Dairy production and the carbon cycle: the importance of land use and land use change

The livestock sector has an important impact on the carbon cycle, and contributes to increased levels of greenhouse gases (GHGs) in the atmosphere via net emission of carbon dioxide (CO2) and methane (CH4). It is generally acknowledged that CO2 emissions from animal respiration should not be included in impact assessments of livestock, because they are assumed to be balanced by CO2 uptake by plants consumed by the animal (short term C-cycle). Carbon fluxes associated with land use and land use change (medium term C-cycle) and CO2 emissions from the combustion of fossil fuels (long term C-cycle), however, are considered of importance. Variability in methods and data used to assess CO2 fluxes related to land use (change), however, is large. This study aims to unravel the complexity of methodological issues related to livestock production and the carbon cycle, and evaluates the impact of methodological choices on emission calculations. We, therefore, computed a carbon footprint (CFP; cradle-to-farm gate) for the case study of a Dutch dairy farm for various time horizons. When excluding emissions from animal respiration and land use (change), the CFP per ton fat-and-protein-corrected milk (FPCM) was 1,132 kg CO2-equivalents (CO2-e). Including the short term C-cycle did not affect the result when correcting the global warming potential of biogenic CH4 for inclusion of biogenic CO2, which emphasises the importance of the new IPCC factors for CH4 from biogenic and fossil sources. Including emissions related to land use change (e.g. deforestation), however, resulted in a CFP of 1,155 to 1,341 kg CO2-e/ton FPCM, whereas including C-sequestration in grassland resulted in a CFP of 712 to 1,132 kg CO2-e/ton FPCM, depending on the method used. Results show that the impact of land use (change) on the CFP of milk can be large. Carbon fluxes related to land use (change), however, are non-recurrent and only impact net emission of GHGs until new equilibrium conditions are reached.