One of the worst recorded methane spills occurred last year at a remote well in Kazakhstan, new analysis revealed by the BBC has shown.
An estimated 127,000 tonnes of gas have entered the atmosphere since an explosion caused a fire that lasted more than six months.
Methane is a much more potent greenhouse gas than carbon dioxide.
Buzachi Neft, the company that owns the well, denies that a "substantial quantity" of methane escaped.
"The magnitude and duration of the leak are frankly unusual," said Manfredi Caltagirone, head of the United Nations' International Methane Emissions Observatory.
"It's extremely large."
On 9 June 2023, an explosion was reported during the drilling of an exploratory well in the Mangistau region of southwestern Kazakhstan, causing a fire that lasted until the end of the year.
It was only brought under control on December 25th.
Local authorities told the BBC that work is currently underway to seal the concrete pit.
Methane is a gas invisible to the human eye.
But when sunlight passes through a methane cloud, it creates a unique fingerprint that some satellites can track.
This particular methane leak was first studied by the French geoanalysis company Kayrros.
Their analysis has now been verified by the Netherlands Institute for Space Research and the Polytechnic University of Valencia, Spain.
By looking at satellite data, scientists discovered that high concentrations of methane were visible on 115 separate occasions between June and December.
Based on these readings, they concluded that 127,000 tons of methane leaked from this well.
That could make it the second-worst human-caused methane spill on record.
Luis Guanter of the Polytechnic University of Valencia, who helped verify the leak, says that "only the sabotage of Nord Stream could have led to a more serious leak".
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