The Southern California natural gas leak was the biggest one in U.S. history, pumping out enough methane to fill a balloon the size of the Rose Bowl every day until utility workers dropped in a cement plug earlier this month.
More than 100,000 tons of methane, a powerful greenhouse gas that has 25 times the warming energy of carbon dioxide, spewed from a natural gas well in Aliso Canyon during 112 days, according to the first study of the accident published today in the journal Science.
Stephen Conley, atmospheric scientist at the University of California Davis, made more than a dozen flights through the methane cloud in a specially equipped airplane. He said it was pretty rough going. Turbulence and the methane gas combined to make the work difficult for researchers.
"These are the worst flights we've ever done," said Conley, who patrols California checking on these kinds of leaks. "You would fly through this hideous smell. Everyone who came in the plane got sick. By the end I just stopped bringing people."
Conley's single-engine Mooney TLS aircraft carried instruments that provided real-time measurements of methane and ethane, two components of natural gas, and captured air samples for more comprehensive analysis later in the laboratory. During the incident, more than 11,000 nearby residents were evacuated and Gov. Jerry Brown declared a state of emergency.
Conley and his colleagues found that the gas leak accounted for an extra 9 percent of California's methane emissions for the year, or about one-quarter of the methane from the Los Angeles Basin. The leak will make it harder for California to meet greenhouse gas emission targets for the year, the researchers said.
President Obama has proposed a 45 percent reduction in methane emissions from industry and agriculture by 2025. The goal is to curb the warming effects of methane, which turns into carbon dioxide after 10 to 12 years in the atmosphere.
"Our results show how failures of natural gas infrastructure can significantly impact greenhouse gas control efforts," said NOAA's Tom Ryerson, co-lead scientist on the study.
Globally, the Aliso Canyon leak is tiny, about a .002 percent of the yearly worldwide total. But it does throw a spotlight on human emissions of methane, which account for about one-quarter of the total greenhouse gasses, and the issue of methane leaks from gas pipelines.
"What this shows is we do have to worry about these large leaks," said Steve Hamburg, a chief scientist at the Environmental Defense Fund. "Globally, methane is rising. We are still trying to figure out why."
Conley says that gas leaks at Aliso Canyon, the BP Deepwater Horizon rig and another well in the North Sea point to the need for a quick-response team of researchers and technicians that can determine how bad things are from the beginning.
"We should have a national plan in place to respond to these events within hours rather than weeks or months," Conley said.