Greenland's ice sheet is melting so fast that researchers will have to move the goalposts to estimate the impact on humans in the coming years. That's according to the Ice Sheet Mass Balance Inter-Comparison Exercise, a consortium of nearly 100 polar scientists who reviewed all satellite observations of the ice sheet from 1992 to 2018. They found Greenland is losing ice seven times faster than it was in the 1990s, at a speed and scale worse than predicted by the Intergovernmental Panel on Climate Change, reports the Guardian. Its mid-range projection in 2013 estimated 360 million people would be at risk of coastal flooding every year by 2100, owing to 60 centimeters of sea level rise, per the BBC. The new findings, published Tuesday in Nature, push that estimate to 67 centimeters, suggesting 400 million people will be at risk.
Essentially, "the mid-range scenario becomes what was previously the upper scenario, and they will have to invent a new upper scenario, because one currently doesn't exist," co-lead investigator Andrew Shepherd tells the Washington Post, noting that "just 1 centimeter of sea-level rise brings another 6 million people into seasonal, annual floods." The ice sheet has already lost about 4 trillion tons of ice since 1992, for a sea-level rise of just over a centimeter. In the '90s, the rate of loss was about 33 billion tons per year, though it now sits at 254 billion tons per year. Ice loss was even worse this year, around 400 million tons. Flooding and more dangerous storms "are not unlikely events or small impacts," Shepherd warns. They "are happening and will be devastating for coastal communities." (More on the melt here.)