Nord Stream Pipeline Releasing Large Amounts of Greenhouse Gas

Danish and Swedish authorities reported the leaks this week. They have created large circles of bubbling water just above the ruptures on the pipelines, which rest on the seabed. Denmark and Sweden say they are investigating the cause of the leaks, but several Western officials have cited sabotage. Some are blaming Russia. Moscow has also called the leaks sabotage but has denied any role.

Sweden and Denmark, in a letter Thursday to the United Nations Security Council, said the leaks had caused plumes of gas rising from the pipeline to the surface, with the largest of the four measuring almost 2,000 yards across.

The letter said “the climate effect would likely be very substantial due to the significant volumes of green-house gases that are being released into the air.” The two governments also said they were concerned the gas release could have an impact on maritime life in the Baltic Sea. It said the operator of one of the damaged pipelines, Nord Stream 1, said that line could be releasing gas until Sunday. It said it hadn’t received an assessment from the Nord Stream 2 operator, a Swiss subsidiary of Russian gas giant Gazprom.

“It’s definitely not good,” said Dr. Amy Townsend-Small, professor of environmental science at the University of Cincinnati. “Methane is a greenhouse gas with a global warming potential much higher than carbon dioxide, so it heats up the Earth really fast right after it is released. It’s really wasteful.”

Some of that escaping natural gas, which contains methane, will probably be absorbed by the ocean before reaching the surface, according to Dr. Zitely Tzompa-Sosa, technical advocate for the Clean Air Task Force, a nonprofit environmental group based in Boston.

“We are talking about a lot,” Dr. Tzompa-Sosa. Due to the pressure in the pipeline, most of the gas likely escaped a few hours after leaks first opened, she said. Satellites that can measure methane emissions from space have been blocked by clouds or stymied by reflecting sunlight off the ocean surface, said Dr. Tzompa-Sosa, making it more difficult to assess the size of the release.

The letter provided new details about what Denmark and Sweden believed happened, based on their investigations so far. They said they believe at least two detonations occurred underwater, damaging the lines and causing the leaks. The magnitude of the explosions measured between 2.1 and 2.3 on the Richter scale, which the letter said was “probably corresponding to an explosive load of several hundred kilos.” The leaks were discovered Monday at 2:03 a.m. and 7:03 p.m. local time. Echoing other Western officials this week, the letter said “all available information indicates that those explosions are the result of a deliberate act.”

Write to Eric Niiler at eric.niiler@wsj.com and Laurence Norman at laurence.norman@wsj.com