Levels of methane—the second biggest contributor to climate change after carbon dioxide—have spiked in the atmosphere in the past decade. And a study says fracking in North America could be partly to blame. 

The gas is linked to climate change, as well as ground-level ozone levels that can harm agriculture. It can also trigger a range of health problems, including chest pains, as well as reducing lung function and worsening conditions such as bronchitis, emphysema and asthma.

In the last half of the 20th, century levels of methane in the atmosphere rose. They then plateaued, and spiking in 2008. Robert W. Howarth of Cornell University, who published a study in the journal Biogeosciences, investigated fracking as a potential culprit. 

Hydraulic fracturing, known as fracking, is the process of extracting gas and oil from shale sedimentary rock using pressurized liquid. The method is controversial and has been linked to contaminated drinking water in the U.S, methane gas escaping from wells into the atmosphere and earthquakes.

First performed in 1949, the fracking industry has boomed in the past decade or so. Between 2005 and 2015, global rates of fracking went from producing 31 billion cubic meters per year to 435 billion, according to Howarth. Of this, 89 percent occurred in the U.S., and 10 percent in Canada. The U.S Department of Energy forecasts production will spike to 1500 billion cubic meters per year by 2040.

For the new study, Howarth looked at existing research on the levels of certain carbon isotopes of atmospheric methane to find a potential source, and created an equation to investigate the link. 

Methane is a compound made up of carbon and hydrogen. While methane released in the late 20th century was enriched with the carbon isotope 13C, Howarth highlights methane released in recent years features lower levels. That's because the methane in shale gas has depleted levels of the isotope when compared with conventional natural gas or fossil fuels such as coal, he explained.

This lead Howarth to conclude: "The commercialization of shale gas and oil in the 21st century has dramatically increased global methane emissions." 

If trends of releasing methane continue, he said, this will "significantly increase global warming and undercut efforts" to meet the United Nations Framework Convention on Climate Change to keep post-industrial revolution global temperatures below 2 C.

Howarth urged those involved in the energy industries to "move as quickly as possible away from natural gas, reducing both carbon dioxide and methane emissions."

The good news, argued Howarth, is that climate reacts quicker to methane than carbon dioxide, meaning cutting emissions of the gas emissions "could provide an opportunity to immediately slow the rate of global warming." 

This could help the commitment of the Paris Agreement be met.

Howarth said in a statement: "This 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."

"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." 

Researchers not involved in the study welcomed Howarth's efforts, but pointed out some limitations. 

Grant Allen, professor of atmospheric physics at the U.K.'s University of Manchester, commented: "A wide range of different methane fluxes from different source types (e.g. fossil fuels, agriculture, wildfires and wetlands) can all simultaneously explain the observed trend in methane (and carbon isotopes of methane) within the limits of uncertainty in our knowledge of their carbon-isotopic fingerprints and estimates of total methane emitted from each source type.

"Other work has also proposed a role for changing chemical sinks of methane in the atmosphere. The jury is still out on the relative importance of all of these sources in explaining methane's rise."

Allen continued: "However, this paper makes a very important point—some sources of methane are within our gift to control, other (natural sources) are not as easily targeted. Controlling emissions from fracking, and fossil fuels in general, represents a potential policy quick fix to stemming the rise of methane still further." 

Quentin Fisher, professor of petroleum geoengineering at the U.K.'s University of Leeds, said he was "deeply skeptical" about the study.

"The results are extremely sensitive to highly questionable assumptions regarding the isotopic composition of methane found in shale. The arguments made by previous studies that increase in methane in the atmosphere is from biogenic sources, such as release from wetlands and agriculture or burning of biomass, seem far more convincing."

"It's also the case that the study itself admits that even if the increased methane concentrations were from shale that they are not a direct result of the hydraulic fracturing process," he argued.

"For example, the USA has an aging gas transportation network, which results in significant methane leakages."

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