Polar sea ice could be gone by the end of the century

Much of the Earth's frozen north will have defrosted by the end of the century, according to the latest study of the effect of global warming on the Arctic.

New measurements of the extent of sea ice around the entire North Pole show that it has reduced by about 4 per cent a decade on average over a 20-year period.

If the warming trend continues, Arctic sea ice could, within 100 years, disappear almost completely during the summer months, said Professor Ola Johannessen of the Nansen Environmental and Remote Sensing Centre in Bergen, Norway.

This would have a serious impact on wildlife, such as the estimated 22,000 polar bears living in the Arctic which need abundant pack ice to hunt for seals during the summer.

Professor Johannessen leads an international team of scientists who measured sea ice across the entire Arctic region using a phenomenon called elastic gravity waves – vibrations that can be used to estimate the thickness of the ice.

The findings, to be published later this year, show the melting of the Arctic ice has got considerably worse over the past 20 years. By 2090, there could be 80 per cent less ice than there is today.

In addition, satellite measurements have clearly shown that the area of the Arctic Ocean covered by sea ice has shrunk on average by about 8 per cent over the past quarter century, with the biggest decline occurring in summer.

Professor Johannessen said the marked and unprecedented thinning of the Arctic sea ice took place in the last two decades of the 20th century. He believes it is largely the result of global warming caused by man-made pollution.

"We believe there are strong indications that neither the warming trend nor the decrease of the sea-ice cover over the last two decades can be explained by natural processes alone," Professor Johannessen said.

"[Two] climate models both predict a dramatic decrease of the ice cover, which could result in a nearly ice-free Arctic Ocean during the summer months at the end of this century," he said.

Previous attempts at measuring the thickness of Arctic sea ice, using declassified sonar data from military submarines, have suggested that the ice has thinned by as much as 40 per cent over the past 50 years.

However, Professor Johannessen said that not all scientists have agreed on the interpretation of these sonar measurements. "The available sonar data remain inadequate for producing a reliable climatology of arctic ice thickness variability," he said.

Using elastic gravity waves, the scientists were able to study ice thickness over a wider area, as opposed to being restricted to the routes followed by military submarines.

Conservationists fear that melting sea ice in the Arctic is forcing polar bears to swim for longer between floating pack ice in search of seals, causing the loss of valuable body fat.

A shortage of ice could also affect hooded and harp seals which rely on the ice to rear pups. A report by the International Fund for Animal Welfare has warned the ice cover on Canada's east coast – estimated to have fallen by up to 60 per cent – is having a serious impact on seal populations.