City methane emissions rising faster than accounts show ^{CEFR B2}

Using TROPOMI observations from the Copernicus Sentinel-5 Precursor satellite, researchers estimated methane emissions for 92 major cities and obtained multi-year trends for 72 of them. Their results show global urban methane in 2023 was 6% above 2019 levels and 10% above 2020 levels, with declines more common in European cities. These satellite-derived trends exceed increases reported by bottom-up inventories, which calculated a rise of about 1.7%–3.7% since 2020.

The gap matters because many city climate plans rely on bottom-up accounting. The study notes common urban methane sources such as old or leaky natural gas infrastructure, landfills and wastewater treatment plants. The researchers estimate urban emissions were about 10% of all human methane emissions in 2023 and nearly four times higher than the oil and gas “ultra emitters” studied previously. For the C40 cities included, 2023 emissions were 10% higher than 2020, adding roughly 2 teragrams per year—about 30% of their reduction targets.

Shortcomings in resolution mean TROPOMI can identify city-level totals but cannot always locate exact sources inside a city. The team and others are exploring higher-resolution satellites that could reveal emissions from individual landfills or facilities. The paper appears in Proceedings of the National Academy of Sciences; funding came from NASA and the National Institute of Standards and Technology. Kort and colleagues note earlier airplane surveys that found much larger leaks from flaring and offshore production, findings that have already influenced policy.

• Key sources: leaky gas pipes, landfills, wastewater plants.
• Data: TROPOMI on Sentinel-5 Precursor, launched 2017.