環境：ノルドストリーム海底パイプラインの漏れによるメタン排出量の調査

Approximately 465,000 metric tons of methane were emitted from the 2022 Nord Stream subsea pipeline leaks, according to three studies published in Nature and Nature Communications. This is the largest recorded amount of methane released from a single transient event reported to date, although it represents just 0.1% of anthropogenic methane emissions for 2022.

Subsea natural gas leaks from pipeline ruptures can emit large quantities of methane — an important greenhouse gas — into the ocean and atmosphere. In September 2022, damage to the Nord Stream twin pipeline systems (a network of offshore pipelines underlying the Baltic Sea) led to the leakage of natural gases, predominantly methane, at four different sites. However, the total amount of methane released into the atmosphere and dissolved into the ocean remains uncertain, and the potential environmental and climatic impacts are unclear.

In a Nature paper, Stephen Harris and colleagues simulated pipeline rupture emission rates and integrated them with other methane estimates to model the atmospheric emission amount from the leaks. The authors also compared these findings with emission estimates derived from airborne, satellite and meteorological tall tower data. Harris and colleagues found that approximately 465 thousand metric tons of methane were emitted into the atmosphere. Atmospheric emissions from the leaks are equivalent to about 1.2% of emissions from the natural gas sector, and 0.3% of methane emissions from agriculture, for 2022.

In an accompanying Nature Communications paper, Martin Mohrmann and colleagues investigated the spread of dissolved methane across different Baltic regions and marine protected areas. They suggest that 14% of the Baltic Sea experienced concentrations 5 times greater than average natural levels. This may have impacted 23 marine protected areas, although consequences for the ecosystem are unclear.

In a second Nature Communications paper, Friedemann Reum and colleagues quantified the secondary release of methane into the atmosphere, which was initially dissolved in the seawater. They were able to estimate the magnitude and distribution of such emissions, helping to constrain the fate of the methane that escaped from the pipelines.