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takyon writes:

https://www.jpl.nasa.gov/news/news.php?release=2017-108&rn=news.xml&rst=6814

A new NASA- and Department of Energy-funded study finds that recent increases in global methane levels observed since 2007 are not necessarily due to increasing emissions, but instead may be due to changes in how long methane remains in the atmosphere after it is emitted.

The second most important human-produced greenhouse gas after carbon dioxide, methane is colorless, odorless and can be hard to track. The gas has a wide range of sources, from decomposing biological material to leaks in natural gas pipelines. In the early 2000s, atmospheric scientists studying methane found that its global concentration -- which had increased for decades, driven by methane emissions from fossil fuels and agriculture -- leveled off as the sources of methane reached a balance with its destruction mechanisms. The methane levels remained stable for a few years, then unexpectedly started rising again in 2007, a trend that is still continuing.

Previous studies of the renewed increase have focused on high-latitude wetlands or fossil fuels, Asian agricultural growth, or tropical wetlands as potential sources of the increased emissions. But in a study published today in the early online edition of the Proceedings of the National Academy of Sciences, researchers at Harvard University in Cambridge, Massachusetts; Caltech in Pasadena, California; and NASA's Jet Propulsion Laboratory, also in Pasadena, suggest that methane emissions might not have increased dramatically in 2007 after all.

Ambiguity in the causes for decadal trends in atmospheric methane and hydroxyl (open, DOI: 10.1073/pnas.1616020114) (DX)

Additional reading:
http://www.caltech.edu/news/detergent-molecules-may-be-driving-fluctuations-atmospheric-methane-concentrations-54742

Original Submission