NASA data: Greenland, Antarctic ice melt worsening (Seth Borenstein)

This April 2003 handout photo provided by the British Antarctic Survey shows a glacier meeting the ocean at Marguerite Bay, Antarctic Peninsula. New satellite data shows that ice sheets in Greenland and western Antarctica continue to thin faster than scientists thought and in some places are already in runaway melt mode. (AP Photo/British Antarctic Survey, Chris Gilbert)

Sept. 23, 2009 -- WASHINGTON (AP) -- New satellite information shows that ice sheets in Greenland and western Antarctica continue to shrink faster than scientists thought and in some places are already in runaway melt mode.

British scientists for the first time calculated changes in the height of the vulnerable but massive ice sheets and found them especially worse at their edges. That's where warmer water eats away from below. In some parts of Antarctica, ice sheets have been losing 30 feet a year in thickness since 2003, according to a paper published online Thursday in the journal Nature.

Some of those areas are about a mile thick, so they've still got plenty of ice to burn through. But the drop in thickness is speeding up. In parts of Antarctica, the yearly rate of thinning from 2003 to 2007 is 50 percent higher than it was from 1995 to 2003.

These new measurements, based on 50 million laser readings from a NASA satellite, confirm what some of the more pessimistic scientists thought: The melting along the crucial edges of the two major ice sheets is accelerating and is in a self-feeding loop. The more the ice melts, the more water surrounds and eats away at the remaining ice.