Methane emissions from oil-and-gas operations are roughly 50 percent higher than estimates reported by the Environmental Protection Agency (EPA), according to a new study.
Researchers found methane emissions in the United States are nearly five times higher in the south-central region, which includes Texas, Oklahoma and Kansas.
The study, conducted by scientists at Harvard University and seven other institutions, was published Monday in the Proceedings of the National Academy of Sciences.
Natural-gas production, cattle farming, landfills, coal mining and more produce the devastating greenhouse gas, although human activities contribute 60 percent of the total.
Across the entire U.S., methane emissions are 1.5 to 1.7 times higher than has been reported by the EPA and the international Emissions Database for Global Atmospheric Research, the study said.
"I think this study highlights how much uncertainty there is in current greenhouse gas emissions in U.S.," lead author of the study Scot M. Miller told The Hill.
"If we want to regulate greenhouse gases successfully two things need to happen: We need to understand how much greenhouse gas and methane is being emitted across the U.S. right now and we need a way of estimating future changes in emission."
The next step is understanding why these discrepancies exist, Miller added.
The difference in estimates, according to a news release from Harvard University on Monday, is the methodology.
Where the EPA uses a "bottom-up" approach to determine emissions, the study used a "top-down" approach that measures the levels of methane present in the atmosphere. It then used meteorological data and analysis to trace it back to the source.
"The bottom-up and top-down approaches give us very different answers about the level of methane gas emissions," Miller said in a statement.
“Most strikingly, our results are higher by a factor of 2.7 over the south-central United States, which we know is a key region for fossil-fuel extraction and refining.
"It will be important to resolve that discrepancy in order to fully understand the impact of these industries on methane emissions," Miller added.
Co-author of the study Anna Michalak, a scientist at the Carnegie Institution for Science in Stanford, Calif., said the paper is the "most detailed estimate to date" of total U.S. methane emissions.
The EPA said it is currently reviewing the study.
"EPA is committed to using the best available data for our inventory and continually seeks opportunities to update and improve our estimates," the agency said in an email to The Hill.
"Research studies like these will add to our knowledge base of (greenhouse gas) emissions and will help us refine our estimates going forward."
Earlier this month, the United Nations reported greenhouse gas in the globe's atmosphere hit a record high in 2012.