Melt warning for Arctic

Posted: 10 November 2003

Author: Helen Briggs

The ice covering the Arctic Ocean is getting thinner as summers lengthen, say British scientists. Melting seen in recent years is set to continue, they warn, with the eventual disappearance of ice during the summer months.

The melting of the Arctic ice is putting the habitat of the polar bear, which relies on it to hunt for seals, under increasing threat.

Polar bear habitats in the Arctic are threatened by global warming, Beaufort Sea, Alaska © Captain Budd Christman / National Oceanic and Atmospheric Administration
Polar bear habitats in the Arctic are threatened by global warming, Beaufort Sea, Alaska © Captain Budd Christman / National Oceanic and Atmospheric Administration
Polar bear habitats in the Arctic are threatened by global warming, Beaufort Sea, Alaska© Captain Budd Christman / National Oceanic and Atmospheric Administration

Melting will also increase the effects of global warming in the northern hemisphere, say researchers from University College London (UCL) and the British Meteorological Office Hadley Centre for Climate Prediction and Research.

The study, reported in the journal Nature, is based on ice thickness measurements from two European Space Agency (Esa) satellites, ERS-1 and ERS-2. The team also used microwave images from an American satellite.

Ice-free summer

Lead researcher Dr Seymour Laxon of UCL said the results from the American satellite showed that the length of summers had increased over the last 25 years.

"When we compared the data from the two satellites we were astonished by the similarity between changes in the ice thickness and the length of the summer melt season," he said. "This result suggests that if this continues, further melting will occur, leading to the eventual disappearance of the ice during summer."

Ice in the Arctic Ocean has already thinned by 40 per cent in the past 40 years, according to the results of submarine surveys.Any further loss could spell disaster for the polar bear, which stands to lose its natural habitat.

Global warming

It also has implications for global warming. As the ice melts, more sunlight is absorbed rather than being reflected back into space, amplifying the effects.

But climate studies are hotly debated and not all researchers agree with this bleak picture.

One of the major debates in Arctic research at the moment is whether the total volume of sea ice in the Arctic has actually reduced as much as submarine results say that it has, says Martin Doble, of the Scottish Association for Marine Science. Computer modelling studies suggest there could be an alternative explanation for the apparent loss of sea ice. Some experts believe a change in atmospheric circulation patterns has led to the ice being redistributed further north. It could all be bunched up in the permanent polar pack north of Greenland and Canada, they say.

Heated debate

Sea ice expert, Martin Doble, is sympathetic to this view. He says the ERS satellites are not designed to study the planet's poles and cannot sample the area beyond 81.5 degrees north.

This means they miss most of the central Arctic pack ice and the area of maximum interest north of Greenland and the Canadian Archipelago.

"One of the major debates in Arctic research at the moment is whether the total volume of sea ice in the Arctic has actually reduced as much as submarine results say that it has," he told BBC News Online.

Settling the argument once and for all may have to wait until the launch of a more advanced Esa satellite - Cryosat - in 2004.