Summary
As of 2021, atmospheric carbon dioxide (CO2) levels have reached historically unprecedented levels, higher than at any time in the past 800,000 years. The increase is incontrovertibly due to anthropogenic CO2 emissions from activities such as fossil fuel burning, agriculture, and historical land-use change. The current level of human emissions greatly exceeds the ability of nature to remove CO2—simply reducing the levels of human emissions may not be enough to stabilize the climate. Carbon dioxide removal (CDR), sometimes referred to as negative emissions technologies, may prove valuable, in conjunction with reduced emissions to meet the global goal of limiting warming to well below 2°C, comparable to preindustrial levels, as established by the Paris Agreement.1
The 2015 National Academies report, Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration, concluded that, to contribute to climate change mitigation, CDR approaches would need to be scaled up massively and that it is critical to begin research now to increase the viability and affordability of existing or new approaches to CDR. In response, the National Academies released a report in 2019 to provide a research agenda for advancing CDR and, specifically, for assessing the benefits, risks, and sustainable scale potential for a variety of land- and coastal-based CDR approaches. The study found that, to meet climate goals, some form of CDR will likely be needed to remove roughly 10 Gt CO2/yr by mid-century and 20 Gt CO2/yr by the end of the century. To help meet that goal, four land-based CDR approaches are ready for large-scale deployment: afforestation/reforestation, changes in forest management, uptake and storage by agricultural soils, and bioenergy with carbon capture and storage, based on the potential to remove carbon at costs below $100/t CO2. The 2019 report did not examine the more global ocean-based approaches but did recognize the potential for ocean-based CDR and the need for a research strategy to explore these options.
To address this gap in understanding and the need for further exploration into CDR options that could feasibly contribute to a larger climate mitigation strategy, with sponsorship from the ClimateWorks Foundation, the National Academies convened the Committee on a Research Strategy
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1 See https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement.
for Ocean-Based Carbon Dioxide Removal and Sequestration. Specifically, this committee was assembled to develop a research agenda to assess the benefits, risks, and potential for responsible scale-up of a range of six specific ecosystem-based and technological ocean-based CDR (or ocean CDR) approaches, as defined by the sponsor. The resulting research agenda is meant to provide an improved and unbiased knowledge base for the public, stakeholders, and policy makers to make informed decisions on the next steps for ocean CDR, not to lock in or advocate for any particular approach. The committee’s Statement of Task is presented in Box S.1. The committee’s deliberations and report writing was informed by review of scientific and social science literature and by a series of public workshops and presentations, drawing expertise from the academic, governmental, and nongovernmental communities.
THE OCEAN AS A STRATEGY
The ocean covers 70 percent of Earth’s surface; it includes much of the global capacity for natural carbon sequestration, and it may be possible to enhance that capacity through implementation of ocean-based CDR approaches. The ocean holds great potential for uptake and longer-term sequestration of anthropogenic CO2 for several reasons: (1) the ocean acts as a large natural reservoir for CO2, holding roughly 50 times as much inorganic carbon as the preindustrial atmosphere; (2) the ocean already removes a substantial fraction of the excess atmospheric CO2 resulting from human emissions; and (3) a number of physical, geochemical, and biological processes are known to influence air–sea CO2 gas exchange and ocean carbon storage.
By acting to remove CO2 from the atmosphere and upper ocean and then store the excess carbon either in marine or geological reservoirs for some period of time, ocean CDR approaches could complement CO2 emission reductions and contribute to the portfolio of climate response strategies needed to limit climate change and surface ocean acidification over coming decades and centuries. While rapid and extensive decarbonization and emissions abatement of other greenhouse gases in the United States and global economies are the primary action required to meet international climate goals, ocean-based and other CDR approaches could help balance difficult-to-mitigate human CO2 emissions and contribute to mid-century to late-century net-zero CO2 emission targets.
It is critical that ocean CDR approaches be assessed against the consequences of no action and as one component of a broad and integrated climate mitigation strategy. Without substantial decarbonization, emissions abatement, and potential options such as CDR, atmospheric CO2 growth will continue unabated with associated rising impacts from climate change and ocean acidification, putting marine ecosystems at risk.
TECHNOLOGIES CONSIDERED
As directed by the Statement of Task (Box S.1), the committee examined six groups of ocean-based CDR approaches, depicted in Figure S.1:
- Nutrient fertilization (Chapter 3): Addition of micronutrients (e.g., iron) and/or macronutrients (e.g., phosphorus or nitrogen) to the surface ocean may in some settings increase photosynthesis by marine phytoplankton and can thus enhance uptake of CO2 and transfer of organic carbon to the deep sea where it can be sequestered for timescales of a century or longer. As such, nutrient fertilization essentially locally enhances the natural ocean biological carbon pump using energy from the sun, and in the case of iron, relatively small amounts are needed.
