Implications of a 'carbon debt' on bioenergy's potential to mitigate climate change

Burning biomass for energy emits CO2 that was earlier sequestered from the atmosphere and will be sequestered again if the bioenergy system is managed sustainably. There may be a significant temporal imbalance, however, between the carbon emissions and carbon sequestration of such bioenergy systems: also referred to as the carbon debt'. The carbon debt issue has resulted in a debate on the role of bioenergy in preventing unwanted climate change. This paper will argue that, while it is important to consider the temporal imbalances in carbon flows from bioenergy systems, at least three additional aspects will need to be considered in determining whether bioenergy has a useful role to play in mitigating climate change: (i) the relevance of a delay in greenhouse gas (GHG) emission savings for bioenergy's potential to mitigate climate change; (ii) whether climate change mitigation is actually likely to be possible without large-scale bioenergy; and (iii) what the (asymmetrical) risks are associated with including or excluding bioenergy in society's portfolio to mitigate climate change. The answers to these questions suggest that bioenergy has an important role to play in mitigating climate change provided that the biomass is produced and harvested in a sustainable manner and significant GHG-emission savings are achieved by 2100. In contrast, the use of bioenergy systems with longer delays in achieving their GHG-emission savings could negatively affect society's ambitions to mitigate climate change. (c) 2013 Society of Chemical Industry and John Wiley & Sons, Ltd