With Congress set to roll back federal rules limiting methane emissions from oil and gas drilling on public and tribal lands, an independent study shows that those emissions have been far higher in recent years than previous estimates.

Between 1980 to 2012, global methane emissions from oil and gas production were 73 percent higher than estimated by the United States Environmental Protection Agency and by EDGAR (the European Commission's emission inventory), according to the study, published recently in Environmental Research Letters.

"It is particularly the emissions from oil production that are higher. For more recent years, my estimates show that methane from global oil production are about the double compared with the estimates by EDGAR and USEPA," says Lena Höglund-Isaksson, a researcher at the International Institute for Applied Systems Analysis in Vienna, Austria. The study is the first to account for different production management systems and geological conditions around the world.

Methane is a potent greenhouse gas, trapping heat 72 times more efficiently than CO2 over a 20-year span. Even though it only persists in the atmosphere for about a decade, scientists rank methane as the second-most important contributor to climate change after carbon dioxide. Significant amounts of methane also come from agriculture, landfills, and melting permafrost. Cutting methane emissions in the short term would help buy some time in the global race to cap warming to less than two degrees Celsius, as targeted by the Paris climate agreement.

The House of Representatives voted recently to undo a federal Bureau of Land Management rule that aims to reduce methane by requiring oil and gas producers to capture it, rather than simply venting it or burning it. The rule took effect on January 17 and withstood a test in federal court; hence the congressional action on behalf of fossil-fuel companies, who claim the rule is too expensive and duplicative of state air pollution control measures. The Colorado Oil and Gas Association, for example, claims that the BLM lacks the authority to impose such a rule.

To undo the rule, House GOP lawmakers used the Congressional Review Act, which enables Congress to repeal executive actions if they impose excessive costs, exceed agency authority, or if Congress deems them redundant.

Concentrations of methane can easily be measured in the atmosphere, but it's much harder to track its sources, and that's crucial information under the Paris climate agreement to hold individual countries accountable for their emissions reductions pledges. The new model developed by the IIASA researchers can help accurately track methane emissions from oil and gas production on a country-by-country basis.

The study in particular shows that emissions from oil production are much higher than previously believed, while emissions from natural gas may be lower than the recent estimates from the EPA and EDGAR. Höglund-Isaksson explains: "In an oil reservoir, there is a layer of gas above the oil which has a methane content of 50 to 85 percent. When you pump the oil to the surface this associated gas will also escape."

Compiling exact tallies of methane emissions and their sources has been somewhat controversial, but efforts like the latest IIASA study are getting closer to establishing the accuracy needed for effective control measures. But more data would help.

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