WASHINGTON - More ominous signs Wednesday have scientists saying that a global warming "tipping point" in the Arctic seems to be happening before their eyes: Sea ice in the Arctic Ocean is at its second lowest level in about 30 years.

The National Snow and Ice Data Center reported that sea ice in the Arctic now covers about 2.03 million square miles. The lowest point since satellite measurements began in 1979 was 1.65 million square miles set last September.

With about three weeks left in the Arctic summer, this year could wind up breaking that record, scientists said.

Arctic ice always melts in summer and refreezes in winter. But over the years, more of the ice is lost to the sea with less of it recovered in winter. While ice reflects the sun's heat, the open ocean absorbs more heat, and the melting accelerates warming in other parts of the world.

Sea ice also serves as primary habitat for threatened polar bears.

"We could very well be in that quick slide downward in terms of passing a tipping point," said senior scientist Mark Serreze at the data center in Boulder, Colo. "It's tipping now. We're seeing it happen now."

Within "five to less than 10 years," the Arctic could be free of sea ice in the summer, said NASA ice scientist Jay Zwally.

"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," he said.

Five climate scientists, four of them specialists on the Arctic, told The Associated Press that it is fair to call what is happening in the Arctic a "tipping point." NASA scientist James Hansen, who sounded the alarm about global warming 20 years ago before Congress, said the sea ice melt "is the best current example" of that.

Last year was an unusual year when wind currents and other weather conditions coincided with global warming to worsen sea ice melt, Serreze said. Scientists wondered whether last year 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 instead, he said.

Researchers also were investigating "alarming" reports in the last few days of the release of methane from long-frozen Arctic waters, possibly from the warming of the sea, said Greenpeace climate scientist Bill Hare, who was attending a climate conference in Ghana.

Giant burps of methane, a potent greenhouse gas, are a long-feared effect of warming in the Arctic that would accelerate warming, scientists say.

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