This commentary originally appeared on the EDF Voices Blog.
Mounting scientific evidence underscores the crucial importance of reducing methane emissions in the U.S. The latest study, published today in the journal Science, reviewed available data from the past 20 years and found that methane emissions from the U.S. natural gas supply chain are almost two times greater than current official estimates – flagging once again that methane emissions are a serious problem. However, the Stanford-led team also concluded that the current levels of methane leakage negates the climate benefit of switching to natural gas under some scenarios and not others, such as moving from coal-powered to natural gas electric generation.
As for what contributes to the higher than expected emissions, the study authors cited differing measurement techniques—including “bottom-up” direct measurement at the source, “top-down” readings from aircraft, and others—as well as the presence of “super-emitters” (a small number of sites or pieces of equipment producing a large share of emissions). Super-emitters are not easily sampled using most bottom-up direct measurement approaches. The team also spotlighted challenges associated with an increasingly ambiguous distinction between emissions from natural gas and oil production, both of which contribute methane to the atmosphere.