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The February 14 issue of the journal Science contains a paper by a group of scientists from Stanford, MIT and elsewhere titled “Methane Leaks from North American Natural Gas Systems.” The paper concludes that “Methane emissions from U.S. and Canadian natural gas systems appear larger than official estimates.” From that, the paper concludes that the greenhouse gas emission advantage of vehicles powered by natural gas compared to gasoline may be less than indicated in other publications and studies, and that the GHG emissions of natural gas vehicles may even be greater than those of diesel vehicles.

NGVAmerica has prepared a fact sheet about the paper that shows why the paper’s conclusions about natural gas vehicles are not correct. We point out that:

• This is NOT a study of the GHG emissions attributable to natural gas vehicles. The natural gas vehicle conclusion almost appears as an afterthought.
• The one study cited by the authors as support for the conclusion about natural gas vehicles is not valid for that purpose.
• If the authors’ conclusion about increased methane from petroleum and natural
gas systems is used, methane emissions attributable to diesel vehicles also would be greater than the authors assumed.
• The study is not based on any new data—it is a literature review, i.e., a study of existing studies with widely varying methodologies, datasets, and conclusions.
• The authors repeatedly acknowledge the significant uncertainty in the studies, and the need for additional science, which fundamentally undermine their proposed conclusions.
• The study arbitrarily assumes that studies using “top-down” methodology, which shows more total methane in the atmosphere, are more accurate and valid than ones using rigorous “bottoms-up” methodology (which shows less), and, therefore,assumes human-caused methane emissions (including from petroleum and natural gas systems) are the cause of the discrepancy.

We expect that this paper will be used by opponents of NGVs to raise doubt about the environment benefits natural gas use—especially in heavy duty vehicles. We hope that the fact sheet will be useful in responding to media and local policy maker inquires. A copy of the fact sheet is available on the NGVAmerica website here.