This solution, at the end of the day, we do not recommend as a climate solution, either because it is not scientifically plausible or it presents a high level of risk.

Deploy Ocean Biomass Sinking

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Summary

Ocean biomass sinking involves sinking terrestrial plant material and/or seaweed in the deep sea, where the carbon it has converted into biomass can be stored. Using terrestrial material diverts biomass that might otherwise break down on land and release CO₂, while using seaweed removes carbon by cultivating and sinking new biomass produced in the ocean. This practice might be able to remove over 0.1 Gt CO₂‑eq/yr, but estimates remain highly uncertain due to limited data, and the adoption levels needed to reach this threshold are probably impractical. Advantages include the use of terrestrial biomass that might otherwise degrade on land and emit CO₂, and the ability to reduce nutrient pollution in some ocean areas when cultivating marine biomass. Disadvantages include its unclear effectiveness and durability, potentially high environmental risks, limited feasibility to operate at scale (particularly for seaweed biomass), and complex monitoring and verification. We conclude that Deploy Ocean Biomass Sinking is “Not Recommended” as a climate solution.

Description for Social and Search
Ocean biomass sinking involves sinking terrestrial plant material and/or seaweed in the deep sea, where the carbon it has converted into biomass can be stored.
Overview

What is our assessment?

Our analysis finds that Deploy Ocean Biomass Sinking could have high potential environmental risks, including unknown impacts on marine ecosystems. It is also unclear how effective or durable carbon storage in the deep sea is from this approach. There are likely better alternative uses for terrestrial biomass, and cultivating seaweed at climate-relevant scales is probably not feasible. Even if it were, seaweed would probably provide greater value through other applications. Therefore, Deploy Ocean Biomass Sinking is currently “Not Recommended” as a climate solution.

Plausible Could it work? Yes
Ready Is it ready? No
Evidence Are there data to evaluate it? Limited
Effective Does it consistently work? No
Impact Is it big enough to matter? No
Risk Is it risky or harmful? Yes
Cost Is it cheap? ?

What is it?

Ocean biomass sinking relies on sinking terrestrial plant material and/or seaweed grown in the ocean to the deep sea or seafloor where it can be stored long-term. Cultivating and sinking seaweed removes carbon from the surface ocean, whereas sinking terrestrial biomass material can help reduce emissions that might otherwise occur if the material instead decomposed on land. While not a current practice, terrestrial biomass grown explicitly for sinking would also constitute a form of carbon removal. When biomass sinks naturally, most of it is degraded into CO₂ or other forms of carbon before reaching the deep sea. Deliberate sinking of biomass might avoid some of this degradation by expediting its delivery to the deep sea, depending on the method used. Once sunk, the biomass and any CO₂ or other forms of carbon produced from its degradation can be isolated from the atmosphere for decades to centuries due to the ocean’s slow circulation times at depth. Biomass sinking can be accomplished using active methods, like submersibles, or passive methods, like letting weighted bundles sink on their own. There has been a recent focus on sinking material in low-oxygen ocean basins (e.g., the Black Sea), which might help further minimize degradation, while improving the durability of sequestered carbon due to the long circulation time-scales typical of these regions.

Does it work?

Global estimates suggest that ~11% of carbon produced in natural seaweed ecosystems might be sequestered at depth, generally defined as below the mixed layer at around 1,000 m. However, very few studies have documented the export efficiency, or the fraction of carbon in surface waters that makes its way to the deep sea, of purposefully sunk terrestrial and seaweed biomass, as this practice is currently in the early stages of development and research. If biomass is quickly sunk, most carbon might make its way to the deep sea, while passive sinking techniques, if slower, could result in higher degradation rates. Sequestration also depends on the storage efficiency and durability of carbon once at depth. Some initial research suggests that biomass degradation may be slowed in low-oxygen basins, but this also remains poorly characterized in field studies. It is similarly unclear how durable the carbon stored below the mixed layer will be over climate-relevant timescales, both in the deep sea in general and in low-oxygen basins specifically.

Why are we excited?

