Satellite images have recorded "unprecedented" melting of Greenland's ice sheet surface, NASA says.

While about half of the surface of Greenland's ice sheet melts naturally in an average summer, 97 percent of the ice sheet surface thawed at some point in the middle of the past month, according to measurements from three independent satellites analysed by NASA and university researchers.

The findings come after a 120 square kilometre-large iceberg broke free from Petermann Glacier, one of Greenland's largest glaciers, earlier this month.

Researchers have not yet determined whether the extensive surface melting will affect the overall volume of ice loss this summer and contribute to a rise in sea levels.


"The Greenland ice sheet is a vast area with a varied history of change. This event, combined with other natural but uncommon phenomena, such as the large calving event last week on Petermann Glacier, are part of a complex story," said Tom Wagner, NASA's cryosphere program manager in Washington.

"Satellite observations are helping us understand how events like these may relate to one another as well as to the broader climate system."

The data was gathered from the Indian Space Research Organisation's (ISRO) Oceansat-2 satellite, and NASA's Terra and Aqua satellites. It was analysed by NASA scientists and University of Georgia and City University of New York climatologists.

They found the melting spread quickly. Melt maps derived from the three satellites showed that on July 8, about 40 percent of the ice sheet's surface had melted. By July 12, 97 percent had melted.

Such a melt has not been recorded in 30 years of observations.

Melting was also recorded around Summit Station in central Greenland, about 3.2km above sea level.

Lora Koenig, a Goddard glaciologist and a member of the research team analysing the satellite data, said ice core samples from the summit indicate such a melting happens every 150 years.

"With the last one happening in 1889, this event is right on time," Koenig said.

"But if we continue to observe melting events like this in upcoming years, it will be worrisome."

This extreme melt event coincided with an unusually strong ridge of warm air, or a heat dome, over Greenland, University of Georgia climatologist Thomas Mote said.

"Each successive ridge has been stronger than the previous one," said Mote.

"This latest heat dome started to move over Greenland on July 8, and then parked itself over the ice sheet about three days later. By July 16, it had begun to dissipate."