NEARLY 90 per cent of the permafrost in Arctic soils could melt in the coming century. Besides giving polar bears and reindeer wet feet, the run-off could alter ocean currents and accelerate global warming.
A quarter of the land surface of the northern hemisphere stays frozen all year round. David Lawrence of the National Center for Atmospheric Research in Boulder, Colorado, modelled changes to the permafrost using a global climate model. He found that as atmospheric warming penetrates the soil, most of the permafrost across northern Canada, Alaska, Siberia and northern Scandinavia will melt to a depth of at least 3 metres, leaving a trail of buckled highways, toppled buildings, broken pipelines and bemused animals.
In some places the melt will create huge lakes and bogs, like those already forming in western Siberia (麻豆传媒, 13 August 2005, p 12). Elsewhere, the water will swell northward-flowing rivers like the Ob in Siberia and the Mackenzie in Canada, increasing freshwater input to the Arctic Ocean. The resulting drop in salinity will weaken the vertical movement of water that drives ocean currents such as the Gulf Stream (Geophysical Research Letters, DOI: 10.1029/2005GL025080).
Advertisement
What鈥檚 more, the thaw could release much of the estimated 400 billion tonnes of methane trapped in the frozen soil, accelerating global warming. There is an 鈥渁larming potential for positive feedbacks to climate from methane鈥�, says Torben Christensen of Lund University, Sweden.
