Scientists had been watching the 15 mile long crack in the floating ice shelf of the glacier for several years.

On Monday, NASA satellites showed it had broken completely, freeing an iceberg measuring 46 square miles.

Break away: A satellite image taken on Monday shows the crescent shaped crack (shown in the red circle) on the Petermann Glacier in northwestern Greenland.

It’s disturbing,’ said University of Delaware professor Andreas Muenchow, who was one of the first researchers to notice the break.

Researchers suspect global warming is to blame, but can’t prove it conclusively yet.

Glaciers do calve icebergs naturally, but what’s happened in the last three years to Petermann is unprecedented, Muenchow and other scientists say.

A massive iceberg larger than Manhattan has broken away from the floating end of a Greenland glacier this week, an event scientists predicted last autumn.

"This is not part of natural variations anymore," 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 it’s not natural: "We’re still in the phase of scratching our heads and figuring out how big a deal this really is.

"Many of Greenland’s 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, Colo.

The ice lost so far was already floating, so the breaks don’t 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.

That broke apart into smaller icebergs headed north, then west and last year started landing in Newfoundland, he said.

Scientists also reported this week that the Arctic had the largest sea ice loss on record for June.

Glaciers form on land, often elevated, and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.

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