Drilling Called Big Methane Culprit

Oil and gas drilling across much of the Southwest produces far more emissions linked to global warming than previously realized, according to a new study by University of California scientists.

One of the pollutants measured in abundance is methane, a gas that contributes to ozone near the Earth’s surface as well as to global warming. The researchers found about twice as much methane as expected, suggesting the United States and other nations have grossly underestimated global releases of the greenhouse gas.

“Based on these findings, it appears that the U.S. is emitting 4 [million] to 6 million tons more methane per year than previously estimated,” said F. Sherwood Rowland, a leading authority on global air pollution at UC Irvine. “In fact, our study suggests that total hydrocarbon emissions are higher than stated in current estimates. This means the American air pollution problem has still another new, significant aspect.”

The study, which appears in the online edition of the Proceedings of the National Academy of Science this week, also shows energy exploration contributes slightly more to smog in cities from New Mexico to Texas to Kansas than previously realized.

Rowland, UCI chemist Donald Blake and three colleagues examined air quality across a 1,000-mile area including parts of Texas, Oklahoma, Kansas, Arkansas, New Mexico and Louisiana. They were doing a follow up to a 1999 air pollution study in which researchers discovered levels of various hydrocarbons in and around Oklahoma City that surpassed those in smoggy cities such as Los Angeles, Houston, New York and Chicago. Hydrocarbons are reactive gases that mix with combustion gases and sunlight to make ozone, the main ingredient in smog.

Using about 350 measurements in 2001 and 2002, scientists discovered high concentrations of hydrocarbons, including methane, ethane, propane and butane, over hundreds of miles in and around Oklahoma City. The Oklahoma capital contained more than double the amount of hydrocarbons than air in more densely populated urban areas of the United States, the study shows. The researchers also found unexpectedly high levels of alkyl nitrates, a byproduct of ozone formation.

While many of those pollutants can contribute to smog, they are less reactive than other chemicals typically emitted by paints and solvents or automobile tailpipes. The result is that the pollutants can boost ozone concentrations over the region, albeit very slightly, Blake said.

“This study shows air pollution is not just a big-city problem and it needs to be fixed,” said John Walke, director of the clean air program for the Natural Resources Defense Council. “The oil and gas industry are bringing more pollution, [lung] disease and global warming to the heartland.”

While oil and gas wells have long been known to emit air pollutants, researchers said they were surprised at the quantities of methane detected. Methane is 21 times more efficient than carbon dioxide, the most common greenhouse gas, at trapping heat near the Earth. It had been estimated that energy production in the United States released about 6 million tons of methane annually.

But the new study shows actual methane emissions from those sources may be nearly double that amount. Possible sources for the extra emissions could be leaky tanks, valves or pipes or natural seepage.

Further, Blake said the findings call into question whether other energy-producing regions of the world, including the North Sea, Venezuela and the Mideast, have underestimated the amount of methane released into the atmosphere. If so, that could complicate efforts to reduce greenhouse gas emissions, he said.

The research was funded by the National Institute for Global Environmental Change, a division of the U.S. Energy Department.