The Antarctic ice sheet is losing mass, according to scientists using data from a pair of satellites orbiting the globe. This is the first time scientists have been able to survey the entire ice blanket. The study confirms prior studies that the sheet is melting.

Ross Ice Shelf in Antarctica (2000 file photo)

The Antarctic ice sheet is responsible for 90 percent of the world's ice. Studies over the past several years have showed that the sheet is losing mass, causing a rise in global sea surface levels.

But the conclusions have been reached based on snapshots of parts of the ice blanket, such as its thinning edges.

"But you know now what's going on which I think is pretty good," said Isabella Velicogna, who is with the University of Colorado's Cooperative Institute for Research and Environmental Sciences and lead scientist on the GRACE project, which stands for Gravity Recovery and Climate Experiment.

Launched by the U.S. space agency NASA and Germany in 2002, GRACE employs two satellites that circle the globe 16 times a day, sensing subtle changes in earth's mass and gravitational field.

Gravity Recovery and Climate Experiment satellite (GRACE)

The satellites orbit 220 kilometers apart. As one satellite passes over an irregular mass on the ice sheet, it emits a slightly increased gravitational pull that slows it down slightly, and the deceleration is recorded by the other satellite.

After many passes back and forth, a picture begins to emerge, according to Velicogna.

"As it turns out if you can measure changes in distance between the two satellites, you can get information about what's underneath and what's causing those changes," she said. "And you can get information when you fly over the ice sheet about the mass change of the ice sheet."

In a paper published in the current issue of Science, Veliconga and co-author John Wahr, also of the University of Colorado, report the ice blanket appears to be losing mass at an annual rate of 152 cubic kilometers.

That confirms estimates from earlier studies. At that rate, Veliconga says, global sea surface levels will rise an average of 0.4 millimeters per year.

The University of Colorado's Isabella Veliconga says no one knows for certain whether the ice sheet will continue to shrink and contribute to a rise in ocean levels.

But she says that scientists now have a more comprehensive way to monitor it.

"If we will be able to have projections for sea level change that will help from a sociological point of view, and it would help our everyday life, maybe not our immediate life but our kids, and the kids of our kids," she said. "So, it's very exciting to be part of this."