Scientists calculate climate impact of methane leak from ruptured Nord Stream pipelines

Methane escaping from sabotaged pipes in the Baltic Sea (September 27, 2022). Credit: Danish Armed Forces

Nord Stream 1 and 2, two undersea pipelines intended to transfer natural gas from Russia to Germany, both ruptured on September 26, 2022. Massive amounts of gas, mostly methane, leaked into ocean and then released into the atmosphere.

Methane is the second most abundant anthropogenic greenhouse gas after CO₂ in terms of volume in the atmosphere, but it has a much stronger greenhouse effect. Therefore, whether any negative climate impacts would result from this incident is of major concern worldwide. Although a press article published in the magazine Nature commented on this issue, no quantitative conclusions were drawn.

Recently, scientists from the Institute of Atmospheric Physics of the Chinese Academy of Sciences estimated the possible climate impact of methane leakage by adopting the energy saving framework of the Panel’s Sixth Assessment Report. Intergovernmental Experts on Climate Change (IPCC AR6), published in 2021. Their findings were published today (11 November) in the journal Advances in atmospheric science.

First, the researchers collected all estimates of the total amount of methane leak available from the world’s media after the incident. Early estimates (1-2 days later) were found to be up to 0.5 million tonnes (Mt). However, it later became clear that the amount of methane that had escaped was probably much lower than first estimated. In particular, a team from Nanjing University, China, provided a more accurate estimate of 0.22 ± 0.03 Mt based on multiple observations, including those from high-resolution satellites.

This value established that it was the largest methane emission from a single event in human history – more than twice that of the Aliso Canyon accident in California in 2015. However, according to IPCC AR6, annual methane emissions from the oil and gas sectors amounted to 70 Mt between 2008 and 2017. This means that methane leakage from Nord Stream pipelines was equivalent to only 1 day of emissions from these sectors .

The IPCC AR6 also pointed out that methane in the atmosphere is gradually removed by reacting with certain radicals, such as the hydroxyl radical, resulting in a lifetime of about 10 years, which is short-lived compared to CO₂. This means that the climate impact of methane depends on the time horizon, which complicates things when trying to calculate it directly.

Instead, the researchers made an indirect estimate using the concept of “global warming potential.” Specifically, they determined that the amount of heat accumulated per unit mass of methane over the next 20 years after it is released into the atmosphere is 82.5 times that of CO₂. Then, armed with this information, they were able to calculate that, considering a time horizon of 20 years, the climate impact of the methane leak is equivalent to that of 20.6 Mt of CO₂which would increase atmospheric CO₂ concentration of only 0.0026 ppm.

Based on latest IPCC AR6 assessments of effective radiative forcing under doubled CO₂climate feedback and the efficiency of heat absorption by the oceans, under energy conservation, the global average surface air temperature would theoretically increase by 1.8 × 10^-5 °VS

“Such a small warming cannot be seen in ecosystems or human society,” says Dr Xiaolong Chen, first author of the study. “Yet anthropogenic methane has been the second most important contributor to global warming and is being emitted by multiple sectors of agriculture and industry. If we are to meet the warming target below 1.5°C or 2°C set out in the Paris Agreement, infrastructure damage like this must be avoided so that we can better control and reduce methane emissions.

Reference: “Negligible Warming Caused by Nord Stream Methane Leaks” by Xiaolong Chen and Tianjun Zhou, November 11, 2022, Advances in atmospheric science.
DOI: 10.1007/s00376-022-2305-x