COSUB2/SUB emissions from biomass combustion for bioenergy: atmospheric decay and contribution to global warming

摘要

Carbon dioxide (COSUB2/SUB) emissions from biomass combustion are traditionally assumed climate neutral if the bioenergy system is carbon (C) flux neutral, i.e. the COSUB2/SUB released from biofuel combustion approximately equals the amount of COSUB2/SUB sequestered in biomass. This convention, widely adopted in life cycle assessment (LCA) studies of bioenergy systems, underestimates the climate impact of bioenergy. Besides COSUB2/SUB emissions from permanent C losses, COSUB2/SUB emissions from C flux neutral systems (that is from temporary C losses) also contribute to climate change: before being captured by biomass regrowth, COSUB2/SUB molecules spend time in the atmosphere and contribute to global warming. In this paper, a method to estimate the climate impact of COSUB2/SUB emissions from biomass combustion is proposed. Our method uses COSUB2/SUB impulse response functions (IRF) from C cycle models in the elaboration of atmospheric decay functions for biomass-derived COSUB2/SUB emissions. Their contributions to global warming are then quantified with a unit-based index, the GWPSUBbio/SUB. Since this index is expressed as a function of the rotation period of the biomass, our results can be applied to COSUB2/SUB emissions from combustion of all the different biomass species, from annual row crops to slower growing boreal forest.