Methane as a Greenhouse Gas
CCSP Research Highlight 1

DOE Scientists are Seeking to Understand the Details of the Many Sources of Methane...

DOE

DOE is developing global inventories and emission scenarios for methane and its precursors (carbon monoxide, volatile organic carbon, and nitrogen oxide) from energy and non-energy sources (i.e., biomass burning, vegetation, soil, the ocean, and non-vehicle mobile sources) in order to understand the influence of these gases on climate and their role in greenhouse gas abatement strategies. Results suggest that emissions from biomass burning are highest in tropical regions, primarily due to forest cutting for croplands and biofuel burning. Biogenic emission estimates indicate that rises in atmospheric CO₂, as well as climate, and land-use changes have caused a net increase in precursor emissions over the past two decades. This suggests that future emission scenarios should account for these effects in order to determine the most accurate local, regional, and global chemical composition and subsequent radiation balance of the atmosphere.

Research is also being undertaken to determine the regional and global emission rates of methane from rice fields and to investigate the connections between methane and nitrous oxide emissions from the shifting use of fertilizers in rice agriculture. These goals require field experimental studies of the processes that control emissions in addition to the emissions themselves. Data have been used to calculate the emissions of methane from rice fields at a site in Qinyuan China and the potential changes in these emission rates over the last 20 years. It has become apparent that there have been major changes in agricultural practices in China over this time. The most significant of these changes are increasing use of nitrogen fertilizers and hence a reduced reliance on organic manure, and the use of intermittent flooding in the rice fields. These practices are reducing the emissions of methane from rice fields and increasing the emissions of nitrous oxide. Since nitrous oxide is a much more potent greenhouse gas than methane small increases can offset large decreases of methane emissions.