Estimating the carbon footprint of milk in dual-purpose dairy production systems: Influence of animal productivity, functional unit, and emission allocation and quantification methods

). Tier 2 method, using system-specific factors, had 27% lower CF than Tier 1. Productivity gain had similar reduction effects on CF when using 100-kcal energy or 100 g protein as FU. Biophysical and economic allocation reduced CF by 47% and 36%, respectively, compared with no allocation. Uncertainty analysis showed wide CF variation across years, and sensitivity analysis identified milk yield and herd structure as the most influential drivers. Enteric fermentation was the dominant emission source (48%), followed by feed (24%), manure (20%), and farm energy (8%). These findings highlight the importance of productivity improvement and methodological choices for shaping CF estimates and evaluating sustainable dairy production in low-input dual-purpose systems.