- Artificial upwelling and downwelling (Chapter 4): Artificial upwelling is a process whereby water from depths that are generally cooler and more nutrient and CO2 rich than
- surface waters is pumped into the surface ocean. Artificial upwelling has been suggested as a means to generate increased localized primary production and ultimately export production and net CO2 removal. Artificial downwelling is the downward transport of surface water; this activity has been suggested as a mechanism to counteract eutrophication and hypoxia in coastal regions by increasing ventilation below the pycnocline and as a means to carry carbon into the deep ocean.
- Seaweed cultivation (Chapter 5): The process of producing macrophyte organic carbon biomass via photosynthesis and transporting that carbon into a carbon reservoir removes CO2 from the upper ocean. Large-scale farming of macrophytes (seaweed) can act as a CDR approach by transporting organic carbon to the deep sea or into sediments.
- Recovery of ocean and coastal ecosystems (Chapter 6): CDR and sequestration through protection and restoration of coastal ecosystems, such as kelp forests and free-floating Sargassum, and the recovery of fishes, whales, and other animals in the oceans.
- Ocean alkalinity enhancement (Chapter 7): Chemical alteration of seawater chemistry via addition of alkalinity through various mechanisms including enhanced mineral weathering and electrochemical or thermal reactions releasing alkalinity to the ocean, with the ultimate aim of removing CO2 from the atmosphere.
- Electrochemical approaches (Chapter 8): Removal of CO2 or enhancement of the storage capacity of CO2 in seawater (e.g., in the form of ions or mineral carbonates) by enhancing its acidity or alkalinity, respectively. These approaches exploit the pH-dependent solubility of CO2 by passage of an electric current through water, which by inducing water splitting
- (“electrolysis”), changes its pH in a confined reaction environment. As one example, ocean alkalinity enhancement may be accomplished by electrochemical approaches.
The assessment of these six ocean-based approaches is a representative sampling of ocean-based CDR and is not intended to be an exhaustive list. The application of the recommendations developed within the report can be extended to ocean CDR approaches broadly.
CDR POTENTIAL
To assess the potential of each of the six ocean CDR approaches as a viable path forward in a larger climate mitigation strategy, the committee used a variety of information sources including a review of the scientific literature and a series of public meetings held in the virtual setting with presentations by more than 65 experts from academic, governmental, and nongovernmental communities (see Appendix B for a list of experts invited to speak to the committee) to understand stakeholder interest, and to explore the current state of knowledge, potential, and limitations of ocean CDR approaches.
Each of the ocean-based CDR approaches was evaluated against a common set of criteria, where feasible, developed by the committee based on specific elements included in the Statement of Task and from a review of previous planning and synthesis documents on CDR. The criteria investigated include knowledge base, efficacy, durability, scale, monitoring and verification, viability and barriers, and governance and social dimensions.
The approaches were evaluated and given a ranking of low, medium, or high, along with a level of certainty, where appropriate. The committee’s evaluation is summarized in Table S.1. Across all approaches, knowledge gaps remain in determining carbon sequestration efficacy, scaling, and durability, as well as environmental and social impacts and costs.
Common Challenges of Ocean CDR
Knowledge: The knowledge base is inadequate, based in many cases only on laboratory-scale experiments, conceptual theory and/or numerical models and needs to be expanded to better understand risks and benefits to responsibly scale up any of the ocean-based CDR approaches.
Governance: Social and regulatory acceptability is likely to be a barrier to many ocean CDR approaches, particularly ones requiring industrial infrastructure. There will be both project-specific and approach-specific social, political, and regulatory discussions, as well as contestation around the role of CDR broadly. Field-scale trials are likely to be a site of wider societal debate around decarbonization and climate response strategies.
Unknown environmental and social impacts: All ocean-based CDR approaches will modify the marine environment in some way, with both intended and unintended impacts. However, the knowledge base is weak on the unintended impacts and the consequences of both intended and unintended CDR impacts on marine ecosystems and coastal human communities.
Monitoring and verification: Monitoring and verification activities are essential to quantify the efficacy and the durability of carbon storage of ocean-based CDR approaches and to identify environmental and social impacts. Potential synergies may exist with other ocean and environmental or climate observing systems. Substantial challenges remain, however, particularly for observing impacts on marine organisms and the resulting implications for marine ecosystems as well as documenting regional- to global-scale impacts on ocean carbon storage.
