That seems to implicate biological sources such as wetlands and livestock, which tend to produce light methane. Daniel Jacob, an atmospheric chemist at Harvard who was not involved in Nisbet’s study, said that explanation squares with his own research. His results suggest most of the additional methane comes from the tropics, which are home to vast wetlands and a large proportion of the world’s cattle.

Source: Los Angeles Times March 01, 2019 13:52 UTC