The role of biomass in climate change mitigation : Assessing the long-term dynamics of bioenergy and biochemicals in the land and energy systems

Abstract

Scientific literature addressing climate change mitigation options have highlighted the potentially important role of biomass as a substitute for fossil fuels in the provision of energy and materials. However significant uncertainties remain concerning the drivers and constraints of the available biomass, the overall greenhouse gas (GHG) benefit, and the most effective supply and demand chains. This thesis builds on the IMAGE integrated assessment model in order to improve the representation of the supply of biomass from different sources and its use in different end use sectors. Improvements include (i) representation of residue costs and supply as a function of agricultural and forestry demand, (ii) investigation of the spatially explicit GHG consequences of energy crop production and how increased production of biofuels affects overall carbon balances, (iii) representation of the long term energy demand and emissions of (bio)chemicals and effects of post-consumer-waste options such as recycling and cascading, and (iv) updating the techno-economic parameterization of different biomass conversion technologies and investigating how different biomass end uses compete with each other and the consequences on GHG mitigation. The improved model is used in order to conduct a scenario analysis covering a broad set of uncertainties concerning the future development of the land and energy systems. The scenarios are differentiated along socioeconomic lines (population growth, globalisation/regionalisation, technological improvements, lifestyle choices, etc.) as well as the application of policies aimed at meeting stringent climate targets, thus presenting a broad overview of different possible futures. The results show that though residues can play an important role in biomass supply (up to 50 EJPrim/yr), the main uncertainty concerning low GHG biomass availability is the development of agricultural production. With increased intensification and land abandonment large volumes of biomass can be produced with small effects on GHG emissions (up to 100 EJPrim/yr with an emission factor below 20 kgCO2/GJPrim). Bioenergy use is driven by fuel demand for transport or heating; however its most effective use (from a GHG perspective) is projected to be electricity production due to the continuing growth and high emissions of this sector. Small volumes are also demanded for the production of chemicals; however the emission mitigation potential of this sector is very small. Land management and technological improvements in second generation biofuel production as well as carbon capture and storage are critical in order to meet stringent climate targets. Overall biomass and bioenergy can contribute up to a quarter of final energy demand and plays a crucial role at reducing greenhouse gas emissions. The projections are compared with those of another integrated assessment model in order to highlight the effect of different model techniques and representations of the land and energy systems, showing that the overall trends are robust; however specific supply and demand strategies may differ. This thesis highlights the drivers, constraints and relevant dynamics of biomass availability, bioenergy demand and GHG consequences. The scenario analysis provides insights on uncertainties and the conditions required in order to maximize the GHG benefit of biomass use while highlighting potential synergies, barriers and pitfalls of different biomass strategies