THE Los Angeles metropolitan region belches out far more methane than previously realised. If other megacities do too, urban methane emissions may represent an important source of this potent greenhouse gas.
A team led by at the California Institute of Technology in Pasadena calculated methane emissions for the Los Angeles region, then subtracted out all known sources of methane, such as livestock, landfills and sewage. That left an enormous amount of methane 鈥� up to half of the total 鈥� that could not be accounted for by known sources.
If similar results are found in other urban areas, then unknown urban sources could account for 7 to 15 per cent of humans鈥� global emissions of the gas, the researchers calculate 鈥� far more than was thought (Geophysical Research Letters, ).
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鈥淵ou鈥檇 like to find out the source, so you can put a stopper in it,鈥� says Wennberg. The extra methane may be leakage from landfills, sewage treatment plants or natural gas pipelines, or it could be natural seepage from oil wells, the team suggest.