Human activities led to a baffling decline in the growth of methane in the atmosphere during the last decades of the 20th century, scientists say.

Researchers have suggested two different theories as the cause of the decline in the growth of methane.

Published in the journal Nature, one of the two theories suggests that commercial use of natural gas caused the decline; while another theory claims that overuse of artificial fertilizers in Asia was responsible for the decline.

Fertilizers are believed to provide a boost to the ability of some bacteria to devour methane which originates in the soil.

Second theory's lead author Dr. Fuu Ming Kai said, "Approximately half of the decrease in methane can be explained by reduced emissions from rice agriculture in Asia associated with increases in fertiliser application and reductions in water use."

Agriculture and fossil fuels are the two leading sources of human-induced emissions of methane.

The two theories are poles apart in suggesting the possible cause, but both agree that human activities are responsible for the decline in the growth of methane in atmosphere.