Rapid Warming, Enormous Forest Fires May Combine To Explain Spike In Atmospheric Methane Post-2007
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About 40% of methane emissions come from natural sources such as wetlands, while 60% come from anthropogenic sources such as cattle farming, fossil fuel extraction and landfill sites. Possible explanations for the rise in methane emissions range from expanding exploration of oil and natural gas, rising emissions from agriculture and landfill, and rising natural emissions as tropical wetlands warm and Arctic tundra melts. But another explanation could be a slowdown of the chemical reaction that removes methane from the atmosphere. The predominant way in which methane is “mopped up” is via reaction with hydroxyl radicals (OH) in the atmosphere.
“The hydroxyl radical has been termed the ‘detergent’ of the atmosphere because it works to cleanse the atmosphere of harmful trace gases,” said Redfern. But hydroxyl radicals also react with carbon monoxide, and an increase in wildfires may have pumped more carbon monoxide into the atmosphere and altered the chemical balance. “On average, a carbon monoxide molecule remains in the atmosphere for about three months before it’s attacked by a hydroxyl radical, while methane persists for about a decade. So wildfires have a swift impact on using up the hydroxyl ‘detergent’ and reduce the methane removal,” said Redfern.
To understand what was driving the methane acceleration, Redfern and his colleague Chin-Hsien Cheng used four decades of methane measurements and analysed changes in the climate to identify how the availability of hydroxyl radicals might have changed and what impact the changing climate might have had on methane sources.
Their findings, published in the journal Nature Communications, suggest global heating is four times more influential in accelerating methane emissions than previously estimated, with rising temperatures helping to produce more methane (by speeding up microbe activity in wetlands for example), while at the same time slowing down the removal of methane from the atmosphere (with increasing numbers of wildfires reducing the availability of hydroxyl radicals in the upper atmosphere). “It was a really shocking result, and highlights that the effects of climate change can be even more extreme and dangerous than we thought,” said Redfern.
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https://www.theguardian.com/environment/2022/jul/05/global-heating-causes-methane-growth-four-times-faster-than-thought-study