TABLE S.1 Summary of Ocean CDR Scale-Up Potential
| Ocean Nutrient Fertilization | Artificial Upwelling/Downwelling | Seaweed Cultivation | Ecosystem Recovery | Ocean Alkalinity Enhancement | Electrochemical Processes | |
|---|---|---|---|---|---|---|
| Knowledge base What is known about the system (low, mostly theoretical, few in situ experiments; medium, lab and some fieldwork, few carbon dioxide removal (CDR) publications; high, multiple in situ studies, growing body of literature) |
Medium–High Considerable experience relative to any other ocean CDR approach with strong science on phytoplankton growth in response to iron, less experience on fate of carbon and unintended consequences. Natural iron-rich analogs provide valuable insight on larger temporal and spatial scales. |
Low–Medium Various technologies have been demonstrated for artificial upwelling (AU), although primarily in coastal regimes for short duration. Uncertainty is high and confidence is low for CDR efficacy due to upwelling of CO2, which may counteract any stimulation of the biological carbon pump (BCP). |
Medium–High Science of macrophyte biology and ecology is mature; many mariculture facilities are in place globally. Less is known about the fate of macrophyte organic carbon and methods for transport to deep ocean or sediments. |
Low–Medium There is abundant evidence that marine ecosystems can uptake large amounts of carbon and that anthropogenic impacts are widespread, but quantifying the collective impact of these changes and the CDR benefits of reversing them is complex and difficult. |
Low–Medium Seawater CO2 system and alkalinity thermodynamics are well understood. Need for empirical data on alkalinity enhancement; currently, knowledge is based on modeling work. Uncertainty is high for possible impacts. |
Low–Medium Processes are based on well-understood chemistry with a long history of commercial deployment, but is yet to be adapted for CO2 removal by ocean alkalinity enhancement (OAE) beyond benchtop scale. |
| Efficacy What is the confidence level that this approach will remove atmospheric CO2 and lead to net increase in ocean carbon storage (low, medium, high) |
Medium–High Confidence BCP known to work and productivity enhancement evident. Natural systems have higher rates of carbon sequestration in response to iron but low efficiencies seen thus far would limit effectiveness for CDR. |
Low Confidence Upwelling of deep water also brings a source of CO2 that can be exchanged with the atmosphere. Modeling studies generally predict that large-scale AU would not be effective for CDR. |
Medium Confidence The growth and sequestration of seaweed crops should lead to net CDR. Uncertainties about how much existing net primary production (NPP) and carbon export downstream would be reduced due to large-scale farming. |
Low–Medium Confidence Given the diversity of approaches and ecosystems, CDR efficacy is likely to vary considerably. Kelp forest restoration, marine protected areas, fisheries management, and restoring marine vertebrate carbon are promising tools. |
High Confidence Need to conduct field deployments to assess CDR, alterations of ocean chemistry (carbon but also metals), how organic matter can impact aggregation, etc. |
High Confidence Monitoring within an enclosed engineered system, CO2 stored either as increased alkalinity, solid carbonate, or aqueous CO2 species. Additionality possible with the utilization of by-products to reduce carbon intensity. |
| Durability Will it remove CO2 durably away from surface ocean and atmosphere (low, <10 years; medium, >10 years and <100 years; high, >100 years), and what is the confidence (low, medium, high) |
Medium 10–100 years Depends highly on location and BCP efficiencies, with some fraction of carbon flux recycled faster or at shallower ocean depths; however, some carbon will reach the deep ocean with >100-year horizons for return of excess CO2 to surface ocean. |
Low–Medium <10–100 years As with ocean iron fertilization (OIF), dependent on the efficiency of the BCP to transport carbon to deep ocean. |
Medium–High >10–100 years Dependent on whether the sequestered biomass is conveyed to appropriate sites (e.g., deep ocean with slow return time of waters to surface ocean). |
Medium 10–100 years The durability of ecosystem recovery ranges from biomass in macroalgae to deep-sea whale falls expected to last >100 years. |
Medium–High >100 years Processes for removing added alkalinity from seawater generally quite slow; durability not dependent simply on return time of waters with excess CO2 to ocean surface. |
Medium–High >100 years Dynamics similar to OAE. |
| Scalability Potential scalability at some future date with global-scale implementation (low, <0.1 Gt CO2/ yr; medium, >0.1 Gt CO2/yr and <1.0 Gt CO2/yr; high, >1.0 Gt CO2/yr), and what is the confidence level (low, medium, high) |
Medium–High Potential C removal >0.1–1.0 Gt CO2/yr (medium confidence) Large areas of ocean have high-nutrient, low-chlorophyll conditions suitable to sequester >1 Gt CO2/yr. Co-limitation of macronutrients and ecological impacts at large scales are likely. Low-nutrient, low-chlorophyll areas have not been explored to increase areas of possible deployment. (Medium confidence based on 13 field experiments.) |
Medium Potential C removal >0.1 Gt CO2/yr and <1.0 Gt CO2/yr (low confidence) Could be coupled with aquaculture efforts. Would require pilot trials to test materials durability for open ocean and assess CDR potential. Current model predictions would require deployment of tens of millions to hundreds of millions of pumps to enhance carbon sequestration. (Low confidence that this large-scale deployment would lead to permanent and durable CDR.) |
Medium Potential C removal >0.1 Gt CO2/yr and <1.0 Gt CO2/yr (medium confidence) Farms need to be many million hectares, which creates many logistic and cost issues. Uncertainties about nutrient availability and durability of sequestration, seasonality will limit sites, etc. |
