Are Microbes Increasing Levels of Methane in the Atmosphere?

Though it breaks down faster than CO2, methane is a greenhouse gas over 80 times as potent as carbon dioxide, reports the Washington Post. It suddenly started increasing in the atmosphere in 2007 - and then in 2020, its growth rate doubled. While scientists have suspected it was natural gas, some researchers have a new theory..."The changes that we saw in the last couple of years - and even since 2007 - are microbial," said Sylvia Michel, lead author of the paper published last month in the Proceedings of the National Academy of Sciences. "Wetlands, if they are getting warmer and wetter, maybe they're producing more methane than they used to...." Michel and her co-authors analyzed samples of methane, or CH4, from 22 sites around the globe at a Colorado laboratory. Then they measured the "heaviness" of that methane - specifically, how many of the molecules had a heavier isotope of carbon in them, known as C13. Different sources of methane give off different carbon signatures. Methane produced by microbes - mostly single-celled organisms known as archaea, which live in cow stomachs, wetlands and agricultural fields - tends to be "lighter," or have fewer C13 atoms. Methane from fossil fuels, on the other hand, is heavier, with more C13 atoms. As the amount of methane has risen in the atmosphere over the past 15 years, it's also gotten lighter and lighter. The scientists used a model to analyze those changes and found that only large increases in microbial emissions could explain both the rising methane and its changing weight.... Researchers say it doesn't mean that the world can just keep burning natural gas. If wetlands are releasing methane faster than ever, they argue, there should be an even greater push to curb methane from the sources humans can control, such as cows, agriculture and fossil fuels. The article includes this quote from Stanford University professor Rob Jackson (who works on the Global Methane Budget, a project tracking the world's methane sources). "You can turn a wrench in an oil and gas field to quench methane emissions," Jackson said. "There's no wrench for the Congo or the Amazon."Another recent study found that two-thirds of current methane emissions are caused by humans - from fossil fuels, rice cultivation, reservoirs and other sources. "Methane forms biologically in warm, wet, low-oxygen environments," Jackson said. "The wetlands of a rice paddy and the gut of the cow are all similar." But evidence is also emerging that natural wetlands may be responding to warming temperatures by pumping out more methane. Satellite data from recent years has shown global methane hot spots in the tropical wetlands of the Amazon and the Congo. "Wetlands will emit more methane as temperatures warm," Jackson said. "This may be the start of a reinforcing feedback, that higher temperatures release more methane from natural ecosystems...." Over 100 countries have pledged to reduce their methane emissions by 30 percent by 2030, compared with 2020 levels - but so far, that pledge has yet to see results. Instead, satellite measurements show concentrations are rising at a rate that is in line with the worst-case climate scenarios.

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