The Nord Stream pipeline leak was responsible for what is probably the largest single methane emission ever recorded, according to new measurements of the leak.
The Nord Stream 1 and 2 pipeline systems were built to bring natural gas from Russia to Europe beneath the Baltic Sea. On 27 September, large blasts punched holes in three of the pipes in what government leaders around the world have called an act of sabotage. Natural gas, which is mostly made of the potent greenhouse gas methane, immediately started bubbling up through the water and into the atmosphere.
As of 2 October, all three pipelines had run out of gas and stopped , according to the Danish Energy Agency. Satellite observations on 3 October at the surface.
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To quantify the size of the leak, at the Norwegian Institute for Air Research and her colleagues used measurements from a network of ground-based monitoring stations in Finland, Norway and Sweden called the Integrated Carbon Observation System (ICOS).
Soon after the leak began, the ICOS stations large spikes in methane as the plume swirled hundreds of kilometres away from the pipeline breach. Satellites were also able to make some measurements of the leak, but their view was mostly obscured by clouds.
The researchers modelled how wind carried methane away from the leak, as well as the rate of methane emission from the pipelines based on where the leak occurred in each pipe. They assumed the rate decreased once the shorter sections of pipeline had emptied out, says , also at the Norwegian Institute for Air Research.
With this modelling, the researchers worked out the total amount of methane that must have been released to create the pattern of detections made by the monitoring stations.
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They found that the pipelines emitted between 56,000 and 155,000 tonnes of methane, depending on the statistical method they used to relate their measurements to their atmospheric model. Their estimate is the first based on actual measurements of the leak and is significantly less than previous estimates. The Danish Energy Agency鈥檚 worst-case of how much methane would be released based on the amount of gas thought to be in the pipeline was about 500,000 tonnes.
The disparity could be because some methane remained in the pipeline or dissipated in the water, says Thompson. 鈥淚 don鈥檛 think all the gas that was in the pipeline reached the atmosphere,鈥� she says. There are also uncertainties in their atmospheric models, which have limited resolution for emissions from a single point. 鈥淚t鈥檚 a blurry image,鈥� says Thompson.
Still, Thompson says the Nord Stream leak was 鈥渜uite likely鈥� the largest ever methane emission from a single point. The largest released about 100,000 tonnes of methane in California in 2015.
While massive for a single event, the emission is roughly equivalent to what the oil and gas industry regularly emits every two or three days, says at the UN Environment Programme鈥檚 International Methane Emissions Observatory.
