600×450 CH4 + CO2, in Still A Bridge to Nowhere: Methane Emissions and the Greenhouse Gas Footprint of Natural Gas, by Bob Howarth and Tony lngraffea, 14 April 2015,
http://www.eeb.cornell.edu/howarth/documents/2015_04_14_Howarth_Ingraffea_4th_Anniversary_Lecture.pdf
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