Global Greenhouse gas Emissions in animal production: towards an
Integrated life cycle sustainability assessment from Ruminant Farming Systems
The objectives of this review were to evaluate the environmental impacts of the greenhouse gas (GHG) emissions and emissions intensity (Ei) for the small ruminants, Dairy and beef cattle livestock production systems using the life-cycle assessment (LCA) method with a system boundaries from “Cradle-to- farm-gate” and to promote the other capability of this internationally accepted approach nowadays in the agriculture world to determine weaknesses and robustness and/or the performance of the livestock production system adapted in any regions or areas of examination. This aim was illustrated using results from LCAs in the literature and from a pilot study of different production systems. The emissions were estimated using a whole farm GHGs models, based on the Intergovernmental Panel on Climate Change (IPCC) methodology with a yearly time-step. By recognizing different farming systems for ruminant species (i.e. pasture, mixed, and zero grazing). with specific reference to recent published models, outline general conclusions from application of these published models, and describe some limitations and risks associated with these approaches. Certain models were adapted (i.e. an economic optimization model, an environmental assessment model) in which it considers all significant CH4, N2O, and CO2 emissions and removals on the farm and off-farm emissions of N2O derived from nitrogen applied on the farm. This review however, shows that LCAs of different case studies currently cannot be compared directly. Such a comparison requires further international standardization of the LCA method. Nonetheless a recent collective global LCA estimated the GHG intensity of ruminant supply chains to produce 5.7 gigatonnes CO2-eq per annum representing about 80% of the livestock sector emissions. Enteric Methane CH4 was the largest contributing source of GHG accounting for 47%. N2O from soil and deposited manure accounted for a further 24%, while LUC is estimated to contribute 9% of the sector’s overall GHG emissions. However, LCAs should be performed at a large number of practical farms for each production system of interest. Application of LCA on practical farms, however, requires in-depth research to understand underlying processes, and to predict, or measure, variation in emissions realized in practice.