More than two years after the leaks observed in the twin “Nord Stream” gas pipeline system in the Baltic Sea, international teams of scientists have provided answers to some of the questions that emerged at the time. The first of these: how much methane has escaped from the pipelines?
If the pipes were not in service at the time of the damage to the infrastructure, a certain volume of gas said “residual” – mainly methane, a gas whose warming effect on the climate is 80 times more powerful than that of carbon dioxide on a 20-year scale (UNEP) – was nevertheless there.
The first estimates made public shortly after the event ranged between 180,000 and 270,000 tonnes of gas released (Centre for Research on Energy and Clean Air). In 2024, a study by the Swedish University of Gothenburg then estimated the portion remaining dissolved in the water at between 10,000 and 50,000 tonnes, the rest being brought to the surface.
The “largest amount of methane” from a transient event
However, according to one of three studies published simultaneously in the journals Nature and Nature Communications on January 15, the methane emitted into the atmosphere is in reality around 465,000 tonnes (S. Harris et al.Nature, 2025) – or “the largest recorded amount of methane from a single transient event to date”said the magazine in a press release.
To determine this, the authors of this study simulated emission rates from pipeline ruptures and then integrated them with other methane estimates to model the amount of air emissions resulting from the leaks. They also compared these results with estimates derived from aerial, satellite and weather tower data.
“While extraordinary in their scale, the Nord Stream explosions remind us of the immediate climate opportunity represented by reducing methane emissions across theoil industry and gas”reacted Manfredi Caltagirone, director of the International Observatory of Methane Emissions of the United Nations Environment Program (UNEP).
This quantity corresponds to approximately 1.2% of emissions from the natural gas sector in 2022, but also to 0.1% of anthropogenic methane emissions that year. For comparison, it is equivalent to 0.3% of emissions from agriculture and livestock – the latter sector producing 12% of human greenhouse gas emissions, according to the FAO.
23 marine protected areas concerned
Another team examined the dispersion of methane. According to his study (M. Mohrmann et al.Nature Communications, 2025), 14% of the Baltic Sea experienced concentrations 5 times higher than average natural levels, which may have impacted 23 marine protected areas. Without knowing, however, what the consequences were for the ecosystem.
“Images of the Nord Stream incident often show natural gas bubbling to the sea surface, so it is too easy to forget that a substantial amount remained in the sea. This dissolved gas remains and spreads for a long time”underlined lead author Martin Mohrmann, Baltic Sea specialist at the Voice of the Ocean foundation (press release).
In the same journal, a second article quantifies the “secondary release” of methane in the atmosphere from the gas initially dissolved in sea water. Knowledge of this process should thus contribute to “better understand the fate of methane” that escaped from the pipelines, the authors hope (Friedemann Reum et al.Nature Communications, 2025).
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