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Since 2007, atmospheric levels of methane, a powerful greenhouse gas, have increased by more than 3%, puzzling and concerning scientists, who have tried to pin the growth on increased natural gas drilling, rising rice cultivation, and a surge in cow-related emissions. At a meeting of the American Geophysical Union, scientists flagged two more potential culprits: In one scenario, methane's rise may come in part from a drop in hydroxyl, a chemical that acts as an atmospheric detergent; in the other, the gas is emanating from tropical wetlands flooded by heavy rains in recent years. Both have likely played a role, along with agriculture, in the methane rise, but uncertain data complicate efforts to pin the cause down. It's possible, scientists say, that an increase in methane from the tropics could be related to warming, and, much like Arctic sea ice, a signal of a system in flux.
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