MIAMI • Sea levels are rising around the world, threatening low-lying cities like Singapore, and the latest satellite data suggests that a rise of 1m or more is unavoidable in the next 100 to 200 years, according to Nasa scientists.
Ice sheets in Greenland and Antarctica are melting faster than ever, and oceans are warming and expanding much more rapidly than they have in years past. Rising seas will have "profound impacts" around the world, said Dr Michael Freilich, director of Nasa's Earth Science Division.
"More than 150 million people, most of them in Asia, live within 1m of present sea level," he said.
Low-lying US states, such as Florida, are at risk of disappearing, as are some of the world's major cities such as Singapore and Tokyo.
"It may entirely eliminate some Pacific island nations," he said.
There is no doubt that global coastlines will look very different in years to come, US space agency experts told reporters .
"Right now, we have committed to probably more than 1m of sea level rise, just based on the warming we have had so far," said Dr Steve Nerem of the University of Colorado, Boulder, and leader of Nasa's sea level rise team. "It will very likely get worse in the future. The biggest uncertainty is predicting how quickly the polar ice sheets will melt," he added.
The last major predictions were made in 2013 by the United Nations Intergovernmental Panel on Climate Change. It said global sea levels would likely rise from 0.3m to 1m by the end of the century. Dr Nerem said the latest satellite data suggests the higher end of that range is more likely.
Nasa's predictions are based on a series of altimeters that measure ocean height from space.
Nasa and French space agency CNES began launching satellites to measure sea levels in 1992.
"The instruments are so sensitive that if they were mounted on a commercial jetliner flying at 40,000 feet, they could detect the bump caused by a dime lying flat on the ground," Dr Freilich said.
The world's oceans have risen by an average of almost 7.6cm since 1992, with some locations rising more than 23cm due to natural variation, according to these instruments, known as Topex/Poseidon, and its successors, Jason-1 and Jason-2, Nasa said.
Much of the extra water is coming from melting ice and glaciers. Scientists are particularly concerned about the Greenland ice sheet, which shed an average of 303 gigatons of ice a year over the past decade. Also, the Antarctic ice sheet has lost an average of 118 gigatons a year.
"Some time in the next 20 years, we will probably see faster-than-average sea level rise, so we have to be prepared," said Mr Josh Willis, oceanographer at Nasa's Jet Propulsion Laboratory in Pasadena, California.