Methane Pollution from Human Activities: Capture It, Convert It, Count It

Next to carbon dioxide (CO2), methane (CH4) is the second largest source of human greenhouse gas (GHG) pollution in the United States (in terms of Global Warming Potential). Much of it is biomethane emitted from landfills, livestock manure management, and sewage. Capturing it and converting it to useful energy can address multiple economic, energy, environmental and climate concerns. But counting the production and use of biomethane for the purposes of meeting climate pollution reduction goals requires more care, according to the California Energy Commission.

On April 16, the U.S. Environmental Protection Agency (EPA) released The Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2010 . According to the EPA press release , "The final report shows overall emissions in 2010 increased by 3.2 percent from the previous year." Total U.S. GHG emissions increased 10.5 percent from 1990 to 2010.

With regard to biomethane emissions, the report finds emissions from landfills have declined 16.2 percent since 1990 due to increased capture and combustion of the methane. However, emissions from manure management and sewage have increased 64 percent and 2.5 percent, respectively. Measured in terms of Global Warming Potential, these three sectors produce about 2.6 percent of total U.S. GHG emissions. The EPA estimates that CH4 is 21 times more potent as a GHG than CO2 over a 100-year time horizon.

Capturing and converting biomethane to useful energy can address multiple economic, energy, environmental and climate concerns. For more perspectives on this, see EESI’s briefing Renewable Biogas: Too Valuable to Waste . Clearly, technologies exist that can significantly reduce biomethane emissions. What is missing are policies that would encourage much more investment to move into these sectors.

However, counting the contribution of biomethane capture and use for meeting climate pollution reduction goals can be problematic. This is especially true when biomethane is upgraded to pipeline quality and shipped via the natural gas grid to the end user. How can state regulators assure that GHG emissions are actually being reduced as a result of biomethane capture and energy conversion? How can they assure that fossil fuels are actually being displaced? How can additionality be assured (i.e., that the biomethane burned in a power plant is not just being diverted from some other equivalent previous use)? How can they assure that the climate benefits are not being double counted?

These are the types of questions that the California Energy Commission (CEC) cited when they decided to suspend the eligibility of biomethane (when shipped via pipeline to electric generation facilities) to be certified as a renewable energy source under California’s renewable portfolio standard. For background on the CEC’s decision, see the March 28 CEC Notice to Consider Suspension of the RPS Eligibility Guidelines Related to Biomethane . Click here to see the CEC resolution of April 6. For additional interpretation and analysis, link to this report from Stoel Rives .