A team of Harvard University scientists contend in a recent study that the U.S. Environmental Protection Agency's (EPA's) methods greatly underestimate the amount of methane released by the oil and gas industry.
The study was published in April's Atmospheric Chemistry and Physics journal. In it, researchers claim the EPA's inventory of greenhouse gas emissions underestimates oil methane release by 35 percent and natural gas methane release by 22 percent. Methane is a primary component of natural gas and is a potent greenhouse gas 25 times more powerful than carbon dioxide in trapping heat in the atmosphere over a 100-year period.
The study was funded by the NASA Carbon Monitoring System program. It used what's called a transport model to simulate the movement of methane from the ground up through the atmosphere by incorporating the EPA's regional estimated emissions maps. The study's authors then compared that data to satellite observations from 2010 through 2015 to determine sources of differences in estimations of the national total. The research teams say this is the first national-level study to make this type of comparison.
While the study found that methane emissions from both oil and natural gas production exceeded EPA estimates, the amount from natural gas distribution, processing and transmission varies much less than that produced by oil.
Lead author Joannes Maasakkers says the EPA's underestimation may be due to how it determines total emissions for the oil and gas industry. For instance, the EPA calculates its estimates based on processes and equipment being used and how much methane those sources could emit based on nationwide operations. The study sees flaws in that approach because it fails to account for what's termed "fat-tail" distribution. That's when a small portion of equipment or facilities emit a large share of emissions. The study implemented atmospheric observations such as satellite and aircraft data along with ground measurements to obtain what its authors believe are more accurate calculations.
According to data from the EPA dated as of 2018, the agency estimates that production accounts for 67 percent of the total methane emissions from the oil and natural gas industry. It cites natural gas production for 47 percent of that number. The emissions result from normal operations, routine maintence, leaks and other system upsets.