The advantages of ocean biomass sinking include its potential ability to use land-based biomass that might otherwise be degraded in landfills or incinerated, both of which lead to CO₂ emissions. In some regions, seaweed cultivation could help reduce nutrient pollution, provide habitat for marine organisms, and locally buffer against ocean acidification. Estimates of potential climate impacts suggest that ocean biomass sinking using biomass from seaweed farms could theoretically exceed 0.1 Gt CO₂‑eq/yr. Still, those estimates remain highly speculative and require more research. Costs are poorly quantified, but some estimates suggest they could be low to moderately expensive compared to other marine carbon dioxide removal approaches, close to US$100/t CO₂.

Why are we concerned?

Ocean biomass sinking has many environmental and social risks that, though not currently fully understood, could make it unfeasible to deploy the technology at scale. Deep-sea and seafloor ecosystems are highly understudied, and it's unclear how new biomass might alter these unique environments. Potential impacts include increased acidification, nutrient pollution, and oxygen depletion of the deep sea, which could affect diverse marine life. Large-scale seaweed cultivation could reduce phytoplankton abundance, disrupt food webs, and deplete nutrients needed by other ecosystems. Cultivation in open ocean areas might relieve demand for coastal space, but they are often nutrient-poor, and adding nutrients raises serious concerns (see Ocean Fertilization). Terrestrial biomass sources could introduce contaminants into the ocean due to inadvertent inclusion of plastics or other pollutants in sunken biomass. This practice also comes with social risks. Some countries might disproportionately bear negative impacts wherever biomass is cultivated and/or sunk, as it could alter marine food webs and livelihoods. There could also be issues with public perception due to historical injustices around ocean dumping, potentially impeding future projects without meaningful community engagement and transparency. 

Moreover, there are numerous technical challenges relating to the effectiveness and durability of carbon sequestration. Biomass sources differ in how easily they break down, affecting how much carbon is stored at depth. Sunk biomass could also potentially release other greenhouse gases, such as methane and nitrous oxide. The location where biomass is disposed of also matters, impacting how much carbon reaches and stays at depth. However, all of these factors remain poorly constrained. Operational and technical challenges are also significant. To remove at least 0.1 Gt CO₂‑eq/yr using marine biomass, nearly 7 million ha of ocean – over 60% of the global coastline – could be needed for seaweed cultivation, which is impractical. Measurement and verification pose additional hurdles. In the case of seaweed cultivation, tracking carbon removal requires monitoring both CO₂ uptake at the ocean’s surface and export as well as storage at depth across large spatial and temporal scales. In addition, the opportunity cost of sinking terrestrial biomass is high due to competing land-based uses, as waste biomass and crop residues are finite resources. Growing new biomass explicitly for ocean sinking would introduce new risks, given that land is also a finite resource. Similarly, seaweed probably has higher value and carbon benefits as food, fertilizer, and other products.

Solution in Action

Arzeno-Soltero, I. B., Saenz, B. T., Frieder, C. A., Long, M. C., DeAngelo, J., Davis, S. J., & Davis, K. A. (2023). Large global variations in the carbon dioxide removal potential of seaweed farming due to biophysical constraints. Communications Earth & Environment, 4(1), 185. Link to source: https://doi.org/10.1038/s43247-023-00833-2

Bach, L. T., Tamsitt, V., Gower, J., Hurd, C. L., Raven, J. A., & Boyd, P. W. (2021). Testing the climate intervention potential of ocean afforestation using the Great Atlantic Sargassum Belt. Nature Communications, 12(1), 2556. Link to source: https://doi.org/10.1038/s41467-021-22837-2

Boettcher, M., Chai, F., Canothan, M., Cooley, S., Keller, D. P., Klinsky, S., ... & Webb, R. M. (2023). A code of conduct for marine carbon dioxide removal research. Link to source: https://www.aspeninstitute.org/publications/a-code-of-conduct-for-marine-carbon-dioxide-removal-research/

Chopin, T., Costa-Pierce, B. A., Troell, M., Hurd, C. L., Costello, M. J., Backman, S., ... & Yarish, C. (2024). Deep-ocean seaweed dumping for carbon sequestration: Questionable, risky, and not the best use of valuable biomass. One Earth, 7(3), 359-364. Link to source: https://doi.org/10.1016/j.oneear.2024.01.013

Duarte, C. M., Wu, J., Xiao, X., Bruhn, A., & Krause-Jensen, D. (2017). Can seaweed farming play a role in climate change mitigation and adaptation?. Frontiers in Marine Science, 4, 100. Link to source: https://doi.org/10.3389/fmars.2017.00100

