Well not to get all involved here, but methane produced by animals is in the form of fecies and the rotting dead heh. I've never seen a deer or a sea otter running dispatch on a fleet of diesel engines, or egineering a locamotive.. Methane produced naturally I would consider part of the process, and needed to preserve the balance. The issue becomes humans outsmarting themselves, and contributing by orders of magnitude to this particular issue. If the only greenhouse gasses humans produced came from taking a dump and buying the farm, I'd have to believe there would be no issue. ;]