An Intro to Carbon Dioxide Removal (CDR)

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February 21, 2025 in
• Climate News

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CDR methods, their viability, and role in achieving climate goals.

It is widely acknowledged that a well-functioning Voluntary Carbon Market (VCM) is required to enable us to meet our global climate aspirations. Within the VCM, two types of carbon credits are typically offered: avoidance and removal. In this post, we will dive deep into the world of carbon removal credits. This post will be the first of many on carbon removals, where our intent is to introduce the topic and summarize all the major types of carbon removal credits being developed in the market.

Carbon Dioxide Removal (CDR) refers to the process by which we remove Carbon Dioxide (CO₂) from the atmosphere and durably store it. When a project removes CO₂ from the atmosphere, the associated CDR credits generated are called removal credits and differ from carbon avoidance credits. CDR is widely acknowledged to play an important role in fighting climate change and limiting global warming, according to the Paris Agreement’s aim of 1.5° C. All modeled pathways to remaining within Paris Agreement limits require significant CDR deployment, with some estimates showing the need to remove up to 10 Gt CO₂ annually by 2050, which is 1000x more than where we currently stand at 10 million metric tons/year.

The global average temperature between February 2023 and January 2024 was 1.52° C higher than it was between 1850 and 1900. This is the first annual period in which the average global temperature exceeded 1.5° C. While the long-term global average temperature is more important than the monthly or annual averages, occasionally surpassing the limit indicates that the global average temperature is approaching the 1.5° C threshold established in the Paris Agreement, driving the urgency to not only work to avoid carbon emissions in the future but also remove the Carbon Dioxide which we have already injected into the atmosphere.

This critical need to develop CDR is driving innovation within the space, attracting investments from businesses and public institutions to pilot and scale reliable, durable CDR projects. However, not all CDR pathways are the same.

Types of CDR

At a high level, there are several ways to remove and store CO₂ from the atmosphere. One general approach is to utilize natural carbon sinks—the largest of these being the ocean, forests, and soil. By leveraging natural processes, these pathways tend to be more cost-effective and have higher short-term viability. However, nature-based CDR pathways can be fraught with questions over integrity and durability. The second type of pathways are technological-based, relying on engineered CDR solutions, such as direct air capture (DAC), which have been showing promising potential. However, many projects are currently still in testing phases and are not ready for at-scale deployment. The last category of CDR methods are hybrid solutions, such as biochar and enhanced rock weathering, which utilize engineered solutions that leverage the carbon removal and sequestration abilities of natural systems.

The carbon removal space is constantly shifting and evolving as new research is conducted and technology evolves. The table below outlines the various ways in which companies are driving CDR via both technology as well as nature-based solutions.

Type of CDR solution	Example project types (non exhaustive)
Primarily nature-based solutions	Soil enrichment Grasslands ARR Biotic Ocean CDR Abiotic Ocean CDR
Primarily technology-based solutions	BECCS DAC Product mineralization
Hybrid solutions	Biochar Carbon mineralization including enhanced rock weathering (ERW)

Key Considerations for CDR

With the wide variety of CDR credits being generated, it is important to have an understanding of various considerations to be kept in mind as carbon buyers explore the type of CDR credit potential of buying CDR credits.. Figure 1 below details some of these.

