Nord Stream pipelines: analysis of methane emissions following damage

"Nine days after the pipelines were damaged, we found large amounts of methane in the air around the leaks, stretching up to 45 kilometres away. By that time, the pipes had already emptied and the methane from them had actually dissipated," explains Friedemann Reum from the DLR Institute of Atmospheric Physics, who led the flight measurement campaign study. "However, the data from 5 October 2022 showed continued emissions of 19 to 48 tonnes of methane per hour. What we saw was methane that had initially dissolved at the leak sites in the Baltic Sea. From there, it was transported around by ocean currents before being released into the air. Our airborne observations provide direct evidence of the outgassing of the dissolved methane into the atmosphere. Thus, we were able to provide a constraint on how much of the methane from the pipelines ended up in the Baltic Sea and where, and what happened to it afterwards."

The flight measurement campaign captured a large-scale snapshot of the outgassing of the initially dissolved methane. The results are largely consistent with those of flow models that estimated the total amount of methane dissolved in seawater based on the spatially limited methane measurements in the water acquired by the University of Gothenburg and Voice of the Ocean. According to these models, between 9,000 and 15,000 tonnes of the greenhouse gas was initially dissolved in the sea before reaching the surface.

The total amount of methane released from the Nord Stream pipeline leaks, between 445,000 and 485,000 tonnes, represents 0.1 percent of all human-caused methane emissions in 2022, according to the UN Environment Programme. This is equivalent to approximately 1.2 percent of emissions from the natural gas sector and 0.3 percent of methane emissions from agriculture for the same year. "This analysis shows the importance of considering complementary observation and estimation methods to characterise methane emissions. This was key to assessing the amount of methane emitted during the Nord Stream leaks," said Andrea Hinwood, Chief Scientist at UNEP. To estimate the emissions from the Nord Stream leaks, the International Methane Emissions Observatory used engineering calculations based on pipeline pressure data as well as various sources of methane data, including measurement towers, satellites, marine-based observations and DLR's airborne measurement data.

'Sniffing' for methane over the sea

The short-notice flight measurement campaign took place on 5 October 2022 in close cooperation with the Institute of Flight Guidance (IFF) at the Technical University of Braunschweig. In total, researchers conducted two helicopter flights with a towed probe starting at the Polish coast near Kolobrzeg. The IFF operates the helicopter-towed HELiPOD probe, which is equipped with extensive technology for atmospheric measurements. The HELiPOD is flown as a suspended load on a 25-metre-long rope below the helicopter. For the flights in autumn 2022, it was additionally equipped with a methane instrument from the DLR Institute of Atmospheric Physics. The Federal Agency for Technical Relief (THW) in Braunschweig provided important assistance with the short-term logistical preparation of the measurements, and the helicopter was provided by the Polish company Helipoland. "We are pleased that the deployment of the HELiPOD towed probe made these measurements possible. This unique research instrument can be flexibly equipped with a wide range of sensors and used almost anywhere in the world. Measuring approximately five metres in length and with a take-off weight of up to 300 kilograms, it provides space for a variety of measurement technologies – for example, to record atmospheric data, particles, fine dust, surface properties and gases such as methane. Combined with an advanced system for data processing and storage, it enables the collection of critical research data," explains Peter Hecker, Head of the Institute of Flight Guidance at TU Braunschweig.

Global, public database for methane emissions

Methane is responsible for approximately one-third of global warming caused by greenhouse gases and is therefore the second most important anthropogenic greenhouse gas after carbon dioxide. The Intergovernmental Panel on Climate Change (IPCC) is urging methane emissions to be cut by at least 30 percent by 2030 to keep the 1.5 degrees Celsius threshold within reach. To support the development of effective measures to reduce methane emissions, the IMEO, under the umbrella of the United Nations Environment Programme, is establishing a global, public database for methane emissions. DLR has already carried out several flight projects within the framework of the IMEO, including in major oil and gas production areas in Africa and on the Arabian Peninsula, as well as in European coal mining regions.

Related studies

• Methane emissions from the Nord Stream subsea pipeline leaks, Harris et al, (Nature)
• Airborne observations reveal the fate of the methane from the Nord Stream pipelines, Reum et al., (Nature Communications)
• Nord Stream methane leaks spread across 14% of Baltic waters, Mohrmann et al., (Nature Communications)
• Technical University of Braunschweig – Helicopter test flights with HELiPOD in Braunschweig

Related links

• DLR aircraft records methane levels off the coast of Central Africa
• Studying methane emissions from Polish coal mines using a novel airborne concept
• First helicopter-based measurements of methane emissions on the Arabian Peninsula from the oil, gas and waste sector
• Research flights over Canada analyse greenhouse gases
• On the trail of methane sources in Scandinavia
• European-wide research flights focus on greenhouse gas methane