Big melt may have dangerous effect on the world's ocean currents, reports Nick Nuttall
GLOBAL warming may have triggered the unprecedented melting of sea ice in the Arctic, which has left the remaining ice up to a third thinner than it was 20 years ago.
Scientists studying sonar readings from British submarines fear that the thaw could lead to huge disruptions of the world's ocean circulations, including the Gulf Stream, which keeps Britain and Western Europe relatively warm.
A failure or a deflection of the Gulf Stream - which keeps Britain's ports free of ice and ensures that winter temperatures are warmer than at similar latitudes in Canada and the former Soviet Union - would have a devastating effect on the climate and the economy.
Dr Peter Wadhams, a reader in polar studies at the Scott Polar Institute in Cambridge, and Dr Norman Davis, a senior research fellow at the institute, said yesterday that they had compared ice thickness measurements taken from HMS Trafalgar in 1996 with those made by submarines from 1976 to 1987.
The earlier readings showed that ice had thinned by 12 to 15 per cent over that 11-year period and Dr Davis said that the latest findings indicated that the ice was becoming more fragile.
"It is looking considerably thinner. We would not be surprised if the final results show a 20 per cent to 30 per cent difference," he said.
Ice thickness was, on average, six metres in the 1970s. The latest findings indicate that it might now be on average up to two metres thinner.The findings add to a growing weight of evidence that dramatic changes are occurring in the Arctic, which may be due to emissions of carbon dioxide and other gases.
The Arctic is crucial region. The melting and freezing of its sea water drives vast ocean circulations that affect the world's weather and climate in ways that scientists are just beginning to understand. The sea ice also reflects back into space heat from the sun that would otherwise be absorbed.
As a key area of the Greenland Sea freezes in winter, the resulting build-up of salty water sinks to the bottom, carrying with it huge quantities of dissolved carbon dioxide from the atmosphere. A slowing of this process could accelerate the build-up of carbon dioxide and, as a consequence, speed up global warming.
Researchers in Norway said that satellite pictures had shown that the total area of the Arctic covered by ice had shrunk by 5 per cent over the past 18 years.
Dr Helge Drange, of the Nansen Environmental Remote Sensing Centre in Bergen, said yesterday: "It is an area the size of France, a substantial reduction in sea ice."
Dr Drange also said that the line at which warm Atlantic waters met cold polar waters had moved about 100km north over the past 20 years.
The findings came a week after 169 nations met in Buenos Aires to plan how to cut back emissions from industrial countries by 5.2 per cent by 2010. Countries agreed to exchange between them, after the year 2000, billions of dollars worth of green energy technology in return for credits to offset emissions at home.
Dr Davis said that researchers were now studying submarine readings dating back to 1967 to help to assess whether the thinning was part of a natural cycle or a trend caused by global warming.
Dr Wadhams said that they were also keen to match their findings with readings from US submarines, which operate on the other side of the Arctic, overlapping with British ones near the pole.
The US data, which is now beginning to be declassified, may include readings dating back to 1957 when Nautilus made the first sub-polar voyage.
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