Low–Medium Potential C removal <0.1–1.0 Gt CO2/yr (low–medium confidence) Given the widespread degradation of much of the coastal ocean, there are plenty of opportunities to restore ecosystems and depleted species. However, ecosystems and trophic interactions are complex and changing and research will be necessary to explore upper limits. |
Medium–High Potential C removal >0.1–1.0 Gt CO2/yr (medium confidence) Potential for sequestering >1 Gt CO2/yr if applied globally. High uncertainty coming from potential aggregation and export to depth of added minerals and unintended chemical impacts of alkalinity addition. |
Medium–High Potential C removal >0.1–1.0 Gt CO2/yr (medium confidence) Energy and water requirements may limit scale. For climate relevancy, the scale will be double to an order of magnitude greater than the current chlor-alkali industry. |
| Ocean Nutrient Fertilization | Artificial Upwelling/Downwelling | Seaweed Cultivation | Ecosystem Recovery | Ocean Alkalinity Enhancement | Electrochemical Processes | |
|---|---|---|---|---|---|---|
| Environmental risk Intended and unintended undesirable consequences at scale (unknown, low, medium, high), and what is the confidence level (low, medium, high) |
Medium (low–medium confidence) Intended environmental impacts increase NPP and carbon sequestration due to changes in surface ocean biology. If effective, there are deep-ocean impacts and concern for undesirable geochemical and ecological consequences. Impacts at scale uncertain. |
Medium–High (low confidence) Similar impacts to OIF but upwelling also affects the ocean’s density field and sea-surface temperature and brings likely ecological shifts due to bringing colder, inorganic carbon- and nutrient-rich waters to surface. |
Medium–High (low confidence) Environmental impacts are potentially detrimental especially on local scales where seaweeds are farmed (i.e., nutrient removal due to farming will reduce NPP, carbon export, and trophic transfers) and in the deep ocean where the biomass is sequestered (leading to increases in acidification, hypoxia, eutrophication, and organic carbon inputs). The scale and nature of these impacts are highly uncertain. |
Low (medium–high confidence) Environmental impacts would be generally viewed as positive. Restoration efforts are intended to provide measurable benefits to biodiversity across a diversity of marine ecosystems and taxa. |
Medium (low confidence) Possible toxic effect of nickel and other leachates of olivine on biota, bio-optical impacts, removal of particles by grazers, unknown responses to increased alkalinity on functional diversity and community composition. Effects also from expanded mining activities (on land) on local pollution, CO2 emissions. |
Medium–High (low confidence) Impact on the ocean is possibly constrained to the point of effluent discharge. Poorly-known possible ecosystem impacts similar to alkalinity enhancement. Excess acid (or gases, particularly chlorine) will need to be treated and safely disposed. Provision of sufficient electrical power will likely have remote impacts. |
| Social considerations Encompass use conflicts, governance-readiness, opportunities for livelihoods, etc. |
Potential conflicts with other uses of high seas and protections; downstream effects from displaced nutrients will need to be considered; legal uncertainties; potential for public acceptability and governance challenges (i.e., perception of “dumping”). | Potential conflicts with other uses (shipping, marine protected areas, fishing, recreation); potential for public acceptability and governance challenges (i.e., perception of dumping). | Possibility for jobs and livelihoods in seaweed cultivation; potential conflicts with other marine uses. Downstream effects from displaced nutrients will need to be considered. | Trade-offs in marine uses to enhance ecosystem protection and recovery. Social and governance challenges may be less significant than with other approaches. | Expansion of mining production, with public health and economic implications; general public’s potential for public acceptability and governance challenges (e.g., if perceived as “dumping”). | Similar to OAE and to any industrial site. Substantial electrical power demand may generate social impacts. |
| Co-benefits How significant are the co-benefits as compared to the main goal of CDR and how confident is that assessment |
Medium (low confidence) Enhanced fisheries possible but not shown and difficult to attribute. Seawater dimethyl sulfide increase seen in some field studies that could enhance climate cooling impacts. Surface ocean decrease in ocean acidity possible. |
Medium–High (low confidence) May be used as a tool in coordination with localized enhancement of aquaculture and fisheries. |
Medium–High (medium confidence) Placing cultivation facilities near fish or shellfish aquaculture facilities could help alleviate environmental damages from these activities. Bio-fuels also possible. |
High (medium–high confidence) Enhanced biodiversity conservation and the restoration of many ecological functions and ecosystem services damaged by human activities. Existence, spiritual, and other non-use values. Potential to enhance marine stewardship and tourism. |
Medium (low confidence) Mitigation of ocean acidification; positive impact on fisheries. |
Medium–High (medium confidence) Mitigation of ocean acidification; production of H2, Cl2, silica. |
| Ocean Nutrient Fertilization | Artificial Upwelling/Downwelling | Seaweed Cultivation | Ecosystem Recovery | Ocean Alkalinity Enhancement | Electrochemical Processes | |
|---|---|---|---|---|---|---|
| Cost of scale-up Estimated costs in dollars per metric ton CO2 for future deployment at scale; does not include all of monitoring and verification costs needed for smaller deployments during R&D phases (low, <$50/t CO2; medium, ~$100/t CO2; high, >>$150/t CO2) and confidence in estimate (low, medium, high) |
Low <$50/t CO2 (low–medium confidence) Deployment of <$25/t CO2 sequestered for deployment at scale is possible, but needs to be demonstrated at scale |
