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

Methane is the second most prevalent anthropogenic greenhouse gas after CO2, although its greenhouse effect is substantially stronger. As a result, whether this catastrophe may have detrimental climatic consequences is a major issue around the world. This problem was discussed in a news article published in Nature, but no quantitative implications were reached.

Recently, scientists from the Chinese Academy of Sciences’ Institute of Atmospheric Physics approximated the potential climatic effect of leaked methane using the energy-conservation framework of the Intergovernmental Panel on Climate Change’s Sixth Assessment Report (IPCC AR6), which was released in 2021. Their discoveries were published in the journal Advances in Atmospheric Sciences.

After gathering all estimates of the total volume of released methane available in the global media following the event, it was discovered that the early estimations (1-2 days after the occurrence) amounted to 0.5 million tons (Mt).

However, it was eventually discovered that the amount of methane that leaked was likely far smaller than initially thought. A group from Nanjing University in China obtained a more precise estimation of 0.22 ± 0.03 Mt by combining various measurements, including those from high-resolution satellites.

This result confirmed that this was the greatest methane emission in a single incident in human history, more than twice that of the Aliso Canyon disaster in California in 2015. However, according to the IPCC AR6, annual methane emissions from the oil and gas sectors could have reached 70 Mt between 2008 and 2017. The amount of methane leaked from the Nord Stream pipelines was comparable to only one day’s equivalent of emissions from these industries.

The IPCC AR6 report also stated that methane in the atmosphere is slowly eliminated by reacting with specific radicals, such as the hydroxyl radical, resulting in an approximate 10-year lifetime, which is short compared to CO2. This indicates that the climatic effect of methane relies on the time horizon, which challenges direct calculations.

Rather, the scientists used the concept of “global warming potential” to make an indirect estimation. They discovered that the amount of heat accumulated per unit mass of methane in the 20 years following its release into the atmosphere is 82.5 times that of CO2.

Equipped with this knowledge, researchers were able to determine that, over a 20-year time horizon, the climatic impact of the leaked methane is comparable to 20.6 Mt of CO2, which would elevate atmospheric CO2 concentration by only 0.0026 ppm.

According to the most recent IPCC AR6 evaluations of efficient radiative forcing under doubled CO2, climatic feedback, and ocean heat uptake efficiency, the global mean surface air temperature would rise by 1.8×10−5 ℃ under the energy conservation framework.

"Such a tiny warming cannot be perceived in ecosystems or human society. Still, anthropogenic methane has been the second largest driver of global warming, and is emitted from multiple sectors of agriculture and industry. If we are going to achieve the warming target of below 1.5 ℃ or 2 ℃ set out in the Paris Agreement, damage to infrastructure such as this should be avoided so that we can better control and reduce methane emissions."

Dr. Xiaolong Chen, Study First Author, Institute of Atmospheric Physics, Chinese Academy of Sciences