Microbes linked to methane increase
Research is indicating that microbial sources such as wetlands and agriculture, rather than fossil fuels, are behind a recent global increase in emissions of methane, a potent greenhouse gas.
But one Colorado-based researcher says that doesn’t diminish the importance of continuing to look for ways to reduce fossil fuel methane emissions — which, while probably not increasing, likely are significantly higher than emissions inventories have suggested.
Recent findings regarding methane emissions recently were summarized in a story at the National Oceanic and Atmospheric Administration website climate.gov. The story can be found at bit.ly/globalmethane.
It notes that global methane levels have been hitting new highs after plateauing between 1999 and 2006. While the recent growth has corresponded with the domestic boom in oil and gas development involving hydraulic fracturing, chemical fingerprinting shows that the concentration of microbial-based methane in the atmosphere is increasing. Overall methane is becoming isotopically lighter, with a reduced amount of carbon 13, a heavy isotope found in methane associated with sources such as fossil fuels, wildfires and biomass cook stoves.
“That suggests that at least a substantial fraction of that methane that is being added is from microbial sources, like wetlands, for example,” Stefan Schwietzke, a Boulder-based research scientist at the Cooperative Institute for Research in Environmental Sciences, a NOAA and University of Colorado Boulder partnership, said in an interview.
Agricultural sources from rice farming to livestock are other microbial methane sources.
Schwietzke, one of the researchers quoted in the NOAA article, said the growth in microbial methane levels doesn’t mean that the level of fossil fuel methane emissions is decreasing, but only that it makes up a smaller share of overall emissions.
He said the evidence suggests it’s most likely that fossil fuel methane emissions aren’t currently increasing. But he and other scientists last year released research concluding that emission inventories have underestimated what fossil fuel methane emissions are occurring by 20 percent to 60 percent, an amount Schwietzke described as “huge.”
His research entailed using atmospheric data, and isotopic information pertaining to specific sources. Inventories are based on emissions measurements involving specific facilities and infrastructure, extrapolated to an entire industry, Schwietzke said. The top-down atmospheric and bottom-up inventory approaches each have pros and cons, he said. The inventories involve little uncertainty regarding measurements, but can easily miss emission sources, he said.
“When you use the atmospheric approach the science is more complicated but you capture all the emissions because everything ends up in the atmosphere,” he said.
He said it’s important to try to determine if global methane levels are increasing, for reasons such as asking whether more wetlands methane emissions may be resulting from climate change, contributing to a looping effect of even more methane emissions and climate change.
But overall, the change in global methane emissions is small relative to how much the emissions from fossil fuels have been underestimated, he said.
“I think what we really need to be aware of is the emissions from sources that we can actually influence right now.”
From a policy perspective, the fact that fossil fuel emissions have been significantly underestimated is more important to Schwietzke than the small amount of overall methane growth that is occurring right now.
The Western Energy Alliance oil and gas group has been pointing to the recent findings about the seeming exoneration of the fracking boom in global methane emissions growth. That science is emerging as the industry takes issue with what it considers overreaching new Bureau of Land Management and Environmental Protection Agency rules targeting oil and gas methane emissions.
Schwietzke said the oil and gas and coal industries clearly have made improvements in reducing emissions — likely as a result of new processes, technologies and management practices — over the last 30 years. Over that time fossil fuel production doubled but methane emissions may have increased by 10 percent or 20 percent at most, he said.
According to a summary of the paper Schwietzke and fellow scientists had published in the journal Nature on the underestimate of fossil fuel methane emissions, “Our findings imply a greater potential for the fossil fuel industry to mitigate anthropogenic climate forcing, but we also find that methane emissions from natural gas as a fraction of production have declined from approximately 8 percent to approximately 2 percent over the past three decades.”
With scientists still trying to better understand what’s specifically behind the growth in microbial methane emissions, and unsure in the case of wetlands emissions whether anything can even be done about it, Schwietzke sees previously underestimated fossil fuel emissions as continuing to represent low-hanging fruit when it comes to cutting methane emissions.
“In terms of what can we do right now, we know better that the fossil fuel source is a source that we probably need to target more than we previously thought we needed to, because the potential to reduce emissions is higher than we previously thought,” he said.