Study analyzes different carbon dioxide removal (CDR) portfolios to achieve the climate goals of the Paris Agreement. It compares individual CDR methods (BECCS, afforestation, DACCS, biochar, enhanced weathering) and their combinations, assessing their impacts on land and energy use and economic costs. Here are the most frequently asked FAQs with detailed answers, based on the resources provided:

Questions and answers

1. What is CDR and why is it important for achieving the goals of the Paris Agreement? Answer: CDR, or carbon dioxide removal, involves technologies and processes that actively remove CO2 from the atmosphere. This is essential because even with drastic reductions in greenhouse gas emissions, an additional way is needed to achieve the Paris Agreement goals of keeping global temperature increases below 1.5°C or 2°C. CDR complements emissions reduction efforts, especially when “negative emissions” are needed to offset remaining emissions. CDR methods include BECCS (bioenergy with carbon capture and storage), afforestation/reforestation, DACCS (direct carbon capture from the air), biochar, and accelerated weathering.
2. Why shouldn't we rely on just one CDR method? Answer: Relying on a single CDR method, such as BECCS, exposes climate strategies to technological, institutional and ecological pressures. Each method has its own unique characteristics, advantages, disadvantages and limitations in terms of mitigation potential, costs, co-benefits and adverse side-effects. For example, large-scale deployment of BECCS may lead to conflicts over land use (for both food and carbon sequestration) and energy (bioenergy production), which calls into question its feasibility and sustainability. Therefore, diversification of the CDR portfolio is important.
3. What are the key elements of a diversified CDR portfolio? Answer: A diversified CDR portfolio combines different methods, such as BECCS, afforestation/reforestation, DACCS, biochar and accelerated weathering. Such an approach allows for: * Reducing over-reliance on a single technology, * Reducing and redistributing land and energy impacts, * Cost-effectiveness in achieving negative emissions, * Adapting to regional conditions and biophysical characteristics. Diversification also reduces the risk of negative environmental impacts, logistics and liability.
4. What are the advantages and disadvantages of using BECCS and biochar as CDR methods? Answer: * BECCS (Bioenergy with Carbon Capture and Storage): BECCS combines bioenergy production with subsequent capture and storage of the released CO2. It has a high CO2 capture efficiency per unit of land. However, it requires extensive land use for biomass cultivation, which creates competition with agriculture and can impact food security and increase crop prices. * Biochar: Biochar is a type of coal obtained from biomass through the process of pyrolysis. It is stable in soil for a long time. It can improve soil quality, water retention, nutrient availability and crop production, and also reduce N2O emissions. However, it has lower energy efficiency than BECCS and requires a large amount of land to grow biomass.
5. How do DACCS and accelerated weathering compare to soil CDR methods in terms of cost, land use, and energy intensity? Answer: * DACCS (Direct Air Carbon Capture): DACCS is a more expensive CDR method due to the high cost and energy intensity required to operate fans, regenerate sorbents, etc. However, it has a much smaller land footprint compared to BECCS and biochar, even when we factor in the energy required for operation. * Accelerated weathering: Accelerated weathering is a method that involves crushing and dispersing silicate rocks (e.g. basalt) on agricultural land or coastlines, which accelerates the processes of sequestering atmospheric CO2. Accelerated weathering has low land requirements, but is energy-intensive and requires extensive mining, processing and transportation of rocks, which has environmental and logistical impacts.
6. What impact does resource constraints have on the CDR portfolio? Answer: The limitation of natural resources (bioenergy crops and rocks for accelerated weathering) reduces the deployment of CDR methods such as BECCS, biochar and accelerated weathering. It also leads to a strategic refocusing of the CDR portfolio towards greater use of DACCS, despite it being more costly. The limitation of resources also motivates more efficient land use for bioenergy crops and reduces pressure on land and food security. Regional adaptation of the CDR portfolio becomes important in optimising the deployment of technologies in terms of cost and resource availability.
7. Why is it important to consider the protection and restoration of natural ecosystems? Answer: Protecting and restoring natural ecosystems, such as forests and grasslands, is important for carbon sequestration and biodiversity conservation, water and air quality, as well as for resilience to disasters and land degradation. Natural ecosystems have important, but difficult to measure, economic and environmental benefits. Preventing the loss of natural areas has a particular impact on regions such as Africa, Brazil and Latin America, as well as on the overall climate strategy, with a minimal impact on global GDP.
8. What happens if the deployment of the CDR portfolio is delayed? Answer: If the deployment of the CDR portfolio is delayed, regional carbon prices will increase dramatically, reaching more than $800 per ton of CO2. High carbon prices could cause significant economic and social problems. It is therefore essential to start deploying CDR in the short term and to put in place adequate policies and financial measures to support this process, in order to avoid a shift away from climate mitigation.

Spring