The Limits of Bioenergy: A Complex Systems Approach to Land Use Dynamics and Constraints

Abstract

This paper summarises a PhD thesis recently defended by the author at Imperial College London. The aim is to present a novel methodology to obtain an understanding of the potential limits of bioenergy by using a complex systems approach for assessing land use dynamics and constraints. Although bioenergy is classified as a renewable energy source, land is a finite resource and its expansion limited. The anthropogenic demands on land result from a combination of multiple provisioning services. These include global food consumption, dietary preference, crop and livestock yields, land use integration, wastes and residues, and bioenergy yields and forms, as well as the allocation of surplus land for forestry and energy crops, and the potential role of negative emission technologies. Thus, bioenergy is just one part of a complex land-use system. The general hypothesis is that there are fundamental limits to the overall scale and rate of the sustainable expansion of bioenergy, which can be assessed by means of combinations of empirical data, mapping tools and complex systems models. To this end, a novel methodological approach is proposed, which is based on two original integrated models. The first one is termed the Global Calculator Land Use Change Model (GCLUC), developed as part of the Global Calculator initiative, in which land is freely allocated worldwide and food security is assumed a priority. The second considers land for dedicated energy crops as a delimited reserve, by integrating Hubbert’s curve principles (originally proposed for peak oil assessments) in agro-ecological zoning schemes (as recently done for sugarcane ethanol in Brazil), resulting in a new model here termed green-Hubbert. The results show ranges of bioenergy potentials and expansion rates in the context of different land use futures. The potential public policies necessary to support sustainable bioenergy are also discussed. Finally, the conclusions show that, indeed, there are fundamental limits to bioenergy, and these limits are dynamic over time.