Methane Gas Emissions in North America More Dire Than Thought: Hundreds of Studies Find EPA Erred
The Environmental Protection Agency (EPA) has underestimated U.S. methane emissions, including those from the natural gas industry, findings from about 200 studies have concluded. The studies have been synethisized into a mega-study entitled "Methane Leakage from North American Natural Gas Systems,"which will be published in Friday's issue of the journal Science. The studies include findings from local gas processing plants to total emissions from the United States and Canada. The Cynthia and George Mitchell Foundation enlisted the nonprofit organization Novim to examine 20 years of methane studies to explain the wide variation in existing estimates.
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Most of those studies which tested gas industry components found the EPA's emission rates to be too low, mostly because emission rates for wells and processing plants were based on operators participating voluntarily. For instance, one EPA study asked 30 gas companies to cooperate in taking emissions measurements, but only six permitted the EPA on site.
"It's impossible to take direct measurements of emissions from sources without site access," said Garvin Heath, a senior scientist with the National Renewable Energy Laboratory and a co-author of the new analysis in a press release. "Self-selection bias may be contributing to why inventories suggest emission levels that are systematically lower than what we sense in the atmosphere."
Even small leaks of from the natural gas infrastructure can be significant because methane is a potent greenhouse gas - about 30 times more potent than carbon dioxide. "Atmospheric tests covering the entire country indicate emissions around 50 percent more than EPA estimates," said lead author, Adam Brandt, an assistant professor of energy resources engineering at Stanford University. The national natural gas infrastructure has a combination of intentional leaks, often for safety purposes, and unintentional emissions, like faulty valves and cracks in pipelines. In the United States, the emission rates of particular gas industry components from wells to burner tips were established by the EPA in the 1990s
In November, Harvard University and seven other institutions, including U.S. government agencies, found that methane emissions from fossil fuel extraction and oil refineries in the United States are nearly five times higher than previous estimates. That study, which was published in the Proceedings of the National Academy of Science (PNAS), asserted that U.S. livestock operations may be emitting twice as much methane as previously thought. That study was one of the 200 included in Thursday's Science study.
Methane can linger in the atmosphere for 10 years - not a ton compared to its partner in greenhouse gas crime, carbon dioxide, which sticks around for up to 100 years. However, methane traps about 70 times more heat than carbon dioxide does. Most methane emissions arise from run-of-the-mill individual human activities, but about 40 percent comes from the production of fossil fuels, cattle farming, landfills, and the like. That's what the PNAS study looked at, providing, what coauthor Anna M. Michalak called "the most solid and the most detailed estimate to date of total U.S. methane emissions."
Dr. Michalak, a faculty member in the Department of Global Ecology at the Carnegie Institution for Science, said when the PNAS study was release that the total methane emissions in the United States appear to be 1.5 times and 1.7 times higher than the amounts estimated by the U.S. Environmental Protection Agency (EPA) and the international Emissions Database for Global Atmospheric Research (EDGAR), respectively. The difference is in how the different environmental groups collected their data.
Several other studies have used airplanes and towers to measure actual methane in the air, so as to test total estimated emissions. The PNAS study, which was authored by researchers from seven universities, several national laboratories and federal government bodies, and other organizations, found these atmospheric studies covering very large areas consistently indicated total U.S. methane emissions of about 25 to 75 percent higher than the EPA estimate.
The EPA and EDGAR collected most of their data from the ground, while the Harvard group procured its more damning evidence from where the gas actually hovers in the atmosphere. EPA and EDGAR also had depended more on number-crunching: calculating the amount of methane typically released per cow or per unit of coal or natural gas sold. The National Oceanic and Atmospheric Administration (NOAA) and the U.S. Department of Energy collected measurements of methane and other gases from research flights as well as from the tops of telecommunications towers, some as tall as the Empire State Building. "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," said Michalak.
Michalak and colleagues found a high correlation between levels of methane and propane in the south-central region suggested a significant role for fossil fuels there. Their results were higher by a factor of 2.7 over the south-central United States, whic is a key region for fossil-fuel extraction and refining.
Thursday's Science study found that a small number of faulty components in a gas system can cause more than their fair share of methane pollution. One earlier study examined about 75 thousand components at processing plants. It found some 1,600 unintentional leaks, but just 50 faulty components were behind 60 percent of the leaked gas. "Reducing easily avoidable methane leaks from the natural gas system is important for domestic energy security," said Robert Harriss, a methane researcher at the Environmental Defense Fund and a co-author of the analysis. "None of us should be content to stand idly by and let this important resource be wasted through fugitive emissions and unnecessary venting."
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