1183. CDR Portfolio towards Net Zero Targets 

According to the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC), it is difficult to limit global warming to the Paris Agreement's climate target of 1.5°C without overshooting under the current GHG emission trend, and the implementation of Carbon Dioxide Removal (CDR) is considered unavoidable. While CDR is not a substitute for mitigation measures that allow immediate and rapid GHG emission reductions to be achieved, all the 1.5°C–2°C scenarios evaluated in AR6 assume the need for net removal of CO2 from the atmosphere.

CDR includes various technologies, such as Bioenergy with Carbon Capture and Storage (BECCS), which combines the use of biomass energy with carbon dioxide capture and storage; Agriculture, Forestry and Other Land Use (AFOLU) for sequestration in land; Direct Air Capture with Carbon Storage (DACCS), which captures CO2 directly from the atmosphere and stores it underground; enhanced weathering (EW); and biochar, among other approaches.

A paper by MIT researchers highlighted the heterogeneous characteristics of different CDR technologies, in terms of carbon removal processes, the time scale of carbon storage, the maturity of technologies, mitigation potentials, costs, co-benefits, negative impacts, and governance requirements, and presented the case that CDR portfolio can be effective in managing land, energy and economic trade-offs while maximizing co-benefits.

The majority of the models referred to in the literature of IPCC reports have so far been limited to BECCS and AFOLU, and there are relatively few scenarios that incorporate DACCS, and there is still little literature that examines other approaches such as EW and biochar. In contrast, there is already a lot of interest in DACCS, or AFOLU approaches (often referred to as "nature-based removal") and biochar, in voluntary carbon markets.

When interpreting the scale of CDR contributions in climate mitigation scenarios, careful consideration should also be given to the role of each individual CDR approach. For example, the large-scale deployment of BECCS raises controversial trade-offs in energy (bioenergy production for other uses) and AFOLU (food security, current and future carbon sinks), raising challenges about the feasibility and sustainability of these scenarios. Also, nature-based removals (e.g., afforestation/reforestation, restoration of peatlands and wetlands, agroforestry or forest management improvements) may be less sustainable because these carbon sinks will eventually become saturated and will be affected by interference events (e.g., fires, droughts, storms, disease or deforestation) that will be exacerbated by climate change. In addition, CDR costs are often set unrealistically low in integrated assessment modelling (IAM) scenarios, reducing the reliability and credibility of CDR pathways.

Bottom-up techno-economic studies show that CDR portfolios are more viable in achieving climate goals than a single CDR approach, but they also depend on socio-political preferences and the likelihood of trade-offs between resource and technology availability. On the other hand, carbon removal may be achieved cost-effectively by adding more CDR options to the CDR portfolio and reducing the deployment of individual CDR options, choosing the most strategically and geographically appropriate CDR option. In addition, the development of a diversified CDR portfolio is expected to reduce over-reliance on a small number of technologies, balance regional deployment, eliminate institutional disparities, and reduce damage to ecosystems.

The paper suggests that by diversifying across multiple CDR technology approaches, up to about 31.5 Gt of CO2 equivalent per year of CDR equivalent will be possible by 2100, indicating that it may be the most cost-effective net-zero strategy. In terms of cost competitiveness for atmospheric CO2 removal, BECCS and biochar topped, followed by rock weathering methods, while DACCS proved to be too expensive and uncompetitive due to capital and energy requirements. The paper found that biochar and EW have the potential to improve soil quality and productivity in 45% of all arable land by 2100, suggesting that future IAM studies need to be modelled to assess the potential for agricultural co-benefits in addition to carbon removal.

Reference
Solene Chiquier et al 2025 Integrated assessment of carbon dioxide removal portfolios: land, energy, and economic trade-offs for climate policy. Environ. Res. Lett. 20 024002. DOI 10.1088/1748-9326/ada4c0 https://iopscience.iop.org/article/10.1088/1748-9326/ada4c0

Contributor: IIYAMA Miyuki, Information Program