By Deborah Zabarenko, Environment Correspondent
WASHINGTON (Reuters) - The thickest, oldest and toughestsea ice around the North Pole is melting, a bad sign for thefuture of the Arctic ice cap, NASA satellite data showed onTuesday.
"Thickness is an indicator of long-term health of sea ice,and that's not looking good at the moment," Walt Meier of theNational Snow and Ice Data Center told reporters in a telephonebriefing.
This adds to the litany of disturbing news about Arctic seaice, which has been retreating over the last three decades,especially last year, when it ebbed to its lowest level.
Scientists have said the trend is spurred byhuman-generated climate change.
Melting Arctic ice does not raise sea levels as the meltingof glaciers on Greenland or Antarctica could, but it doescontribute to global warming when reflective white ice isreplaced by dark water that absorbs the sun's heat.
Using satellites that measure how much ice covers water inthe Arctic and Antarctic, Meier and other climate scientistsfound a steep drop in the amount of perennial ice -- the hardy,thick ice that is over a year old -- in the north.
The oldest Arctic ice that has survived six years or moreis the toughest, and even that shrank dramatically, Meier andthe other scientists said.
OLD ICE "TOUGH AS NAILS"
Some 965,300 square miles (2.5 million sq kms) of perennialice have been lost -- about one and a half times the area ofAlaska -- a 50 percent decrease between February 2007 andFebruary 2008, Meier said.
The oldest "tough as nails" perennial ice has decreased byabout 75 percent this year, losing 579,200 square miles (1.5million sq kms, or about twice the area of Texas, he said.
This doesn't mean the Arctic is open water during thewinter, but it does mean that in many areas, the strongerperennial ice is being replaced by younger, frailer new icethat is more easily disturbed by wind and warm seatemperatures.
"It's like looking at a Hollywood set," Meier said of anArctic largely covered with younger ice. "It may look OK but ifyou could see behind you'd see ... it's just empty. And whatwe're seeing with the ice cover is it's becoming more and moreempty underneath the ice cover."
Perennial ice is also vulnerable to a recurring pattern ofswirling winds and currents known as the Arctic oscillation,which ejects the old ice out of the zone around the pole andaims it south where warmer waters will melt it.
The scientists also analyzed satellite data for Antarcticabut found less dramatic change there.
This was attributed to the difference in the two polarregions. The Arctic is an ocean surrounded by land while theAntarctic is a continent surrounded by ocean.
However, the scientists noted sharp warming on theAntarctic Peninsula, which stretches northward from thesouthern continent toward South America.
