WASHINGTON Ė An iceberg twice the size of Manhattan tore off one of Greenlandís largest glaciers, illustrating another dramatic change to the warming island.
For several years, scientists had been watching a long crack near the tip of the northerly Petermann Glacier. On Monday, NASA satellites showed it had broken completely, freeing an iceberg measuring 46 square miles.
A massive ice sheet covers about four-fifths of Greenland. Petermann Glacier is mostly on land, but a segment sticks out over water like a frozen tongue, and thatís where the break occurred.
The same glacier spawned an iceberg twice that size two years ago. Together, the breaks made a large change thatís got the attention of researchers.
ďItís dramatic. Itís disturbing,Ē said University of Delaware professor Andreas Muenchow, who was one of the first researchers to notice the break. ďWe have data for 150 years, and we see changes that we have not seen before.
ďItís one of the manifestations that Greenland is changing very fast,Ē he said.
Researchers suspect global warming is to blame but canít prove it conclusively yet. Glaciers calve icebergs naturally, but whatís happened in the last three years to Petermann is unprecedented, Muenchow and other scientists say.
ďThis is not part of natural variations anymore,Ē said NASA glaciologist Eric Rignot, who camped on Petermann 10 years ago.
Ohio State University ice scientist Ian Howat said there is still a chance it could be normal calving, like losing a fingernail that has grown too long, but any further loss would show itís not natural.
ďWeíre still in the phase of scratching our heads and figuring out how big a deal this really is,Ē Howatt said.
Many of Greenlandís southern glaciers have been melting at an unusually rapid pace. The Petermann break brings large ice loss much farther north than in the past, said Ted Scambos, lead scientist at the National Snow and Ice Data Center in Boulder.
If it continues, and more of the Petermann is lost, the melting would push up sea levels, he said. The ice lost so far already was floating, so the breaks donít add to global sea levels.
Northern Greenland and Canada have been warming five times faster than the average global temperature, Muenchow said. Temperatures have increased there by about 4 degrees Fahrenheit in the last 30 years, Scambos said.
The new iceberg is likely to follow the path of the one in 2010, Muenchow said.
That iceberg broke apart into smaller icebergs headed north, then west and last year started landing in Newfoundland, he said.
Itís more than glaciers in Greenland that are melting. Scientists also reported this week that the Arctic had the largest sea ice loss on record for June.
NASA, University of Delaware/AP