Hurd, C. L., Gattuso, J. P., & Boyd, P. W. (2024). Air‐sea carbon dioxide equilibrium: Will it be possible to use seaweeds for carbon removal offsets?. Journal of Phycology, 60(1), 4-14. Link to source: https://doi.org/10.1111/jpy.13405

Hurd, C. L., Law, C. S., Bach, L. T., Britton, D., Hovenden, M., Paine, E. R., ... & Boyd, P. W. (2022). Forensic carbon accounting: Assessing the role of seaweeds for carbon sequestration. Journal of Phycology, 58(3), 347-363. Link to source: https://doi.org/10.1111/jpy.13249

Jones, D. C., Ito, T., Takano, Y., & Hsu, W. C. (2014). Spatial and seasonal variability of the air‐sea equilibration timescale of carbon dioxide. Global Biogeochemical Cycles, 28(11), 1163-1178. Link to source: https://doi.org/10.1002/2014GB004813

Keil, R. G., Nuwer, J. M., & Strand, S. E. (2010). Burial of agricultural byproducts in the deep sea as a form of carbon sequestration: A preliminary experiment. Marine Chemistry, 122(1-4), 91-95. Link to source: https://doi.org/10.1016/j.marchem.2010.07.007

National Academies of Sciences, Engineering, and Medicine. (2021). A research strategy for ocean-based carbon dioxide removal and sequestration. Link to source: https://www.nationalacademies.org/our-work/a-research-strategy-for-ocean-carbon-dioxide-removal-and-sequestration

Raven, M. R., Crotteau, M. A., Evans, N., Girard, Z. C., Martinez, A. M., Young, I., & Valentine, D. L. (2024). Biomass storage in anoxic marine basins: Initial estimates of geochemical impacts and CO2 sequestration capacity. AGU Advances, 5(1), e2023AV000950. Link to source: https://doi.org/10.1029/2023AV000950

Raven, M. R., Evans, N., Martinez, A. M., & Phillips, A. A. (2025). Big decisions from small experiments: observational strategies for biomass-based marine carbon storage. Environmental Research Letters, 20(5), 051001. Link to source: https://doi.org/10.1088/1748-9326/adc28d

Ricart, A. M., Krause-Jensen, D., Hancke, K., Price, N. N., Masqué, P., & Duarte, C. M. (2022). Sinking seaweed in the deep ocean for carbon neutrality is ahead of science and beyond the ethics. Environmental Research Letters, 17(8), 081003. Link to source: https://doi.org/10.1088/1748-9326/ac82ff

Ross, F. W., Boyd, P. W., Filbee-Dexter, K., Watanabe, K., Ortega, A., Krause-Jensen, D., ... & Macreadie, P. I. (2023). Potential role of seaweeds in climate change mitigation. Science of the Total Environment, 885, 163699. Link to source: https://doi.org/10.1016/j.scitotenv.2023.163699

Sheppard, E. J., Hurd, C. L., Britton, D. D., Reed, D. C., & Bach, L. T. (2023). Seaweed biogeochemistry: Global assessment of C: N and C: P ratios and implications for ocean afforestation. Journal of Phycology, 59(5), 879-892. Link to source: https://doi.org/10.1111/jpy.13381

Strand, S. E., & Benford, G. (2009). Ocean sequestration of crop residue carbon: recycling fossil fuel carbon back to deep sediments. Environmental Science and TechnologyLink to source: https://doi.org/10.1021/es8015556

Visions, O. (2022). Answering Critical Questions About Sinking Macroalgae for Carbon Dioxide Removal: A Research Framework to Investigate Sequestration Efficacy and Environmental Impacts. Link to source: https://oceanvisions.org/wp-content/uploads/2022/10/Ocean-Visions-Sinking-Seaweed-Report_FINAL.pdf

Wu, J., Keller, D. P., & Oschlies, A. (2023). Carbon dioxide removal via macroalgae open-ocean mariculture and sinking: an Earth system modeling study. Earth System Dynamics, 14(1), 185-221. Link to source: https://doi.org/10.5194/esd-14-185-2023

Xiao, X., Agusti, S., Lin, F., Li, K., Pan, Y., Yu, Y., ... & Duarte, C. M. (2017). Nutrient removal from Chinese coastal waters by large-scale seaweed aquaculture. Scientific Reports, 7(1), 46613. Link to source: https://doi.org/10.1038/srep46613

Xiao, X., Agustí, S., Yu, Y., Huang, Y., Chen, W., Hu, J., ... & Duarte, C. M. (2021). Seaweed farms provide refugia from ocean acidification. Science of the Total Environment, 776, 145192. Link to source: https://doi.org/10.1016/j.scitotenv.2021.145192

Credits

Lead Fellow

  • Christina Richardson, Ph.D.

