New research at the University of Rochester (UoR) says we’ve been severely underestimating the levels of methane humanity is emitting into the atmosphere via fossil fuels.

The findings are particularly worrying as although methane naturally breaks down quickly in the atmosphere (relative to CO2), it’s also a very powerful greenhouse gas, with a global warming potential (GWP) 104 times greater than CO2 over a 20-year time frame. Reducing methane emissions is critical in our effort to curb climate change, the team adds.

Too much of a bad thing

“Placing stricter methane emission regulations on the fossil fuel industry will have the potential to reduce future global warming to a larger extent than previously thought,” says lead author Benjamin Hmiel, a postdoctoral associate in the lab of Vasilii Petrenko, who is a professor of earth and environmental sciences at the UoR.

Methane is currently considered to be the second-largest contributor to global warming produced and released by human activity. Unlike CO2 (which ranks first), methane breaks down quickly — nine years on average, while CO2 can last for up to a century. This makes methane a more attractive target for short-term climate stabilization efforts, as any reductions in methane levels would translate into temperature stabilization much more quickly.

Hmiel explains that atmospheric methane comes from two sources: fossil methane and biological methane. Researchers distinguish between the two by looking at the nature of the carbon isotopes this molecule contains — carbon-14 for fossil methane (which was locked in fossil fuel deposits) and ‘regular’ carbon-13 for biological methane. Biological methane is released by all manner of biological activity; fossil methane is released either through geologically-exposed deposits (rare) or as a result of the extraction and exploitation of fossil fuels (which is much more common). Himel focused on this latter type.

“As a scientific community we’ve been struggling to understand exactly how much methane we as humans are emitting into the atmosphere,” says Petrenko, a coauthor of the study.

“We know that the fossil fuel component is one of our biggest component emissions, but it has been challenging to pin that down because in today’s atmosphere, the natural and anthropogenic components of the fossil emissions look the same, isotopically.”

The team collected ice cores from Greenland in order to establish a baseline atmospheric methane level before the onset of anthropogenic (man-made) factors. They melted the cores to extract the gas locked away in the ancient air bubbles they formed and studied its chemical composition.

Before the start of the Industrial Revolution in the 18th century, they found that virtually all the methane in the atmosphere was of biological origin. Things started to change after about 1870, when the fossil component began rising rapidly; they explain that this coincides with a sharp increase in fossil fuels at the time.

But the real finding was that levels of naturally released fossil methane are about 10 times lower than previously reported. Hmiel and his colleagues estimate that man-made fossil methane levels today are 25-40% (38-58 billion kgs) higher than previously estimated.

This may actually be good news. If we’re responsible for more of the methane in the atmosphere today, efforts to reduce our emissions would have an even better impact on the climate. If we reduce our emissions, that is.

“I don’t want to get too hopeless on this because my data does have a positive implication: most of the methane emissions are anthropogenic, so we have more control,” Hmiel concludes. “If we can reduce our emissions, it’s going to have more of an impact.”

The paper “Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions” has been published in the journal Nature.