On sustainability of bioenergy production: Integrating co-emissions from agricultural intensification

Biomass from cellulosic bioenergy crops is seen as a substantial part of future energy systems, especially if climate policy aims at stabilizing CO2 concentration at low levels. However, among other concerns of sustainability, the large-scale use of bioenergy is controversial because it is hypothesized to increase the competition for land and therefore raise N2O emissions from agricultural soils due to intensification. We apply a global land-use model that is suited to assess agricultural non-CO2 GHG emissions. First, we describe how fertilization of cellulosic bioenergy crops and associated N2O emissions are implemented in the land-use model and how future bioenergy demand is derived by an energy-economy-climate model. We then assess regional N2O emissions from the soil due to large-scale bioenergy application, the expansion of cropland and the importance of technological change for dedicated bioenergy crops. Finally, we compare simulated N2O emissions from the agricultural sector with CO2 emissions from the energy sector to investigate the real contribution of bioenergy for low stabilization scenarios. As a result, we find that N2O emissions due to energy crop production are a minor factor. Nevertheless, these co-emissions can be significant for the option of removing CO2 from the atmosphere (by combining bioenergy use with carbon capture and storage (CCS) options) possibly needed at the end of the century for climate mitigation. Furthermore, our assessment shows that bioenergy crops will occupy large shares of available cropland and will require high rates of technological change at additional costs. (C) 2010 Elsevier Ltd. All rights reserved.