Scientists have determined that levels of atmospheric methane - an influential greenhouse gas - have stayed almost flat for the past seven years, following a rise over 20 years. The finding, published inthis week's edition of Geophysical Research Letters, suggests that methane may no longer be as big a global warming threat as once thought, and shows that methane levels can be controlled.

Methane, the big component of natural gas, warms the atmosphere through the greenhouse effect and helps to form ozone, an ingredient in smog. Since the Industrial Revolution in the late 1700s, atmospheric methane has more than doubled. About two-thirds of methane emissions can be traced to human activities such as fossil-fuel extraction, rice paddies, landfill sites and cattle. Methane is also produced by termites and wetlands.