Greenland Provides Clues To Tipping Point In Arctic Meltdown

From the June 9, 2007 Washington Post:

In Arctic Ice, Lessons on Effects of Warming
Researchers Drill, Map, Blast In Greenland in Hunt for Clues

If Manhattan floods, it may start here, on an ice field that
stretches in frozen silence to every horizon.

Global warming is working away at the Greenland ice cap. The frozen
interior of the Arctic island is shedding ice much faster than simple melting
should explain...

As ice on glaciers moves over rock, it snags and lurches. That creates
"icequakes" measurable in the same way as earthquakes. In 1993, there were seven such quakes in Greenland. In 2005, as the ice accelerated, there were 32.

"For a long time it was thought that a change of climate could affect
the ice sheets very slowly," said Meredith Nettles, a scientist from
Lamont-Doherty Earth Observatory at Columbia University, who monitors a large glacier in eastern Greenland. "Now we believe the Greenland ice can respond to changes in climate much more quickly than anyone thought."

In geologic terms, "quickly" still means decades or centuries. But some scientists say the Earth is approaching a point when the process cannot be stopped. Only in recent years did scientists conclude that sea levels are rising twice as fast as they had estimated, said H. Jay Zwally, a senior research scientist from NASA's Goddard Space Flight Center in Greenbelt, Md.

"We are seeing things taking place in the ice now that weren't expected, that five years ago we didn't even know about," said Zwally, who will spend his 14th summer on the Greenland ice cap this year. "I think eventually Greenland will reach a point that the change is irreversible in the current climate."