Observations from 11 satellite missions monitoring the Greenland and Antarctic ice sheets have revealed that the regions are losing ice six times faster than they were in the 1990s.
If the current melting trend continues, the regions will be on track to match the "worst-case" scenario of the Intergovernmental Panel on Climate Change (IPCC) of an extra 17 centimetres of sea-level rise by 2100.
The findings, published online 12 March in the journal Nature from an international team of 89 polar scientists from 50 organisations, are the most comprehensive assessment to date of the changing ice sheets.
The Ice Sheet Mass Balance Intercomparison Exercise team combined 26 surveys to calculate changes in the mass of the Greenland and Antarctic ice sheets between 1992 and 2018.
The assessment was supported by NASA and the European Space Agency. The surveys used measurements from satellites including NASA's Ice, Cloud, and land Elevation Satellite and the joint NASA-German Aerospace Center Gravity Recovery and Climate Experiment.
Andrew Shepherd at the University of Leeds in England and Erik Ivins at NASA's Jet Propulsion Laboratory in southern California led the study.
The team calculated that the two ice sheets together lost 81 billion tons (74.5 billion tonnes) per year in the 1990s, compared with 475 billion tons (431 billion tonnes) of ice per year in the 2010s – a sixfold increase. All total, Greenland and Antarctica have lost 6.4 trillion tons (5.8 trillion tonnes) of ice since the 1990s.
The resulting meltwater boosted global sea levels by 17.8 millimetres. Together, the melting polar ice sheets are responsible for a third of all sea-level rise. Of this total sea-level rise, 60 per cent resulted from Greenland's ice loss and 40 per cent resulted from Antarctica's.
"Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea-level rise. While computer simulations allow us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable, evidence," said Ivins.
The IPCC in its Fifth Assessment Report issued in 2014 predicted global sea levels would rise 71 centimetres by 2100. The Ice Sheet Mass Balance Intercomparison Exercise team's studies show that ice loss from Antarctica and Greenland tracks with the IPCC's worst-case scenario.
Combined losses from both ice sheets peaked at 552 billion tons (500 billion tonnes) per year in 2010 and averaged 475 billion tons (431 billion tonnes) per year for the remainder of the decade.
The peak loss coincided with several years of intense surface melting in Greenland, and last summer's Arctic heatwave means that 2019 will likely set a new record for polar ice sheet loss, but further analysis is needed. IPCC projections indicate the resulting sea-level rise could put 400 million people at risk of annual coastal flooding by the end of the century.
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