Reuters: A thaw of Arctic permafrost is a "wild card" that could stoke global warming by releasing vast frozen stores of greenhouse gases, the UN Environment Programme (UNEP) said on Wednesday. More research was urgently needed into the possibility of a runaway release of methane, a powerful heat-trapping gas trapped in frozen soils in Siberia, Canada, Alaska and Nordic nations, it said in a 2008 yearbook issued at 154-nation talks in Monaco. "The unknowns about the …