The sudden jump was detected almost simultaneously last year at all measurement stations around the world.

Researchers from the Massachusetts Institute of Technology (MIT) say that before methane began increasing in 2007, it appeared that manmade and natural sources of the gas were in balance with the atmosphere’s ability to neutralize it with a compound known as hydroxyl free radical (OH).

The team says the recent rise observed in the Northern Hemisphere may be due to very warm conditions in Siberia in 2007, which increased bacterial emissions from tundra and wetlands.

The reason for the comparable increase south of the equator is unclear. And since it takes more than one year for air pollution to spread from the northern to southern hemispheres due to the chemical equator, the methane emissions must have risen by a similar amount in both hemispheres at the same time.

The amount of methane in the atmosphere has more than doubled since before the Industrial Revolution, accounting for about one-fifth of the human contribution to greenhouse gas-driven global warming.

The researchers said it is too soon to tell whether the one-year rise in the amount of atmospheric methane is the start of an upward trend or a short-lived phenomenon.

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