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A TEAM of scientists has refuted the findings of a controversial and frequently-cited study published by a US university last year, which claimed that shale gas is more of a danger to the environment than coal.

The original study by Cornell University ecology professor Robert Howarth concluded that the shale gas industry is emitting large volumes of fugitive methane emissions into the atmosphere, and as methane has a higher global warming potential than the CO₂ produced by coal, the environmental footprint of shale gas is at least 20% to more than twice the size of coal.

The finding flew in the face of claims that the US’ ever-increasing shale plays could provide large volumes of ‘cleaner’ gas that would help the nation wean itself off ‘dirtier’ coal and make the transition towards a greener energy mix eventually dominated by renewables.

Howarth concluded that: “The large greenhouse gas footprint of shale gas undercuts the logic of its use as a bridging fuel over the coming decades, if the goal is to reduce global warming.”

Environmental and anti-fracking protestors cited the study in support of their own cause.

Now, a second study by a different group of researchers from Cornell, including chemical engineer Andrew Hunter, has published what it claims is a more rigorous paper that overturns Howarth’s “inappropriate” assumptions.

Howarth, they say, fails to recognise that technical advances are being developed and adopted to reduce emissions from shale gas operations, while promoting those used by the coal industry; ignores the low residence time of methane in the atmosphere; and overestimates the volume of methane leaking from shale gas wells.

“[Howarth] assumes that initial production statistics can be extrapolated back to the gas venting rates during the earlier periods of well completion and drill out. This is incompatible with the physics of shale gas production, the safety of drilling operations, and the fate of the gas that is actually indicated in their references,” the authors write.

The new study concludes that by “using more reasonable leakage rates and bases of comparison, shale gas has a greenhouse gas footprint that is half and perhaps a third that of coal”.

Climate Change doi: 10.1007/s10584-011-0333-0