Internal Reviewer

  • Christina Swanson, Ph.D.
Speed of Action
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Caveats
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Risks
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Consensus
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Trade-offs
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Action Word
Deploy
Solution Title
Ocean Biomass Sinking
Classification
Not Recommended
Lawmakers and Policymakers
Practitioners
Business Leaders
Nonprofit Leaders
Investors
Philanthropists and International Aid Agencies
Thought Leaders
Technologists and Researchers
Communities, Households, and Individuals
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Produce Blue Hydrogen

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An image of a large, metal hydrogen storage tank that says 'H2 Hydrogen' on the side
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Summary

Blue hydrogen production involves making hydrogen (H2) from fossil fuel feedstocks while using carbon capture and storage (CCS) to reduce CO₂ emissions from the production process. The captured CO₂ is concentrated, compressed, and permanently stored underground. Blue hydrogen is more expensive than grey hydrogen, the predominant hydrogen production method, but less expensive than zero-emissions green hydrogen. Blue hydrogen production could facilitate the expansion of hydrogen infrastructure and the development of the global hydrogen economy. However, current adoption is low, its effectiveness at reducing GHG emissions is variable, and it could compete with technologies that offer greater climate benefits. Because of its reliance on fossil fuels for both feedstock and energy, the expansion of blue hydrogen production would perpetuate and potentially expand the use of fossil fuels. Based on this risk, we conclude that producing blue hydrogen is “Not Recommended” as a climate solution.

Description for Social and Search
Blue hydrogen is hydrogen produced from fossil fuels, with some of the GHGs captured and stored to prevent their release. This hydrogen, considered a low-carbon fuel or feedstock, is an alternative to hydrogen produced from fossil fuels without carbon capture (gray hydrogen).
Overview

What is our assessment?

Based on our analysis, blue hydrogen is feasible and ready to deploy, but there is little real-world evidence for its effectiveness or ability to scale. The expansion of this technology to replace current grey hydrogen production or to support the transition to a global hydrogen economy will perpetuate and possibly expand the use of fossil fuels. Because of this risk, we conclude that producing blue hydrogen is “Not Recommended”.

Plausible Could it work? Yes
Ready Is it ready? Yes
Evidence Are there data to evaluate it? Limited
Effective Does it consistently work? No
Impact Is it big enough to matter? No
Risk Is it risky or harmful? Yes
Cost Is it cheap? Yes

What is it?

Blue hydrogen production is an industrial process that produces hydrogen (H2) from fossil fuels – either natural gas or coal – combined with carbon capture and storage (CCS) technology to reduce CO₂ emissions produced during the process. Today, most hydrogen is grey hydrogen made from natural gas without any CCS. The addition of CCS prevents the release of some of the CO₂ generated during the hydrogen production process; capturing, concentrating, and then storing it permanently underground. 

Does it work?

The technologies for making hydrogen from natural gas, predominantly steam methane reformation (SMR), are well-established and have been used to produce hydrogen for close to a century. CCS technology is also available and currently deployed in multiple industrial and power generation applications. The SMR hydrogen production process generates GHG emissions from two sources: methane leaks from the gas used as feedstock and fuel used to power the production process, and GHG emissions from both the SMR process and combustion of gas (or other fuels) for energy, including CO₂, methane, nitrous oxide, and black carbon. CCS can be applied to capture CO₂ produced during the SMR process, for post-combustion capture of CO₂ from the plant’s energy use, or for both. Incorporating CCS to capture emissions from the H2 production process adds costs and increases energy use, but it could theoretically reduce CO₂ emissions by more than 90%. However, current adoption of blue hydrogen is very low – less than 1% of global hydrogen production – and there is little real-world evidence to support its effectiveness and scalability. The few commercial facilities currently in operation capture only about 60% or less of the emitted CO₂. Because CCS is energy-intensive, it requires more fuel to power the blue hydrogen production plant. This can also increase fugitive methane leaks due to increased gas-powered energy consumption. If implemented adequately, carbon storage can be permanent. The captured CO₂ can also be used as a chemical precursor for the manufacture of other products or for enhanced oil recovery; however, these post-capture uses of CO₂ emit GHGs, thereby reducing or eliminating the emissions reduction efficacy of CCS. Currently, only ~8% of CO₂ captured from blue hydrogen production is injected into dedicated geological storage, with the rest used in industry, enhanced oil recovery, and other applications. 

