A 21st century shift from fossil-fuel to biogenic methane emissions indicated by 13CH4

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Science  10 Mar 2016:
DOI: 10.1126/science.aad2705

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Between 1999 and 2006, a plateau interrupted the otherwise continuous increase of atmospheric methane concentration [CH4] since pre-industrial times. Causes could be sink variability or a temporary reduction in industrial or climate sensitive sources. We reconstruct the global history of [CH4] and its stable carbon isotopes from ice cores, archived air and a global network of monitoring stations. A box-model analysis suggests that diminishing thermogenic emissions, probably from the fossil-fuel industry, and/or variations in the hydroxyl CH4-sink caused the [CH4]-plateau. Thermogenic emissions didn’t resume to cause the renewed [CH4]-rise after 2006, which contradicts emission inventories. Post-2006 source increases are predominantly biogenic, outside the Arctic, and arguably more consistent with agriculture than wetlands. If so, mitigating CH4-emissions must be balanced with the need for food production.

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