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Preindustrial CH4 indicates greater anthropogenic fossil CH4 emissions

Benjamin Hmiel, V V Petrenko, M N Dyonisius, C Buizert, A M Smith, P F Place, C Harth, R Beaudette, Q Hua, B Yang, I Vimont, S E Michel, J P Severinghaus, D Etheridge, T Bromley, J Schmitt, X Faïn, R F Weiss, E Dlugokencky (2020)

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The paper seeks to determine the magnitude of methane emissions from fossil fuel extraction. It does so by using pre-industrial-era ice core methane measurements to demonstrate that natural geological methane emissions to the atmosphere were much lower than currently used estimates. As a result, measurements of anthropogenic fossil methane emissions are an underestimate, suggesting the human impact on the climate from such emissions is higher than previously thought.  


The methods used in the study include using a large-diameter ice drill and large-volume ice-melting apparatus to obtain sufficient methane for analysis. Carbon-14 in methane can be used to distinguish between fossil methane emissions and contemporaneous biogenic sources. The study finds an increase in the total methane emissions, from negligible levels in the mid-19th century to 64.8 teragrams of methane per year in 1940.  


This result suggests that anthropogenic fossil CH4 emissions are underestimated by 38-58 teragrams CH4 per year, or about 25-40% of recent estimates. The study also demonstrates that fossil fuel-based methane emissions now account for around 30% of the global source of methane and for almost 50% of anthropogenic methane emissions. This indicates the importance of reducing methane emissions in climate mitigation efforts.  


The article demonstrates the considerable contribution the oil and gas sectors make to methane emissions, and the underestimation of recent bottom-up inventory estimates. It can be used to challenge assessments for methane emissions inventories, providing more accurate baselines against which anthropogenic methane can be measured.

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