The natural gas well blowout in Aliso Canyon, California, first reported on October 23, 2015, vented over 100,000 tons of the powerful greenhouse gas methane into the atmosphere before the well was finally sealed almost four months later, on February 11, 2016. That’s the largest methane leak in U.S. history, according to the first study of the accident, published in the journal Science on February 25, 2016.
The research showed that during the peak of the Aliso Canyon event, enough methane poured into the air every day to fill a balloon the size of the Rose Bowl. Total emissions during the 112-day event were equal to one-quarter of the annual methane pollution from all other sources in the Los Angeles basin combined.
The disaster’s impact on climate, said the researchers, will be equivalent to the annual greenhouse gas emissions from over half a million passenger cars.
Co-lead scientist and pilot Stephen Conley of Scientific Aviation and UC Davis said first readings in early November were so high he had to recheck his gear. He said in a statement:
It became obvious that there wasn’t anything wrong with the instruments. This was just a huge event.
At the time, Conley and his specially equipped plane were working with University of California Davis on a California Energy Commission project searching for pipeline methane leaks. The state agency asked him to overfly the area around the breached SoCalGas well.
Conley and his team’s measurements confirmed that high concentrations of methane and ethane were surging from the breached well into the densely populated San Fernando Valley.
Eventually, more than 5,726 families were evacuated and Gov. Jerry Brown declared a state of emergency.
The analysis found that at its peak, the blowout doubled the rate of methane emissions from the entire Los Angeles basin and temporarily created the largest known human-caused point source of methane in the United States, twice as large as the next-largest source, an Alabama coal mine.
NOAA’s Tom Ryerson was co-lead scientist on the study. He said:
The disaster will substantially impact California’s ability to meet greenhouse gas emission targets for the year, the researchers said.
Our results show how failures of natural gas infrastructure can significantly impact greenhouse gas control efforts.
Bottom line: The Aliso Canyon, California natural gas well blowout was the largest methane leak in U.S. history, according to the first study of the accident, published in the journal Science on February 25, 2016. The leak, first reported on October 23, 2015, vented over 100,000 tons of the powerful greenhouse gas methane into the atmosphere before the well was finally sealed almost four months later, on February 11, 2016.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.