Fred Pearce, New Scientist 25 Mar 09;
"I AM shocked, truly shocked," says Katey Walter, an ecologist at the University of Alaska in Fairbanks. "I was in Siberia a few weeks ago, and I am now just back in from the field in Alaska. The permafrost is melting fast all over the Arctic, lakes are forming everywhere and methane is bubbling up out of them."
Back in 2006, in a paper in Nature, Walter warned that as the permafrost in Siberia melted, growing methane emissions could accelerate climate change. But even she was not expecting such a rapid change. "Lakes in Siberia are five times bigger than when I measured them in 2006. It's unprecedented. This is a global event now, and the inertia for more permafrost melt is increasing."
The dramatic changes in the Arctic Ocean have often been in the news in the past two years. There has been a huge increase in the amount of sea ice melting each summer, and some are now predicting that as early as 2030 there will be no summer ice in the Arctic at all.
Discussions about the consequences of the vanishing ice usually focus either on the opening up of new frontiers for shipping and mineral exploitation, or on the plight of polar bears, which rely on sea ice for hunting. The bigger picture has got much less attention: a warmer Arctic will change the entire planet, and some of the potential consequences are nothing short of catastrophic.
Changes in ocean currents, for instance, could disrupt the Asian monsoon, and nearly two billion people rely on those rains to grow their food. As if that wasn't bad enough, it is also possible that positive feedback from the release of methane from melting permafrost could lead to runaway warming.
The danger is that if too much methane is released, the world will get hotter no matter how drastically we slash our greenhouse gas emissions. Recent studies suggest that emissions from melting permafrost could be far greater than once thought. And, although it is too early to be sure, some suspect this scenario is already starting to unfold: after remaining static for the past decade, methane levels have begun to rise again, and the source could be Arctic permafrost.
What is certain is that the Arctic is warming faster than any other place on Earth. While the average global temperature has risen by less than 1 °C over the past three decades, there has been warming over much of the Arctic Ocean of around 3 °C. In some areas where the ice has been lost, temperatures have risen by 5 °C.
This intense warming is not confined to the Arctic Ocean. It extends south, deep into the land masses of Siberia, Alaska, Canada, Greenland and Scandinavia, and to their snowfields, ice sheets and permafrost. In 2007, the North American Arctic was more than 2 °C warmer than the average for 1951 to 1980, and parts of Siberia over 3 °C warmer. In 2008, most of Siberia was 2 °C warmer than average (see map).
Most of this is the result of positive feedbacks (see illustration) from lost ocean ice, says David Lawrence of the National Center for Atmospheric Research in Boulder, Colorado. His modelling studies show that during periods of rapid sea-ice loss, warming extends some 1500 kilometres inland from the ice itself. "If sea-ice continues to contract rapidly over the next several years, Arctic land warming and permafrost thaw are likely to accelerate," he says.
Changes in wind patterns may accelerate the warming even further. "Loss of summer sea ice means more heat is absorbed in the ocean, which is given back to the atmosphere in early winter, which changes the wind patterns, which favours additional sea ice loss," says James Overland, an oceanographer at the Pacific Marine Environmental Laboratory in Seattle. "The potential big deal is that we now may be having a positive feedback between atmospheric wind patterns and continued loss of sea ice."
Incidentally, the changing winds might also be to blame for some of the cold and snowy weather in North America and China in recent winters, Overland says. Unusual poleward flows of warm air over Siberia have displaced cold air southwards on either side.
The rapid warming in the Arctic means that a global temperature rise of 3 °C, likely this century, could translate into a 10 °C warming in the far north. Permafrost hundreds of metres deep will be at risk of thawing out.
This is where things go global. The Arctic is not just a reflective mirror that is cracking up. It is also a massive store of carbon and methane, locked into the frozen soils and buried in icy structures beneath the ocean bed.
A quarter of the land surface of the northern hemisphere contains permafrost, permanently frozen soil, water and rock. In places, deep permafrost that formed during the last ice age, when the sea level was much lower, extends far out under the ocean, beneath the seabed. Large areas of permafrost are already starting to melt, resulting in rapid erosion, buckled highways and pipelines, collapsing buildings and "drunken" forests.
