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Arctic Meltdown

polar bear in Arctic ice cap for jerry bowen piece on global warming
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The year-round ice in the Arctic Sea could be gone by the end of the century, say National Aeronautics and Space Administration scientists.

A NASA study finds that perennial sea ice in the Arctic is melting faster than previously thought, at a rate of 9 percent per decade. At that rate, the Arctic's "perennial sea ice" could disappear in a few more decades.

Perennial sea ice floats in the polar oceans and remains at the end of the summer, when the ice cover is at its minimum and seasonal sea ice has melted. On average, this year-round ice is just under 10 feet thick, but can be as much as 23 feet in depth.

The study also finds that temperatures in the Arctic are increasing at the rate of 2.2 degrees Fahrenheit per decade.

Melting sea ice would not affect sea levels, but it could profoundly impact summer shipping lanes, plankton blooms, ocean circulation systems, and global climate, NASA said.

"If the perennial ice cover, which consists mainly of thick multi-year ice floes, disappears, the entire Arctic Ocean climate and ecology would become very different," said Josefino Comiso, a researcher at NASA's Goddard Space Flight Center, Greenbelt, Md., who wrote the study.

Comiso used satellite data to track trends from 1978 to 2000. Before satellite data, most records came from sparsely located ocean buoys, weather stations, and research vessels.

Comparing the differences between Arctic sea ice data from 1979 to 1989 and data from 1990 to 2000, Comiso found the biggest melting occurred in the western area (Beaufort and Chukchi Seas) while considerable losses were also apparent in the eastern region (Siberian, Laptev and Kara Seas). Also, perennial ice actually advanced in relatively small areas near Greenland.

In the short term, reduced ice cover would open shipping lanes through the Arctic. Also, massive melts could increase biological productivity, since melt water floats and provides a stable layer conducive to plankton blooms.

But it would be just the arctic climate that would be affected. Summer sea ice reflects sunlight out to space, cooling the planet's surface, and warming the atmosphere.

As polar ice caps melt, less sunlight gets reflected into space. It is instead absorbed into the oceans and land, raising the overall temperature, and fueling further melting.

Although not included in the study, Comiso also analyzed more recent data and discovered that this year's perennial ice cover is the least extensive observed during the satellite era.

The study appears in the late October issue of Geophysical Research Letters, and was funded by NASA's Cryospheric Sciences Program and the NASA Earth Science Enterprise/Earth Observing System Project.

The mission of NASA's Earth Science Enterprise is to develop a scientific understanding of the Earth System and its response to natural or human-induced changes to enable improved prediction capability for climate, weather and natural hazards.