Estimates of how much the world's sea level would rise because of global warming may have been significantly underestimated, German researchers said.

Their study, using newer models, suggested that a rise in sea level could be twice as much as previously thought, researchers at Potsdam Institute for Climate Impact Research in Potsdam, Germany, said.

The semi-empirical modeling researchers used combined computer modeling and actual observations, which can correlate the rise in sea level to a given rise in temperature, NewScientist.com said.

At the high end of possible temperature increases, the increase in sea levels could be as much as 56 inches by the year 2100, said lead researcher Stefan Rahmstorf. At the low end of rising temperatures, the predicted increase in sea level would be about 20 inches, he said.

Even though other factors affect sea levels, Rahmstorf said new calculations showed the uncertainties in sea level predictions are greater than expected.

"We should not take this risk," Rahmstorf said. "We should start with very effective emission reduction measures. The global temperature increase should be kept to under 2 degree C."