10 December 2019
The Greenland ice sheet is melting rapidly. Between 1992 and 2018, it lost 3.8 trillion tonnes of ice, according to a comprehensive assessment.
That is roughly in line with the most extreme scenario of future ice losses set out in the 2014 Fifth Assessment Report by the Intergovernmental Panel on Climate Change. In that scenario, global sea level will rise by 52 to 98 centimetres by 2100, partly due to ice loss from Greenland. “The ice losses are tracking the upper scenario from the IPCC,” says Andrew Shepherd at the University of Leeds, UK.
Shepherd and his colleagues combined 26 satellite data sets to reconstruct how the ice sheet has changed due to the warming climate. “The uncertainty on our estimate is a lot smaller than that on any individual estimate,” he says.
As late as the 1990s, Greenland’s ice sheet was in a state of balance. Ice was lost as glaciers flowed into the sea and when the ice surface melted in summer, but this was replaced by winter snowfall. The climate had already warmed, but temperatures on Greenland were still mostly below 0°C.
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However, since the early 2000s, the losses have outweighed the gains. “The glaciers are flowing too quickly because the oceans are too warm,” says Shepherd. “The surface is melting because the air is too warm. It’s a two-pronged assault for Greenland.”
Since 1992, ice losses from Greenland have contributed 1.06 centimetres to sea level rise, according to the new analysis. Ice losses from other glaciers and from Antarctica, plus the expansion of seawater as it warms, combine to give a total rise of about 7.5 centimetres over roughly the same period.
Such small rises aren’t enough to permanently submerge much land, but they dramatically increase the risk of coastal flooding during storms. The flooding from big storms like Hurricane Sandy, which affected swathes of North America in 2012, is being worsened by sea level rise.
“Small changes in sea level do matter,” says Shepherd. “If we don’t do anything, a million people in the UK will be affected by coastal flooding every year in 2100. That’s just from 60 or 70 centimetres of sea level rise.”
Globally, 630 million people are estimated to live on coastal land that will be flooded every year by 2100. Ice losses from Greenland are expected to accelerate and may become irreversible.
Journal reference: Nature , DOI: 10.1038/s41586-019-1855-2
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