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A melting iceberg floats away from Greenland's ice sheet near Nuuk.
A melting iceberg floats away from Greenland's ice sheet near Nuuk.
Image: AP/Brennan Linsley/PA

Greenland ice sheet surface melts at extreme rate

Data shows 97 per cent of the ice sheet melted by 12 July.
Jul 25th 2012, 9:56 AM 4,460 18

SURFACE ICE ON Greenland’s huge ice sheet melted over a much wider area this month than at any point over the past 30 years, according to NASA scientists.

While about half of the surface ice melts over the summer, the extent of melting jumped considerably over several days this month. By 12 July, an estimated 97 per cent of the ice sheet surface had thawed.

During the thaws, melt water at higher elevations generally re-freezes quickly in situ, while some of the meltwater closer to the coast is lost to the ocean.

NASA Jet Propulsion Lab researcher Son Nghiem said he was so stunned by the data he was analysing of the July thaw level that he initially was unsure if what we was seeing was due to a data error.

Satellite images comparing melt levels on 8 July (left) and 12 July. The areas marked in light pink as ‘probably melt’ are sites where at least one satellite detected surface melting, while the dark pink ‘melt’ areas are sites where two or three satellites detected surface melting. (Images: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory)

Satellite images of Greenland showed that about 40 per cent of the ice sheet’s surface had melted by 8 July. Four days later, 97 per cent had melted.

University of Georgia climatologist Thomas Mote said that the higher melt levels coincided with a series of ‘heat domes’, or strong ridges of warm air, over Greenland since the end of May.

“Each successive ridge has been stronger than the previous one,” he said.

NASA says that scientists have not yet determined if the recent high thaw level will result in a greater ice volume loss this year and contribute to rising sea levels.

But Goddard Space Flight Center gaciologist Lora Koenig says that there’s no reason to worry unless the extreme melt repeats in the next few years:

Ice cores from Summit show that melting events of this type occur about once every 150 years on average. With the last one happening in 1889, this event is right on time. But if we continue to observe melting events like this in upcoming years, it will be worrisome.

NASA’s cryosphere programme manager Tom Wagner said that events like the Greenland thaw escalation are being monitored by satellite to help scientists understand how similar events relate to one another “as well as to the broader climate system”.

VIDEO: ‘That day was almost our last’ – narrow escape from ‘iceberg tsunami’

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Susan Ryan

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