Medium–High. >$100–$150/t CO2 (low confidence) Development of a robust monitoring program is the likely largest cost and would be of similar magnitude as OIF. Materials costs for pump assembly could be moderate for large-scale persistent deployments. Estimates for a kilometer-scale deployment are in the tens of million dollars. |
Medium ~$100/t CO2 (medium confidence) Costs should be less than $100/t CO2. No direct energy used to fix CO2. |
Low <$50/t CO2 (medium confidence) Varies, but direct costs would largely be for management and opportunity costs for restricting uses of marine species and the environment. No direct energy used. |
Medium–High >$100–$150/t CO2 (low–medium confidence) Cost estimates range between tens of dollars and $160/t CO2. Need for expansion of mining, transportation, and ocean transport fleet. |
High >$150/t CO2 (medium confidence) Gross current estimates $150–$2,500/t CO2 removed. With further R&D, it may be possible to reduce this to <$100/t CO2. |
| Cost and challenges of carbon accounting Relative cost and scientific challenge associated with transparent and quantifiable carbon tracking (low, medium, high) |
Medium Challenges tracking additional local carbon sequestration and impacts on carbon fluxes outside of boundaries of CDR application (additionality). |
High Local and additionality monitoring needed for carbon accounting similar to OIF. |
Low–Medium The amount of harvested and sequestered carbon will be known. However, an accounting of the carbon cycle impacts of the displaced nutrients will be required (additionality). |
High Monitoring net effect on carbon sequestration is challenging. |
Low–Medium Accounting more difficult for addition of minerals and non-equilibrated addition of alkalinity, than equilibrated addition. |
Low–Medium |
| Cost of environmental monitoring Need to track impacts beyond carbon cycle on marine ecosystems (low, medium, high) |
Medium (medium–high confidence) All CDR will require monitoring for intended and unintended consequences both locally and downstream of CDR site, and these monitoring costs may be substantial fraction of overall costs during R&D and demonstration-scale field projects. This cost of monitoring for ecosystem recovery may be lower. |
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| Additional resources needed Relative low, medium, high to primary costs of scale-up |
Low–Medium Cost of material: iron is low and energy is sunlight. |
Medium–High Materials, deployment, and potential recovery costs. |
Medium Farms will require large amounts of ocean (many million hectares) to achieve CDR at scale. |
Low Most recovery efforts will likely require few materials and little energy, though enforcement could be an issue. Active restoration of kelp and other ecosystems would require more resources. |
Medium–High Adaptation and likely expansion of existing fleet for deployment; infrastructure for storage at ports. Infrastructure support for expansion of mineral extraction, processing, transportation, and deployment. |
Medium–High High energy requirements (1–2.5 MWh/t CO2 removed) and build-out of industrial CDR. |
Cost: Accurate estimation of the cost of a CDR approach at low technological readiness is challenging, and costs presented come with considerable uncertainty. It is typical for early-stage assessments to underestimate costs, and for that reason some recommend the inclusion of capital cost contingencies over 100 percent (effectively doubling the calculated capital cost). Cost discovery will be an important feature of a research strategy that aims to investigate approaches through increasing technology readiness.
RESEARCH RECOMMENDATIONS
Expanded research including field research is needed to assess ocean-based CDR techniques’ potential efficacy in removing and sequestering excess carbon away from the atmosphere and the permanence or durability of the sequestered carbon on timescales relevant to societal policy decisions. Research is also needed to identify and quantify environmental impacts, risks, benefits, and co-benefits as well as other factors governing possible decisions on deployment such as technological readiness, development timelines, energy and resource needs, economic costs, and potential social, policy, legal, and regulatory considerations. Additionally, research on ocean CDR would greatly benefit from targeted studies on the interactions and trade-offs between ocean CDR, terrestrial CDR, greenhouse gas abatement and mitigation, and climate adaptation, including the potential of mitigation deterrence.
The specific research needed to advance understanding of ocean CDR is listed in Tables S.2 and S.3, including associated time-frame and cost estimates. Table S.2 summarizes the foundational research identified in Chapters 2 and 9 as research priorities common across ocean CDR approaches including potential social, policy, legal, and regulatory considerations. The research included in Table S.2 is meant to inform the framework for any future ocean-based CDR effort. Table S.3 then summarizes research needed to better understand the feasibility of that particular approach, with bolded text indicating priority. Additional details on the research activities listed in Table S.2 and S.3 can be found in the corresponding chapters.
Early research findings might indicate a low viability for particular approaches. The research agenda below is to be adaptive, meaning that decisions on future investments in research activities will need to take into account new findings on the efficacy and durability of a technique, whether the social and environmental impacts outweigh benefits or face social and governance challenges. Generally speaking, showstoppers can be anticipated for some approaches from factors both internal and external to the research. Internal showstoppers include findings that indicate that the viability is so low as to not warrant further research investments. There may also be external showstoppers to the research, such as lack of social license or governance challenges that preclude further investigation. A conceptual diagram depicting how the research program could start and evolve is shown in Figure S.2.
