A scientific analysis of a natural gas leak near Los Angeles says that it was the biggest in US history.
By Matt McGrath Environment correspondent
The Aliso Canyon blowout vented almost 100,000 tonnes of methane into the atmosphere before it was plugged.
The impact on the climate is said to be the equivalent of the annual emissions of half a million cars.
Researchers say it had a far bigger warming effect than the BP oil spill in the Gulf of Mexico in 2010.
First detected on 23 October, the leak came from one of the 115 wells connected to a massive underground natural gas storage facility, the fifth largest in the US.
Seven unsuccessful attempts were made to shut down the billowing plumes of methane and ethane by the owners, Southern California Gas Company (SoCalGas).