How high will sea level rise? Sea level rose about 6 inches during the 20th century, after rising no more than 1 inch in any of the previous 20 centuries. It rose at a rate of 8 inches per century over 1993-2002, 12 inches per century over the next decade, and 17 inches per century over the most recent decade. The rate has doubled every 20 years. But sea level rose 70 inches per century from 11,000 to 8,000 years go, as the great ice sheets of North America melted. When Earth last had this much CO2 in the air, sea level was 100 feet (±30 feet) higher than now. Projections are for 1-7 feet of sea level rise by 2100. (The 1-foot projection assumes no net melting in the Antarctic ice sheet.) But sea level will keep rising for many centuries, at a rate faster than today. We can do very little to stop it, except to cool Earth off, partly by removing most of the CO2 we have already put in the air. It is not possible for sea level to rise more than 240 feet.