Methane leak under the Baltic Sea was far bigger than estimated

In September 2022, a catastrophic event unfolded beneath the Baltic Sea. The Nord Stream gas pipelines, which transport natural gas from Russia to Europe, suffered severe ruptures. What followed was an unprecedented emission and release of methane, one of the most potent greenhouse gases.

At the time, experts scrambled to estimate the scale of the damage. Initial assessments suggested a significant but relatively contained leak. However, new research published in the journal Nature has revealed a much graver reality.

The methane emission was over twice the first estimates, making it one of the biggest leaks ever. This discovery has sparked fresh concerns about the environmental impact of fossil fuel infrastructure failures and the urgency of global methane reduction efforts.

The study, coordinated by the United Nations Environment Programme (UNEP), offers a more precise understanding of the emissions and the role of advanced satellite technology in detecting such events.

Nord Stream methane emission

The Nord Stream pipelines ruptured in September 2022, leading to an uncontrolled release of methane into the atmosphere. The research shows the leak did more damage than experts first thought.

According to the study, the total volume of methane leaked ranged between 445,000 and 485,000 tonnes. This sharply contrasts with earlier estimates, which suggested a much lower figure of 75,000 to 230,000 tonnes.

Methane traps heat in the atmosphere much faster than carbon dioxide, making it a powerful driver of global warming. Releasing so much of it at once speeds up climate change in ways we can’t ignore.

Advanced satellite data collection

To determine the true extent of the leak, the researchers used data from multiple sources.

This included several Earth observation satellites such as Copernicus Sentinel-1 and Sentinel-2, along with the Infrared Atmospheric Sounding Interferometer (IASI) instrument on Eumetsat’s MetOp-B satellite. Additional data came from ESA’s third-party missions, Landsat 8, and GHGSat.

The researchers also incorporated marine observations, atmospheric in-situ measurements, aerial monitoring, and engineering calculations. These diverse data sources allowed for a much more accurate analysis of the methane emissions.

Stephen Harris, a scientist at UNEP’s International Methane Emissions Observatory (IMEO), emphasized the importance of this approach.

“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,” noted Harris.

Tracking methane emissions

The study involved 70 scientists from 30 research organizations. It was partially funded by two ESA Earth Observation Science for Society initiatives: MethaneCamp and Methane+.

“This study shows the benefits and importance of methane concentrations provided by satellites on a regular basis,” said Edward Malina, an ESA Earth Observation Atmosphere Scientist.

Diego Fernandez Prieto, Head of ESA’s Earth Observation Science Section, explained the significance of satellite advancements in tracking methane emissions.

“Sustained ESA support to scientific advances on methane measurements from satellites have improved our ability to characterize 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,” said Fernandez Prieto.

Extent of the methane leak

The Nord Stream methane leak is now one of the biggest ever recorded. At its highest estimate, it released more than four times the methane from the 2015–2016 Aliso Canyon leak in the United States, which was previously one of the largest known emissions.

However, despite its scale, the Nord Stream event accounted for just 0.1% of all human-caused methane emissions in 2022.

“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,” said Harris.

Methane emissions are a global issue

The International Energy Agency estimates that the production and use of fossil fuels resulted in nearly 120 million tonnes of methane emissions in 2023.

Another 10 million tonnes came from bioenergy. Methane levels have remained consistently high since peaking in 2019.

The findings of this study reinforce the need for stronger global efforts to track and reduce methane emissions. The Global Methane Pledge, which aims to cut methane emissions significantly, relies on improved monitoring and scientific advancements to drive climate action.

Understanding the leak’s impact

Before this study, there was significant uncertainty about the actual volume of methane released from the Nord Stream leak. The latest research offers the most accurate assessment to date, using extensive data analysis and satellite-based measurements.

“The initial estimates, 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,” noted Harris.

”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.”

Image Credit: ESA

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