Anchorage Daily News

Arctic sea ice has melted back farther this year than in 25 years of satellite monitoring, marking the fourth consecutive summer with "a stunning reduction" in the polar pack north of Alaska, Asia and Europe, according to scientists at the National Snow and Ice Data Center and NASA.

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Combined with record or near record declines since 2002, the ice appears to be slipping into a long-term meltdown that may be slowly accelerating as the summer sun pumps more and more heat into the green-dark surface of the sea.

If the sea ice continues to shrink at the same rate, the summertime Arctic could be completely ice-free well before the end of this century, the scientists said.

While many factors contribute to the ice loss -- warm water creeping north from the Bering Sea and Atlantic Ocean, changes in air circulation, thinning floes that don't rebound in winter -- overall warming across the Arctic appears to be a growing influence.

"The sea ice cover seems to be rapidly changing and the best explanation for this is rising temperatures," said climate researcher Mark Serezze, a senior scientist at the snow and ice center. "My view is it's getting increasingly difficult to argue against the notion that what we're seeing is a greenhouse gas effect taking hold."

Shrinking ice may be the most dramatic consequence of widespread climate change in the Arctic that includes melting glaciers and disintegrating permafrost. The loss of ice could disrupt Native subsistence life, expose coastal communities to devastating storms and erosion, and threaten the existence of marine mammals like polar bears. Until recent years, the ice melted in summer then rebounded during the long, dark Arctic winter. But during the past four seasons, something has changed.

The refreezing of ice during the 2004-05 winter season produced the smallest recovery ever measured by satellites, with nine of the past 10 months setting new records for low ice cover, the scientists said.

During the five days centered on Sept. 21 -- the general period when sea ice reaches an annual minimum and starts refreezing -- the ice pack covered only 2.05 million acres. That left hundreds of miles of mostly open water off northwest Alaska and Far Eastern Russia and appeared to beat the previous record of open Arctic water set in 2002. The pack also is smaller than previous low-ice periods of the 1930s and 1940s, the scientists said in their release.

Comparing the average extent of September coverage since 1979 to last week's observations, it's as though an area the size of Texas had melted away.

"Considering the record low amounts of sea ice this year leading up to the month of September, 2005 will almost certainly surpass 2002 as the lowest amount of ice cover in more than a century," said Julienne Stroeve, a scientist at the data center, in a statement.

The trend has been moving faster. Between 1979 and 2001, sea ice cover retreated 6.5 percent per decade. By this summer, the rate had leapt to about 8 percent.

"That means, come autumn and winter, it's harder to grow sea ice back in again," Serreze said. "It's not that you had one really low year. It's four in a row now. At least part of what we're seeing is a greenhouse gas signal, and it's starting to kick in."

The results are consistent with predictions made last year by the Arctic Climate Impact Assessment and match what scientists would expect from more water soaking up ever more solar heat instead of white ice and snow reflecting it back, several Alaska researchers said.

"Basically, you're dimming down the Arctic," said ice researcher Hajo Eicken, an associate professor of geophysics at the University of Alaska Fairbanks Geophysical Institute. "If you remove that ice, then you start heating the water by as much as a factor of 10 or more. And, as a result, you expect that the ice doesn't fully recover and it just keeps inching back."

"You don't have to be a rocket scientist to interpret this picture," said Lawson Brigham, Alaska office director for the U.S. Arctic Research Commission in Anchorage and a former captain of a U.S. Coast Guard icebreaker. "With the sunlight for 24 hours in the summer and all that dark (ocean) area, it's just like you painted your house a dark color. It's going to warm it even more."

One mystery in the situation is that researchers don't have a good way to measure the total volume of ice in the Arctic, what Serreze called the "Holy Grail" of sea ice science. But a clear harbinger of thinning ice occurred this season, when a record nine ships reached the North Pole, including the first vessel that was not specifically an icebreaker, said Brigham, who in 1994 captained the first U.S. icebreaker across the pole from the Bering to the Atlantic.

This summer, the passage along the Arctic coast of Russia between Europe and the Bering Strait remained ice free between Aug. 15 and Sept. 28, the scientists said. The Northwest Passage through Canada, the fabled route of Arctic lore, opened up except for one 60-mile-long stretch.

Though shrinking ice might sound like an immediate boon to transportation, actual conditions could become more complex and difficult, Eicken said. Ice floes can blow into open areas fast, making navigation especially treacherous.

"You can't say, you can just take a whole bunch of barges up there and you'll never see sea ice," he said. "That ice may move a heck of a lot faster than it would have before, and it may be present throughout the summer."

Still, of the 61 ships to ever visit the North Pole, 17 traveled there in the past two years, Brigham said. Two of the seven ships ever to cross the ice pack from ocean to ocean made the transit in 2005.

"The numbers aren't huge, but I think that one can correlate the retreating sea ice and changing ice conditions with the increasing number of ships," Brigham said. "So, here at the beginning of the century, I would say you can, if you've got the right kind of boat, routinely go to the North Pole. Pretty amazing, huh?"

Daily News reporter Doug O'Harra can be reached at do'harra@adn.com.