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The dramatic rise in fracking for shale gas in the US and Canada has been blamed for the puzzling surge in concentrations of a powerful greenhouse gas over the past decade.

Methane is a shorter-lived but more potent greenhouse gas than carbon dioxide. Levels of the gas in the atmosphere have been climbing since 2008, but researchers have been unsure why. Some studies in 2016聽 such as wetlands releasing more methane as the world warms, rather than fossil fuels.

Now a new study proposes that the boom in shale gas, which is largely composed of methane, is to blame. It also warns that if shale gas extraction continues to rise, it will endanger the goals of the Paris climate change agreement.

Robert Howarth at Cornell University in New York state says that taking into account methane leaks from wells and the carbon released when shale gas is burned, fracking in North America was responsible for more than half of the increase in global fossil fuel emissions in the past decade. The finding could reframe the view in some quarters that shale gas is useful for climate action, because it .

Howarth鈥檚 work looked at studies of the chemical signature of methane in the atmosphere and from shale gas operations. Natural gas obtained by conventional extraction methods contains more of a heavy sort of carbon atom called carbon-13 than methane obtained through fracking or that from natural sources.聽Howarth saw that since 2008, the composition of atmospheric methane has become lighter, meaning it has less carbon-13. Rejecting the earlier conclusions of a natural methane spike聽as erroneous, he says the result points towards more of the methane coming from fracking.

Surprising, but wrong

鈥淭hose papers from three years ago said their results were surprising,鈥� says Howarth. 鈥淭hey were surprising 鈥� but wrong. They missed this one subtle aspect.鈥�

However, Hinrich Schaefer at the National Institute of Water and Atmospheric Research in New Zealand says: 鈥淭he main problem with the scenario is that it would place about a third of rising emissions in North America.鈥� Satellite observations don鈥檛 show such high methane emissions in North America, he says.

Rebecca Fisher at Royal Holloway London says we need more data on the isotopic signatures of all methane sources, including more on shale gas, plus others such as agriculture and waste.

The research comes as the . Howarth, who聽wrote , says his new study shows shale gas shouldn鈥檛 be considered a 鈥渂ridge fuel鈥� from coal to renewables. 鈥淚t鈥檚 really a call for us to move much more aggressively away from fossil fuels,鈥� he says.