied Physics Lab at the University of Washington. “Several satellites are beginning to fail and all three methods for determining ice sheet mass balance will be negatively affected as satellites fail and it takes time to build new ones.”
The AAAS Board of Directors warned of a “sharply diminished U.S. capacity” in Earth-observing satellites in 2007, recommending that the U.S. Congress reverse budget cuts that threatened the maintenance and replacement of the satellite fleet.
Read the abstract, “A Reconciled Estimate of Ice-Sheet Mass Balance,” by Andrew Shepherd and colleagues.
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Listen to a Science press teleconference about the research.
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