Urban emissions of methane—a potent greenhouse gas—are rising faster than bottom-up accounting estimates anticipated, according to a study led by University of Michigan Engineering. The discrepancy was found with satellite measurements of methane over 92 major cities around the world. For 72 of the cities, there were sufficient data to track changes in methane emissions between 2019 and 2023. Overall, global urban methane emissions in 2023 were 6% higher than 2019 levels and 10% higher than 2020 levels, although they tended to decrease in European cities.
In contrast, accounting methods—which tally emission estimates of individual methane sources—suggest that urban methane emissions have only risen between 1.7% and 3.7% since 2020. The work is published in the journal Proceedings of the National Academy of Sciences.
The study included over half of the C40 network, a group of 97 cities around the world aiming to reach net-zero emissions by 2050. Total methane emissions across all the studied C40 cities in 2023 were also 10% higher than 2020 levels, and the cities will have to contend with an extra two teragrams of methane emissions per year, which is about 30% of their emission reduction target. The gap between official estimates and satellite measurements warns that city policies designed with accounting estimates may not reduce methane emissions as desired.
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