Figure 1. Aspects to Consider for CDR Methods

Aspect	Description
Removal Potential	Each CDR method has its limits. Removal potential refers to the maximum removal or reservoir storage capacity, in addition to the rate of carbon removal that a particular method can deliver. There is a significant variation in the confidence level of exact quantification of carbon dioxide removal based on type of project and this important parameters needs to be factored in when exploring CDR credit purchase. Typically, technology based removal credits have more robust quantification than nature based removal credits.
Additionality	Additionality refers to CDR that would not have happened without intervention. All projects should have an established baseline and understanding that the CDR being accounted for would not have happened without the project. Typically the best way to prove additionality is if a project is not economically viable without estimated revenue by selling carbon credits.
Durability	Also sometimes referred to as permanence, durability of CDR is the concept of safe and stable storage of CO2 with low risk of reversal, or the re-entering of stored carbon into the atmosphere. Once again, technology based projects typically provide a higher level of confidence in durability than nature based removals given the limited potential of the process getting reversed.
Maturity	The CDR landscape is varied and constantly evolving. Thus, it is important to consider the maturity of the removal method when evaluating them. For example, some methods like reforestation are readily deployed, have relatively lower costs, and are generally well understood and accepted. At the other end of the spectrum, some methods, like artificial upwelling, and downwelling still require much work to evaluate feasibility and a pathway to scale.
Measurement, Reporting, and Verification (MRV)	Monitoring, Reporting and Verification (MRV) is a critical part of every carbon credit generating project. It is imperative that a third party provides robust monitoring of the project, confirming that the benefits claimed by the project developer are actually being realized and reporting on it consistently to all relevant stakeholders. Type of MRV requirements vary depending on the type of the project, e.g., a DAC project would require sensors which measure amount of air passing through the carbon capture equipment and the amount of CO2 being sequestered while a grasslands project where soil is naturally being used to capture atmospheric CO2 requires routine sampling to confirm that the estimated amount of CO2 is actually being captured and retailed by the soil. Having a robust MRV process is critical to confirm carbon dioxide removal and a lot of work is currently being done to ensure its robustness including utilizing technologies such as LIDAR, satellite imagery etc. to enable real-time monitoring, verification and reporting.
Cost	There is a significant variation in costs associated with CDR projects depending on type of project, project location, maturity of technology, co-benefits being pursued etc. DAC project can run more than $500/ton while a nature based Afforestation project is typically only about $20-50/ton of CO2.
Socioeconomic Impacts	A CDR project typically does not only capture CO2 but also provides co-benefits to the communities around where it is developed. While deciding on the location of a project, beyond just feasibility, cost, and availability of technology, the benefits it creates in the communities they are developed are also considered. Efforts are now increasingly being made that as this new wave of projects comes online, it enables equitable distribution of environmental impact benefits and associated economic prosperity. It is important that growth in sustainable technologies does not become a way of taking resources from the poor and allocating it to the developed. For e.g., there are deliberate discussions to avoid utilization of lands in less developed countries to grow organic matter which could then be converted in biochar and transported to developed countries to capture carbon dioxide from the atmosphere thereby providing environmental benefits in developed countries while reducing cropland in developing countries.
Land Use	The need to scale CDR comes with increased competition for land use and availability. Many terrestrial CDR methods require large amounts of space to deploy and can sometimes require the use of arable land. This can have consequences on the global food supply chain, in addition to socioeconomic considerations for equitable land use.
Nature & Biodiversity	While carbon removal is a critical issue for our planet, the nature crisis cannot be ignored. When developing and deploying CDR methods, it is important to account for and mitigate any negative impacts on nature and biodiversity. Some nature-based CDR approaches have positive co-benefits, such as improved soil health through soil organic carbon or habitat restoration through reforestation.

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CDR Methods Comparison

1. Solvent-based DAC

• Description: Uses chemical reactions and liquid solvents to remove CO₂ from the atmosphere
• Benefits:
  • Removes historic CO₂ emissions
  • Carbon removals are easily measurable and verifiable
• Risks/Considerations:
  • Requires safe solvent disposal
  • Energy-intensive process
  • Needs secure storage to prevent leakage into the environment
  • May compete with agricultural land use
  • Must be powered by renewable energy to ensure climate benefits
• Cost:
  • Initial Investment: Very High
  • Operating & Maintenance: High
  • Price (per MT CO₂): $300-1000
• Maturity: Not yet matured

2. Sorbent-based DAC

• Description: Uses chemical reactions and solid sorbents to remove CO₂ from the atmosphere
• Benefits:
  • Removes historic CO₂ emissions
  • Carbon removals are easily measurable and verifiable
• Risks/Considerations:
  • Requires safe solvent disposal
  • Energy-intensive process
  • Needs secure storage to prevent leakage
  • May compete with agricultural land use
  • Must be powered by renewable energy to ensure climate benefits
• Cost:
  • Initial Investment: Very High
  • Operating & Maintenance: High
  • Price (per MT CO₂): $300-1000
• Maturity: Not yet matured

