A chunk of ice twice the size of Manhattan has parted from Greenland's Petermann glacier, a break researchers at the University of Delaware and Canadian Ice Service attributed to higher ocean temperatures. The separation along Greenland's northwest coast represents the second major calving event for the glacier in the past three years. In August 2010, the Petermann glacier lost an area of roughly 97 square miles, compared with the 46 square miles that split off last week. Andreas Muenchow, an associate professor of physical ocean science and engineering at the University of Delaware, said the glacier's end point is now at "a location where it has not been for at least 150 years." "The Greenland ice sheet is changing rapidly before our eyes," said Muenchow, adding that recent warming has transformed the overall ice sheet. "The Greenland ice sheet is being reduced not just in size, but in volume. The big and broader climate change story is what's happening all around Greenland."

Scientist Ted Scambos of the National Snow and Ice Data Center at the University of Colorado said scientists will now monitor whether the glacier's flow rate will accelerate "because of its loss of this chunk of ice at the front of it." "It's going to take awhile to understand how significant a loss this is," he said.

The Petermann glacier's flow accelerated 10 to 20 percent after the 2010 calving event, Muenchow said. He said researchers were still waiting to see if that was a short-term increase or would persist over time.

Researcher Jason Box of Ohio State University noted that the 2010 calving was "the largest in the observational record for Greenland." He predicted last summer that the piece that just broke off, about half the size, was on the brink. Air temperatures in the region have warmed more than 4.5 degrees since 1987, a rate five times that of the rest of the world. But Muenchow cautioned against directly linking air temperatures to the glacier's behavior, saying: "Because 80 percent of the melting of this glacier takes place from below, in the ocean."