Large local effect but small global climate impact of Nord Stream

The leakage of methane gas from the Nord Stream pipelines has a large local effect on ocean chemistry, but the global climate impact is likely to be small. This according to geochemist Volker Brüchert at Stockholm University.

Flygbild på metanläckaget från Nord Stream.
Flygbild på metanläckaget från Nord Stream. Foto: Danska försvaret/SVT

The suspected explosions of the gas pipelines Nord Stream 1 and 2 outside Bornholm mean that large amounts of methane gas flow into the sea. How much of the methane goes on into the atmosphere and thus affects the climate has not yet been determined.

– The only available estimate of annual emissions of methane from the Baltic Sea is about 20,000 tons per year. However, this figure may be an underestimate as it ignores the high discharges in shallow water during the summer and also ignores coastal areas, but the order of magnitude can serve as a useful guideline.

That's what Volker Brüchert, associate professor of geochemistry at the Department of Geological Sciences, Stockholm University, says. He is also the research leader for the research theme Water, biogeochemical cycles and climate at the Bolin Center for Climate Research, where he focus on the biogeochemical cycle of nutrients, methane, nitrogen oxide and carbon dioxide in the Baltic Sea and the Arctic Ocean.


About 100,000 tonnes of methane in each pipeline

The reported volume of gas in the Nord Stream 1 and Nord Stream 2 pipelines varies greatly and has been reported to be between 177 and 778 million cubic meters.

– Assuming a pressure of one bar and a purity of 98 percent of the natural gas, this corresponds to 121,000 to 544,000 tons of methane in the pipelines, assuming no new supply of gas through the pipelines. It has also been reported that the pipelines experienced a sudden pressure drop from 105 bar to 7 bar. If we assume that the pressure in the pipelines was about 105 bar before the event, that would give an amount of about 100,000 tons of methane in each pipeline, says Volker Brüchert.


Sudden release produces large bubbles

The leakage sites are at depths between 70 and 88 meters. The discharge from the pipelines occurs as free gas. Methane is very insoluble in seawater and only about 3–4 percent can be dissolved in seawater, and the rate of dissolution is relatively slow.

– At a depth of 90 meters, approximately 380 grams of methane can be dissolved in one cubic meter of water. When the hydrostatic pressure decreases, as in surface water, only about 32 grams can dissolve. For a sudden emission like in this incident, very large bubbles will form and rise very quickly, at a speed of about 20-30 cm per second, to the surface, giving little time for the methane to dissolve. But when the pressure decreases in the pipeline, the size of the bubbles will decrease, the bubbles will rise more slowly and more methane can be dissolved, says Volker Brüchert.

Dissolved methane can be oxidized to carbon dioxide in water, a process catalyzed by microbes, regardless of whether this occurs with oxygen or other oxidants. As the concentrations of carbon dioxide in the affected water would increase, the pH would drop, at least temporarily in the affected area.


Small global climate impact

At present, Volker Brüchert makes the assessment that much of the initially leaking methane will end up in the atmosphere. The average lifetime of methane in the atmosphere is about 9–12 years and depends on the concentrations of hydroxyl radicals in the atmosphere, which are dependent on UV radiation. Oxidation reactions are slower during the fall and winter months, which normally leads to a small increase in methane concentrations during fall, winter, and early spring.

– All in all, the emissions from Nord Stream will therefore have a measurable impact on the regional methane budget and a local effect on ocean chemistry, but the global climate impact is small. The annual global emissions of methane are estimated at around 550 million tonnes per year, so even in the worst case scenario this incident would contribute 0.1 percent to the annual emission, says Volker Brüchert.

Translation of the article
Stor lokal effekt men liten global klimatpåverkan av Nord Stream

Volker Brüchert
Volker Brüchert

Volker Brüchert is Associate Professor of Geochemistry at the Department of Geological Sciences and Research Leader for the research theme Water, biogeochemistry and climate at the Bolin Center for Climate Research. His research focuses on understanding the regulation of the major biogeochemical cycles in aquatic environments through the action of macro- and microorganisms and their response and adaptation to climate change and eutrophication effects.


Further reading in Swedish:

Gasläckorna från Nord Stream kan förgifta torsken. Artikel i Forskning & Framsteg med bland annat Elias Broman vid Stockholms universitet som forskar om metanoxiderande bakterier.

Gasläckorna – så ser seismologen att de orsakats av explosioner Vetenskapsradion Nyheter med bland annat Christian Stranne, maringeolog vid Stockholms universitet

Inslag i radio och tv med juridikprofessorer vid Stockholms universitet om Nord Stream