Over its full cycle of production, distribution, and use, natural gas emits just over half as many greenhouse gas emissions as coal does for equivalent energy output, according to a new study from the Worldwatch Institute (www.worldwatch.org) and the Deutsche Bank Climate Change Advisors.
The analysis clarifies the role of methane releases in the calculation of comparative emissions between the two fossil fuels and explores how the growing share of natural gas production from shale formations could change that fuel's footprint.
Earlier this year, the U.S. Environmental Protection Agency (EPA) updated its methodology for estimating methane emissions from natural gas systems, generating concern that the new, higher methane figures could minimize the greenhouse gas advantage that natural gas is seen widely to have over coal.
Applying the EPA's new estimates, the life-cycle greenhouse gas footprint of natural gas-fired electricity increased roughly 11 percent, according to the study.
'Despite a substantial increase in the methane assumed to be emitted during natural gas production, we found that U.S. natural gas-fired electricity generation still released 47 percent fewer greenhouse gases than coal from source to use,' said Saya Kitasei, a Worldwatch Institute Sustainable Energy Fellow and one of the contributing writers.
The authors stress that although methane emitted during natural gas production might not make natural gas-fired electricity dirtier than coal, it can and must be mitigated immediately. 'In addition to being a potent greenhouse gas, methane is a valuable energy source that natural gas producers should be capturing for sale,' said Kitasei.
'Because some of the same technologies that prevent methane from entering the atmosphere also reduce emissions of smog-forming compounds, tackling methane emissions is a win-win-win proposition.'
The study points out that regulatory and technological tools to reduce methane emissions are being demonstrated in some U.S. states and by some companies.
Although reducing methane emissions has been largely voluntary to date in the United States, new EPA rules could require the natural gas industry to measure and report its greenhouse gas emissions and to use control technologies that will significantly reduce associated methane emissions as early as 2012.
Further highlights from the study:
- The EPA's recent upward revisions of methane emissions from natural gas are related largely to the production share of the gas value chain, especially during the unloading of liquids and (in the case of hydraulically fractured wells) during flowback.
- The life-cycle greenhouse gas footprint of natural gas is lower than coal under all 'global warming potentials' tested, with the smallest difference calculated using a GWP of 105, where the emissions are 27 percent less than those of coal-fired generation.
- Methane emissions during natural gas production, processing, transport, storage, and distribution can be mitigated now at moderately low cost using existing technologies and best practices. Such capture potential presents a commercial and investment opportunity that would further improve the life-cycle greenhouse gas