The growth of methane emissions slowed around the turn of the millennium, but began a rapid and mysterious uptick around 2007. The spike has caused many researchers to worry that global warming is creating a feedback mechanism that will cause ever more methane to be released, making it even harder to rein in rising temperatures.
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[S]ince 2007, when methane levels began to rise more rapidly again, the proportion of methane containing 13C began to fall (see ‘The rise and fall of methane’). Some researchers believe that this suggests that much of the increase in the past 15 years might be due to microbial sources, rather than the extraction of fossil fuels.
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Regardless of how this mystery plays out, humans are not off the hook. Based on their latest analysis of the isotopic trends, Lan’s team estimates that anthropogenic sources such as livestock, agricultural waste, landfill and fossil-fuel extraction accounted for about 62% of total methane emissions since from 2007 to 2016 (see ‘Where is methane coming from?’).
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