Why are we excited?

Hydrogen can be combusted as a zero-emissions fuel, used to store energy to produce electricity, or deployed as a feedstock in industrial, transportation, and energy systems. The production of any hydrogen type – blue, grey, or green hydrogen – could facilitate the expansion of hydrogen infrastructure and the development of the global hydrogen economy, which is an important step in scaling hydrogen. Blue hydrogen is more technologically ready and cheaper than green hydrogen, which is made from water using electrolysis powered by renewable energy. Blue hydrogen is more expensive to produce than grey hydrogen, but the cost per ton of CO₂ removed could be relatively low. Estimates range from US$60–110/t CO₂, although these costs are uncertain and, with lower CCS effectiveness, they could increase to ~US$260/t CO₂. If implemented with low fugitive methane emissions and high CCS efficiencies, blue hydrogen could substantially reduce emissions compared to current grey hydrogen production. The climate impact of scaling blue hydrogen could be high. Estimates and targets for blue hydrogen production by 2050 range from ~30–85 Mt H2. At that scale, even modest emissions savings relative to grey hydrogen would have a climate impact above 0.09 Gt CO₂‑eq/yr by 2050. However, achieving this depends on the quality of the infrastructure and rate of technology scaling, both of which are unproven. 

Why are we concerned?

Currently, 6% of the world’s natural gas and 2% of its coal are used to make hydrogen. As hydrogen production ramps up, blue hydrogen – even though it reduces production emissions compared to grey hydrogen – would perpetuate and could even increase the global market for fossil fuels. If the future implementation of green hydrogen is delayed, blue hydrogen could create a long-term dependency on fossil fuels. Furthermore, any hydrogen produced from natural gas leads to methane leaks, regardless of whether CO₂ is captured. Methane is a potent short-lived GHG, meaning its impact on climate warming is stronger in the near-term. This is why reducing methane emissions is an urgent emergency brake climate action. Building and expanding a new industry that relies on natural gas as both a feedstock and fuel, and which inevitably leaks methane, is counterproductive to solving the climate crisis. 

If and when there is a transition to a global hydrogen economy, blue hydrogen is a less effective climate solution than green hydrogen. Although this technology could be a transitional solution between grey and green hydrogen, blue hydrogen risks diverting resources away from green hydrogen development or ready-to-deploy renewable energy technologies, such as onshore wind or distributed solar PV. There are mixed expert opinions about the realistic level of avoided emissions that blue hydrogen may reach. Additionally, there is uncertainty around whether CCS can meet its technical potential at a reasonable cost.

Solution in Action

Ajanovic, A., Sayer, M., & Haas, R. (2022). The economics and the environmental benignity of different colors of hydrogen. International Journal of Hydrogen Energy47(57), 24136–24154. Link to source: https://doi.org/10.1016/j.ijhydene.2022.02.094 

Arcos, J. M. M., & Santos, D. M. F. (2023). The hydrogen color spectrum: Techno-economic analysis of the available technologies for hydrogen production. Gases3(1), Article 1. https://doi.org/10.3390/gases3010002

Bauer, C., Treyer, K., Antonini, C., Bergerson, J., Gazzani, M., Gencer, E., Gibbins, J., Mazzotti, M., McCoy, S. T., McKenna, R., Pietzcker, R., Ravikumar, A. P., Romano, M. C., Ueckerdt, F., Vente, J., & Spek, M. van der. (2021). On the climate impacts of blue hydrogen production. Sustainable Energy & Fuels6(1), 66–75. https://doi.org/10.1039/D1SE01508G

