A team of 96 polar scientists from 50 international organisations have produced a revealing picture of long-term Greenland ice loss.
Published today in Nature, the findings show that Greenland has lost 3.8 trillion metric tons of ice between 1992 and 2018, enough to raise global sea levels by more than a centimeter. This amounts to a seven-fold increase in ice loss in less than three decades — from 33 billion tons per year in the 1990s to 254 billion tons per year in the last decade.
Combining 26 surveys and data from 11 different satellite missions to quantify shifts in Greenland's ice sheet — smaller only than Antarctica's and covering roughly 80% of the world's largest island — the study is the most comprehensive look at the ice sheet's changing volume, flow and gravity across recent decades.
Known as the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE), the work was led by Professor Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA's Jet Propulsion Laboratory in California, with support by the European Space Agency (ESA) and NASA.
"While computer simulation allows us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable, evidence," Ivins said of the state-of-the-art study. "Our project is a great example of the importance of international collaboration to tackle problems that are global in scale."
Millions more vulnerable to rising seas
The faster than expected ice loss will make tens of millions more people vulnerable to sea level rise by the end of the century, according to the study's authors.
"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," said Professor Shepherd.
In 2013, the Intergovernmental Panel on Climate Change (IPCC) predicted that global sea levels will rise by 60 centimetres by 2100, putting 360 million people at risk of annual coastal flooding. But this latest research shows that Greenland's increasing ice sheet loss is in line with the IPCC's high-end climate warming scenario, which predicts another 7 centimeters of rise.
The current trends indicate that the accelerated Greenland ice melt will mean that 400 million people in total will experience sea level rise by the end of the century, Shepherd said.
"These are not unlikely events or small impacts; they are happening and will be devastating for coastal communities," he added.
Both surface and ocean temperatures to blame
The study further employed regional climate models to show that half of the ice losses were due to surface melting caused by rising air temperatures; the other half due to increased glacier flow triggered by rising ocean temperatures.
Intense surface melting in 2011 caused ice losses to peak at 335 billion tonnes that year — ten times the 1990s rate. But the average 238 billion tonne ice loss in the seven years since could rise by the end of 2019, an exceptional year for summer melting in Greenland that could set a new high.
Guofinna Aoalgeirsdottir, professor of glaciology at the University of Iceland and lead author of the IPCC's sixth assessment report, but who was not involved in the study, said:
"The IMBIE Team's reconciled estimate of Greenland ice loss is timely for the IPCC. Their satellite observations show that both melting and ice discharge from Greenland have increased since observations started."
He added that very high ice mass loss in his native Iceland this year could replicate the study's findings on the island that Donald Trump famously expressed interest in purchasing.
"I would expect a similar increase in Greenland mass loss for 2019," he said.