The Gravity Satellite -The Global-Warming Watchdog

The twin satellite's of the NASA and the German Space Agency collaboration on the Gravity Recovery and Climate Experiment (GRACE) now completing its fifth year, are doing far more than measuring the attractive pull of Earth on objects.

Orbiting 310 miles above Earth, GRACE's precise measurements of mountain peaks and ocean depths, of underground watersheds and other hidden concentrations of mass offer a new understanding of changes in Earth's natural systems.

The tandem satellites take advantage of Newton's law that objects receive a stronger gravitational tug from more massive objects. The satellites sense the slightest changes in gravitational pull from different planetary features, including craters deep below the Antarctic ice or the seafloor displacement that activated the Indian Ocean tsunami of 2004.

When warmer conditions melt Alaskan glaciers or major water shifts occur elsewhere, the water change registers as a minute, gravity related change in the distance between the tandem GRACE satellites.

Since March 2002 scientists have used the GRACE satellite's sensitivity to detect everything from the climate-related melting of Greenland's ice sheet, to water storage changes in the Amazon river basin.

GRACE's discoveries include findings of ice loss in Greenland. In other instances, relatively small features have been the focus, such as the depletion of groundwater in India, likely at the hands of farmers, and altered water storage caused by China's Three Gorges Dam.

Michael Watkins, the GRACE Project Scientist at NASA's Jet Propulsion Laboratory, noted that even subtle changes, such as in oceans' circulation, are beginning to be monitored with GRACE along with water distribution changes at polar caps, river basins and elsewhere. "These small changes in ocean mass are almost impossible to detect from space with any technique but GRACE," the University of Texas at Austin alumnus said.

Researchers have used GRACE to confirm that a change in water current direction on the Arctic Ocean floor affects other oceans. The findings have matched those obtained from hundreds of bottom-pressure gauges installed by extensive drilling through ice.

GRACE data and data from other satellites have helped identify global warming-related sea level rises in the Antarctic and elsewhere. Dr. John Ries, another senior researcher with Bettadpur at the Center for Space Research, said, "It's important to understand what those sea levels will be in the future without having to put instruments throughout oceans."

Posted by Casey Kazan.