Greenhouse gas emissions Storage emissions Life cycle assessment Emission uncertainty a b s t r a c t Climate change and energy policies often encourage bioenergy as a sustainable greenhouse gas (GHG) reduction option. Recent research has raised concerns about the climate change impacts of bioenergy as heterogeneous pathways of producing and converting biomass, indirect impacts, uncertainties within the bioenergy supply chains and evaluation methods generate large variation in emission profiles. This research examines the combustion of wood pellets from forest residues to generate electricity and considers uncertainties related to GHG emissions arising at different points within the supply chain.Different supply chain pathways were investigated by using life cycle assessment (LCA) to analyse the emissions and sensitivity analysis was used to identify the most significant factors influencing the overall GHG balance. The calculations showed in the best case results in GHG reductions of 83% compared to coal-fired electricity generation. When parameters such as different drying fuels, storage emission, dry matter losses and feedstock market changes were included the bioenergy emission profiles showed strong variation with up to 73% higher GHG emissions compared to coal. The impact of methane emissions during storage has shown to be particularly significant regarding uncertainty and increases in emissions. Investigation and management of losses and emissions during storage is therefore key to ensuring significant GHG reductions from biomass.

Non-technical summaryBiomass energy with carbon capture and storage (BECCS) is represented in many integrated assessment models as a keystone technology in delivering the Paris Agreement on climate change. This paper explores six key challenges in relation to large scale BECCS deployment and considers ways to address these challenges. Research needs to consider how BECCS fits in the context of other mitigation approaches, how it can be accommodated within existing policy drivers and goals, identify where it fits within the wider socioeconomic landscape, and ensure that genuine net negative emissions can be delivered on a global scale.

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