Blank, T. K., Molloy, P., Ramirez, K., Wall, A., & Weiss, T. (2022, April 13). Clean energy 101: The colors of hydrogen. RMI. https://rmi.org/clean-energy-101-hydrogen/

Collodi, G., Azzaro, G., Ferrari, N., & Santos, S. (2017). Techno-economic Evaluation of Deploying CCS in SMR Based Merchant H2 Production with NG as Feedstock and Fuel. Energy Procedia114, 2690–2712. Link to source: https://doi.org/10.1016/j.egypro.2017.03.1533

Gorski, J., Jutt, T., & Wu, K. T. (2021). Carbon intensity of blue hydrogen production. https://www.pembina.org/reports/carbon-intensity-of-blue-hydrogen-revised.pdf

Hossain Bhuiyan, M. M., & Siddique, Z. (2025). Hydrogen as an alternative fuel: A comprehensive review of challenges and opportunities in production, storage, and transportation. International Journal of Hydrogen Energy102, 1026–1044. https://doi.org/10.1016/j.ijhydene.2025.01.033

Howarth, R. W., & Jacobson, M. Z. (2021). How green is blue hydrogen? Energy Science & Engineering9(10), 1676–1687. https://doi.org/10.1002/ese3.956

IEA. (2019). The future of hydrogen. Link to source: https://iea.blob.core.windows.net/assets/9e3a3493-b9a6-4b7d-b499-7ca48e357561/The_Future_of_Hydrogen.pdf 

IEA. (2023). Hydrogen: Net zero emissions guide. Link to source: https://www.iea.org/reports/hydrogen-2156#overview

IEA. (2023). Net zero roadmap: A global pathway to keep the 1.5 °C goal in reach. Link to source: https://www.iea.org/reports/net-zero-roadmap-a-global-pathway-to-keep-the-15-0c-goal-in-reach

IEA. (2024). Global hydrogen review 2024. Link to source: https://www.iea.org/reports/global-hydrogen-review-2024

IEA. (2025, February). HydrogenLink to source: https://www.iea.org/energy-system/low-emission-fuels/hydrogen 

Ighalo, J. O., & Amama, P. B. (2024). Recent advances in the catalysis of steam reforming of methane (SRM). International Journal of Hydrogen Energy51, 688–700. Link to source: https://doi.org/10.1016/j.ijhydene.2023.10.177 

Incer-Valverde, J., Korayem, A., Tsatsaronis, G., & Morosuk, T. (2023). “Colors” of hydrogen: Definitions and carbon intensity. Energy Conversion and Management291, 117294. Link to source: https://doi.org/10.1016/j.enconman.2023.117294

Lewis, E., McNaul, S., Jamieson, M., Henriksen, M. S., Matthews, H. S., White, J., Walsh, L., Grove, J., Shultz, T., Skone, T. J., & Stevens, R. (2022). Comparison of commercial, state-of-the-art, fossil-based hydrogen production technologies. https://netl.doe.gov/projects/files/ComparisonofCommercialStateofArtFossilBasedHydrogenProductionTechnologies_041222.pdf

Massarweh, O., Al-khuzaei, M., Al-Shafi, M., Bicer, Y., & Abushaikha, A. S. (2023). Blue hydrogen production from natural gas reservoirs: A review of application and feasibility. Journal of CO2 Utilization70, Article 102438. Link to source: https://doi.org/10.1016/j.jcou.2023.102438 

Massarweh, O., Bicer, Y., & Abushaikha, A. (2025). Technoeconomic analysis of hydrogen versus natural gas considering safety hazards and energy efficiency indicators. Scientific Reports15, Article 29601. Link to source: https://doi.org/10.1038/s41598-025-14686-6 

Pettersen, J., Steeneveldt, R., Grainger, D., Scott, T., Holst, L.-M., & Hamborg, E. S. (2022). Blue hydrogen must be done properly. Energy Science & Engineering10(9), 3220–3236. https://doi.org/10.1002/ese3.1232

Romano, M. C., Antonini, C., Bardow, A., Bertsch, V., Brandon, N. P., Brouwer, J., Campanari, S., Crema, L., Dodds, P. E., Gardarsdottir, S., Gazzani, M., Jan Kramer, G., Lund, P. D., Mac Dowell, N., Martelli, E., Mastropasqua, L., McKenna, R. C., Monteiro, J. G. M.-S., Paltrinieri, N., … Wiley, D. (2022). Comment on “How green is blue hydrogen?” Energy Science & Engineering10(7), 1944–1954. https://doi.org/10.1002/ese3.1126

