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    • Scientists may have solved the mystery behind a major climate threat
    patheur

    Scientists may have solved the mystery behind a major climate threat

    Sakege Posted on

    shannon osaka
    | Washington Post

    Nearly two decades ago, levels of methane in the atmosphere, a dangerous greenhouse gas that is 80 times more potent than carbon dioxide in the short term, began to rise. And go up.

    Methane concentrations, which had remained stable for years, soared by 5 to 6 parts per billion each year from 2007 onwards. Then in 2020, the growth rate almost doubled.

    The scientists were baffled… and worried. Methane is the big question mark hanging over global climate estimates; Although it decomposes in the atmosphere much faster than fossil fuels, it is so powerful that higher-than-expected levels of methane could cause the world to reach much higher temperatures.

    But now, a study sheds light on what is causing record methane emissions. The culprits, scientists believe, are microbes, the small organisms that live in the stomachs of cows, agricultural fields and wetlands. And that could mean a dangerous feedback loop. – in which these emissions cause warming that releases even more greenhouse gases – is already underway.

    “The changes we have seen in recent 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 Science. “Wetlands, if they are getting warmer and wetter, maybe they are producing more methane than before.”

    It is difficult for scientists to identify all the sources of methane in the world. It comes from oil and gas leaks at operations, cow belches, landfills and marshes, and thawing permafrost in the Arctic. When methane emissions increase, finding the cause is like solving a complicated algebra problem with too many unknowns.

    And it is a problem that will determine the fate of the climate.

    For a time, scientists thought that rising methane emissions were due to growth in the use of natural gas, which is largely methane. Leaks from boreholes or pipelines can release greenhouse gases into the atmosphere.

    But the new paper points to microbes as the biggest source of the methane increase. Michel and his co-authors analyzed samples of methane, or CH4, from 22 sites around the world in a Colorado laboratory. They then measured the “heaviness” of that methane—specifically, how many of the molecules had a heavier carbon isotope, known as C13.

    Different sources of methane emit different carbon signatures. Methane produced by microbes – mostly small, 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 and has more C13 atoms.

    As the amount of methane has increased in the atmosphere over the past 15 years, it has also become increasingly lighter. The scientists used a model to analyze these changes and found that only large increases in microbial emissions could explain both the increase in methane and its change in weight.

    “The key thing about their conclusion is that it was neither fossil nor geological,” said Rob Jackson, a Stanford University professor who was not involved in the study and is part of the Global Methane Budget, a project that tracks the sources and emissions of methane around the world. the planet.

    However, the research does not show how many of those emissions were natural or man-made. While wetland microbes are largely natural, these tiny creatures can also pump methane from reservoirs, farmland, and landfills.

    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 hot, humid, low-oxygen environments,” Jackson said. “The wetlands of a rice field and the intestine of the cow are all similar.”

    But evidence is also emerging that natural wetlands may be responding to rising temperatures by pumping out more methane. Satellite data in recent years has shown global methane hot spots in the tropical wetlands of the Amazon and Congo.

    “Wetlands will emit more methane as temperatures rise,” Jackson said. “This may be the beginning of a feedback that reinforces the fact that higher temperatures release more methane from natural ecosystems.”

    Michel says it’s too early to say whether this is the start of a vicious cycle. “Do they come from human-caused changes in freshwater systems or are they some kind of scary climate feedback?” she said. “I want to be careful about what we can and can’t say with this data.”

    Researchers say this doesn’t mean the world can continue burning natural gas. If wetlands are releasing methane faster than ever, they argue, there should be an even bigger push to curb methane from sources humans can control, such as cows, agriculture and fossil fuels.

    More than 100 countries have pledged to reduce their methane emissions by 30 percent by 2030, compared to 2020 levels, but so far, that pledge has yet to see results. Instead, satellite measurements show that concentrations are increasing at a rate consistent with worst-case climate scenarios.

    “You can turn a wrench in an oil and gas field to turn off methane emissions,” Jackson said. “There is no problem for the Congo or the Amazon.”

    Sakege
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