Leakage Rates ‘Threaten Green Benefits of Natural Gas’

by | Apr 11, 2012

Failure to reduce methane leaks has the potential to eliminate much, if not all, of the greenhouse gas advantage of natural gas over coal, according to research published in the Proceedings of the National Academy of Sciences.

Methane is the main ingredient in natural gas and burns cleaner than other fossil fuels when combusted, but un-combusted methane is a greenhouse gas many times more potent than carbon dioxide – the principal contributor to man-made climate change. As a result the gas’s leakage from production and transportation has the potential to remove any environmental benefits it boasts over traditional fuels, according to Greater Focus Needed on Methane Leakage from Natural Gas Infrastructure, whose five authors hail from Princeton, Duke, the Rochester Institute of Technology and the Environmental Defense Fund.

Assuming the EPA’s 2009 leakage rate of 2.4 percent (from well to city) is correct, new natural-gas combined cycle power plants reduce climate impacts compared to new coal plants, and do so as long as leakage remains under 3.2 percent.

However, assuming the EPA’s estimates for leak rates, compressed natural gas-fueled vehicles are not a viable mitigation strategy for climate change because of methane leakage from natural gas production, delivery infrastructure and from the vehicles themselves, the paper finds. For light-duty CNG cars to become a viable short-term climate strategy, methane leakage would need to be kept below 1.6 percent of total natural gas produced. This is approximately half the current amount for well to wheels leakage.

Methane emissions would need to be cut by more than two-thirds to immediately produce climate benefits in heavy-duty natural gas-powered trucks. At current leakage rate estimates, converting a fleet of heavy duty diesel vehicles to natural gas would result in nearly 300 years of climate damage before any benefits were achieved, the report says.

A methane leakage model created by the Environmental Defense Fund and based on the science described in the PNAS paper allows anyone to test a range of scenarios to quantify the climate benefits, or damages, of natural gas production and usage given specific methane leakage rates.

Companies the world over have been quick to buy CNG fleets and highlight their green credentials as a result. In January, AT&T ordered 1,200 Chevrolet Express compressed natural gas cargo vans while Waste Management announced a pilot program to introduce natural gas powered Rotopress waste collection trailers. In June last year, Chicago and Los Angeles rolled out CNG-fueled fleets of Ford Transit Connect Taxis.

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