3. BiCRS (Biomass Carbon Removal and Storage)

• Description: Process of storing carbon by utilizing organic matter to capture atmospheric CO₂ and processing it into durable form, e.g., biochar, bio-oil, etc., before putting it in storage
• Benefits:
  • Enhances soil
  • Utilizes waste
  • Supports economic growth
• Risks/Considerations:
  • May compete with agricultural resources, increasing food prices
  • Land-use changes could displace ecosystems and food production
  • Challenges in monitoring and verifying carbon removal
  • Needs to minimize supply chain emissions
• Cost:
  • Initial Investment: Low
  • Operating & Maintenance: Low
  • Price per MT CO₂: $75-250
• Maturity: Not yet matured

4. Bio-Energy with Carbon Capture and Storage (BECCS)

• Description: Process which produces energy and removes CO₂ from the atmosphere by capturing and storing it. BECCS uses biomass, like plants and trees, to generate energy and then captures and stores the CO₂ emissions from that process
• Benefits:
  • Generates renewable energy
  • Cost-effective
  • Supports rural development and job creation
• Risks/Considerations:
  • May impact food production by converting land for biomass
  • Land-use changes could displace ecosystems and food production
  • Challenges in monitoring and verifying carbon removal
  • Needs to minimize supply chain emissions
• Cost:
  • Initial Investment: Low
  • Operating & Maintenance: Low
  • Price per MT CO₂: $20-$400
• Maturity: Not yet matured

5. Enhanced Rock Weathering

• Description: A process that accelerates the natural weathering process of certain kinds of rocks, resulting in the removal of CO₂ from the atmosphere
• Benefits:
  • Improved soil fertility when weathered rocks release minerals into the soil
  • Stable and durable form of CO₂ storage
• Risks/Considerations:
  • Risk of heavy metal contamination if the right kind of rocks are not selected
  • Impact in air quality by generating dust
  • Increasing sodium levels through weathering of rocks can damage soil fertility
• Cost:
  • Initial Investment: Low
  • Operating & Maintenance: Low
  • Price per MT CO₂: $150-250
• Maturity: Not yet matured

6. Biochar

• Description: A process involving heating of biomass through pyrolysis to create biochar. This is further stored in soil or other durable ways thereby preventing CO₂ going to atmosphere
• Benefits:
  • Provides a long term storage option for carbon
  • Enhances soil fertility through mineral and water retention
  • Waste management through converting wastes into useful products
• Risks/Considerations:
  • Risk of releasing CO₂ when not handled properly or burned
  • Ensuring low emissions from the pyrolysis process
• Cost:
  • Initial Investment: Low
  • Operating & Maintenance: Low
  • Price per MT CO₂: $100-200
• Maturity: Relatively mature

7. Soil Organic Carbon

• Description: Enhances agricultural practices to improve soil’s carbon sequestration and storage
• Benefits:
  • Improves soil health
  • Increases water retention
  • Reduces erosion
  • Enhances biodiversity
• Risks/Considerations:
  • Excessive tillage could turn soil into a greenhouse gas source
  • Land-use changes could displace ecosystems and food production
  • Challenges in monitoring and verifying carbon removal
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price per MT CO₂: $45-$100
• Maturity: Higher maturity than other but yet to be scaled

8. Reforestation

• Description: Plants trees in deforested areas to reduce CO₂ through photosynthesis
• Benefits:
  • Improves air and water quality
  • Stabilizes soil
• Risks/Considerations:
  • Invasive species could threaten ecosystems
  • Challenges in monitoring and verifying carbon removal
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price (per MT CO₂): $20-50
• Maturity: Highest maturity among carbon removals

9. Afforestation

• Description: Plants trees in areas that were previously not forested
• Benefits:
  • Improves soil stability and water quality
• Risks/Considerations:
  • Large-scale afforestation could reduce water availability for local communities
  • Overstocked forests increase wildfire risks
  • Challenges in monitoring and verifying carbon removal
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price (per MT CO₂): $20-50
• Maturity: Highest maturity among carbon removals

