DENVER -- Arctic sea ice is melting into the record books-again.

With several weeks left in the 2008 summer melt season, the extent of sea ice in the Arctic is now less than in 2005.

That means Arctic sea ice is now at the second-lowest extent recorded since the advent of satellites, according to the National Snow and Ice Data Center (NSIDC), located in Boulder.

While polar ice always melts during the summer and refreezes during the winter, significant summertime melt has been a trend in the Arctic during the past decade.

2007 shattered the previous record ice melt that had been established during the summer of 2005.

The fabled Northwest Passage was ice-free for the first time in memory during the summer of 2007, opening that portion of the Arctic for freight transportation and tourism.

Unlike the summer of 2005, when the decline in ice began to slow during August, the ice continues melting at a steady and brisk rate this summer. As of August 27, the extent of sea ice is down to 2.03 million square miles, of which 795,000 square miles have melted since the beginning of August.

Will the 2007 record fall as well? According to NSIDC scientist Walt Meier, it's going to be a photo-finish.

"It's not speeding up, but it's not slowing down, either. If it keeps going at this pace, most certainly," Meier said, "think of Michael Phelps and his photo-finish win at the Olympics. It's going to be pretty close."

The rapidly melting ice is an ominous sign for the future.

According to Meier, the Arctic could be ice-free during the summer by 2020. More extreme estimates suggests it could happen within the next five to 10 years.

"It could be sooner, it might be later. One year doesn't change the long-term trend," Meier said.

"It also means that climate warming is also coming larger and faster than the models are predicting, and nobody's really taken into account that change yet," NASA scientist Jay Zwally said.

Last year was an unusual year when wind currents and other weather conditions coincided with global warming to worsen sea ice melt, said NSIDC senior scientist Mark Serreze. Scientists wondered if last year's melt was an unusual event or the start of a new and disturbing trend.

This year's results suggest the latter because the ice had recovered a bit more than usual thanks to a somewhat cooler winter, Serreze said. Then this month, when the melting rate usually slows, it sped up, he said.

And the melt in sea ice has kicked in another effect, long predicted, called "Arctic amplification," Serreze said. That's when the warming up north is increased in a feedback mechanism and the effects spill southward starting in autumn, he said. Over the last few years, the bigger melt has meant more warm water that releases more heat into the air during fall cooling, making the atmosphere warmer than normal.