Study Reveals US Methane Emissions 50% Higher than Government Suggests

US government calculations of methane emissions could underestimate the true total value of methane emissions by 50 percent, according to new comprehensive research by several leading institutions.

Researchers from Harvard University, the Carnegie Institute for Science and five other institutions report in the Proceedings of the National Academy of the Sciences that the US Environmental Protection Agency's move to downscale its methane emissions estimate may be ill considered.

Methane is a potent heat-trapping gas, able to trap significantly more heat than carbon dioxide, the most abundant global warming gas, despite not staying in the air as long. The researchers report that nearly 25 percent of the methane emissions in the US comes from Texas, Kansas and Oklahoma. Texas and Oklahoma have many refineries that turn oil into gasoline, while Kansas is a large cow-producing state. Cows' manure, as well as their flatulence, contributes notably to methane levels.

For their study, the researchers used atmospheric observations from across North America from 2007 to 2008, seeking to improve estimates of methane gas emissions from a variety of human sources, including refining, agriculture and fossil fuel drilling.

The researchers found significant discrepancies with government estimates of methane emissions, especially in the south-central US, where total methane emissions were 2.7 times greater than those reported in most inventories.

"Emissions from oil and gas drilling and processing in this region could account for 50% of that total, representing a source of methane almost five times higher than in the most commonly used global emissions database," the Carnegie Institute for Science wrote in a statement.

The researchers say their results offer a comprehensive baseline for assessing policies designed to reduce greenhouse gasses.

"The bottom-up and top-down approaches give us very different answers about the level of methane gas emissions," Harvard's Scot 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."

The study estimates that in 2008, there were 49 million tons of methane pumped into the air from US-based sources. According to The Associated Press, that means US methane emissions trapped about as much heat as all the carbon dioxide pollution coming from cars, trucks and planes in the country in half a year's time.

The researchers' estimate of methane emissions is higher than the 32 million tons estimated by the EPA.

"Something is very much off in the inventories," Anna Michalak, study co-author and Earth scientist at the Carnegie Institution for Science, told the AP. "The total U.S. impact on the world's energy budget is different than we thought, and it's worse."

According to the AP, the EPA said it has not had time to review the research but that agency will consider the research as it moves forward.

"The beauty of the approach we're using is that, because we're taking measurements in the atmosphere, which carry with them a signature of everything that happened upwind, we get a very strong number on what that total should be," Michalak said in a statement. "Now that we know the total does not equal the sum of the parts, that means that either some of those parts are not what we thought they were, or there are some parts that are simply missing from the inventories. It really offers an opportunity for governments to re-examine the inventories in light of what we now know."