Fracking blamed for all that methane
Chemical fingerprint reveals a tell-tale change in carbon composition.
Cows, wetlands and other biological sources are not the major cause of an alarming increase in atmospheric methane levels, a new US study suggests.
Instead, the finger should probably be pointed at fracking – the process of high-volume hydraulic fracturing used to produce increasingly popular shale oil and gas.
In fact, says Robert Howarth, from Cornell University, in a paper in the journal Biogeosciences, shale-gas production in North America alone over the past decade “may have contributed more than half of all of the increased emissions from fossil fuels globally and approximately one-third of the total increased emissions from all sources globally over the past decade”.
The evidence is in the chemical fingerprint, Howarth says.
Unlike last century, when a rise in atmospheric methane was accompanied by an enrichment in carbon-13, the heavier carbon stable isotope of methane, in recent years there has been an increase in methane more depleted in 13C – such as that produced by fracking. [The numbers denote the weight of the carbon atom at the centre of the methane molecule.]
Atmospheric methane levels rose steadily during the last few decades of the twentieth century before levelling off. However, they began rising steeply again a decade ago.
“This recent increase in methane is massive,” Howarth says. “It’s globally significant. It’s contributed to some of the increase in global warming we’ve seen, and shale gas is a major player.”Methane is considered the second most important greenhouse gas behind carbon dioxide. It also leads to increased ground-level ozone levels, affecting public health and agriculture.
The one upside, Howarth says, is that it behaves differently. While carbon dioxide emitted today will influence the climate for centuries, the atmosphere responds quickly to changes in methane emissions.
“If we can stop pouring methane into the atmosphere, it will dissipate,” he says. “It goes away pretty quickly, compared to carbon dioxide. It’s the low-hanging fruit to slow global warming.”
There’s plenty of scope to do that. As Howarth states in his paper, while methane emissions are often referred to as “leaks”, not all are.
“…some of the emissions include purposeful venting, including the release of gas during the flowback period immediately following hydraulic fracturing, the rapid release of gas from blowdowns during emergencies but also for routine maintenance on pipelines and compressor stations and the steadier but more subtle release of gas from storage tanks and compressor stations to safely maintain pressures,” he writes.
Against that is the economic reality. Over that past decade, he notes, about two-thirds of all new gas production has been shale gas produced in the US and Canada.