One of Greenland's largest glaciers has been significantly reduced in size after a massive iceberg broke away.

The Petermann glacier "calved" a 74 sq km iceberg, realising the fears of scientists who have been watching a growing crack in the ice sheet for years.

Here are five implications of the calving, a major environmental event:

1. It reveals how global warming may be working on Greenland, which is largely covered in ice.

2. The pace of environmental change on Greenland is accelerating. "It's dramatic. It's disturbing," University of Delaware's Prof Andreas Muenchow told Associated Press.

Muenchow was one of the first polar researchers to notice the glacier crack.

"We have data for 150 years and we see changes that we have not seen before. It's one of the manifestations that Greenland is changing very fast," he noted.

3. More icedbergs may be calved by the same glacier.

"This is not part [of the cycle] of natural variations any more," Nasa glaciologist Eric Rignot, who camped on Petermann 10 years ago, said.

He said topographic and environmental changes to Petermann were unprecedented. Changes in the last three years have been significant, he added.

4. Scientists are scrutinising the glacier even more closely.

"We're still in the phase of scratching our heads and figuring out how big a deal this really is," Ohio State University ice scientist Ian Howat told AP. Any further loss of ice in Petermann would confirm the changes are unnatural, he said.

5. Sea levels could rise more rapidly than expected.

Ted Scambos, lead scientist at the National Snow and Ice Data Centre in Boulder, Colorado, said melting icebergs would push up sea levels if more segments of Petermann would break free.

Muenchow said the new iceberg could split into smaller bergs and float north.

Scientists reported that Arctic ice loss hit a new record in June.

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