U.S. scientists using satellite data have established a more accurate figure of the amount of annual sea-level rise from melting glaciers and ice caps which should aid studies on how quickly coastal areas may flood as global warming gathers pace.

John Wahr of the University of Colorado in Boulder and colleagues, in a study published this week, found that thinning glaciers and icecaps were pushing up sea levels by 1.5 millimetres a year, in line with a 1.2 to 1.8 mm range from other studies, some of which forecast sea levels could rise as much as two metres by 2100.

Sea levels have already risen on average about 18 centimetres since 1900 and rapid global warming will accelerate the pace of the increase, scientists say, threatening coastlines from Vietnam to Florida and forcing low-lying megacities to build costly sea defences.

To get a better picture of the pace of the melting, Wahr and colleagues used a satellite that measures variations in gravity fields to study changes in the mass of large ice-covered areas. The data covered 2003-2010.

Globally, the rate of sealevel rise has accelerated in recent decades to reach about 3.5 millimetres a year, with more than half coming from thermal expansion of the oceans, since water expands as it gets warmer.

Using satellite data instead of more limited and time-consuming data from ground measurements was crucial, Wahr said.

The team found that ice loss from Greenland and Antarctica was pushing up sea levels by just over one millimetre a year, comprising most of the 1.5-mm annual rise.

Glaciers and mountain icecaps elsewhere comprised the rest, at 0.4 mm per year between 2003-10.

"That's a large number, and represents a lot of melting ice," said Wahr. "But it's at least 30 per cent smaller than previous global estimates," he said.