The photos and videos made the rounds of the media and social networks. They show bubbling on the surface of the Baltic Sea, with a diameter ranging from 200 meters to 1 kilometer. In question: massive leaks on the Nord Stream 1 and 2 gas pipelines detected off the coast of Denmark, possibly due to sabotage. They fear a “climate and environmental disaster”said Stefano Grassi, Head of Cabinet of the European Commissioner for Energy, on Tuesday 27 September. “There are a number of uncertainties but, if these pipelines fail, the impact on the climate will be disastrous and could even be unprecedented”said David McCabe, scientist for the think tank Clean Air Task Force, in a press release.
If the concerns are great, it is that the gas pipelines, even if they were not operational, contain for technical reasons natural gas mainly composed of methane, a very powerful greenhouse gas. Its warming potential is much higher than that of carbon dioxide (CO2): 82 times more over a twenty-year horizon, 29 times more over a hundred years. Methane is like this responsible for a quarter of global warming since the pre-industrial era, and its emissions have risen sharply in recent years.
If all the gas escaped, then emissions would be equivalent to a third or even half of Denmark’s annual emissions
How much methane has been released into the atmosphere? This estimate is difficult to make because it depends on the pressure or temperature of the gas in the pipelines and how much has dissolved in the water. “A clear majority of gas [de Nord Stream 1 et 2] has already come out of the pipessaid the director of the Danish energy authority, Kristoffer Böttzauw, during a press conference on Wednesday. We expect the rest to slip away by Sunday. » The German Federal Environment Agency estimated, for its part, that 300,000 tonnes of methane were released into the air.
According to various scientists, the gas pipelines would contain between 300 and 500 million m3 of gas, i.e. between 200,000 and 300,000 tonnes of methane. This quantity has the same warming power, over a period of twenty years, as 17 to 25 million tonnes of CO2. If all the gas escaped, emissions would then be equivalent to a third or even half of Denmark’s annual emissions or 4 to 7% of French emissions. “The impact would be similar to that of a million cars for a year, it’s colossal”adds Thomas Lauvaux, researcher at the Laboratory of Climate and Environmental Sciences.
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