NASA has released satellite pictures of Greenland showing that the surface thaw level of the Greenland ice-cap in July accelerated dramatically from just over half of the ice-cap area to a full 97 per cent in connection with unusually high temperatures.

“On average in the summer, about half of the surface of Greenland's ice sheet naturally melts. At high elevations, most of that melt water quickly refreezes in place…..According to satellite data, an estimated 97 per cent of the ice sheet surface thawed at some point in mid-July,” NASA says in a news release.

"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.

Last week, a vast iceberg the twice the size of Manhattan broke off Greenland’s Petermann glacier.

Information on the unusual Greenland-wide melt came last week as Son Nghiem of NASA's Jet Propulsion Laboratory was studying data from an Indian satellite. The data seemed so extraordinary that Nghiem suspected a data error.

But checks with other satellites confirmed the data. On July 8, about 40 per cent of the ice sheet's surface had melted. By July 12, 97 per cent had melted.

Even at the area known as Summit – the highest point of Greenland’s ice sheet – temperatures hovering around zero caused surface ice to melt.

"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," says Lora Koenig, a Goddard glaciologist and a member of the research team analysing the satellite data. "But if we continue to observe melting events like this in upcoming years, it will be worrisome."

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