The boom in fracking for shale gas has “dramatically increased” global methane emissions in the past decade, a study has warned.
While the rapid rise in levels of methane, a significant greenhouse gas, in recent years has been attributed to biological sources such as cows, tropical wetlands and rice fields, new research points to the role of fracking.
The research from Cornell University looks at the “chemical fingerprint” of methane in the atmosphere and concludes that around a third in the past decade has come from exploiting shale gas.
Methane levels rose steadily in the last decades of the 20th century before levelling off for the first decade of the 21st century, but since 2008 they have been rising rapidly again.
If the rise continues in coming decades, it will significantly increase global warming and undercut efforts to meet international targets to curb dangerous climate change under the Paris Agreement, the study warns.
Methane from different sources has a different chemical signature, relating to the weight of the carbon atom at the centre of the gas molecule.
Methane from fossil fuels has higher concentrations of the heavier carbon-13 variant compared with lighter carbon-12, while the gas emitted from biological sources is lighter, with less carbon-13.
The rise in methane since 2008 has also seen the carbon composition of the gas change, with lower levels of carbon-13.
This led experts to attribute the spike to biological sources, most likely tropical wetlands, rice culture or animal agriculture.
But the research shows methane that leaks or is vented from the process of fracking for shale gas also has a lower carbon-13 content than conventional fossil fuels.
There has been a boom in the US exploiting shale gas through hydraulic fracturing, or fracking, which involves pumping liquid at high pressure deep underground to fracture shale rock and release gas.
The study concludes that methane from fossil fuels has probably exceeded emissions from biological sources in the past decade – with shale gas accounting for more than half of the total from fossil fuels.
Around a third of the total increased emissions from all sources globally over the past decade is down to shale gas production, according to the study published in Biogeosciences, a journal of the European Geosciences Union.
The study said: “The commercialisation of shale gas and oil in the 21st century has dramatically increased global methane emissions.”
Study author Professor Robert Howarth said the recent increase in methane “is massive”.
“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 a potent greenhouse gas, but while carbon dioxide has a long-term impact in the atmosphere the climate responds more quickly to changes in methane.
Prof Howarth said: “If we can stop pouring methane into the atmosphere, it will dissipate. It goes away pretty quickly, compared to carbon dioxide. It’s the low-hanging fruit to slow global warming.”
In the UK, the Committee on Climate Change has warned that emissions from nascent shale gas industry must be strictly limited with tight regulation, close monitoring and rapid action to address methane leaks.
But the study said that given its finding that gas – both shale and conventional – was responsible for much of the recent increase in methane, “the best strategy is to move as quickly as possible away from natural gas”, warning it was not a “bridge fuel” from fossil fuels such as coal to cleaner technology.
