Wastewater treatment plants, such as this one, emit nitrous oxides and methane, both potent greenhouse gases. Credit: Justin Sullivan/Getty Wastewater systems are emitting more greenhouse gases than nations are reporting. As much as 150 million metric tonnes of carbon dioxide equivalent could be sneaking into the atmosphere from these sources per year1. Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any time Subscribe to this journal Receive 51 print issues and online access $199.00 per year only $3.90 per issue Rent or buy this article Prices vary by article type from$1.95 to$39.95 Prices may be subject to local taxes which are calculated during checkout doi: https://doi.org/10.1038/d41586-026-00514-y Song, C., Ponder, D., Peng, W. & Ren, Z. J. Nature Clim. Change https://doi.org/10.1038/s41558-025-02540-6 (2026).…