Nord Stream methane leak far bigger than estimated

The leak is among the biggest ever methane releases related to human activity and occurred when the two Nord Stream pipelines were ruptured at the end of September 2022.

The study puts the likely methane volume that escaped from the gas pipes under the Baltic Sea in a range between 445 000 and 485 000 tonnes. Earlier studies put the amount much lower, between 75 000 and 230 000 tonnes. The study was coordinated by the United Nations Environment Programme (UNEP).

Methane data from space

The researchers used data from several satellites including the Copernicus Sentinel-1 and Copernicus Sentinel-2 missions, as well as the Infrared Atmospheric Sounding Interferometer (IASI) instrument on Eumetsat’s MetOp-B satellite. Data from ESA third-party missions, Landsat 8 and GHGSat, were also used. In addition to the satellite data, the study looked at sources including atmospheric in-situ instrumentation, marine observations, aerial measurements and engineering estimates.

The study compared the datasets with models of the pipeline emission rates caused by the leaks. Stephen Harris, a scientist at UNEP’s International Methane Emissions Observatory (IMEO), explains, “Satellite observations were just one component of a broader set of measurement approaches, which together enabled the study to provide a comprehensive and accurate assessment of methane emissions from the event – highlighting the importance of integrating diverse, complementary methane measurement methods.”

The research, conducted by 70 scientists from 30 research organisations, was part funded by two ESA Earth Observation Science for Society initiatives: MethaneCamp and Methane+. According to Edward Malina, an ESA Earth Observation Atmosphere Scientist, “This study shows the benefits and importance of methane concentrations provided by satellites on a regular basis.”

And Diego Fernandez Prieto, Head of ESA’s Earth Observation Science Section, noted, “Sustained ESA support to scientific advances on methane measurements from satellites have improved our ability to characterise methane leaks globally. I believe this is a good example of how science is transferred into climate action as we are now better equipped to monitor progress and respond to the Global Methane Pledge.”

The study was coordinated by the IMEO, which is also a core implementing partner of the Global Methane Pledge.

The upper estimate for the Nord Stream leak would dwarf the world’s previous largest methane leak. This is estimated at 109 000 tonnes of methane released from the Aliso Canyon Natural Gas Facility in the US, between October 2015 and February 2016. Despite the huge volumes emitted during one-off events, Stephen Harris points out that the Nord Stream release was just 0.1% of global human-caused methane emissions in 2022.

He explained, “This is equivalent to only two days of the oil and gas industry’s annual methane emissions. This highlights the vast number of other human-caused methane sources that still require global mitigation efforts.”

The International Energy Agency estimates that the production and use of fossil fuels resulted in close to 120 million tonnes of methane emissions in 2023, while a further 10 million tonnes came from bioenergy. Methane emissions have remained at this level since they reached a peak in 2019.

First accurate assessment

Prior to this study there was significant uncertainty regarding the impact of the methane release by the Nord Stream leaks in 2022. The study published in Nature provides the first coherent and accurate assessment of its impact.

So why the huge difference in the estimated size of the leak in this study? The initial estimates, according to Stephen Harris, including those from UNEP’s IMEO, were based on data from a limited number of studies, many of which relied on incomplete sources available at the time. “Furthermore, these estimates varied widely, each capturing only part of the story from a different perspective. This study presents the first updated estimate that incorporates all available data to account for every aspect of the emission event: the methane present in the pipeline before and after the ruptures, the amount dissolved in the Baltic Sea, and the portion ultimately released into the atmosphere. Satellite-based measurements played a crucial role in understanding the latter.”