Using radar altimeter data from ESA's ERS-1 and ERS-2, Jay Zwally, a scientist at NASA's Goddard Space Flight Center, and his colleagues mapped the height of the ice sheets and found there was a net loss of ice from the combined sheets between 1992 and 2002 and a corresponding rise in sea level.
Polar ice plays a crucial role in regulating global climate because it reflects about 80 percent of the incoming sunlight. If the ice caps over the polar ocean melt, the ocean water would absorb a large part of the radiation energy, which would lead to further melting of the ice and further warming of the climate.
According to the NASA study, published in the March edition, 20 billion net tonnes of water are added to oceans each year as a result of Greenland's ice sheet gaining some 11 billion tonnes of water annually, while Antarctica loses about 31 billion tonnes per year.
The study found that Antarctica lost much more ice to the sea than it gained from snowfall, resulting in an increase in sea level, while the Greenland ice sheet gained more ice from snowfall at high altitudes than it lost from melting ice along its coast.
A recent study by Eric Rignot of NASA's Jet Propulsion Laboratory and University of Kansas scientist Pannir Kanagaratnam, published in Science in February, showed Greenland glaciers are melting into the sea twice as fast as previously believed.
Using satellite data collected between 1996 and 2005 by ESA's remote sensing satellites ERS-1 and ERS-2, ESA's Envisat and Canada's Radarsat-1, they found Greenland's southern glaciers are now dumping twice as much ice yearly into the Atlantic as they did in 1996, accounting for nearly 17 percent of the estimated 2.54 millimetre annual rise in global sea levels.'"/>