Greenland's glaciers are melting faster than thought, meaning estimates of sea-level rise could be too low, scientists warn.

Eric Rignot of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Pannir Kanagaratnam of the University of Kansas included recent changes in glacier velocity in estimates of overall ice loss in Greenland.

Their findings were presented on Thursday at the annual meeting of the American Association for the Advancement of Science in St. Louis, Mo., and appear in Friday's issue of the journal Science.

A rushing stream of water, top, flushes down an opening in the glacier, below.

"The behaviour of the glaciers that dump ice into the sea is the most important aspect of understanding how an ice sheet will evolve in a changing climate," Rignot said in a statement.

"It takes a long time to build and melt an ice sheet, but glaciers can react quickly to temperature changes."

If all of the ice on Greenland melted, it could raise sea levels seven metres. Most researchers say that would take at least 1,000 years, but, they add even half a metre could devastate low-lying countries.

Eric Rignot of NASA's Jet Propulsion Laboratory.

"I would say the ice sheet could evolve in a very major way on the time scale of 100 years rather than 1,000 years," said Rignot. "This is something which is not so far from our lifetime."

Climate researchers have previously said rising sea levels could increase storm surges and affect people living in coastal regions.

Rignot and Kanagaratnam report that when faster glacier speeds are taken into account, Greenland contributes about 0.5 millimetres per year to global sea-level rise, which currently stands at three millimetres per year.

Snow and ice are shown in white, glaciers in blue and grey in this satellite image of Greenland's coast. Photo shows an area almost 32 km wide. (Courtesy: NASA)

"This change, combined with increased melting, suggests that existing estimates of future sea level rise are too low," Julian Dowdeswell of the Scott Polar Research Institute at Britain's Cambridge University wrote in a commentary in the journal.

Ice loss due to glacier flow increased from 50 cubic kilometres of ice loss per year in 1996 to 150 cubic kilometres of ice loss annually in 2005, the team said.

Warmer temperatures may increase the amount of melt water reaching the ice, lubricating its slide towards the Atlantic, the researchers propose.

Increasing the amount of snowfall in Greenland is the only way to stem the loss of ice, Dowdeswell said.