Life Cycle-based Assessment of Energy Use and Greenhouse Gas Emissions in Almond Production, Part II: Uncertainty Analysis through Sensitivity Analysis and Scenario Testing

This is the second part of a two-article series examining California almond production. The part I article describes development of the analytical framework and life cycle-based model and presents typical energy use and greenhouse gas (GHG) emissions for California almonds. This part II article builds on this by exploring uncertainty in the life cycle model through sensitivity and scenario analysis, and by examining temporary carbon storage in the orchard. Sensitivity analysis shows life cycle GHG emissions are most affected by biomass fate and utilization, followed by nitrous oxide emissions rates from orchard soils. Model sensitivity for net energy consumption is highest for irrigation system parameters, followed by biomass fate and utilization. Scenario analysis shows utilization of orchard biomass for electricity production has the greatest potential effect, assuming displacement methods are used for co-product allocation. Results of the scenario analysis show that 1 kilogram (kg) of almond kernel and associated co-products are estimated to cause between -3.12 to 2.67 kg carbon dioxide equivalent (CO2-eq) emissions and consume between 27.6 to 52.5 megajoules (MJ) of energy. Co-product displacement credits lead to avoided emissions of between -1.33 to 2.45 kg CO2-eq and between -0.08 to 13.7 MJ of avoided energy use, leading to net results of -1.39 to 3.99kg CO2-eq and 15.3 to 52.6MJ per kg kernel (net results are calculated by subtracting co-product credits from the results for almonds and co-products). Temporary carbon storage in orchard biomass and soils is accounted for by using alternative global warming characterization factors and leads to a 14% to 18% reduction in CO2-eq emissions. Future studies of orchards and other perennial cropping systems should likely consider temporary carbon storage.