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The case of the disappearing methane

Methane, emitted in large amounts by wetlands and rice paddies, is being released into the atmosphere at a declining rate but the reason for this remains unclear. Flickr/Kansas Poetry

Methane has been floating into the atmosphere at a slower rate over the last three decades but two new papers published in the journal Nature put forward very different theories as to why it’s happening.

Methane is the second-biggest contributor to climate change after carbon dioxide but the decline in the rate at which it is released has confounded experts for years.

In two new papers, scientists agree that the rate of methane release has been affected by human activity but have offered two different explanations as to why it is happening.

Fuu Ming Kai from the Department of Earth System Science at the University of California studied methane from fossil fuels and methane from microbial sources like wetlands and rice paddies.

He argued in his paper that because Asian farmers are using less water and more fertiliser, less methane is being emitted from rice paddies, traditionally a big producer of the gas.

In a separate study, Dr Murat Aydin, also from the University of California’s Department of Earth System Science, extracted 100-year old samples of ethane (which shares some of the same sources as methane but is easier to measure) from glaciers in Greenland and Antarctica.

His research suggested that less methane is reaching the atmosphere because it is now commonly harvested and used as a natural gas energy source.

“Ethane levels rose from early in the century until the 1980s, when the trend reverses, with a period of decline over 20 years,” Aydin wrote.

“We find this variability is primarily driven by changes in emissions from fossil fuels.”

Professor James Randerson, co-author on the Fuu Ming Kai paper, said it was important to consider both theories.

“The important thing is that we must figure out — as scientists and a society — ways to reduce methane emissions.”

Reporting by Alexandra Back

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