Abstract
In the push to reduce greenhouse gas emissions, methane matters.
The cataclysmic effects of global climate change-mass extinctions and rising oceans-are compelling scientists to develop innovative ways to cool down the atmosphere. But short of wrapping parts of Earth in reflective foil, reducing the buildup of greenhouse gases is the surest way to mitigate the problem, according to the Intergovernmental Panel on Climate Change, a project of the World Meteorological Organization and the U.N. Environment Programme. Carbon dioxide, the most abundant greenhouse gas, is the culprit that gets most of the attention, but what about the other greenhouse gases?
Take methane, for instance. With a lifetime of approximately eight years and 20 times the global warming potency of carbon dioxide, methane is the second-most abundant and influential greenhouse gas. F. Sherwood Rowland, an atmospheric chemist and Nobel laureate at the University of California-Irvine, is one of many scientists who argue that reducing methane emissions could prove ecologically beneficial in the long run, partially canceling out the effect of rising carbon dioxide concentrations.
Diminishing the emission of methane and other hydrocarbons, such as butane, ethane, and propane, would also reduce the production of tropospheric ozone, a greenhouse gas that is a major component of smog. “You could kill two birds there,” Rowland says.
Tracking down the sources
Methane comes naturally from termites' by-products, the world's oceans, and the decomposing organic matter often found in wetlands. But the majority of known global methane emissions about 60 percent–can be traced back to human activities.
Plugging leaks
Recovering released methane from coal mines, landfills, and waste-treatment plants has helped reduce emissions. Researchers have also proposed innovative ways to increase the digestive efficiency of livestock and to fiddle with rice growing techniques to reduce emissions. But Rowland argues that one of the quickest ways to reduce methane emissions globally would be to decrease the leakage of natural gas production and transportation systems. In addition to patching leaks, some scientists suggest that methane usually burned off at the wellheads of oil pumps could instead be captured and put to use to fuel industry and, even, space exploration.
Research conducted by Rowland and his team in the late 1990s and early 2000s identified the air above Oklahoma City as the most polluted in the United States. Indeed, much of the oil- and gas-producing southwestern states (shown above) showed intense concentrations of methane and other hydrocarbons in the air. “A lot of the oil and gas superstructure goes back 50 years, so it is not surprising that it leaks,” Rowland says. “If there were a concerted effort to plug the leaks, then you could reduce the amount of methane by a substantial amount … thereby helping to ameliorate the greenhouse effect.”
The ups and downs
It's unclear why, but the growth of atmospheric methane concentrations began to level off in the early 1990s. The phenomenon may be related to the fall of the Soviet Union and the resulting decrease in demand on its leak-prone natural gas distribution system. Spikes in methane levels could be caused by the burning of biomass, as when Indonesians set massive land-clearing fires in 1997, because it releases large amounts of the gas into the atmosphere, according to Rowland.
Supplementary Material
Climate Change 2007: The Physical Science Basis