PARIS (AFP) - New studies have warned of triggers in the natural environment, including a greenhouse-gas timebomb in Siberia and Canada, that could viciously amplify global warming. Thawing subarctic tundra could unleash billions of tonnes of gases that have been safely stored in frosty soil, while oceans and forests are becoming less able to suck carbon dioxide (CO2) out of the atmosphere, according to papers presented this weekend. Together, these phenomena mean that more heat-trapping gases will enter the atmosphere, which in turn will stoke global warming, thrusting the machinery of climate change into higher gear. Researchers in Finland and Russia discovered that nitrous oxide is leaking into the air from so-called "peat circle" ecosystems found throughout the tundra, a vast expanse of territory in higher latitudes. CO2 and methane account for the lion's share of the gases that have driven global temperatures inexorably higher over the last century. Nitrous oxide, or N2O, is far less plentiful in volume, but 300 times more potent as a greenhouse gas than CO2. It accounts for about six percent of total global warming, mainly due to a shift toward chemical-intensive agriculture. In experiments near the Russian city of Vorkuta, Pertti Martikainen of the University of Kuopio in Finland and colleagues found that N2O leaked as a result of cryoturbation, a process that occurs when frozen soil is thawed and then refreezes. There is evidence that warming of the Arctic will accelerate cryoturbation, which would lead to an increased abundance of peat circles in the future.