On Sunday, the Danish Energy Agency announced that a series of leaks in natural gas pipelines running under the Baltic Sea had been stopped. But the rupture, preceded by multiple explosions last week, appears to be the single largest discharge of methane, an extremely potent greenhouse gas.
"It dwarfs the previous known leaks," says Ioannis Binietoglou, who works on monitoring methane emissions for the Clean Air Task Force, a non-profit environmental organization.
Methane is the main component in natural gas. When released into the atmosphere, it's initially more than 80 times better than carbon dioxide at trapping heat, although that effect tapers off over time.
The Nord Stream 1 and Nord Stream 2 were not actively carrying natural gas when explosions rocked the pipelines off the coast of Denmark, though there was some gas in the lines. Russian President Vladimir Putin has accused the West of sabotaging the Russia-built pipelines, a charge vehemently denied by the United States and its allies.
There were at least three separate leaks. While the exact amount of the gas released is still not known, as much as half a million metric tons of methane was leaked from the pipelines, according to an Associated Press analysis of estimates from the Danish government.
That's approximately five times more than what had been the largest leak up to that point, in Aliso Canyon in California in 2015 and 2016. The Aliso Canyon leak had about the same impact on the climate as burning nearly a billion gallons of gasoline, according to the California Air Resources Board.
Scientists have separately estimated different amounts for the Nord Stream leak, ranging from 100,000 tons to almost 400,000 tons.
"There are contradicting estimates, but all of them point to something really, really huge," says Binietoglou.
The leak is equal to a few days of methane emissions from fossil fuel production
Scientists say reducing methane emissions is a critical part of tackling climate change in the short term, because the gas has such a strong warming effect when in the atmosphere. Major leaks make that work harder, but are not the main culprit.
"It is important to put it in context of a larger problem that we have, that we need to fix," says Manfredi Caltagirone, head of the International Methane Emissions Observatory with the United Nations Environment Programme.
In 2021, the energy sector emitted around 135 million metric tons of methane, most from oil and gas production, according to estimates by the International Energy Agency. That means even though the Nord Stream leak is likely the single biggest emission event, it's only equivalent to a day or two of regular methane emissions from the fossil fuel industry, Caltagirone says.
Adds Binietoglou: "This doesn't mean that the leak is small. It means that oil and gas is really leaky, and really emitting a lot of gas."
Research into the size and damage caused by the leaks is ongoing. On Monday, the Swedish government sent a dive team to the site of the leaks, Reuters reported.
Binietoglou says the global scientific community has invested in more technology to detect emissions, and he's hopeful these tools will be applied not just to major international incidents, but also to target smaller leaks and bring overall methane emissions down.
The Associated Press contributed to this report.
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