Methane emissions from landfills differentially underestimated worldwide

Landfill methane (CH₄) emissions account for ~10% of all anthropogenic CH₄ emissions globally, amounting to ~50 Tg per year. The current emission inventories utilize a first-order decay model as recommended by the Intergovernmental Panel on Climate Change. In contrast to recent top-down atmospheric inversion results, the mainstream bottom-up inventories exhibit significant biases, largely stemming from the inaccuracy in the a priori decay constant (k), an essential rate-controlling parameter in the model. We improve the k estimation method by incorporating compositional- and environmental-specific corrections, which are readily integrated into the Intergovernmental Panel on Climate Change’s model. The accuracy of CH₄ emission predictions is significantly improved by using the corrected k values, which are benchmarked against the atmospheric inversion results. We extend the emission estimations to landfills worldwide and reveal up to 200% underestimations for individual landfills. Our findings highlight the importance of prioritizing landfill CH₄ emission monitoring and reduction as one of the most cost-effective mitigation options to achieve current climate goals.