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Melting permafrost threatens homes and roads

David Adam

A major change in climate is expected by the end of the century.

GLOBAL WARMING could melt almost all of the top layer of Arctic permafrost by the end of the century. Scientists say the thaw would release vast stocks of carbon into the atmosphere, threaten ocean currents and wreck roads and buildings across Canada, Alaska, and Russia.

David Lawrence, a climate scientist with the U.S. National Centre for Atmospheric Research in Boulder, Colorado, said: "There's a lot of carbon stored in the soil. If the permafrost does thaw, as our model predicts, it could have a major influence on climate." Thawing permafrost is one of several climate "tipping points" feared by environmental experts, because carbon released by melted soil would accelerate global warming. Permafrost makes up about a quarter of the land surface in the northern hemisphere and the upper layer is believed to hold at least 30 per cent of the carbon stored in soil worldwide.

Prof. Lawrence said: "In terms of its impact on the global climate, I don't see how it can be good news, but it is unclear just how bad it is. It's very difficult to see how we can halt it. We may be able to slow it down."

Prof. Lawrence and Andrew Slater, of the University of Colorado's national snow and ice data centre, used a computer to simulate how the Arctic permafrost — defined as soil that remains below freezing for at least two years — would react to the earth's changing climate.

Assuming that emissions of carbon dioxide and other greenhouse gases from cars, power stations, and other sources continue to rise, they found the area holding permafrost within about 3.5 metres of the surface will shrink from 4 million square miles to a little over 1 million square miles by 2050. The area of surface permafrost will shrink further by 2100, to about 400,000 square miles. Deeper permafrost will remain largely unaffected.

Under a low emission scenario, which assumes that new technology and energy efficiency measures will slash future greenhouse gas pollution, the permafrost area shrinks to about 1.5 million square miles by 2100. The results appear in the journal Geophysical Research Letters.

Prof. Lawrence said the study was the first to examine permafrost in a model that accounted for interactions between the atmosphere, ocean, land and sea ice, as well as the freezing and thawing of soil.

- Guardian Newspapers Limited 2005

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