[NEW YORK] The shale boom that flooded the US with cheap natural gas, displacing coal and nuclear power generation, isn't as green as you think.

An estimated 2.3 per cent of the gas pumped from American fields is lost to leakage from well sites, processing plants and compressor stations, according to an Environmental Defense Fund report published in the journal Science on Thursday. That's higher than the Environmental Protection Agency's 1.4 per cent estimate.

The result was based on ground measurements and aircraft observations in areas accounting for about 30 per cent of American gas production, according to the EDF. Those results were extrapolated on a national scale to calculate the leakage estimate. The report said the losses equated to enough gas to fuel 10 million homes and had a value of US$2 billion a year.

While carbon dioxide grabs most of the attention as the top contributor to climate change, methane that makes up the bulk of the natural gas stream is 80 times more potent over a 20-year period, according to the New York-based environmental advocacy group.

"The bottom line is that the amount of methane being lost across the supply chain is substantial, it's higher than current estimates from the EPA, and the amount is large enough to double the climate footprint of natural gas on a 20-year basis," Ramon Alvarez, associate chief scientist at EDF and lead author of the study, said in a telephone interview.

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The studies that were synthesised in the report were funded by the Heising-Simons Foundation, Bill and Susan Oberndorf, the Robertson Foundation, TomKat Charitable Trust and others, according to the EDF.

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