Study finds near-zero growth in methane levels

The development, according to researchers from the University of California at Irvine and the American Geophysical Union, could be an encouraging sign that the world can control at least one contributor to global warming.

"If one really tightens emissions, the amount of methane in the atmosphere 10 years from now could be less than it is today," Sherwood Rowland, a professor at UC Irvine, said in a statement Monday. (Rowland received the 1995 Nobel Prize for helping discover that chlorofluorocarbons released by aerosol sprays were damaging the ozone layer.)

The main ingredient of natural gas, methane has been a global-warming threat since the Industrial Revolution began in the late 1700s, when activities like fossil-fuel extraction contributed to its rise. Since that time, concentration levels of methane have doubled, also because of cattle ranching and landfills. The emissions warm the atmosphere because of the greenhouse effect and also help form ozone, a component of smog.

But scientists consider methane less threatening than carbon dioxide, the chief greenhouse gas produced by burning fossil fuels for energy and transportation. Methane stays in the Earth's atmosphere for about eight years, while carbon dioxide remains for up to a century.

"If carbon dioxide levels were the same today as they were in 2000, the global warming discussion would leave the front page," Rowland said. "But to stabilize this greenhouse gas, we would have to cut way back on emissions."

To conduct their study, scientists in Rowland's laboratory used canisters to collect sea-level air in locations around the world. They measured the amount of methane in each canister and calculated a global average.

The scientists traced an 11 percent rise in methane levels from 1978 to 1987, a more than 1 percent increase each year, followed by a period of slight decreases. The levels climbed again in the 1990s because of natural events like wildfires, which they believe contribute to atmospheric methane. From 1998 to 2005, the scientists detected near-zero growth.

They attributed lower methane concentrations to possible precautions taken within the oil and gas industry. For example, preventing leaks in oil pipelines and storage facilities--which release methane into the air--could be a contributor, along with decreases in emissions from coal mining and natural gas production, they said.