updated 9/16/2008 4:49:21 PM ET 2008-09-16T20:49:21

Crucial Arctic sea ice this summer shrank to its second lowest level on record, continuing an alarming trend, scientists said Tuesday.

The ice covered 1.74 million square miles last Friday, marking a low point for this summer, according to NASA and the National Snow and Ice Data Center in Boulder, Colo.

"This appears to have been the lowest point of the year, as sea has now begun its annual cycle of growth in response to autumn cooling," the center said in a statement. "The 2008 minimum is the second-lowest recorded since 1979, and is 2.24 million square kilometers (0.86 million square miles) below the 1979 to 2000 average minimum."

Last summer, the sea ice covered only 1.59 million square miles, the lowest since satellite-based records began in 1979.

Arctic sea ice, which floats on the ocean, expands in winter and retreats in summer. In recent years it hasn't been as thick in winter.

Sea ice is crucial to worldwide weather patterns, both serving as a kind of refrigerator and reflecting the sun's heat. Given recent trends, triggered by man-made global warming, scientists warn that within five to 10 years the Arctic could be free of sea ice in the summer.

Even though the sea ice didn't retreat this year as much as last summer, "there was no real sign of recovery," said Walt Meier of the snow and ice data center. This year was cooler and other weather conditions weren't as bad, he said.

"We're kind of in a new state of the Arctic basically, and it's not a good one," Meier said. "We're definitely sliding towards a point where the summer sea ice will be gone."

The final summer report for 2008 echoed a preliminary one issued last month by the data center.

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