May 07, 2007
Monday PM

ANCHORAGE, Alaska -- Imagine three-fourths of the land mass of Alaska disappearing in a decade. That's roughly the amount of sea ice that has vanished from the Arctic ice cap in recent years - and now it's melting faster.

So say two new reports from ice experts last week that climate-change scientists consider troubling, since sea ice keeps the Earth cool. An ice-free ocean warms it up.

One report noted there was less Arctic sea ice in April than had ever been recorded that month since satellite imagery of the northern ocean began in 1979. Another found that the melting of the Arctic ice cap is proceeding faster than anyone expected.

That second finding - announced jointly by scientists at the National Snow and Ice Data Center and the National Center for Atmospheric Research - concludes that all the summer Arctic sea ice should disappear "about 30 years" sooner than mainstream climate models earlier predicted.

The Intergovernmental Panel on Climate Change, widely regarded as the gold standard for such projections, had estimated that summer sea ice in the Arctic probably declined at a rate of 2.5 percent a decade from 1953 to 2006. At that rate, the IPCC said, the summer ice cap would disappear sometime between 2050 and next century.

That estimate reflected the average of 18 separate IPCC climate scenarios, the most pessimistic of which placed the rate of ice shrinkage at 5.4 percent a decade.

But newly available data, "blending early aircraft and ship reports with more recent satellite measurements," show that the September ice actually declined at a rate of about 7.8 percent per decade from 1953 to 2006, the ice data center reported in a press statement.

"Because of this disparity, the shrinking of summertime ice is about 30 years ahead of the climate model projections," said NSIDC scientist and co-author Ted Scambos.

That means the summer ice cap could disappear earlier than 2050. If it does, scientists say, the Earth will begin warming much more rapidly - as the Arctic Ocean begins to soak up all of the sun's rays without the protective shield of the ice cap to bounce them back into space.

In Alaska, polar bears would lose the summer ice floes they depend upon to hunt for seals. Instead, they'd have to find food on the mainland. But that might be the least of the Earth's ills. If a rapidly warming climate causes major portions of Greenland or Antarctica to melt, the rising sea level would drown low-lying seaports and communities all around the world. Portions of Manhattan and the coast of Florida would disappear.

Drastic sounding scenarios such as those grew only more credible last week as scientists who measure the Arctic ice reported a new low for the month of April. Satellite imagery that can peer through clouds found only 13.9 million square kilometers of ice. By comparison, the long-term average April ice pack (measured from 1979 to 2000) is about 15 million square kilometers. The difference between that and this April - 1.1 million square kilometers - represents the loss of an area of ice more than 1 1/2 times the size of Texas. Or three-fourths the area of Alaska.

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