More on underestimated methane leakage. How can climate action address natural gas?

Natural gas is commonly referred to as a ‘transition fuel’ away from coal because at the point of combustion, natural gas (56.1 mtCO₂/TJ) is less carbon intensive than coal (96.1 mtCO₂/TJ for sub-bitumous coal and 101.0 mtCO₂/TJ for lignite). However, this emission factor does not take into account the impact of leakage throughout the natural gas supply chain, which result in methane emissions (a greenhouse gas that has a global warming potential 28-36 times that of CO₂). When you take the lower emissions factor and these leakages into account, does natural gas stand up to its proponents’ claims of climate benefit?

As identified in her 2016 blogpost “Methane Emissions from the Oil and Gas Industry: Is the World getting it Right?”, Lisa Hanle called attention to the adjustments in the U.S. GHG Inventory that were required to more accurately reflect higher levels of natural gas leakage from the oil and gas sector than previously reported. These adjustments increased reported methane emissions from natural gas systems in the U.S. by 12% or 18 MMTCO₂ eq (nearly equivalent to the total annual emissions of Lithuania). The primary culprits for this inaccuracy in the previous estimation methods were low availability of data on the millions of gas wells and hundreds of thousands of miles of pipeline, and the uncertainty around emissions factors for each piece of natural gas equipment. The adjustments then came from better data and emission factors, which were then used to produce new estimates and recalculate estimates for past years. It is laudable that the USA has continued to make such improvements in its inventory, especially given the sensitive politics on natural gas consumption in the country. The next logical step, given this new understanding of the climate impact of natural gas consumption, is to question the climate benefit of natural gas as a transition energy source.

As Hanle identifies in her blog, “According to the Environmental Defense Fund, new natural gas combined cycle power plants reduce climate impacts compared to new coal plants; as long as leakage rates remain under 3.2%.”¹ this is a narrow margin of error to realize climate benefit. But even with the adjustment, the national GHG inventory from 2016 was still below this break-even point. This marginal improvement from our coal-burning baseline, is not exactly the promise of a transition fuel – especially when research continues to identify underestimation of leakage across the supply chain.²

A recent study measuring methane levels in the air above six dense, urban areas along the east coast, highlights a portion of the natural gas supply chain exhibiting actual rates of leakage (attributable to the distribution and use of natural gas in these cities) that are close to a tenfold increase above the Gridded Environmental Protection Agency (EPA) inventory for natural gas sectors. According to this study, the revealed underestimation warrants adding another 18.62 MMTCO₂ eq to the GHG inventory (and that’s just for the cities measured in the study).³ The study evaluated methane leakage (among other gases) by flying planes over six cities from Washington DC to Boston to collect samples and analyze the air. The EPA estimate of methane leakage from the same urban areas accounted for leakage from the natural gas distribution system, but it did not account for leaks occurring ‘beyond the meter’ – at homes and businesses. The study posits that underestimation of leakage and/or not including these end-use emissions is responsible for the inaccuracy of the EPA’s estimate.

While the climate benefit of natural gas usage continues to be debated, the “Madrid Call for Fast Action on Climate Super-Pollutants”, which emerged from COP25 this past December, is one initiative urging immediate action by world leaders to address these leakages. The initiative calls attention to the life-saving benefit of these reductions, through halting the rapid advance of climate change, and is calling on nations to incorporate methane reduction goals by 2030 within their NDCs. This initiative draws attention to achievable methane leakage reductions that can, and should be implemented like improvements to the natural gas pipelines and distribution infrastructure. These measures (which call for further investment in natural gas infrastructure) should be appropriately placed within the context of the ‘transition fuel’ goal, to eventually be phased out and replaced by renewables.

Natural gas leakage reductions are practical, low-cost and high reward climate actions, but where in the Madrid Call is the transition to renewables? Continued investment in a fuel that, even if leak-proof, will add to our climate’s warming and extend the lifespan of natural gas infrastructure could easily perpetuate reliance on natural gas further into the future. As a global community we must ensure the short-term gains from addressing natural gas leakage do not set us back in our long-term shift to carbon neutral energy sources.

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[1] EDF calculation based on IPCC AR4 values for radiative efficiency and atmospheric lifetimes of CH₄ and CO₂. https://www.edf.org/energy/methaneleakage

[2] https://doi.org/10.1126/science.aar7204 https://science.sciencemag.org/content/361/6398/186

[3] The study finds the total NG flux observed to be 0.75 and 0.87 Tg CH₄/year (95% confidence interval) based on the two assessment methods. Taking the lesser of these two estimates and applying the lower range of the global warming potential for CH4 (28): 0.75tgCH₄ = 0.75MMTCH₄ * 28 = 21MMTCO₂ eq. Then subtract the Gridded EPA inventory value 0.085 TgCH4/year (converting by the same methods) and you get = 18.62 MMTCO₂. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL082635