Petermann Glacier's ice shelf on July 16, 2012, just an hour or so before a giant iceberg broke off and began to float away (NASA/AP)

A massive iceberg twice the size of Manhattan has broken off one of Greenland's major glaciers -- a development which scientists say is due to alarming warming in the region.

The iceberg, measuring 46 square miles, is the second of its nature to break from Greenland in just two years. In 2010 an iceberg twice its size, one of the largest ever recorded in Greenland, broke free.

"It's dramatic. It's disturbing," said University of Delaware professor Andreas Muenchow, one of the first researchers to notice the break. "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."

"This is not part of natural variations anymore," said NASA glaciologist Eric Rignot, referring to the vast changes the glacier has seen in the past three years.

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Scientists are concerned about rising sea levels due to melting ice in the north. The Arctic had the largest sea ice loss on record for June, scientists reported this week, and Northern Greenland and Canada are warming five times faster than the average global temperature.

"The Greenland ice sheet as a whole is shrinking, melting and reducing in size as the result of globally changing air and ocean temperatures and associated changes in circulation patterns in both the ocean and atmosphere," stated Muenchow.

Left: the new ice island. Right: the ice island that calved from Petermann Glacier in 2010. The crack that led to the 2012 calving also is clearly visible. Courtesy of Andreas Muenchow, University of Delaware. (MongaBay)