The research needs, Tables S.2 and S.3, are presented within the context of adhering to Recommendations 1, 2, and 3 (below). Those research needs shown in bold in Table S.3 are identified as priorities for taking the next steps to advance understanding of that particular approach while the elements in Table S.2 lay the framework for ocean CDR broadly. Recommendation 1 includes elements that should be included in any ocean CDR research program. Recommendation 2 prescribes components common to implementation of any ocean CDR research program, and Recommendation 3 defines priorities for any ocean CDR research program. Recommendations 1, 2, and 3 are broadly applicable to any ocean-based CDR approach; they are not limited to the six approaches explored in this report.
Recommendation 1: Ocean CDR Research Program Goals. To inform future societal decisions on a broad climate response mitigation portfolio, a research program for ocean CDR should
be implemented, in parallel across multiple approaches, to address current knowledge gaps. The research program should not advocate for or lock in future ocean CDR deployments but rather provide an improved and unbiased knowledge base for the public, stakeholders, and policy makers. Funding for this research could come from both the public and private sectors, and collaboration between the two is encouraged. The integrated research program should include the following elements:
- Assessment of whether the approach removes atmospheric CO2, in net, and the durability of the CDR, as a primary goal.
- Assessment of intended and unintended environmental impacts beyond CDR.
- Assessment of social and livelihood impacts, examining both potential harms and benefits.
- Integration of research on social, legal, regulatory, policy, and economic questions relevant to ocean CDR research and possible future deployment with the natural science, engineering, and technological aspects.
- Systematic examination of the biophysical and social interactions, synergies, and tensions between ocean CDR, terrestrial CDR, mitigation, and adaptation.
Common Components
No single research framework will be adequate for all CDR approaches within a comprehensive research strategy, because knowledge base and readiness levels differ substantially. There are, however, several common components that are relevant to research into any ocean CDR approach.
TABLE S.2 Foundational Research Priorities Common to All Ocean-Based CDR
| Estimated Budget | Duration (years) | Total Cost | |
|---|---|---|---|
| Model international governance framework for ocean CDR research | $2M–3M/yr | 2–4 | $4M–$12M |
| Application of domestic laws to ocean CDR research | $1M/yr | 1–2 | $1M–$2M |
| Assessment of need for domestic legal framework specific to ocean CDR | $1M/yr | 2–4 | $2M–$4M |
| Development of domestic legal framework specific to ocean CDR | |||
| Mixed-methods, multi-sited research to understand community priorities and assessment of benefits and risks for ocean CDR as a strategy | $5M/yr | 4 | $20M |
| Interactions and trade-offs between ocean CDR, terrestrial CDR, adaptation, and mitigation, including the potential of mitigation deterrence | $2M/yr | 4 | $8M |
| Cross-sectoral research analyzing food system, energy, sustainable development goals, and other systems in their interaction with ocean CDR approaches | $1M/yr | 4 | $4M |
| Capacity-building research fellowship for diverse early-career scholars in ocean CDR | $1.5M/yr | 2 | $3M |
| Transparent, publicly accessible system for monitoring impacts from projects | $0.25M/yr | 4 | $1M |
| Research on how user communities (companies buying and selling CDR, nongovernmental organizations, practitioners, policy makers) view and use monitoring data, including certification | $0.5M/yr | 4 | $2M |
| Analysis of policy mechanisms and innovation pathways, including the economics of scale-up | $1–2M/yr | 2 | $2M–$4M |
| Development of standardized environmental monitoring and carbon accounting methods for ocean CDR | $0.2M/yr | 3 | $0.6M |
| Development of a coordinated research infrastructure to promote transparent research | $2M/yr | 3–4 | $6M–$8M |
| Development of a publicly accessible data management strategy for ocean CDR research | $2–3M/yr | 2 | $4M–$6M |
| Development of a coordinated plan for science communication and public engagement of ocean CDR research in the context of decarbonization and climate response | $5M/yr | 10 | $50M |
| Development of a common code of conduct for ocean CDR research | $1M/yr | 2 | $2M |
| Total Estimated Research Budget (Assumes all 6 CDR approaches moving ahead) |
$29M/yr | 2–10 | $125M |
TABLE S.3 Research Needed to Advance Understanding of Each Ocean CDR Approach (Bold type identifies priorities for taking the next step to advance understanding of each particular approach; more details on each research need provided in individual chapters)
| Estimated Budget | Duration (years) | Total Budget | |
|---|---|---|---|
| Ocean Fertilization | |||
| Carbon sequestration delivery and bioavailability | $5M/yr | 5 | $25M |
