Paris: Climate change could release unexpectedly huge stores of carbon dioxide from Arctic soils, which would in turn fuel a vicious circle of global warming, a new study warned on Sunday. And according to one commentary, current models of climate change have not taken this extra source of greenhouse gas into account. Scientists have long known that organic carbon trapped inside a blanket of frozen permafrost covering one fifth of the world's land mass would, if thawed, release greenhouse gases into the atmosphere. But until now they simply did not have a good idea of how much carbon is actually locked inside this Arctic freezer. To find out, a team of American researchers led by Chien-Lu Ping of the University of Alaska Fairbanks examined a wide range of landscapes across North America. They took soil samples from 117 sites, each to a depth of at least one metre, in order to provide a full assessment of the region's so-called "carbon pool.' The study, published in the journal Nature Geoscience, found that the stock of carbon "is considerably higher than previously thought'