Evaluation of allocation methods for calculation of carbon footprint of grass-based dairy production

Allocation is a major methodological issue for life cycle assessment (LCA), which is commonly used to quantify greenhouse gas (GHG) emissions from livestock systems. When a process produces multiple outputs, the environmental... [ view full abstract ]

Allocation is a major methodological issue for life cycle assessment (LCA), which is commonly used to quantify greenhouse gas (GHG) emissions from livestock systems. When a process produces multiple outputs, the environmental burden has to be shared between the outputs, such as milk and liveweight from a dairy herd. Standards and Guidelines provide different recommendations but there is no objective function for choosing the best method. This study evaluated 7 allocation methods to calculate the global warming potential (GWP) of the economically average dairy farm in Ireland considering both milk and liveweight. The allocation methods were: economic, energy, protein, emergy, mass (liveweight), mass (carcass) and physical causality. System expansion was also assessed using an ‘avoided burden’ approach. The data quality for each method determined using a pedigree matrix of reliability, completeness, temporal applicability, geographical alignment and technological appropriateness. Scenario analysis was used to compare the normalised impact calculated by the different allocation methods for the best and worst third of farms (economically). For the average farm, GWP / FU ranged from 0.75 to 1.22 kg CO2-eq/kg FPC milk. Pedigree scores ranged from 6.0 to 15.9 with economic allocation and protein content having the best pedigree. The choice of allocation method should be based on the quality of the data available, but a range of allocation methods should be used to understand the uncertainty of the outcome.