The sabotage of the Nord Stream pipelines in September 2022 not only heightened geopolitical tensions but also unleashed an unprecedented environmental event, releasing the largest recorded amount of methane from a single human-caused incident – 465,000 metric tons – into the atmosphere and surrounding waters, according to three new studies.
The Nord Stream pipelines, which transport natural gas from Russia to Germany under the Baltic Sea, were heavily damaged in September 2022. An underwater explosion ripped apart the NS1 and NS2 pipes near the island of Bornholm in Denmark, causing a flurry of gas to rise to the sea surface.
The culprit behind the attack hasn’t been identified, although it has been linked to the wider fallout of the Russia-Ukraine war. In 2024, Germany reportedly issued an arrest warrant for a Ukrainian national in connection with the event, but the Ukrainian government has denied any involvement.
The Voice of the Ocean Foundation quickly deployed an underwater drone (known as a glider) to a region just outside the exclusion zone of the leaks. It continued to monitor the situation for three months after the explosion, and observed the extent of dissolved methane in the surrounding waters.
Map over the maximum concentration of methane in the southern Baltic.
Image credit: Martin Mohrmann/VOTO
“To get the most robust estimations, we combined observations from the gliders with surface observations collected by our colleagues at the German research institute IOW from a ferry. It was gratifying to see how well it matched the results from University of Gothenburg’s research vessel’s expedition to the Nord Stream leak area too,” Bastien Queste, an oceanographer at the University of Gothenburg, said in a statement.
“All this together makes us feel confident that we have a really good picture of how the methane spread in the Baltic Sea, both across time and space,” said Queste.
Much of the gas ended up in Earth’s atmosphere, although a significant quantity was absorbed into the sea. In the initial wake of the explosion, dissolved methane levels in the waters were sometimes 1,000 times above usual. Overall, 14 percent of the Baltic Sea saw concentrations of methane at least five times greater than average natural levels.
Researchers also found that ocean currents transported the dissolved methane to 23 marine protected areas in the Baltic Sea. However, the impact on the surrounding marine ecosystems isn’t clear yet, not least because an event of this scale has never been seen before.
“The honest answer is that we don’t know about the long-term ecosystem effects of the increased methane concentrations. Luckily, methane is not very toxic, but there has been no previous event of this scale. Even though small concentrations of methane are not harmful, it is not yet clear what high concentrations over a long time can do,” Martin Mohrmann, a researcher at Voice of the Ocean, told IFLScience.
According to the researchers, one thing is clear: the safety of underwater gas pipelines must be re-evaluated, particularly in today’s increasingly uncertain world where unusual events like this are becoming all the more likely.
“I believe that the risk assessment for gas pipelines like the Nord Stream pipelines have to be reevaluated. The Nord Stream risk assessments (2009) state that the probability of a gas escape would be about one event in 20,000 years, and that the solubility of natural gas in water is negligible. Both are now questionable,” added Mohrmann.
The three new studies were published in the journal Nature (here), as well as Nature Communications (here and here).