10. Coastal Wetland Restoration

• Description: Restores mangroves, salt marshes, and seagrasses to remove CO₂
• Benefits:
  • Prevents floods
  • Conserves biodiversity
  • Improves water quality
  • Stabilizes shorelines against erosion
• Risks/Considerations:
  • Invasive species could threaten ecosystems
  • Changes in water flow patterns could negatively impact restoration
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price (per MT CO₂): $20-50
• Maturity: Higher maturity than other but yet to be scaled

11. Seaweed Cultivation

• Description: Grows and harvests seaweed to remove CO₂.
• Benefits:
  • Mitigates coastal pollution
  • Provides coastal erosion control
  • Supports local communities through job creation
• Risks/Considerations:
  • Growing lines could entangle marine life
  • Invasive species could threaten ecosystems
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price (per MT CO₂): TBD
• Maturity: Not matured

12. Ocean Nutrient Fertilization

• Description: Adds nutrients to the ocean surface to stimulate phytoplankton growth, increasing CO₂ absorption
• Benefits:
  • Enhances marine productivity
• Risks/Considerations:
  • May disrupt ecosystems by causing harmful algal blooms
  • Could create oxygen-minimum zones in deeper waters
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price per MT CO₂: $50-500
• Maturity: Not matured

13. Artificial Upwelling & Downwelling

• Description: Mimics natural ocean processes by pumping nutrient-rich deep ocean water to the surface (upwelling) to stimulate phytoplankton growth and absorb carbon dioxide while simultaneously pumping carbon-saturated surface water down to deeper depths (downwelling)
• Benefits:
  • Increases algal and phytoplankton growth
• Risks/Considerations:
  • May disrupt marine ecosystems by causing harmful algal blooms
  • Could create oxygen minimum zones in deeper layers to water due to sinking organic material
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price (per MT CO₂): TBD
• Maturity: Not matured

14. Ocean Alkalinity Enhancement

• Description: Alkaline substances are added to seawater, increasing its ability to absorb CO₂ from the atmosphere by converting it into stable bicarbonate and carbonate ions, essentially enhancing the ocean's natural carbon sink
• Benefits:
  • Enhances marine life and biodiversity
• Risks/Considerations:
  • Could impact the marine food chain
  • Potential risk of reducing water quality if heavy metals are added
• Cost:
  • Initial Investment: Very Low
  • Operating & Maintenance: Very Low
  • Price per MT CO₂: $40-$300
• Maturity: Not matured

15. Electrochemical CDR

• Description: Utilizes electricity to rearrange water and salt molecules in seawater into an acidic and basic solution and removes CO₂ from the acidic solution
• Benefits:
  • Enhances marine life and biodiversity
• Risks/Considerations:
  • Energy-intensive process
  • Must be powered by renewable energy to maintain climate benefits
• Cost:
  • Initial Investment: High
  • Operating & Maintenance: Low
  • Price (per MT CO₂): TBD
• Maturity: Not matured

Conclusion

The world needs to invest in CDRs to meet the ambitious yet gradually elusive 1.5 degC target which we set for ourselves in Paris. While governments have to implement policy incentives to fund and scale these nascent technologies, corporations need to play their part by generating demand and incorporating these credits to meet their sustainability goals. We are already nearing ~420 ppm of CO₂ in the air, more than 50 ppm higher than it used to be in 2002. This rise in CO₂ levels needs to be extensively managed over the next few decades while continuing to meet the ever-growing demand for energy needs. Avoiding CO₂ will not be enough—we need removal solutions. Carbon dioxide removal (CDR) will be critical in our fight against climate change.

CDR provides a way to address the emissions from hard to abate industries such as agriculture or transportation where measures to reduce the emissions take a longer time and more research. CDR technologies provide a way to reduce atmospheric CO₂ levels which is necessary even if global systems manage to decarbonize by 2050. CDR methods along with decarbonization strategies will play a pivotal role in addressing climate solutions. As corporations strive for net-zero goals, integrating CDR credits into sustainability strategies can help address residual emissions while supporting long-term climate solutions. By incorporating high-quality CDR credits, companies can strengthen their climate commitments, support innovation in negative-emission technologies, and enhance their sustainability leadership in a rapidly evolving regulatory landscape.

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