Satellite measurements showed sea levels rose 3.2mm a year between 1993 and 2011, 60% above the 2mm estimate in central projections made by the Intergovernmental Panel on Climate Change (IPCC) in its most recent climate science review.
A study in the Institute of Physics (IOP) journal Environmental Research Letters said it was "very unlikely" the higher rate of sea level rise was due to natural variability such as temporary ice discharge from ice sheets.
Lead author Stefan Rahmstorf said: "It shows once again the IPCC is far from alarmist, but in fact has underestimated the problem of climate change."
It came after Scotland suffered the seventh wettest summer on record this year, with 384.6mm (15in) of rain since June.
Further downpours last week caused flooding problems for people across the country. About 100 residents were evacuated from their homes in one of the worst-hit communities, the Perthshire town of Comrie.
Further flooding after a weekend of storms continued to bring death and misery to England and Wales yesterday.
In St Asaph, north Wales, the body of an elderly woman was discovered in her flooded home. Rescue teams had to haul other residents from their properties.
About 100 properties were affected by flooding after the River Elwy rose above 14ft compared with its usual 3ft-6ft.
Prime Minister David Cameron visited flood-ravaged homes in Buckfastleigh, Devon, where he told people the Government would help them.
The IPCC researchers have also warned the rate of annual sea level rise may increase as global temperatures go up, a suggestion backed up by past sea level data and which leads to larger projections of future sea level rise than the IPCC predicts.
They said the concern the IPCC's estimates for future sea level rise are low is supported by the fact ice sheets in Greenland and Antarctica are increasingly losing mass, while the panel's projections assume Antarctica will gain enough ice to compensate for losses from Greenland.
The study analysing global temperature and sea level data over the past two decades also found temperature rises are consistent with the IPCC's projections in the fourth assessment report, published in 2007.
Once factors which cause natural variability in global temperatures, including solar and volcanic activity and the El Nino weather patterns in the Pacific, are removed, there is an overall warming trend of 0.16°C a decade.
This closely matches predictions by the IPCC, the researchers found.