Enhancing Transparency in Livestock GHG Assessments: Methodological Sensitivity and Climate-Dependent Spatial Patterns

Livestock production is a major source of greenhouse gas (GHG) emissions, yet quantification is challenging because default IPCC Tier 1 approaches often fail to capture country-specific production and manure management practices. This study evaluates how methodological choices influence GHG estimates and mitigation priorities across livestock production systems. Using 1990–2023 activity data and country-specific emission factors, we compare IPCC Tier 1 methodologies based on the 1996 and 2006 Guidelines and the 2019 Refinement with a country-specific Tier 2 approach. CH4 and N2O emissions from enteric fermentation and manure management are estimated for dairy cattle, other cattle, swine, and poultry. To capture the temperature sensitivity of manure CH4, high-resolution gridded climate data and regional temperature-adjusted MCFs are integrated. The results show that methodological choice affects emissions and source composition. Compared with the 1996 Guidelines, Tier 2 generally produces lower estimates and alters contributions of pathways. For ruminants, Tier 2 amplifies the dominance of enteric CH4, whereas for swine and poultry, manure CH4 becomes the primary source. Spatial analysis identifies CH4 and N2O hotspots in intensive livestock regions and differences in manure CH4 potential associated with climatic variability. These findings highlight the importance of country-specific methods, system-specific information, and climatic variability for livestock GHG mitigation strategies.