The world's sea level is rising 60 percent faster than the central projections of the Intergovernmental Panel on Climate Change (IPCC), says a new study.
Satellite measurements show the sea level is actually rising at a rate of 3.2 mm a year compared to the estimate of two mm a year in the IPCC report.
Results were obtained by taking averages from the five available global land and ocean temperature series, the journal Environmental Research Letters reports.
The study was led by Stefan Rahmstorf, professor of physics of the oceans at the Potsdam Institute for Climate Impact Research, Germany. It included researchers from Tempo Analytics, US, and Laboratoire d'Etudes en Geophysique et Oceanographie Spatiales, France
The researchers believe the findings are important for keeping a track of how well past projections match the accumulating observational data.
"This study shows once again that the IPCC is far from alarmist. But in fact has under-estimated the problem of climate change. That applies not just for sea-level rise, but also to extreme events and the Arctic sea-ice loss," Rahmstorf said.
The study involved an analysis of global temperatures and sea-level data over the past two decades, comparing them both to projections made in the IPCC's third and fourth assessment reports, according to a Postdam statement.
After removing the three known phenomena that cause short-term variability in global temperatures -- solar variations, volcanic aerosols and El Nino/Southern Oscillation -- the researchers found the overall warming trend at the moment is 0.16 degree Celsius per decade, which closely follows the IPCC's projections.
Satellite measurements of sea levels, however, showed a different picture with current rates of increase being 60 percent faster than the IPCC's AR4 projections.
Satellites measure sea-level rise by bouncing radar waves back off the sea surface and are much more accurate than tide gauges as they have near-global coverage; tide gauges only sample along the coast.
Tide gauges also include variability that has nothing to do with changes in global sea level, but rather with how the water moves around in the oceans, such as under the influence of wind.