Roy, R., Antonini, G., Hayibo, K. S., Rahman, M. M., Khan, S., Tian, W., Boutilier, M. S. H., Zhang, W., Zheng, Y., Bassi, A., & Pearce, J. M. (2025). Comparative techno-environmental analysis of grey, blue, green/yellow and pale-blue hydrogen production. International Journal of Hydrogen Energy116, 200–210. Link to source: https://doi.org/10.1016/j.ijhydene.2025.03.104 

Sun, T., Shrestha, E., Hamburg, S. P., Kupers, R., & Ocko, I. B. (2024). Climate impacts of hydrogen and methane emissions can considerably reduce the climate benefits across key hydrogen use cases and time scales. Environmental Science & Technology58(12), 5299–5309. Link to source: https://doi.org/10.1021/acs.est.3c09030

Udemu, C., & Font-Palma, C. (2024). Potential cost savings of large-scale blue hydrogen production via sorption-enhanced steam reforming process. Energy Conversion and Management302, 118132. Link to source: https://doi.org/10.1016/j.enconman.2024.118132

Vallejo, V., Nguyen, Q., & Ravikumar, A. P. (2024). Geospatial variation in carbon accounting of hydrogen production and implications for the US Inflation Reduction Act. Nature Energy9(12), 1571–1582. Link to source: https://doi.org/10.1038/s41560-024-01653-0

Wu, W., Zhai, H., & Holubnyak, E. (2024). Technological evolution of large-scale blue hydrogen production toward the U.S. Hydrogen Energy Earthshot. Nature Communications15(1), 5684. https://doi.org/10.1038/s41467-024-50090-w

Credits

Lead Fellow 

  • Sarah Gleeson, Ph.D.

Contributor

  • Christina Swanson, Ph.D.

Internal Reviewers

  • Heather Jones, Ph.D.
  • Heather McDiarmid, Ph.D.
Speed of Action
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Caveats
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Risks
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Consensus
left_text_column_width
Trade-offs
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Action Word
Produce
Solution Title
Blue Hydrogen
Classification
Not Recommended
Lawmakers and Policymakers
Practitioners
Business Leaders
Nonprofit Leaders
Investors
Philanthropists and International Aid Agencies
Thought Leaders
Technologists and Researchers
Communities, Households, and Individuals
Updated Date

Deploy Stratospheric Aerosol Injection

Mode
Other
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An image of the upper atmosphere
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Summary

Stratospheric aerosol injection (SAI) is a geoengineering technology wherein reflective particles are injected into the stratosphere to reduce the amount of sunlight hitting the Earth, cooling the planet and counteracting global warming driven by increasing GHG concentrations. SAI is not a climate solution because it does not address or affect the causes of global warming, but proponents argue that it could be a “bridge” to buy time to cut GHG emissions over the longer term. The technology has never been tested in the field. However, numerous modeling studies indicate that its efficacy is highly uncertain and that it could adversely impact atmospheric conditions, including damaging the ozone layer, and destabilize weather and rainfall patterns, with resultant harm to ecosystems, agriculture, and human well-being. Deployment of SAI would also pose immense geopolitical, legal, and ethical challenges, and it could distract from or delay action on real solutions to climate change. Once deployed, SAI would require sustained action to avoid termination shock and rapid temperature increase. For these reasons, we conclude that stratospheric aerosol injection is “Not Recommended”.

Description for Social and Search
Injecting huge amounts of reflective aerosols into the stratosphere to counteract or mask GHG-driven warming is not a serious or plausible climate solution.
Overview

What is our assessment?

Injecting huge amounts of reflective aerosols into the stratosphere to counteract or mask GHG-driven warming is not a serious or plausible climate solution. Its effectiveness is highly uncertain, and its potential for harmful unintended impacts to Earth and ecological systems, as well as on human well-being, is extremely high. Based on these significant problems and risks, we conclude that deploying Stratospheric Aerosol Injection is “Not Recommended”.

