Reuters: A rise in concentrations of a powerful greenhouse gas over the Arctic after a decade of stability is stirring worries about a possible thaw of vast stores trapped in permafrost, experts said. Levels of methane in the atmosphere rose 0.6 percent in 2008, according to preliminary data from the Zeppelin station on a remote island in the Norwegian Arctic, after a similar 0.6 percent gain in 2007, Norwegian officials said. The 2007 rise outpaced a global rise in methane of 0.34 …