A recently published article (Brandt et al.) assessed methane leakage rates from the natural gas sector and concluded that “official inventories consistently underestimate actual CH4 emissions, with the [natural gas] and oil sectors as important contributors…” The report stacks up 20 years of research—with different scales and seemingly different findings—along a common baseline. It compares bottom-up leakage surveys to top-down atmospheric studies, and it compares both types of analyses to official emission factors published by the EPA. It concludes that there is a significant emissions gap, meaning that CH4 emissions reported by the EPA are too low by 25 – 75%.
One reason for the existence of this emissions gap is the variation in leakage rates across sites and across the country, which makes it difficult and costly to accurately sample emissions rates. A small number of “super-emitters” are likely to make up a significant part of the emissions gap, and these sources tend to be underrepresented in studies with small sample sizes. On the other hand, some regional studies measured emissions that are probably higher than the national average. But one thing is clear, official methane emissions estimates are far lower than what they should be, considering the actual amount of methane observed in the atmosphere.
It is widely known that not all of the methane in the atmosphere is from the oil and gas sectors, but Brandt et al. make the case that much of methane emissions gap is in fact due to methane emitted by these sectors. First, it is easy to separate biogenic methane (from livestock, landfills, etc.) from non-biogenic methane (from fossil fuels) by analyzing the methane’s isotopic composition. Less trivial, however, is separating non-biogenic methane from oil and gas production from other sources of non-biogenic methane, including from abandoned oil and gas wells and geologic seeps. Brandt et al. find estimates in the literature about emissions from these various sources and compare them to the total methane emissions gap. While methane emissions from abandoned oil and wells are notable, the largest component of the emissions gap can indeed be attributed to oil and gas production and distribution.
Despite the higher methane emissions rates discussed by Brandt et al., natural gas still has climate advantages over coal in the electric power sector, but they also found that the climate benefits of natural gas in the transportation sector are doubtful at best, at this point. And, burning natural gas still emits CO2, and, as this study highlights, the methane emissions are significant. Carbon capture and storage must be an essential part of reducing CO2 emissions from natural gas combustion. Likewise, cost-effective technologies to reduce methane emissions from the production, processing, and transportation of natural gas must be implemented. Doing so is critical to meeting the President’s publicly stated pledge to reduce greenhouse gas emissions by 17% by 2020. Therefore, we are urging this Administration to tightly regulate methane emissions from the oil and gas industry. While studies like this are helpful, we need to act now to curb emissions.