Greenland losing ice faster than expected
Polar scientists paint a grim climate-change picture.
Polar scientists say Greenland is losing ice seven times faster than in the 1990s and is tracking the Intergovernmental Panel on Climate Change's (IPCC) high-end climate warming scenario.
The Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) team, comprising 96 researchers from 50 international organisations, combined 26 separate surveys to compute changes in the mass of Greenland's ice sheet between 1992 and 2018.
Data from 11 different satellite missions were used, including measurements of the ice sheet's changing volume, flow and gravity.
The findings, published in the journal Nature, show that Greenland has lost 3.8 trillion tonnes of ice since 1992 – enough to push global sea levels up by 10.6 millimetres.
The rate of ice loss has risen from 33 billion tonnes per year in the 1990s to 254 billion tonnes per year in the last decade – a seven-fold increase within three decades.
In 2013, the IPCC predicted that global sea levels would rise by 60 centimetres by 2100, putting 360 million people at risk of annual coastal flooding. However, this new study shows that Greenland's ice losses are rising faster than expected and are instead tracking the IPCC's high-end climate warming scenario, which predicts seven centimetres more.
"As a rule of thumb, for every centimetre rise in global sea level another six million people are exposed to coastal flooding around the planet," says Andrew Shepherd from the University of Leeds, UK, who led the assessment with NASA’s Erik Ivins.
"On current trends, Greenland ice melting will cause 100 million people to be flooded each year by the end of the century, so 400 million in total due to all sea level rise."
The IMBIE team also used regional climate models to show that half of the ice losses were due to surface melting as air temperatures have risen. The other half were linked to increased glacier flow, triggered by rising ocean temperatures.
Ice losses peaked at 335 billion tonnes per year in 2011 – 10 times the rate of the 1990s – during a period of intense surface melting. Although the rate of ice loss dropped to an average 238 billion tonnes per year since then, this remains seven times higher and does not include all of 2019, which could set a new high due to widespread summer melting.
"Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea level rise," Ivins says.
"While computer simulation allows us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable, evidence."