Leaks of methane, a powerful greenhouse gas, have been detected in Paris: they originate from sewers, building boilers, and pipes.
Nearly 570 million metric tons methane (CH4) are produced worldwide each year, of which 60 % are believed to be caused by human activity, according to the’International Energy Agency (IEA). Yet this greenhouse gas is no less dangerous than carbon dioxide (CO2) : even though it is present in smaller quantities in the atmosphere, over a hundred years, its warming effect is twenty-eight times larger per kilogram than that of the CO2. Hence the importance of the study, published on June 23 in the journal Environmental Science & Technology, which aims to measure concentrations of this gas in Paris. The goal: to achieve reduce emissions in the city by identifying them at the source.
« The sources of methane are still not well understood, explains to ReporterreJean-Daniel Paris, a researcher at the Laboratory of Climate and Environmental Sciences (LSCE–IPSL) and co-author of the report. When we talk about methane emissions, we tend to think of leaks in the pipelines that transport this raw material, agriculture, or waste management. » Methane is, in fact, produced and emitted during the decomposition of livestock manure and the organic components of agro-industrial wastewater. « But we don't think about cities, even though they are sources of emissions. »
To carry out their research, scientists at the LSCE–IPSL Researchers from Saclay conducted measurements in Paris between September 2018 and March 2019 using mobile sensors installed in cars. The scientists traveled throughout 30 % on the streets of the capital, and in certain neighborhoods of Issy-les-Moulineaux and Boulogne-Billancourt (Hauts-de-Seine). « Paris isn't considered a major source of methane emissions, but we wanted to get to the bottom of it », said Jean-Daniel Paris. As expected, a large portion of the emissions come from leaks in the gas distribution network. « More surprisingly, we also detected emissions from sewers and, likely, from private heating systems. »
Scientists have thus detected ninety potential leaks in Paris. Twenty-seven of these have been clearly identified and classified into three categories: emissions from the natural gas distribution network—which spans approximately 2,000 kilometers—account for 63 %, those from the sewer system 33 %, and building heating 4 %. Scientists have identified two outbreaks in the 16the district and in the southwestern suburbs of Paris.
- The sewers of Paris. Flickr/CC BY–SA 2.0/ Salim Virji
Identifying Sources to Reduce Emissions
Based on these findings, the research team estimates that approximately 190 metric tons of methane are emitted each year in Paris, ranking the capital as « city with average methane emissions » compared to the cities in the United States and Europe that were studied. « These figures are probably an underestimate because we didn't cross every street, ", Jean-Daniel Paris clarifies. In addition, the leaks detected in the buildings originated from boilers on the ground floor or in basements, which the sensors were able to detect from the street. We do not have data for the upper floors. »
Understanding the sources of methane is an important first step toward effectively combating greenhouse gas emissions, the study notes. Especially since the CH4 is often overlooked in climate change policies, even though it is increasingly being incorporated into national action plans. « As for the sewer lines, we need to invest in order to increase the number of repair projects. As for sewers, better maintenance of the systems could help reduce the presence of organic matter, which produces methane as it decomposes. And for private boilers, we need to ensure that the equipment is modern enough to prevent leaks. »
If no action is taken, methane emissions from human activities are expected to continue rising for the rest of the century, increasing by 70 % or more by 2100, for a global total exceeding 600 million metric tons per year. However, a a study by the Environmental Defense Fund published in April 2021 indicates that, thanks to a wide range of existing solutions, it is possible to cut emissions by half CH4 planned for 2030. Most of them—about 60 % are inexpensive, and half of them have a « negative cost », which means that companies will make money by taking action.
The United Nations Climate and Clean Air Coalition had already highlighted the importance of addressing methane emissions: rapidly reducing them using the tools already available would help limit global warming by 0.3 °C by 2040. By reducing global methane emissions by up to 45 % by 2030—and thus the global warming attributable to it—the European Union could also prevent 22,689 premature deaths caused by ozone each year and 1.4 million metric tons of annual crop losses.
