September 17, 2008

Arctic Sea Ice Still Shrinking

U.S. scientists say global warming caused arctic sea ice to melt to its second-lowest level this year, rising slightly from 2007's record but still showing a downward trend.

The National Snow and Ice Data Center said in March, that the thick, older sea ice was continuing to decline.

According to NASA-processed satellite microwave data, this perennial ice used to cover 50-60 percent of the Arctic. Researchers found this winter it covered less than 30 percent.

Temperatures have been lower in the Arctic this year compared to 2007, due to La Nina conditions, which create a colder climate globally from their source in the Pacific.

"I think this summer has been more remarkable than last year, in fact, because last year we had really optimal conditions to melt a lot of ice," said Walt Meier, a research scientist at NSIDC in Boulder, Colorado.

Experts say perennial sea ice is the long-lived layer of ice that remains even when the surrounding short-lived seasonal sea ice melts to its minimum extent during the summer.

The ice slipped to its minimum extent for 2008 on September 12, when it covered 1.74 million square miles (4.52 million square km), and now appears to be growing as the Arctic starts its seasonal cool down,

"We didn't have any of this year, and yet we still came within 10% of the record; so people might be tempted to call it a recovery, but I don't think that's a good term, we're still on a downwards trend towards ice-free Arctic summers," said Meier. 

Last month, the ice center said there was a major ice melt in the Chukchi Sea off the Alaskan coast in the Eastern Siberian Seas off Russia's east coast, home to one of the world's largest polar bear populations.

Polar bears use sea ice platforms for hunting seals, and are forced to swim longer distances when the ice melts, making them more likely to tire and drown.
Experts say arctic ice is a factor in global climate and weather patterns.

Global warming could speed up without the help of sea ice. It helps hold in the cold around the North Pole because its white color reflects sunlight. When sea ice goes away, the newly exposed dark water absorbs more of the sun's rays, accelerating the heating effect.

"In terms of long-term climate, it's not a recovery in any sense of the word," Meier said. "The long-term trend is still steeply downward and getting steeper."

Meier said, the emission of the greenhouse gas carbon dioxide is pushing global climate change, and its effects are amplified in the Arctic.

The last seven years are among the seven lowest on record in terms of Arctic sea ice, according to Meier.

"That's a real indication that this isn't any kind of temporary climate cycle. It's more an indication that we're heading toward the point where we're going to have that sea ice completely melt in the coming decades or perhaps sooner."

The NSIDC team will continue to monitor the ice area and will give a full analysis towards the end of this month.


Image 1: The Advanced Microwave Scanning Radiometer (AMSR-E) is a high-resolution passive microwave Instrument on NASA's Aqua satellite. AMSR-E provides a remarkably clear view of sea ice dynamics in greater detail than has ever been seen before. Researchers use this information to study polar bear habitats, plan expeditions to the ice, and to study the interactions between the ocean and sea ice from season to season. This data visualization shows Arctic sea ice from July 1 to Sept. 10, 2008. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio; Blue Marble Next Generation data courtesy Reto Stockli (NASA/GSFC). View animation

Image 2: Polar ice reflects light from the sun. As this ice begins to melt, less sunlight gets reflected into space. It is instead absorbed into the oceans and land, raising the overall temperature, and fueling further melting. This results in a positive feedback loop called ice albedo feedback, which causes the loss of the sea ice to be self-compounding. The more it disappears, the more likely it is to continue to disappear. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab. View animation


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