Coastal cities including New York, London, Shanghai and Hong Kong could be flooded before the end of the century. The dramatic new study, published Wednesday in the journal Nature, predicts global warming could melt the West Antarctic ice sheet within decades—far faster than previously predicted. The collapse of this sheet, combined with ice melting in other regions, could cause seas to rise up to six feet by 2100. The study’s authors, Robert DeConto of the University of Massachusetts Amherst and David Pollard of Pennsylvania State University, also found the melting of the West Antarctic ice sheet is not yet inevitable, but that the emission reduction plans outlined in the 2015 Paris climate deal are far too weak to stop the sheet from melting.