The finding is based on data from a worldwide National Aeronautics and Space Administration-funded study of the atmospheric levels of the potent greenhouse gas.

NASA scientists said they determined atmospheric levels of methane have more than tripled since pre-industrial times, accounting for approximately one-fifth of the human contribution to global warming.

Until recently, researchers suspected that the stability of methane levels suggested the rate of its emission from the Earth's surface was being approximately balanced by the rate of its destruction in the atmosphere.

It's too early to tell whether the increase represents a return to sustained methane growth, or the beginning of a relatively short-lived anomaly, said Matthew Rigby and Ronald Prinn of the Massachusetts Institute of Technology. But given that methane is about 25 times stronger as a greenhouse gas per metric ton of emissions than carbon dioxide, they said the situation will require careful monitoring in the near future to better understand methane's impact on future climate change."

The study led by Rigby and Prinn appears in the journal Geophysical Review Letters.