AbstractReducing anthropogenic GHG emissions globally is a key driver for the development of renewable energy sources. A key route towards achieving thisis to replace fossil-based fuels with renewable and low carbon energy technologies such as biofuels from energy crops. Cereals and oil-seed crops such as corn, wheat, and soybean are the main feedstocks primarily used for biofuels production and the key characteristics of these crops are high biomass and energy yield per ha. However, there are concerns about the availability and sustainability of these crops for biofuels production in the face of a changing climate since crop productivity is inherently sensitive to climate. Therefore, an understanding of the impacts of climate change on energy crops production as feedstocks for biofuels production and their potential for life cycle GHG emissions reductions is crucial for making decisions on future biofuels production.
This thesis examined potential climate change impacts on the productivity of two major biofuel crops: corn (Zea maysL.) and soybean (Glycine max) in Gainesville, USA and one major biofuel crop: wheat (Triticumspp.) in Rothamsted, UK. The overall objective was to calculate the potential impacts of combined changes in climate variables: surface air temperature (T), precipitation (P), and atmospheric concentration of CO2([CO2]) on life cycle GHG emissions savings of biofuels from corn, soybean, and wheat.
The methodology was underpinned by life cycle thinking. Life cycle assessment (LCA) models linked to cropping system models (CSM) were used in the analysis. In assessing the impact of climate change on corn, wheat, and soybean crops yields, two applications of the CERES (Crop-Environment Resource Synthesis) model: CERES-Wheat (for wheat) and CERES-Maize (for corn), and CROPGRO (Crop Growth) model application: CROPGRO-Soybean of the Decision Support System for Agrotechnology Transfer (DSSAT-CSM) v22.214.171.124 model were used using observed weather data from the baseline (1981-1990) period for each study site. These models describe, based on daily data, the basic biophysical processes taking place at the soil-plant-atmosphere interface as a response to the variability of different processes such as: photosynthesis, specific phenological phases, evapotranspiration, and water dynamics in soil. Compared with the baseline, T was projected to increase by +1.5, +2, +2.5, +3, +3.5, +4, +4.5, and +5 oC, P was projected to change by ±5, ±10, ±15, and ±20%, and [CO2]was projected to increase by +70, +140, +210, +280, and + 350 ppm for Gainesville, USA. For Rothamsted, UK, T was projected to increase by +0.5, +1.5, +2.5, +3.5, and +4.5 oC, Pwas projected to change by ±10, and ±20%, and [CO2]was projected to increase by +70, +210, and + 350 ppm.
Simulated yields output (grain/seeds and biomass) from the CSM models were used as inputs into the LCA models. Potential life cycle GHG emissions savings were calculated for corn-based biofuels: corn bioethanol (CBE), corn integrated biomethanol (CIBM), and corn integrated bioelectricity (CIBE); soybean-based biofuels: soybean biodiesel (SBD), soybean integrated biomethanol (SIBM), and soybean integrated bioelectricity (SIBE); wheat-based biofuels: wheat bioethanol (WBE), wheat integrated biomethanol (WIBM), and wheat integrated bioelectricity (WIBE).
Results indicated that under the baseline (1981-1990) scenario, production and use of CBE, CIBM, CIBE, SBD, SIBM,SIBE, WBE, WIBM, and WIBE could save-4743.32 kg CO2-equiv. ha-1, -8573.31 kg CO2-equiv. ha-1, and -10996.7 kg CO2-equiv. ha-1, -2655.41 kg CO2-equiv. ha-1, -3441.1 kg CO2-equiv. ha-1, and -1350.04 kg CO2-equiv ha-1, -2776.1 kg CO2-equiv. ha-1, -500.87 kg CO2-equiv. ha-1and -4648.93 kg CO2-equiv. ha-1respectively, of the total life cycle GHG emissions of CO2, CH4, and N2O for the production and utilization of an energetically equivalent amount of fossil-based fuel counterpart, which they displaced.
However, model predictions of future life cycle GHG emissions savings for both crops showed that the responses of corn, soybean, and wheat to simultaneous changes in T, P, and [CO2] were different under different climate change scenarios. In the future period life cycle GHG emissions savings of corn-based biofuels was predicted to decline in all cases ranging from -4.2% to -46.1%, -2.6% to -37.7%, and -1.6% to -33.4% for CBE, CIBM, and CIBE, respectively compared with the baseline (1981-1990) period. In contrast, model predictions showed that life cycle GHG emissions savings of wheat-based biofuels would increase under all climate change scenarios ranging from +2.5% to +33.5%, +0.1% to+37.8%,and +1.0% to +34.4% for WBE, WIBM, and WIBE, respectively .On the other hand, the life cycle GHG emissions savings of soybean-based biofuels was predicted to increase by +0.22% to +27%, +0.1% to 28%, and +0.1% to +31.6% for SBD, SIBM, and SIBE, respectively under some climate change scenarios (e.g., [CO2] = 680; P= +20%; and T= +1.5 oC scenario) and also decline by -0.7% to -60.8%, -0.1% to -44.6%, and -0.1% to -82.6% for SBD, SIBM, and SIBE, respectively under some climate change scenarios (e.g., [CO2]= 400; P= -20%; and T= +5 oC scenario).
These results revealed that the potential impacts of climate change on energy crops productivity and net life cycle GHG emissions savings could be very large and diverse, and that the anticipated life cycle GHG emissions reductions of biofuels would not be the same in the future.
|Date of Award||2014|
|Supervisor||William Hall (Supervisor), Les Duckers (Supervisor) & Liz Trenchard (Supervisor)|