At current rates heights may reach 30 inches above the modern level by 2100 and 8 feet by 2200, researchers from the University of Southampton and the Australian National University reported Thursday.
The scientists used geological evidence of the past few million years to derive a background pattern of natural sea-level rise, then compared that with historical tide-gauge and satellite observations of sea-level change for the "global warming" period since the industrial revolution.
"Historical observations show a rising sea level from about 1800 as sea water warmed up and melt water from glaciers and ice fields flowed into the oceans," said Gavin Foster of Southampton's National Oceanographic Center. "Around 2000, sea level was rising by about three mm per year. That may sound slow, but it produces a significant change over time."
The natural background pattern allowed the researchers to see whether recent sea-level changes are exceptional or within the normal range, and whether they are faster, equal, or slower than natural changes.
"For the first time, we can see that the modern sea-level rise is quite fast by natural standards," Eelco Rohling of the Australian National University said. "Based on our natural background pattern, only about half the observed sea-level rise would be expected."