While it ranks far behind carbon dioxide in total emissions, methane is the second most common greenhouse gas emitted in the U.S. from human activities, accounting for 9 percent. Its lifetime in the atmosphere is much shorter than that of carbon dioxide — about 10 years — but methane is better at trapping and holding onto radiation than the other gas. Pound for pound, methane's effect on climate change is 20 times that of carbon dioxide over 100 years, according to the Environmental Protection Agency.
Knowing how much of the stuff exists in the atmosphere, then, is crucial for lawmakers and scientists alike, who collaborate on national and state greenhouse-gas reduction plans. Pinning down a national estimate, however, is proving to be tricky.
Earlier this month, a pair of senators asked EPA to reconsider its estimates of methane emissions from natural-gas operations, and even rethink how it measures atmospheric methane, at a Senate Environment and Public Works Committee hearing. David Vitter, R-La., and Jim Inhofe, R-Okla., cited a September report funded by the Environmental Defense Fund and several gas operators that said the gas industry emits 10 percent less methane than what EPA's inventory indicates.
And now, research published Monday in Proceedings of the National Academy of Sciences suggests that the government database may underestimate the true values of U.S. methane gas emissions by 50 percent.
Researchers traced atmospheric methane measurements across North America in 2007 and 2008 back to known emissions-producing sites, such as landfills, livestock ranches, and oil and gas facilities.
Emissions from oil and gas drilling in Texas, Oklahoma, and Kansas, researchers found, were nearly triple that of most inventories, and almost five times higher than the the Emissions Database for Global Atmospheric Research, the most commonly used global emissions inventory.
EPA's latest report from its Greenhouse Gas Reporting Program showed that methane-gas emissions have slightly decreased in recent years in some industries such as fossil fuels and petroleum and natural gas.
The agency is not oblivious to the discrepancies that exist between its own measurements and those of civil scientists. "EPA has not yet had the opportunity to fully review the PNAS study on methane emissions," the agency said in a statement to National Journal. "However we are encouraged that more methane emissions measurement data are now available to the public. Research studies like these will add to our knowledge base of [greenhouse gas] emissions and will help us refine our estimates going forward."
If EPA's own measurement data is not immune to change, it's unlikely that state-level and other nations' greenhouse-gas emissions inventories are either, especially as the technology that measures the potent gas and where it originates continues to develop.