The Greenhouse Gas Methane (CH4): Sources and Sinks, the Impact of Population Growth, Possible Interventions

Heilig, G.K. (1992). The Greenhouse Gas Methane (CH4): Sources and Sinks, the Impact of Population Growth, Possible Interventions. IIASA Working Paper. IIASA, Laxenburg, Austria: WP-92-042

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Abstract

Methane is one of the trace gases in the atmosphere that is considered to play a major role in what is called the "greenhouse effect". Despite its still extremely minute concentration (around 1.7 ppmv) this radiatively and chemically reactive gas has been accumulating in the atmosphere at the rate of 1% per year. Today the methane concentration is about double that in the preindustrial era.

There are six major sources of atmospheric methane: emission from anaerobic decomposition in (1) natural wetlands and (2) paddy rice fields; (3) emission from livestock production systems (including intrinsic fermentation and animal waste); (4) biomass burning (including forest fires, charcoal combustion, and firewood burning); (5) anaerobic decomposition of organic waste in landfills, and (6) fossil methane emission during the exploration and transport of fossil fuels. Obviously, human activities play a major role in increasing methane emissions from most of these sources. Especially the worldwide expansion of paddy rice cultivation, livestock production and fossil fuel exploration have increased the methane concentration in the atmosphere.

The paper first reviews the evidence for an increase in atmospheric methane concentration. There are several data sets available from sampling programs and ice core studies that help estimate atmospheric methane concentration up to several ten thousand years back. Then major sources and sinks of present-day methane emission and their relative contribution to the global methane balance are discussed. It is demonstrated that there are great uncertainties in the identification and quantification of individual sources and sinks. The paper also presents the most recent methane projections of the Intergovernmental Panel on Climate Change (IPCC) for 2025 and 2100 and discusses their validity. These projections are also used to estimate the contribution of population growth to future methane emission. Finally the paper discusses options and restrictions of reducing anthropogenic methane emissions to the atmosphere.

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