Oceans to rise at 'accelerated' rate

Sea levels might rise at a far faster rate over the next 100 years than previously thought because of an acceleration in the rate at which glaciers are melting, scientists said yesterday at a meeting in Boston.

A study of mountain glaciers has found that they are more susceptible to global warming than was believed possible by the UN Intergovernmental Panel on Climate Change (IPCC) when it estimated sea-level changes over the coming century.

Speaking at a meeting of the American Association for the Advancement of Science, Mark Meier, a glaciologist at the University of Colorado, said that the new research suggests that melting glaciers could result in a rise in sea levels of an extra 8in (19cm) over the coming century, almost double the figure that the IPCC estimated to be the maximum contribution from melting glaciers.

Combined with the effects of an expanding ocean caused by a warmer world, this would mean sea levels might be up to 2ft (61cm) higher than now. "These estimates in sea-level rise may seem small, but a one-foot rise in sea level typically will cause a retreat of shoreline of 100ft or more, which would have substantial social and economic impacts," Professor Meier said.

The Colorado scientists analysed the volume of the world's glaciers from several thousand years ago to the present day and paid particular attention to what has happened over the past 40 years, when global warming has become most noticeable.

They found that glaciers are increasingly sensitive to global warming as air temperatures rise and that larger glaciers, that currently do not influence sea levels, will begin to have an effect as global temperatures rise and they begin to melt.

"Some glaciers around the world now are smaller than they have been in the last several thousand years. The rate of ice loss since 1988 has more than doubled," Professor Meier said.

The IPCC had estimated that melting glaciers would contribute to a sea-level rise of 3mm per year, but it failed to take into account the large maritime glaciers of Alaska because much of the data on them was then unavailable. These huge glaciers are the largest contributors to sea-level rise, Professor Meier said.

"The large glaciers of Alaska and adjacent Canada currently are contributing about half of the rate of global ice loss, exclusive of Greenland and Antarctic ice sheets. But they contain only 17 per cent of the glacier ice area," he said.

In addition to glaciers and an expanding ocean, sea levels will also be affected by the rate at which the ice sheets of the Antarctic melt over the coming decades.