Methane is more than 100 times more potent that carbon dioxide as a greenhouse gas emission, and it’s been on the rise for about a decade. Scientists have been debating what’s behind the spike — wetlands, cows and landfills all emit methane. But a recent study by Robert Howarth, an ecology and environmental biology professor at Cornell University, in the journal Biogeosciences ties much of that increase to shale gas released through fracking.

Howarth found his culprit by lifting chemical fingerprints from methane in the atmosphere. The emission’s chemical makeup varies slightly depending on the source, and Howarth found at least a third of new methane has a lower proportion of carbon-13 in relation to carbon-12 , suggesting it came from shale gas.

“Shale gas is the methane that’s been trapped over geological time in the shale, and it’s released only when we use high-volume hydraulic fracturing — technology that’s only been in widespread commercial use for the last decade or so,” Howarth said. “Conventional natural gas is methane which broke free from shale, migrated through semi-porous rock materials like sandstone over periods of tens to hundreds of millions of years until trapped inside some sort of a cavity. That migration … results in a loss of the lighter carbon-12 isotope.

“So the conventional natural gas that we’ve been harvesting in the 20th century ends up having more carbon-13 than shale gas from fracturing,” he said.

Shale gas is released rapidly, so it hasn’t lost carbon-12.

Howarth said his paper underscores the importance of reducing use of natural gas.

“Reducing methane emissions offers us a real chance — the only chance, I would say — of reaching the UN COP21 target of trying to keep our planet well below 2 degrees Celsius from the pre-industrial baseline,” he said. “I think the way to go is to move as quickly as we can away from all fossil fuels. We need to do so anyway to get rid of the carbon dioxide, but a lot of times people say let’s focus...