Ice loss from Greenland’s vast sheet may happen mainly in short bursts, research by Danish scientists suggests.
They used aerial photos dating back to the 1980s to plot shrinking of glaciers around the island’s northwest coast.
In the journal Science, they show that most of the ice loss happened in two periods – 1985-1993 and 2005-10 – with relative stability in between.
They say it will be hard to project sea level changes from Greenland ice melt until these patterns are deciphered.
A complete melt of the ice sheet would raise sea levels globally by about 7m, but it could take centuries for this to occur.
Last month, Nasa released evidence showing that ice melting had been observed across virtually the whole extent of the Greenland ice sheet, unprecedented in the satellite era.
Days earlier, an iceberg twice the size of Manhattan broke away from the Petermann glacier in northwest Greenland.
Dramatic though those events were, neither means much on its own for the long-term picture.
The last global climate assessment by the Intergovernmental Panel on Climate Change (IPCC) in 2007 said that “dynamic” melting – where ice loss suddenly accelerates, for example because sea temperatures rise – was too poorly understood to be accurately modelled.
The new Danish paper is one of a number that have emerged since in an attempt to improve understanding.
In recent years, satellites have found fast rates of retreat in a number of Greenlandic glaciers, as well as an overall loss of mass as measured by the Grace mission, which detects minuscule changes in the Earth’s gravitational field.
But other studies suggested the rapid retreat was not consistent.
With the two most important satellite missions – Grace and ICESat – dating back less than a decade, there is obviously a danger that scientists will decipher accurately what is happening now and assume this is a constant pattern.