By measuring this distance change, scientists can derive a picture of mass concentrations on the planet's surface. "We were able to do that every 10 days for Greenland," Luthcke notes. "What we see is a massive amount of mass shedding that far outweighs an interior growth."Additional data confirming the observation comes from a second techinque: laser altimetry.
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In perfect agreement with previous results, these new GRACE measurements revealed that the same three glacial systems--including Kangerdlugssuaq, now one of the fastest moving glaciers in the world--are racing to the sea. "The glaciers are accelerating," Zwally says. "We are now losing 20 percent more coming out each year than goes in as snowfall."
This USGS article estimates that, if the complete ice sheet of Greenland melted, global sea levels would rise by about 6.5 meters. (Throw in the entire Antarctic and you get something crazy like 80 meters.) In a fairly quick web search, I wasn't able to find information on the rate at which the study suggests ocean levels will rise, or estimates of the contributions the three glacier systems would make, however.