Throughout the 1990s, Greenland and Antarctica together lost 81 billion tons of ice per year. But this month, a comprehensive assessment of the changing ice sheets published in the journal Nature, found that in the 2010s, the rate of ice loss has risen by a factor six. This means that the two ice sheets are now losing 475 billion tons of ice per year.

The IPCC Fifth Assessment Report predicted a rise in global sea levels of 28 inches by 2100. But this new study shows that ice losses from both Antarctica and Greenland are rising faster than expected, tracking with the IPCC’s worst-case scenario.

The Ice Sheet Mass Balance Intercomparison Exercise team, an international team of 89 polar scientists from 50 organizations, conducted the study. They combined 26 surveys to calculate changes in the mass of the Greenland and Antarctic ice sheets between 1992 and 2018, using data from 11 satellite missions, including measurements of the ice sheets’ changing volume, flow and gravity.

The ice loss coincides with several years of intense surface melting in Greenland, including last summer’s Arctic heatwave, which means that 2019 is also likely to set a new record for polar ice sheet loss.

According to Professor Andrew Shepherd from the University of Leeds, who led the assessment, “Almost all of the ice lost from Antarctica and half of that lost from Greenland has been triggered by oceans melting their outlet glaciers, which causes them to speed up. The remainder of Greenland’s ice losses are due rising air temperature, which has melted the ice sheet at its surface.”

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.