How many tons of pure methane have escaped since September 26 and the three explosions of the Nord Stream 1 and 2 pipelines, victims of a “deliberate” act of sabotage in international waters, off the Danish island of Bornholm?
Initially, an estimate of 300 million cubic meters, or 200,000 tons, had been advanced.
A theoretical calculation based on the likely amount of gas stored along the entire length of these huge underwater pipes and the very high pressure, 105 bars, inside the facilities.
The first atmospheric observation data, gathered by the Laboratory of Climate and Environmental Sciences (LSCE), which depends on the Atomic Energy Commission (CEA), the CNRS and the University of Paris-Saclay, book this Wednesday evening a result well below.
“In total, around 700,000 tonnes of pure methane escaped, i.e. three times less than initially estimated, explains Antoine Berchet, research engineer at LSCE, with September 28 at the time of the peak of emanation 1,300 tonnes per hour on Nord Stream 2 and 2,300 tonnes per hour on Nord Stream 1. This corresponds to emissions over one year for the city of Paris within the city walls.
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A surprising difference
To achieve this result, the scientists rely on air monitoring data from the network called ICOS (Integrated Carbon Observation System), with 40 stations for measuring and observing the flow of greenhouse gases in Europe.
"The values were very high just after the explosions, as we could observe on the readings of the three stations near the area and on the path of the gas plume, in southern Norway and in Sweden", specifies Michel Ramonet, CNRS researcher in charge of network management.
How to explain such a difference in the results?
French scientists, who admit to being "surprised" by this discrepancy, put forward several hypotheses.
“It is possible that the quantity of gas in the pipelines has been overestimated, suggests Michel Ramonet, or that a massive quantity of methane has remained trapped in the water without having been released into the atmosphere.
It may be that the gas dissolved in seawater or was kept in small bubbles that methanotrophic marine bacteria, i.e. bacteria that feed on methane, digested it and transformed it into CO2 which, it dissolves very quickly in water.
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No climate bomb
As a precaution, the LSCE researchers are however awaiting confirmation of their observations, by cross-checking them with the work carried out, in particular using satellites, by other teams in Europe.
As for the effects on the environment of the plume of methane released, which wandered through the atmosphere from the Baltic Sea, then to the south of Norway, towards Sweden, the United Kingdom and then Brittany, Michel Ramonet believes that it is “exaggerated” to speak of a “climate bomb”.
“It's obviously bad for the greenhouse effect but this plume represents, even according to the initial estimate that was made, what the whole of France rejects in one year, a drop of water compared to the global emissions.
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While Sweden and Denmark believe, in an official report submitted to the United Nations, that "all available information indicates that these explosions are the result of a deliberate act", Russia demanded on Wednesday to participate in the investigation. on leaks led by Sweden.
In charge of the investigations, Stockholm decided to block access to the area.
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