SCIENCE and politics are inextricably linked. At a scientific conference on climate change held this week in Copenhagen, four environmental experts announced that sea levels appear to be rising almost twice as rapidly as had been forecast by the United Nations just two years ago. The warning is aimed at politicians who will meet in the same city in December to discuss the same subject and, perhaps, to thrash out an international agreement to counter it.

The reason for the rapid change in the predicted rise in sea levels is a rapid increase in the information available. In 2007, when the Intergovernmental Panel on Climate Change convened by the UN made its prediction that sea levels would rise by between 18cm and 59cm by 2100, a lack of knowledge about how the polar ice caps were behaving was behind much of the uncertainty. Since then they have been closely monitored, and the results are disturbing. Both the Greenland and the Antarctic caps have been melting at an accelerating rate. It is this melting ice that is raising sea levels much faster than had been expected. Indeed, scientists now reckon that sea levels will rise by between 50cm and 100cm by 2100, unless action is taken to curb climate change.

Konrad Steffen of the University of Colorado, Boulder, leads one study of the Greenland ice sheet. He told the conference that this sheet is melting not only because it is warmer but also because water seeping through its crevices is breaking it up. This effect had been neglected in the earlier report.

The impact of the melting ice has been measured by John Church of the Centre for Australian Weather and Climate Research. He told the conference that satellite and ground-based systems showed that sea levels have been rising more rapidly since 1993 than they were earlier in the 20th century. He is concerned that more climate change could cause a further acceleration in this rate.

Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research has examined data stretching over 125 years that link increases in sea temperatures to rises in sea levels. He told the conference that, based on past experience, “I expect that sea-level rise will accelerate as the planet gets hotter.” He was supported in this view by the fourth expert, Eric Rignot of the University of California, Irvine, who called for the world's leaders to slash the emission of carbon dioxide and other greenhouse gases.

Advance negotiations on the UN Climate Change Conference are due to begin in Bonn in just over a fortnight's time. The scientists hope that their startling warnings will change the outcome of that pre-meeting meeting. With much still to argue over, they hope that a clear scientific lead will both help to narrow the room for disagreement and galvanise the desire to get a treaty agreed.