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Methane Levels Have Surged, and Scientists Don’t Know Why

As Earth heads toward climate crisis, the pressure is on to learn more about CH4

Rice paddies are one source of global methane emissions. (sandeepachetan.com travel - Flickr/Creative Commons)
smithsonian.com

Scientists have long known that methane presents a serious danger to a warming world. After all, the gas warms the planet up to 86 times more than carbon dioxide. So news that levels of methane have spiked in Earth’s atmosphere is cause for alarm, even though scientists aren’t sure what’s going on. As Jonathan Amos reports for the BBC, a sudden surge in Earth’s methane levels is a potent warning that losing sight of the impacts from this greenhouse gas could have terrible consequences.

In a new editorial in the journal Environmental Research Letters, researchers call the rise in atmospheric methane, or CH4, “puzzling.” Between 2014 and 2015, atmospheric methane concentration shot up by 10 parts per billion or more both years—as opposed to the previous decade, during which they grew by only 0.5 ppb on average every year. That mysterious rise suggests that something has shifted in the methane cycle, they write, and the reasons behind the spike are unclear.

“We do see some increased fossil fuel emissions over the last decade,” Robert Jackson, who co-authored the paper, tells Amos, “but we think biological sources, and tropical sources, are most likely.” Like carbon dioxide, methane has a global budget that’s determined by emissions and sinks. Cattle and agriculture spew methane into the atmosphere, but so do other sources like wetlands and rice paddies. In turn, some of the methane is stored in sinks like permafrost soil and destroyed in the atmosphere by hydroxyl radicals.

There’s just one problem: Scientists don’t know enough about those sinks or the methane cycle. “There is no consensus scenario of methane sources and sinks that explains the atmospheric increase since 2007,” the researchers write. They call for scientists to further study those factors and also commit themselves to mitigation strategies like covering landfills and venting methane in coal mines.

In their recent report on global methane budget from 2000 to 2012 in the journal Earth Science Systems Data, a slew of researchers set forth priorities for methane research. But will their suggestions be implemented too late? It’s possible: As the Earth warms, methane emissions grow. Earlier this year, the World Meteorological Association announced that the world is more than halfway toward a critical temperature threshold that could mean mitigation efforts will no longer be enough to avoid a global climate crisis. That doesn’t mean all is lost: The more scientists know about how methane sinks and sources work, the more the world will be able to do to shield itself from future disaster. But first, they’ll have to figure out what exactly is going on—and given the elusive nature of the gas, they’ve got their work cut out for them.

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