Forest bioenergy, carbon capture and storage, and carbon dioxide removal: an update

As global emissions of carbon dioxide (CO2) continue to exceed levels compatible with achieving Paris Agreement targets, attention has been focusing on the role of bioenergy as a ‘renewable’ energy source and its potential for removing CO2 from the atmosphere when associated with carbon capture and storage (CCS). The European Academies’ Science Advisory Council (EASAC) examined these issues in 2017/18, but since then many peer-reviewed papers and international reviews have been published. EASAC has thus revisited these important issues and updates its earlier findings in this commentary.

EASAC’s earlier analysis of the effects of substituting fossil fuels with forest biomass showed that the lower energy density of biomass and supply-chain emissions were increasing atmospheric CO2 and thus accelerating the pace of global warming. Carbon accounting rules that record biomass exploitation as land use change and emissions from biomass combustion as zero were contributing to this trend. More recent findings increase the urgency of applying standards compatible with the science in both European Union (EU) and national policies on large-scale biomass use in electricity generation—especially those involving imports of wood pellets from other countries. Biomass should not be regarded as a source of renewable energy under the EU’s Renewable Energy Directive (RED) unless the replacement of fossil fuels by biomass leads to real reductions in atmospheric concentrations of CO2 within a decade or so. Reporting requirements under the EU Emissions Trading Scheme should be amended to reflect the real contribution of biomass energy to climate change mitigation over this timescale, to avoid incentivising practices that contribute to an overshoot of Paris Agreement targets.

The EASAC analysis of the role of negative emission technologies (NETs) had noted the importance of CCS and the lost opportunities resulting from the lack of progress in its development in Europe. Since then, some progress has been made in the concept of transport and storage clusters that can accept captured CO2, but the priority remains to actually implement carbon capture technologies for large fossilcarbon emitters.

Regarding the role of NETs involving carbon dioxide removal (CDR), this update refines our earlier conclusions as follows:

• Existing Nationally Determined Contributions (NDCs) need to be strengthened and mitigation made the first priority ahead of any reliance on future NETs.

• The current failure to reverse the growth in global emissions means that meeting Paris Agreement targets depends increasingly on deployment of NETs.

• Reversing deforestation, reforestation, increasing soil carbon levels and enhancing wetlands remain the most cost-effective and currently viable approaches to CDR, and should be implemented now as low-cost solutions relevant both to developed and to developing countries. The capacity of these sinks, however, is likely to be fully used within a few decades.

• The role of bioenergy with carbon capture and storage (BECCS) remains associated with substantial risks and uncertainties, both over its environmental impact and ability to achieve net removal of CO2 from the atmosphere. The large negative emissions capability given to BECCS in climate scenarios limiting warming to 1.5°C or 2°C is not supported by recent analyses, and policy-makers should avoid early decisions favouring a single technology such as BECCS. A suite of technologies is likely to be required.

• Significant technological progress has been achieved with direct air capture with carbon storage (DACCS) but it is not yet possible to identify a preferred technology.

• Enhancing weathering and in situ and ex situ carbon mineralisation requires further basic research before its potential can be properly assessed.

• Climate models suggest that early application of NETs in parallel with mitigation offers a greater chance of achieving Paris Agreement targets and avoiding catastrophic environmental and social impacts, than applying NETs at a larger scale later this century.

• EU and national governments should identify a European research, development and demonstration programme for NETs which is in line with their own skills and industrial base.