Comparing farm-level carbon footprint calculators for dairy production with a case study of Viikki Research Farm in Finland

Dairy farms are under pressure to reduce greenhouse gas (GHG) emissions. Various carbon footprint (CF) accounting tools have been developed for calculating GHG emissions and pinpointing hotspots to support mitigation efforts. However, inconsistent methodologies often lead to variations of their results, unclear discrepancies pose barriers to credible reporting and decision making. Five open access, farm-level CF accounting tools applicable to EU livestock production were evaluated and compared for their methodologies. They were further tested through a case study of a dairy Farm in Finland for their consistency in quantifying emissions of milk production. The sensitivity of each tool was analyzed across nine mitigation scenarios to evaluate their practical utility in guiding mitigation strategies. A significant variability in total GHG emissions was observed, ranging from 415 to 913 t CO2 eq y-1, derived mainly from differences in scopes and the adoption of varying method tiers (in IPCC 2006 or IPCC 2019). While enteric fermentation and feed production remained the primary emission sources across all tools, their contributions fluctuated based on calculation methods. Solagro and the Cool Farm Tool were most responsive to mitigation strategies regarding manure management and yield improvements, while GLEAM-i and CAP'2ER (level 1) lacked the flexibility to model specific management shifts. The lack of methodological harmony causes inconsistent results, requiring careful tool selection to align with specific goals and data availability. Methodological frameworks can be harmonized with evolving standards (Product environmental footprint category rules for dairy products), meanwhile adapting scientific advances into calculations to ensure transparency and comparability.