Opinion Scientists using a network of ground sensors emplaced in Antarctica say that NASA satellites have overestimated the amount of ice that is melting and running off into the ocean from the polar continent.

The new results come from the West Antarctic GPS Network (WAGN), which uses 18 locator stations "bolted to bedrock outcrops" in the Western antarctic to discover "ground truth" regarding the phenomenon of "postglacial rebound", where the bedrock lifts as the mile-thick ice sheet atop it diminishes.

Postglacial rebound is important, as NASA's Gravity Recovery and Climate Experiment (GRACE) satellites estimate ice loss by measuring regional gravitational forces as they fly overhead. Both ice loss and bedrock rebound contribute to GRACE grav-scan readings, and according to the WAGN measurements, rebound figures used to estimate ice loss have now been shown to be wrong.

"The take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear," says Ian Dalziel, lead investigator for WAGN.

The WAGN boffins say they are sure that recent figures for ice loss calculated from GRACE readings have been overestimated, but they are not yet sure by how much. However, they say that there is no dispute about the fact that ice is disappearing from the antarctic sheet - this process has been underway for 20,000 years, since the thickness peaked during the last "glacial maximum".

"The published results are very important because they provide precise, ground-truth GPS observations of the actual rebound of the continent," said Vladimir Papitashvili of the Antarctic Earth Sciences Program at the National Science Foundation, which supported the research.

The results are given in the paper Geodetic Measurements of Vertical Crustal Velocity in West Antarctica and the Implications for Ice Mass Balance, published here in the journal Geochemistry, Geophysics, Geosystems (subscriber link). There's also some layman-level exposition from Texas uni here. ®