A comparative assessment of greenhouse gas emissions in California almond, pistachio, and walnut production.

A process-based life cycle assessment (LCA) model was constructed for almond, pistachio, and walnut production in California. Agrochemical inputs, mechanized operations, soil processes, geospatial variation, and biomass accumulation were explicitly modeled based on technical reports, economic cost-and-return studies, field data collection, and grower interviews. Mean annual greenhouse gas (GHG) footprints for a typical hectare of orchard, from nursery to hulling/shelling facility gate, were calculated at 4260 kg CO2e ha yr for almond, 3480 kg CO2e ha yr for pistachio, and 4050 CO2e ha yr kg for walnut. These results can be expressed by orchard product (nut kernel) as 1.76 CO2e kg for almond, 0.95 CO2e kg for walnut, and 3.83 CO2e kg for pistachio. Variations in biomass accumulation, yield and orchard lifespan between these crops result in different total life cycle emissions and potential management options for net GHG reduction and credit opportunities under California GHG cap-and-trade legislation.