Regulators may have underestimated by half the amount of the greenhouse gas methane emitted in the United States, according to a study published by the Proceedings of the National Academy of Sciences.
The study, led by researchers at Harvard University, found the discrepancy was greatest in south-central United States, where total emissions are nearly five times greater than measurements by the US Environmental Protection Agency and others.
The researchers said their findings, published on Monday, also "cast doubt on the EPA's recent decision to downscale its estimate of national natural gas emissions by 25 to 30 per cent".
The EPA is setting federal limits on greenhouse gas emissions. Accurate measurements of methane - the second most prevalent greenhouse gas - were essential, the report said.
It said emissions were likely to be 1.5 times higher than the EPA's estimate, and 1.7 times higher than that of the international Emissions Database for Global Atmospheric Research.
Methane is produced in a variety of ways from gas escaping during oil and gas production to manure from livestock.
The study differed from the EPA's as it measured what is in the atmosphere using meteorological data and statistical analysis. The EPA method is based on estimated emissions per cow, for example, or per unit of coal or gas sold.