Air Pollution as a Climate Forcing: A Workshop

Day 1 Presentations

Opportunities for Global Methane Emission Reduction

Paul M. Gunning
U.S. Environmental Protection Agency, Washington D.C., U.S.A.

You may download a MS PowerPoint version (3.2 MB) of this presentation.


Methane (CH4) is the second largest contributor to global warming among anthropogenic greenhouse gases, after carbon dioxide. According to the IPCC Third Assessment Report, in 1990 global anthropogenic CH4 emissions were 310 Tg, approximately 50 to 55 percent of total CH4 emissions (Table 1). Efforts to reduce these emissions as part of a multi-gas abatement strategy have received increased emphasis due to the multiple benefits that this approach offers. Recent studies have demonstrated that multi-gas abatement strategies reduce costs (Burniaux, 2000; Godal, 2002; Hayhoe et al., 1999; Manne and Richels, 2000; 2001; Reilly et al., 1999, 2000) and that such strategies can also have significant environmental benefits, particularly in the near-term (Hansen et al., 2000).

Table 1: Global Anthropogenic Methane Emission Sources
Source Category Description Estimated 1990 Emissions
(Tg CH4)
Enteric Fermentation Ruminant livestock (cattle, sheep, goats) emit CH4 as a by-product of their normal digestive process 80 - 97
Livestock Manure Management Decomposition of animal waste in anaerobic conditions produces CH4
Natural Gas and Oil Systems Methane is the major component (95%) of natural gas and is emitted during its production, processing, transmission, and distribution 68 - 94
Coal Mining Methane is trapped within coal seams and the surrounding rock strata during coal formation and is released during coal mining
Landfills Landfills produce CH4 when organic materials are decomposed by bacteria under anaerobic conditions. This is the principal source of CH4 in the European Union and the United States 51 - 62
Wastewater Methane is emitted from wastewater that decomposes under anaerobic conditions
Rice Production Rice is grown on flooded fields where organic matter in the soil decomposes under anaerobic conditions and produces CH4 29 - 61
Biomass Burning and Biofuel Burning releases greenhouse gases, including CH4 27 - 46
Source: IPCC, TAR, 2001

In the United States, the Environmental Protection Agency's (EPAs) work with the private sector has demonstrated that the economic and environmental benefits of methane emission reduction can be significant. Since 1993, EPA has been working collaboratively with industry to reduce methane emissions from the major anthropogenic sources. By 2000, these programs had succeeded in reducing United States methane emissions more than 6 percent from 1990 levels, and methane emissions are expected to remain below 1990 levels in spite of robust economic growth through 2020 (see Table 2). The success of United States efforts to reduce methane emissions stems from the fact that methane is essentially natural gas. Thus, methane emissions can frequently be collected and used as fuel instead of being emitted into the atmosphere. The value of the natural gas provides a significant source of revenue for companies undertaking methane reduction projects.

Table 2. US Methane Emissions, Reductions and Projections 1990-2020
Emissions - MMTCE 1990 2000 2010 2020
Baseline Emissions 175.5 178.8 186.7 185.1
Emission Reductions - 16 27 32.8
Net Emissions 175.5 162.8 159.7 152.3
Source: USEPA, 2001
Sector-based abatement curves

Figure 1: U.S. sector-based marginal abatement curves for selected regions year 2010. (Source: USEPA, 2002)

The opportunity for international application of the lessons learned from EPA's efforts in the United States is significant. Recent work by EPA suggests that in 2025 CH4 emissions could nearly be stabilized at 2000 levels with a carbon price signal of $100/TCE through the broad deployment of currently available mitigation technologies for the four major CH4 sources (landfills, coal mines, natural gas and oil systems, and manure management systems). Maintaining stabilization in later years will require additional reductions from agricultural sources, particularly rice production and ruminant livestock. Figure 1 displays the United States sector-based marginal abatement curves for the selected regions. Table 3 outlines the mitigation potential from these selected emission sources.

The complete presentation on the workshop website provides an overview of global mitigation potential for all the major anthropogenic CH4 emission sources, describes some of the key technologies that could achieve these climate benefits, and provides suggestions for the prioritization of future CH4 mitigation efforts.

Table 3. Selected Region Baseline Emissions and Reductions1 for 2010
Source Reference Baseline 2010 (MMTCE) Reductions at $150/TCE (MMTCE) % of Baseline
Natural Gas 216 109 50%
Underground Coal Mining2 88 57 65%
Landfills 159 74 47%
Livestock Manure Management3 44 31 69%
13 Regional Total 507 270 53%
Global Total4 for above sources 725 Coverage as % of Global 70%
Global Total4 for all sources 1,588 Coverage as % of Global 32%
Notes: Regions include: Australia / New Zealand, Brazil, Canada, China, Eastern Europe, European Union, India, Japan, Mexico, Russia, South Korea, Ukraine and the US.
1Reductions based on applying US sector-based MACs to each region's sectors and adding up.
2Underground coal mining excludes surface mining emissions.
3Manure management includes swine and cattle, but excludes "other" for US only.
4Global methane estimates from MiniCAM runs courtesy of H.Pitcher, PNNL. Global Total all sources adds entire fermentation, rice production, biomass burning, domestic sewage to the 4 previous sources.

Workshop Homepage * Background
Summaries: Overview, Gases, Aerosols, Tech., Health, Agri./Eco.
Abstracts: Day 1, Day 2, Day 3, Day 4, Day 5 * Participants