The jury is still out on the culprit behind the recent increase in global methane emissions.

A new study published yesterday found that fossil fuel production has emitted significantly more of the potent greenhouse gas since 2000 and could account for much of the unexplained uptick in global atmospheric methane since 2007. That is an opposite finding from other recent research, which has blamed sources like agriculture, animal husbandry and wetlands instead.

“What’s going on in the gas and oil sector has been the big question with methane,” said Andrew Rice, a researcher at Portland State University and the lead author of the new research, published in the journal Proceedings of the National Academy of Sciences. “It’s not settled, but we give some new pieces to the puzzle.”

The back-and-forth results have electrified the debate over President Obama’s expanded regulations on the energy industry.

U.S. EPA is preparing rules to curb methane leaks from existing oil and gas sources, pointing to its data that show increasing methane emissions from fossil fuel extraction points in the United States. House Republicans will likely question those data at a Thursday hearing on the regulations titled “A Solution in Search of a Problem.”

Scientists around the world have been trying to figure out whether oil and gas production, particularly a boom in the United States, could be responsible for the global rise in methane. It is one of the most enduring mysteries in the planet’s atmosphere. Global levels of methane, a greenhouse gas many times more potent than carbon dioxide, have more than doubled since the Industrial Revolution. But growth slowed to zero in the 1990s. Levels began climbing again in 2007. About 17 teragrams more methane is now emitted every year compared to the annual emissions between 2000 to 2006.

Researchers have focused on disentangling the trends for different sources to figure out which ones might be responsible for the recent rise. Wildfires, bacteria in wetlands, submerged rice fields and cows all release methane. So does leaky equipment in oil fields.

Old air samples lead to new models

Rice’s study suggests that oil and gas production might be to blame.

The new results come from old air samples. Rice and his colleague analyzed the isotopic fingerprint of methane captured in air samples collected at Cape Meares, Ore., from 1977 to 1998. The data gave them a rough sketch of the rise and fall of individual sources of methane. Then they had to come up with more specific guesses about long-term trends and test them out, comparing the model’s results with the observations.

The model that most closely matched the data showed that fugitive fossil fuel emissions have been increasing since 1984, with the majority of the growth after 2000. Methane from livestock and landfills rose over the time period from 1984 to 2009. Methane from rice fields trended down, while methane from wetlands varied year-to-year, then dropped significantly from 2000 to 2009.

Francis O’Sullivan, director of research at the Massachusetts Institute of Technology’s Energy Initiative, praised the research as a useful contribution to an ongoing scientific debate.

“It’s a very complex landscape,” he said. “No one team out there has been able to say, ‘This is the correct answer.’”

In a landmark study published in Science in March, a group of international researchers from New Zealand, Germany and Boulder, Colo., found that agriculture or dairy farming, particularly in the tropics, was more likely responsible for the rise in methane (ClimateWire, March 11).

The two groups of researchers used similar fingerprinting methods, but different models. Lori Bruhwiler, a physical scientist at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory, suggested that Rice’s process may be sensitive to first-guess assumptions. She called the inversion modeling technique used by Rice “tricky to interpret” because it uses more variables.

“You’re trying to retrieve a lot of unknowns with not a lot of data,” she said. “You can often get a solution that matches the data very well but comes to the wrong conclusion about sources. ... If you run an inversion and instead of allowing anthropogenic emissions to increase, you hold them constant, you will get a much smaller increase in anthropogenic emissions and an increase in another source.”

“It all comes down to how much you believe your first-guess emissions versus how well you think you can simulate the observations with your model,” she added.

Other research, including a 2012 Nature paper, has also suggested fugitive fossil fuel emissions were decreasing from 2000 to 2009 because of trends in ethane, a non-greenhouse gas that often correlates with methane. Ethane emissions decreased from 1984 to about 2010. It is tricky to link ethane and methane trends because scientists do not know the ratio at which they are co-emitted, but the ethane trends can hold some clues.

Rice suggested that the researchers in the Nature paper may have wrongly assumed wildfires and biomass burning were releasing more ethane during that period. His model and some other studies show emissions from biomass burning decreasing.

The worldwide ethane trend has recently reversed, however, at least partly because of oil and gas development (ClimateWire, June 20).

Gearing up for a policy fight Thursday

The scientific uncertainties have set a tricky backdrop for regulators and policymakers looking to weigh the economic and climate benefits of the boom in domestic natural gas production with Obama’s mission to combat climate change-causing gases. Critics say the industry is decreasing greenhouse gas emissions already and the regulations will hurt the economy.

House Science, Space and Technology Committee lawmakers are planning to scrutinize EPA’s plans to expand methane regulations to existing oil and gas operations Thursday (E&E Daily, Sept. 12). The agency is working to finalize a request for up-to-date information from the industry, which has called the effort a “rushed job.”

EPA earlier this year finalized a set of rules targeting methane emissions from new and heavily modified oil and gas operations, which has drawn legal challenges from several states.

Environmental advocates say the regulations are necessary to avoid some of the worst methane leaks from a few “super-emitters” and spur better technology at other sites.

David Lyon, a scientist at the Environmental Defense Fund, praised Rice’s study as an alternative hypothesis for global methane trends but suggested it may be “irrelevant” to the discussion about EPA’s methane rules.

“It is valuable to understand some trends in methane emissions, but the more important question is that we know current methane emissions are really high, and that oil and gas is a big part of that,” he said. “If they’re decreasing, they’re not decreasing fast enough.”

Katie Brown, a spokeswoman for Energy in Depth, a project of the Independent Petroleum Association of America, said she does not think Rice’s paper has big implications for policy because other research has found the opposite. She’s “still seeing a positive story for methane” from oil and gas because emissions have not spiked despite an increase in production, she said.

Witnesses testifying at the hearing include Elgie Holstein, senior director for strategic planning at the Environmental Defense Fund; Erik Milito, director of upstream and industry operations for the American Petroleum Institute; Anthony Ventello, executive director of the Progress Authority; and Bernard Weinstein, associate director of the Maguire Energy Institute at Southern Methodist University.

Weinstein called the methane rules “regulatory overreach.”

He noted that methane is a product that natural gas producers want to sell, so there is already an economic incentive for drillers to capture fugitive emissions. There are already state-level environmental regulations for methane, and many companies in the United States are moving on their own to limit methane releases.

“There’s no question that the industry has kind of become the whipping boy,” he said.

He said the larger concern should be methane emissions coming from other parts of the world that are drilling for fossil fuels with lower environmental standards. “If the rest of the world follows our example, we would have this problem of emissions more or less under control,” he said.

Reporter Umair Irfan contributed.

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. E&E provides daily coverage of essential energy and environmental news at Click here for the original story.