| Tracking carbon sequestration | $3M/yr | 5 | $15M |
| In-field experiments, >100 t Fe and >1,000 km2 initial patch size followed over annual cycles | $25M/yr | 10 | $250M |
| Monitoring carbon and ecological shifts | $10M/yr | 10 | $100M |
| Experimental planning and extrapolation to global scales | $5M/yr | 10 | $50M |
| Total Estimated Research Budget | $48M/yr | 5–10 | $440M |
| Estimated Budget of Research Priorities | $33M/yr | 5–10 | $290M |
| Artificial Upwelling and Downwelling | |||
| Technological readiness: Limited and controlled open-ocean trials to determine durability and operability of artificial upwelling technologies (~100 pumps tested in various conditions) | $5M/yr | 5 | $25M |
| Feasibility studies | $1M/yr | 1 | $1M |
| Tracking carbon sequestration | $3M/yr | 5 | $15M |
| Modeling of carbon sequestration based on achievable upwelling velocities and known stoichiometry of deep-water sources. Parallel mesocosm and laboratory experiments to assess potential biological responses to deep water of varying sources. | $5M/yr | 5 | $25M |
| Planning and implementation of demonstration-scale in situ experimentation (>1 year, >1,000 km) in region-sited-based input from modeling and preliminary experiments | $25M/yr | 10 | $250M |
| Monitoring carbon and ecological shifts | $10M/yr | 10 | $100M |
| Experimental planning and extrapolation to global scales (early for planning and later for impact assessments) | $5M/yr | 10 | $50M |
| Total Estimated Research Budget | $54/yr | 5–10 | $466M |
| Estimated Budget of Research Priorities | $5M/yr | 5–10 | $25M |
| Seaweed Cultivation | |||
| Technologies for efficient large-scale farming and harvesting of seaweed biomass | $15M/yr | 10 | $150M |
| Engineering studies focused on the conveying of harvested biomass to durable oceanic reservoir with minimal losses of carbon | $2M/yr | 10 | $20M |
| Assessment of long-term fates of seaweed biomass and by-products | $5M/yr | 5 | $25M |
| Implementation and deployment of a demonstration-scale seaweed cultivation and sequestration system | $10M/yr | 10 | $100M |
| Validation and monitoring of the CDR performance of a demonstration-scale seaweed cultivation and sequestration system | $5M/yr | 10 | $50M |
| Evaluation of environmental impacts of large-scale seaweed farming and sequestration | $4M/yr | 10 | $40M |
| Total Estimated Research Budget | $41M/yr | 5–10 | $385M |
| Estimated Budget of Research Priorities | $26M/yr | 5 | $235M |
| Ecosystem Recovery | |||
| Restoration ecology and carbon | $8M/yr | 5 | $40M |
| Marine protected areas: Do ecosystem-level protection and restoration scale for marine CDR? | $8M/yr | 10 | $80M |
| Macroalgae: Carbon measurements, global range, and levers of protection | $5M/yr | 10 | $50M |
| Benthic communities: disturbance and restoration | $5M/yr | 5 | $25M |
| Marine animals and CO2 removal | $5M/yr | 10 | $50M |
| Animal nutrient-cycling | $5M/yr | 5 | $25M |
| Commercial fisheries and marine carbon | $5M/yr | 5 | $25M |
| Total Estimated Research Budget | $41M/yr | 5–10 | $295M |
| Estimated Budget of Research Priorities | $26M/yr | 5–10 | $220M |
| Ocean Alkalinity Enhancement | |||
| Research and development to explore and improve the technical feasibility/and readiness level of ocean alkalinity enhancement approaches (including the development of pilot-scale facilities) | $10M/yr | 5 | $50M |
| Laboratory and mesocosm experiments to explore impacts on physiology and functionality of organisms/communities | $10M/yr | 5 | $50M |
| Field experiments | $15M/yr | 5–10 | $75M–$150M |
| Research into the development of appropriate monitoring and accounting schemes, covering CDR potential and possible side effects | $10 | 5–10 | $50M–$100M |
| Total Estimated Research Budget | $45M/yr | 5–10 | $180M–$350M |
| Estimated Budget of Research Priorities | $25M/yr | 5–10 | $125–$200M |
| Electrochemical Processes | |||
| Demonstration projects including CDR verification and environmental monitoring | $30M/yr | 5 | $150M |
| Development and assessment of novel and improved electrode and membrane materials | $10M/yr | 5 | $50M |
| Assessment of environmental impact and acid management strategies | $7.5M/yr | 10 | $75M |
| Coupling whole rock dissolution to electrochemical reactors and systems | $7.5M/yr | 10 | $75M |
| Development of hybrid approaches | $7.5M/yr | 10 | $75M |
| Resource mapping and pathway assessment | $10M/yr | 5 | $50M |
| Total Estimated Research Budget | $72.5M/yr | 5–10 | $475M |
| Estimated Budget of Research Priorities | $55M/yr | 5–10 | $350M |
Recommendation 2: Common Components of an Ocean CDR Research Program. Implementation of the research program in Recommendation 1 should include several key common components:
- The development and adherence to a common research code of conduct that emphasizes transparency and open public data access, verification of carbon sequestration, monitoring for intended and unintended environmental and other impacts, and stakeholder and public engagement.
