Of all the projected nightmare scenario effects of global warming, one has seized my imagination like no other. I cannot erase the image of a lone polar bear standing on an island of ice barely bigger that it is, floating alone in the Arctic Sea. Drifting toward certain death by starvation or drowning.
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.
"To some extent it's a runaway effect. The question is how far will it run?" said the study's lead author, Hamish Pritchard of the British Antarctic Survey. "It's more widespread than we previously thought."