Carbon accounting in Bio-CCUS supply chains – Identifying key issues for science and policy

Jun 2022

Bio-CCUS (bioenergy with carbon capture and utilization or storage), is increasingly becoming a matter of on-the-ground deployment. However, while the technological aspects of capture, utilization and storage of biogenic CO2 are rather well understood and have in many cases already been used in commercial settings, there are still substantial gaps on the policy and governance side. Particularly important aspects here are carbon accounting, how to quantify the climate impact of Bio-CCUS systems and how to include these elements in policy frameworks. This report – developed by IEA Bioenergy Task 45 (Sustainability) and Task 40 (Deployment) – reviews key issues to focus on and discusses different options for how these could be addressed from a scientific as well as from a policy perspective.

The full report is available here:
Carbon accounting in Bio-CCUS supply chains – Identifying key issues for science and policy


Main conclusions:

While it is common for CCU and CCS systems – be they based on biogenic or fossil CO2 – to be jointly discussed as (bio-) CCUS, there are important differences between the two. This pertains to post-capture CO2 accounting, as well as policy systems and business models.

For Bio-CCS, analysis of post-capture CO2 flows should be fairly straightforward, as the CO2 is to be permanently stored and immobilized in geological formations. This is assuming avoidance of e.g., leakages in transport and storage as well as the minimization of use of fossil energy for CO2 transport. The major policy challenge around Bio-CCS concerns how to design policy frameworks to incentivize carbon dioxide removal (CDR), also referred to as negative emissions. A key question is if, or to what extent, policy frameworks for carbon dioxide removal should be integrated into existing systems for emission reductions – such as the EU emissions trading system – or whether there should be specific ring-fenced systems for CDR.

Analysis of the post-capture CO2 flows for Bio-CCU is more complicated than for Bio-CCS. CO2 can be utilized for a wide range of purposes, including as feedstock for many different products, which means that there are many cases to analyse to understand the net climate impact in detail. This concerns aspects such as the process efficiency, the kinds of energy used and what existing product the Bio-CCU product could be replacing. In addition, a very important issue that has thus far not received sufficient attention is how to factor in the variation in CO2 storage permanence between different CCU products, i.e., for how long time CO2 used in a product stays away from the atmosphere. This can vary from less than a year for a fuel or a chemical, via decades for non-packaging plastics and up to possibly centuries in the case of some building materials. Given the growing interest in (bio-)CCU projects, it is essential to find approaches to (a) quantify how the climate impact of CCU products depends on CO2 storage permanence and (b) how these aspects can be integrated into policy frameworks.

To this end, we suggest to draw inspiration from similar frameworks, such as the UNFCCC accounting framework for Harvested Wood Products. However, there is a clear and urgent need for more research into this. To ensure that Bio-CCUS systems can fulfil their potential to mitigate climate change, it is key to strike a balance between properly understanding the full picture of the climate impacts Bio-CCUS systems and finding reasonably straightforward means how to include these aspects in policy frameworks.

While both Bio-CCU and Bio-CCS can be important pieces in the puzzle of getting the world to net-zero GHG emissions by 2050, their roles are bound to be quite different. Bio-CCS is clearly a means to generate negative emissions. For Bio-CCU this is a more difficult question where the answer will vary between contexts and where there may be a substantial grey area depending on the carbon storage permanence. Regardless, Bio-CCU can provide society with fuels, chemicals and materials with a very low GHG footprint – one that will also tend towards zero as electricity generation is increasingly decarbonized.


Figure: Conceptual illustration of the carbon flows related to Bio-CCS and Bio-CCU
[the term ‘net neutral’ implies, net neutral at best].
BC=Biomass combustion & FC=Fossil fuel combustion.
Figure by Lappeenranta University of Technology (Olsson et al. 2020)