California methane leak was the biggest ever in US: study

A natural gas leak that left Los Angeles residents sick and forced thousands off their homes is the largest known release of climate-changing methane in US history, scientists reported yesterday.

The 16-week blowout from a well at a Southern California Gas Co storage facility discharged 107,000 tons of greenhouse gas methane, a study published in the journal Science revealed.

While preliminary figures from the study had been reported earlier, the article included results and put the leak in context with other disasters as also other sources of global warming.

The findings assume importance with SoCalGas working on plans to mitigate the environmental impact of the blowout.

The release of the study came on the day people who had moved to short-term housing were due to return home. But in an order, a judge has asked the company to provide housing for three more weeks.

According to the report, the first leak reported 23 October at the Aliso Canyon storage facility near Porter Ranch released the greenhouse gas equivalent of 572,000 cars in a year.

At its peak, 60 tons per hour of natural gas was being discharged from a ruptured underground pipeline at the Aliso Canyon storage field, which effectively doubled the methane emissions of the entire Los Angeles metropolitan area, the researchers said.

From 23 October, when the discharge was first detected a total of 97,100 tons - or 5 billion cubic feet (142 million cubic meters) - of methane was released into the environment. The leak was plugged earlier this month, according to the study.

"Our finding means that the Aliso Canyon leak was the largest accidental release of methane in the history of the US," Tom Ryerson, a scientist for the National Oceanic and Atmospheric Administration , and co-lead of the study, said in a NOAA statement about the research.