- Full consideration of, and compliance with, permitting and other regulatory requirements. Regulatory agencies should establish clear processes and criteria for permitting ocean CDR research, with input from funding entities and other stakeholders.
- Co-production of knowledge and design of experiments with communities, Indigenous collaborators, and other key stakeholders.
- Promotion of international cooperation in scientific research and issues relating to the governance of ocean CDR research, through prioritizing international research collaborations and enhancement of international oversight of projects (e.g., by establishing an independent expert review board with international representation).
- Capacity building among researchers in the United States and other countries, including fellowships for early-career researchers in climate-vulnerable communities and underrepresented groups, including from Indigenous populations and the Global South.
Research Priorities
Based on the present state of knowledge, there are substantial uncertainties in all of the ocean CDR approaches evaluated in this report. The best approach for reducing knowledge gaps will involve a diversified research investment strategy that includes both crosscutting, common components (Table S.2) and coordination across multiple individual CDR approaches (Table S.3) in parallel (Figure S.2). The development of a robust research portfolio will reflect a balance among several factors: common elements and infrastructure versus targeted studies on specific approaches; biotic versus abiotic CDR approaches; and more established versus emerging CDR approaches.
Crosscutting foundational research priorities listed in Table S.2 include research on international governance and the domestic legal framework of ocean CDR research. Other priorities include the development of a common code of conduct for ocean CDR research and coordinated research infrastructure including components on standardized environmental monitoring and carbon accounting methods, publicly accessible data management, and science communication and public engagement.
The research priorities in Table S.3 for each of the four biotic ocean CDR approaches differ based on the current knowledge base, extent of previous research, and distinctions in the underlying biological processes. Evaluation of research needs across CDR approaches is more challenging, suggesting some investment in all methods; however, a first-order attempt at prioritization can be constructed based on current knowledge. Among the biotic approaches, research on ocean iron fertilization and seaweed cultivation offer the greatest opportunities for evaluating the viability of possible biotic ocean CDR approaches; research on the potential CDR and sequestration permanence for ecosystem recovery would also be beneficial in the context of ongoing marine conservation efforts.
For abiotic ocean CDR approaches, the research agenda (Table S.3) will be most impactful if it combines a thorough understanding of potential environmental impacts alongside technology development and upscaling efforts. Based on present understanding, there is considerable CDR
potential for ocean alkalinity enhancement, which spans a number of approaches including, but not restricted to, ocean liming, accelerated rock weathering, and electrochemical methods for alkalinity enhancement, among others. Next steps for alkalinity enhancement research offer large opportunities for closing knowledge gaps but include the complexity of undertaking large-scale experimentation to assess whole ecosystem responses across the range of technologies and approaches for increasing alkalinity. Therefore, among the abiotic approaches, research on ocean alkalinity enhancement, including electrochemical alkalinity enhancement, has priority over electrochemical approaches that only seek to achieve CDR from seawater (also known as carbon dioxide stripping).
Recommendation 3: Ocean CDR Research Program Priorities. A research program should move forward integrating studies, in parallel, on multiple aspects of different ocean CDR approaches, recognizing the different stages of the knowledge base and technological readiness of specific ocean CDR approaches. Priorities for the research program should include development of
- Overarching implementation plan for the next decade adhering to the crosscutting strategy elements in Recommendation 1 and incorporating from its onset the common research components in Recommendation 2 and Table S.2. Progress on these common research components is essential to achieve a foundation for all other recommended research.
- Tailored implementation planning for specific ocean CDR approaches focused on reducing critical knowledge gaps by moving sequentially from laboratory-scale to pilot-scale field experiments, as appropriate, with adequate environmental and social risk reduction measures and transparent decision-making processes (priority components bolded in Table S.3).
- Common framework for intercomparing the viability of ocean CDR approaches with each other and with other climate response measures using standard criteria for efficacy, permanence, costs, environmental and social impacts, and governance and social dimensions.
- Research framework including program-wide components for experimental planning and public engagement, monitoring and verification (carbon accounting), and open publicly accessible data management.
- Strategy and implementation for engaging and communicating with stakeholders, policy makers, and publics.
- Research agenda that emphasizes advancing understanding of ocean fertilization, seaweed cultivation, and ocean alkalinity enhancement.
CONCLUDING REMARKS
Ocean CDR approaches are already being discussed widely, and in some cases promoted, by scientists, nongovernmental organizations, and entrepreneurs as potential climate response strategies. At present, society and policy makers lack sufficient knowledge to fully evaluate ocean CDR outcomes and weigh the trade-offs with other climate response approaches, including climate adaptation and emissions mitigation, and with environmental and sustainable development goals. Research on ocean CDR, therefore, is needed to decide whether or not society moves ahead with deployment, and to assess at what scales and locations the consequences of ocean CDR would be acceptable.
