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"The main concern is that the more we look, the more positive feedbacks we find," says Olivier Boucher, a climate scientist at the Met Office. "That's not the case when it comes to negative feedbacks. There seems to be far fewer of them." The sentiment is echoed by Chris Rapley, the director of the British Antarctic Survey in Cambridge: "When we look at the list of all the feedbacks in the climate, the list of positive feedbacks is worryingly long - a lot longer than the negative feedbacks. To be honest, it's a wonder that the climate has remained so stable."
Let's stick with Arctic sea ice a bit longer before looking at other issues that emerged 2006. In March, Nasa satellites monitored a 28-year record low for winter sea ice. Normally sea ice recovers during the long Arctic winter, but this was the second consecutive year that the ice failed to re-form fully to is previous winter extent. This meant there was less ice at the start of the northern summer, with the result that last September saw the second monthly minimum for summer sea ice - almost hitting the record minimum set in September 2005. During the past four or five years, there has been an acceleration in the rate at which sea ice is melting, a change that some scientists put down to a positive feedback. "Our hypothesis is that we've reached the tipping point," says Ron Lindsay of the University of Washington in Seattle. "For sea ice, the positive feedback is that increased summer melt means decreased winter growth and then even more melting the next summer, and so on."
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While we are in the northern hemisphere, take a look at another positive feedback that scientists investigated in 2006. This is connected to the frozen permafrost of Siberia and northern Canada, which lock up vast stores of carbon in the form of methane, a gas formed by the decomposition of organic matter. For more than 12,000 years, this methane - a greenhouse gas 20 times more potent than carbon dioxide - has been safely stored under the permanently frozen ground. But now the permafrost is melting and the gas is bubbling free into the atmosphere.
Sergei Kirpotin, a botanist at Tomsk State University in Russia, has been studying the extent of the melting permafrost of Western Siberia, the site of the world's biggest frozen peat bog. During the past few years, he has watched lakes getting bigger and bigger as the solid permafrost underneath liquifies. Normally, patches on white lichen on high Siberian ground reflect the sun's rays and help to keep the ground underneath cold. But as the dark lakes expand, more heat is absorbed and more permafrost melts. "As we predicted in the early 1990s, there's a critical barrier," says Professor Kirpotin. "Once global warming pushes the melting process past that line, it begins to perpetuate itself."
The once-frozen peat bogs of Siberia - bigger than France and Germany combined - began to "boil" furiously in the summer of 2006 as methane bubbled to the surface. Exactly how much is being released into the atmosphere is unknown, although some estimates put it as high as 100,000 tons a day - which means a warming effect greater than America's man-made emissions of carbon dioxide. But Katey Walter of the University of Alaska believes even this could be seriously underestimated. In a study published in Nature in September, Walter and her colleagues calculated that the level of methane emissions from Siberia could be anywhere between 10 per cent and 63 per cent higher than anyone had hitherto suspected. "We have shown that the North Siberian lakes are a significantly larger source of atmospheric methane than previously recognised," she says.
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http://www.ecoearth.info/shared/reader/welcome.aspx?linkid=65583
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