By BBC News Online's Jonathan Amos in Boston

Scientists may have seriously underestimated the likely rise in sea levels this century.

The claim comes from a research team that has examined the rate at which glaciers and ice caps are melting because of rising temperatures on Earth.

Professor Mark Meier himself has made a study of the South Cascade Glacier in Washington

They say new data show these areas to be retreating far faster than previously thought, with the run-off waters set to lift the height of the oceans well above that recently predicted by the UN's Intergovernmental Panel on Climate Change.

"The glacier wastage at the moment is unprecedented," Professor Mark Meier of the University of Colorado at Boulder, told the annual meeting of the American Association for the Advancement of Science in Boston.

"In some glaciers, like the South Cascade Glacier in Washington that I have studied for years, we know that the present rate of melting is greater than it ever has been for the last 5,000 years."

Latest data

Professor Meier, of the University of Colorado at Boulder, US, and his colleague Mark Dyurgerov analysed information about glacier volumes from several thousand years ago to the present, and studied the last 40 years in more detail.

Their work suggests glacier wastage will have a much bigger impact on sea levels than the scientific "consensus" has accepted.

"The IPCC thinks there will be an increase in sea levels by 2100 of 1-23 centimetres due to glacier melt alone. We think it will be nearer 23-46 cm - and that's a conservative estimate," said Professor Meier.

He said there were several reasons for the different assessment. He said the IPCC had not had the benefit of studying the latest data - especially from Alaska which has two giant glaciers. It had also not taken account of the increased sensitivity of glaciers to rising temperatures.

Many reports

Professor Meier concedes that much of the data on glaciers are patchy, predominantly from Europe, and those which do exist have only been fully reported from the 1960s onwards. Nevertheless, he claimed a clear picture of behaviour was emerging.

Glacier melting is only one aspect of sea level rise; thermal expansion as a result of increasing temperatures in the oceans is a much bigger factor.

The overall headline figures from the IPCC expect global sea levels to rise by between 11 and 88 cm this century, and to rise further after that. These are figures based on computer modelling.

Currently, measured sea levels are going up by about 0.8 millimetres per year with no apparent acceleration in that increase.

The IPCC is supposed to represent a broad scientific consensus on climate change - and it will examine Meier and Dyurgerov's evidence, as it will information from many other research groups. It might accept the assessment; it could continue to take a different view.