Melting of permafrost a global threat, scientists say

Global warming could melt most 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 US National Center for Atmospheric Research in Boulder, CO, 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 land surface in the northern hemisphere, and the upper layer is believed to hold at least 30 percent of the carbon stored in soil worldwide. Lawrence said: "In terms of its impact on the global climate, I don't see how it can be good news, but just how bad, it is unclear. It's very difficult to see how we can halt it. We may be able to slow it down." Lawrence and Andrew Slater, of the University of Colorado's National Snow and Ice Data Center, 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 yards of the surface will shrink from four million square miles to a little over one 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. 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. He said the predictions of the computer model were already being backed up by observations in and around the Arctic. In August, scientists working in Siberia reported an unprecedented thaw in the world's largest peat bog, which they fear could release billions of tons of methane, a greenhouse gas 20 times more potent than carbon dioxide. Melting permafrost frees carbon because warmer temperatures allow bacteria to break down previously frozen dead vegetation. Recent warming has degraded large sections of surface permafrost across central Alaska, with pockets of soil collapsing as the ice within it melts. The melting has buckled roads, destabilized houses and produced so-called "drunken forests" in which the trees lean at wild angles. Sections of the Alaskan Arctic oil pipeline buried in sensitive areas are refrigerated to keep the permafrost around it solid. The computer model also predicted that the massive thaw would significantly increase the amount of fresh water draining into the Arctic Ocean, which could affect global currents. "Thawing permafrost could send considerable amounts of water to the oceans," said Slater. Water runoff from permafrost to the ocean has increased by seven percent since the 1930s. In the high-emission simulation, the computer predicted a further increase of 28 percent by 2100. About half of this is due to ice melting within the surface soil, with the rest because of increased rainfall, snowfall and increased drainage.