Large-scale fires make a significant contribution to methane emissions

Vincent Simonneaux, IRD

Methane's impact on the climate may be less than previously thought, say researchers who observed that its atmospheric levels have remained constant for the past seven years.

The findings are significant because they suggest that human activity can help cut down methane emissions, says Isobel Simpson, of the US-based University of California, Irvine, who led the study.

The research, published tomorrow (23 November) in Geophysical Research Letters, analysed global levels of methane since 1978.

Large-scale fires in Indonesia and Russia in the past decade produced observable peaks in atmospheric levels of the gas, confirming that biomass burning can significantly increase levels of this gas in the atmosphere.

"Two-thirds of methane sources are [caused by people]. These include energy use, landfills, ruminants [cattle], rice agriculture, and biomass burning," Simpson told SciDev.Net.

Given that atmospheric methane levels are currently stable, reducing emissions from any of these sources would reduce methane concentration.

Also, because methane has a much shorter lifespan as a greenhouse gas than carbon dioxide — eight years compared to 100 — any reductions take effect quickly. This means that even small emission reductions would help bring methane concentrations down, says Simpson.

"The fact that methane has not increased [means that] climate impact may be less than previously indicated," says Donald Blake, an atmospheric scientist at the Univerisity of California, Irvine and one of the study's authors.

Blake suggests that methane emissions could be cut by pumping it out of landfills and re-using it as a fuel. Also, improved technologies could prevent leaks from oil and gas lines and storage facilities, which the researchers believe partly explain why methane emissions have stopped rising.

Methane is produced mainly by landfills, rice paddies, swamps, natural gas fields and cattle. Although significantly less methane is emitted than carbon dioxide, the gas traps more than 21 times more heat per molecule.