The sudden and sustained rise in atmospheric levels of the potent greenhouse gas methane since 2007 has posed one of the most significant and pressing questions in climate research: Where is it coming from?

Fossil fuel emissions? Biological sources? A diminished capacity by the atmosphere to break down methane? A climate tipping point?

The question has been the subject of intense scientific interest for a decade. Now a research team led by Xin Lan, a CIRES scientist working at NOAA’s Global Monitoring Laboratory, has tested the leading theories for surging methane levels by analyzing the stable carbon isotope ratios (δ13C-CH4) from methane captured in a large set of global air samples to determine if one of the theories is more feasible than the others.

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