LiveScience: Thanks in large part to gas wells and cow farms, the United States is spewing 50 percent more methane, a potent greenhouse gas, than previous estimates have measured, according to a new study. For the study, published Monday (Nov. 25) in the journal Proceedings of the National Academy of Sciences, researchers from universities and government labs fanned out across the United States in 2007 and 2008 and measured levels of methane gas in the air. Though methane breaks down in the atmosphere after...