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Source: California Air Resources Board Source: California Air Resources Board

Over the course of three years, NASA flew a plane carrying gas-imaging equipment above California and made a discovery that surprised even the state’s own environmental agencies: A handful of operations are responsible for the vast majority of methane emissions.

In a report published in Nature on Wednesday, scientists estimated that 10% of the places releasing methane -- including landfills, natural gas facilities and dairy farms -- are responsible for more than half of the state’s total emissions. And a fraction of the 272,000 sources surveyed -- just 0.2% -- account for as much as 46%.

The report doesn’t identify these “super emitters,” but notes that landfills give off more methane than any other source in the state. NASA’s equipment found that a subset of these landfills were the largest emitters in California and exhibited “persistent anomalous activity.”

The study marks the first time anyone has ever carried out a systematic survey across California of methane, a greenhouse gas that’s 25 times more potent than carbon dioxide in trapping heat and contributing to global warming. The release of methane has been a continual challenge for California, which has some of the most aggressive goals in the nation for curbing emissions and slowing the impacts of climate change.

NASA’s aircraft made dozens of flights across 10,000 square miles from 2016 through 2018. Landfills accounted for 41% of the source emissions it identified, manure management 26% and oil and gas operations 26%.

Researchers cautioned that the survey wasn’t foolproof. It was, after all, their first attempt at estimating emissions from individual sources on such a large scale over multiple years. Some of the emissions detected were intermittent, some were too small to measure and others were affected by winds.

The results, however, are already effecting change. The survey revealed four incidents of leaking natural gas distribution lines and one leaking liquefied natural gas storage tank, which operators confirmed and repaired.

— With assistance by Eric Roston