Scientists made "major overestimations" of methane emissions from oil and gas production in the United States by relying on faulty measurements, according to new research sponsored by NOAA.
The finding is important because methane emissions are the second-most potent source of greenhouse gases causing global warming. Recent studies showing increases of methane emissions from oil and gas production have overestimated their volume by as much as 10 times, according to the research.
The estimates were faulty because they used ethane, another gas emitted during oil and gas drilling, as an invariable tracer for the resulting emissions. It amounted to what was thought to be a useful measuring shortcut.
But the ratio between ethane and methane emissions from drilling is not a constant. It can increase depending upon the region of the United States where the measurement occurred, according to NOAA. The result is that while natural gas production in the United States has increased 46% since 2006, the amount of methane emissions from this activity has shown only a "modest increase," according to the new research. Most of the increase came from biological sources.
"What this means is if you want to track methane, you have to measure methane," said Xin Lan, the lead author of the new study and a research scientist at CIRES, a partnership between NOAA and the University of Colorado.
"We analyzed a decade's worth of data and while we do find some increase in methane downwind of oil and gas activity, we do not find a statistically significant trend in the U.S. for total methane emissions," explained Lan.
Overall, according to the study, global methane emissions were nearly stable from 1999 through 2006, but have "increased significantly" since then. Some studies, relying on ethane measurements, assumed that the oil and gas operations in the United States have made the biggest increases.
Instead, according to Lan and other researchers, the spike in methane is more likely to have been caused by natural emissions whose sources can include the digestive tracts of cows, rotting vegetable matter and the activities of termites.
Methane is 28 times more potent than carbon dioxide in trapping heat in the atmosphere over 100 years.
High methane leakage levels calculated from recent oil and gas production has raised opposition to increased reliance on natural gas by environmental groups.
But despite the fact that natural gas production sharply increased in the United States, the new study monitoring 20 long-term methane sampling sites around the nation showed little difference between methane emissions in the United States and global levels of emissions.