Global Methane Intensity in Dairy Systems: Structural Drivers, Uncertainty, and Mitigation Potential from Species-Portfolio Reallocation

Methane emissions from dairy production systems remain a major climate challenge, yet global assessments rarely integrate species structure and uncertainty. This study evaluated methane emission intensity in the dairy sector during 2020–2023 using harmonized FAOSTAT data. A total of 183 reporting entities were initially identified; after deduplication of the “China” aggregate, analyses were conducted for 181 countries. Exact Shapley decomposition separated structural effects (species mix) from intraspecific effects, while a Bayesian hierarchical model quantified between-country heterogeneity. Results showed that cattle had the lowest average methane intensity, whereas camels and small ruminants exhibited substantially higher values. Between 2020 and 2023, structural changes contributed to a modest decline in aggregate methane intensity, although this effect was partly offset by intraspecific increases. Robust portfolio optimization under reallocation constraints indicated an average national reduction potential of 12.6%, with diminishing returns beyond a 10% reallocation budget. These findings show that methane intensity in the dairy sector is shaped not only by production efficiency but also by livestock species composition. The probabilistic framework provides a basis for climate policy design that explicitly incorporates uncertainty in livestock production systems.