Many commentators and policymakers, including the Obama administration in the United States tout natural gas as a “bridge” fuel in the transition to decarbonizing the world’s economy. However, while natural gas produces far more energy per carbon dioxide molecule formed than coal (177%) and oil (144%) major concerns have been raised about the leakage of methane from natural gas from the point of extraction to consumption. Indeed, given the global warming potential of methane over a 100-year time horizon (25x more potential carbon dioxide), recent studies have indicated that natural gas leakage rates of more than 3.2% would yield greater climatic impacts than from combustion of coal.
Unfortunately, the rate of methane emissions from natural gas production remain highly contested. For example, in the United States, the U.S. EPA’s estimates of leakage rates have varied by as much as a factor of 10 over the course of only a few years. In a new study published in Geophysical Research Letters, nineteen researcher contend that this disparity in estimates may be attributable to “bottom up” assessments “in which emission factors for multiple processes are multiplied by an inventory of activity data.” Moreover, EPA’s 80 different EPA emissions factors associated with the oil and gas industry are based on a study conducted in the 1990s and, questionably, assumes consistency by industries in a number of different regions.
The researchers sought to assess emissions factors using a “mass balance” approach, a measure-based method to estimate total emissions released from a defined point, facilitating direct assessment of uncertainties associated with the magnitude of methane leakage rates. The study presented results from a natural gas and oil production field in the Uintah Basin in eastern Utah.
The results of the study yielded a natural gas leakage rate of 6.2-11.7% on February 3, 2012, negating an short-term (<70 years) climate benefit of natural gas production compared to electricity production from oil or coal. Appropriately, the researchers of the study cautioned against drawing hasty conclusions given the fact that this was only a one-day snapshot of regional emissions. However, they also pointed out that their results were consistent with several other recent “top-down” studies utilizing that had found bottom-down inventory assessments substantially underestimating methane leakage rates.
At the very least, this study emphasizes the need for continued research in this context. This study would afford students with extensive energy and atmospheric science expertise with an excellent opportunity to wrestle with the merits of starkly different methodological approaches. For students with less expertise, it would provide an excellent gateway into discussing the importance of global warming potentials of various greenhouse gases and to remind them of the importance of life cycle assessments of various energy options.