28 dec. 2008

Methane Mystery

Research Highlights

Nature Reports Climate Change

Alicia Newton | Geophys. Res. Lett. 35, L22805 (2008)

Atmospheric levels of the potent greenhouse gas methane rose sharply in early 2007, having remained largely stable over the past decade. Methane is released from wetlands and wildfires as well as from human activities, such as fossil fuel use and farming, but is destroyed in the atmosphere through reaction with a compound known as the hydroxyl radical.

Now Matthew Rigby of the Massachusetts Institute of Technology and colleagues have examined the change in global emissions of methane over a ten year period. They retrieved atmospheric measurements of methane and other chemical compounds from two monitoring networks with a total of 12 worldwide locations. Methane levels rose simultaneously across all global sites since early 2007. The team propose that the increase may have coincided with a slight decline in levels of the hydroxyl radical, but the changes in hydroxyl chemistry alone were insufficient to explain the entire methane rise.

By combining the data with numerical simulations from an atmospheric transport and chemistry model, they were able to attribute the methane spike to a worldwide rise in emissions between 2006 and 2007, the bulk of which originated in the Northern Hemisphere. The exact source of the extra methane, however, remains a mystery.

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