Reference Velicogna, I. and Wahr, J. 2006. Measurements of time-variable gravity show mass loss in Antarctica. Sciencexpress: 10.1126science.1123785. What was done Using measurements of time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) satellites, the authors determined mass variations of the Antarctic ice sheet for the 34 months between April 2002 and August 2005. What was learned Velicogna and Wahr concluded that "the ice sheet mass decreased significantly, at a rate of 152 ± 80 km3/year of ice, equivalent to 0.4 ± 0.2 mm/year of global sea level rise," all of which mass loss came from the West Antarctic Ice Sheet, since they calculated that the East Antarctic Ice Sheet mass balance was 0 ± 56 km3/year. What it means What these results imply about the real world is highly dependent upon their ability to truly represent what they presume to describe; and in this regard Velicogna and Wahr say there is "geophysical contamination ... caused by signals outside Antarctica," including "continental hydrology ... and ocean mass variability." The first of these confounding factors, according to them, "is estimated [our italics] using monthly, global water storage fields from the Global Land Data Assimilation system," while "the ocean contamination is estimated [our italics] using a JPL version of the Estimating Circulation and Climate of the Ocean (ECCO) general circulation model [our italics]." In addition to these problems, the two researchers note that the GRACE mass solutions "do not reveal whether a gravity variation over Antarctica is caused by a change in snow and ice on the surface, a change in atmospheric mass above Antarctica, or post-glacial rebound (PGR: the viscoelastic response of the solid Earth to glacial unloading over the last several thousand years)." To adjust for the confounding effect of the variable atmospheric mass above Antarctica, Velicogna and Wahr utilize European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological fields, but they acknowledge that "there are errors in those fields," so they "estimate [our italics] the secular component of those errors by finding monthly differences between meteorological fields from ECMWF and from the National Centers for Environmental Prediction."