Arctic ice thinned dramatically since 2004: NASA

By Deborah Zabarenko, Environment Correspondent

WASHINGTON (Reuters) - Arctic sea ice has thinned dramatically since 2004, with the older, thicker ice giving way to a younger, thinner kind that melts in the northern summer, NASA scientists reported on Tuesday.

Researchers have known for years that ice covering in the Arctic Sea has been shrinking in area, but new satellite data that measure the thickness of ice show that the volume of sea ice is declining as well.

That is important because thicker ice is more resilient and can last from summer to summer. Without ice cover, the Arctic Sea's dark waters absorb the sun's heat more readily instead of reflecting it as the light-colored ice does, accelerating the heating effect.

Using NASA's ICESat spacecraft, scientists figured that overall Arctic sea ice thinned about 7 inches a year since 2004, for a total of 2.2 feet over four winters. Their findings were reported in the Journal of Geophysical Research-Oceans.

The total area covered by thicker, older ice that has survived at least one summer shrank by 42 percent.

Beyond that, the new satellite data showed that the proportion of tough old ice is decreasing at the same time as the amount of young fragile ice is increasing, information that was hard to discern from earlier data.

LOSING THE OLD ICE

In 2003, 62 percent of the Arctic's total ice volume was stored in multi-year ice and 38 percent in first-year seasonal ice. By last year, 68 percent was first-year ice and 32 percent the tougher multi-year ice.