Agence France-Presse: Scientists issued a dire warning Tuesday to UN climate negotiators in Bonn of a vicious global warming cycle that will be unlocked with the thawing of carbon-bearing permafrost. There may be 1,500 billion tonnes of carbon locked away in permafrost -- perennially frozen ground covering about a quarter of exposed land in the Northern Hemisphere -- said Susan Natali, a researcher with the Woods Hole Research Center in Massachusetts. The carbon will be released incrementally as global temperatures...