Optimizing Carbon Dioxide Removal Portfolios Considering the Cost of Permanent Removal
This week, we look closer at the paper published in Chemical Engineering Transactions. The study was led by Maria Victoria Migo-Sumagang, from the Department of Chemical Engineering of the University of the Philippines Los Baños, in the Philippines.
Available Negative Emission Technologies (NETs) vary along different dimensions, notably, their technological cost and their permanence, which is their probability of being susceptible to reversal. As ensuring a permanent removal comes with a cost and affects the evaluation of the removal potential, the cost of permanent removal (CPR) should be carefully considered in the economic evaluation of the overall cost-effectiveness of these technologies and their portfolios.
This paper applies the concept of CPR to NETs portfolios’ optimization to determine which combination of solutions can achieve cost-effective and scalable negative emissions, accounting both for technological costs and sequestration permanence.
Two models are used to optimize a NET portfolio under CPR, resource, budget, and capacity constraints, subject to target negative emission objectives. The objective of Model 1 (case study 1) is to determine the optimal allocation of solutions that minimize the total cost of the portfolio while achieving a minimum level of negative emissions given the time of permanence.
Model 2 (case study 2) aims to determine the optimal allocation to maximize the total negative emissions’ capacity under a budget limit given the time of permanence.
Results show that the optimal choice of technology mix depends on the time permanence horizon considered. Afforestation/reforestation (AR), direct air carbon capture and storage (DACCS), and enhanced weathering (EW) are consistent choices for minimizing costs in short or long term permanence horizons. Biochar (BC) is only a good choice if the time horizon is in the range of 500 years. AR and biochar BC are good choices for maximizing capacity under a budget limit if the time horizon ranges between 50-250 years. BECCS is a good choice if the land resource limit is not binding. Overall, EW is the best choice for maximizing CDR capacity in longer horizons.
A wrap-up of the main findings from this study:
- Relying on a diversified portfolio of NETs is more cost-effective than relying on a single solution.
- Technologies ensuring permanent CO₂ removal (e.g., BECCS, DAC) are more expensive than those with temporary storage but essential for long-term climate goals.
- Achieving permanent carbon removal requires careful consideration of both costs and the potential reversal risks over time.
- Lower-cost, lower-permanence options (e.g., afforestation) are less attractive when permanence is factored into the optimization.
- Policymakers should incentivize a mix of CDR technologies that balance cost-effectiveness and permanence to scale up carbon removal.
Read the full paper here: Optimizing Carbon Dioxide Removal Portfolios Considering the Cost of Permanent Removal