Between 60 and 90 percent of the world’s fresh water is frozen in the ice sheets of Antarctica, a continent roughly the size of the United States and Mexico combined. If all that ice melted, it would be enough to raise the world’s sea levels by roughly 200 feet.

While that won’t happen overnight, Antarctica is indeed melting, and a study published Wednesday in the journal Nature shows that the melting is speeding up.

The rate at which Antarctica is losing ice has more than doubled since 2012, according to the latest available data. The continent is now melting so fast, scientists say, that it will contribute six inches (15 centimeters) to sea-level rise by 2100. That is at the upper end of what the Intergovernmental Panel on Climate Change has estimated Antarctica alone could contribute to sea level rise this century.