Plausible Could it work? No
Ready Is it ready? No
Evidence Are there data to evaluate it? No
Effective Does it consistently work? ?
Impact Is it big enough to matter? ?
Risk Is it risky or harmful? Yes
Cost Is it cheap? ?

What is it? 

Stratospheric aerosol injection (SAI) is a geoengineering technology that uses airplanes or balloons to inject fine particles, usually sulfates, into the stratosphere, the layer of air that begins about 6 to 20 km (20,000 to 65,000 ft) above the Earth’s surface. These aerosols would scatter some of the sunlight striking the planet, reflecting it back into space. Reducing the amount of sunlight hitting the Earth is intended to cool the planet and counteract the warming effects of increasing GHG concentrations. Because SAI does not affect the atmospheric concentration of GHGs, the direct cause of global warming, this technology is not actually a solution to climate change. Instead, it is a temporary action to mask the ongoing warming effects of GHG emissions. 

Does it work?

The injection of large amounts of reflective aerosol particles into the stratosphere does have a cooling effect on the planet. Following the 1991 eruption of Mount Pinatubo, which injected 20 million tons of sulfur dioxide into the stratosphere, average global temperatures were about 0.5°C lower for more than a year. In another example, modeling studies suggest that recent reductions in East Asian air pollution have contributed to the acceleration of global warming. Therefore, in theory, deploying SAI could achieve a similar effect. However, other than modeling simulations, SAI has never been tested in the field, and researchers agree that there are substantial uncertainties and risks. For example, the ways that GHGs and stratospheric aerosols affect global temperatures differ. GHGs warm the planet more in winter than in summer, and more in the high latitudes, especially in the Northern Hemisphere, than in the equatorial regions. Because aerosols reflect solar radiation, they have a greater impact during the summer and in the equatorial zone. Finally, the solar radiation reflective effect of SAI is temporary. Depending on the location and altitude of injection, the aerosols remain in the stratosphere for only months to a few years.  

Why are we excited?

We’re not. The only argument in favor of deploying SAI is based on the concern that we cannot reduce GHG emissions fast enough to avoid the catastrophic environmental and societal impacts of climate change. SAI proponents argue that this geoengineering approach to reduce global temperatures could be a “bridge,” buying time to cut GHG emissions and remove atmospheric CO₂ over the longer term. 

Why are we concerned?

SAI is an untested technology designed to alter planetary energy balance and atmospheric dynamics. Numerous modeling studies indicate that its efficacy to reduce global or regional temperatures as intended is highly uncertain and that it has high risks for unintended impacts on Earth, ecological, and human systems. These studies show that SAI could have substantial effects on the physics, chemistry, and circulation of the upper atmosphere, including harm to the ozone layer. It could destabilize weather and rainfall patterns, reducing the amount of sunlight striking the Earth’s surface, and changing the balance of “direct” and “diffuse” sunlight, effectively making the sky look more hazy. These effects will, in turn, have profound impacts on ecosystems, including the rates of photosynthesis in forest carbon sinks, agriculture, and human well-being. Even if it works to lower temperatures as planned, SAI will have no impact on the non-climatic effects of increasing carbon dioxide, such as ocean acidification. SAI is also inherently a temporary intervention; it will require sustained deployment for as long as 100 years, according to one study, to avoid “termination shock” and an abrupt temperature increase if GHG concentrations are still high. SAI also poses immense geopolitical, legal, and ethical challenges, including international responsibilities for implementation, financing, compensation for negative impacts, and procedural justice questions, such as those around informed consent. And finally, beyond these scientific, environmental, political, and socio-economic concerns, SAI poses a serious “moral hazard” that could distract or delay action on real solutions to climate change.

Solution in Action

Baur, S., Nauels, A., Nicholls, Z., Sanderson, B. M., and Schleussner, C.-F. (2023). The deployment length of solar radiation modification: an interplay of mitigation, net-negative emissions and climate uncertainty, Earth Syst. Dynam., 14, 367–381, Link to source: https://doi.org/10.5194/esd-14-367-2023 

Bednarz, E. M., Butler, A. H., Visioni, D., Zhang, Y., Kravitz, B., & MacMartin, D. G. (2023). Injection strategy–a driver of atmospheric circulation and ozone response to stratospheric aerosol geoengineering. Atmospheric Chemistry and Physics, 23(21), 13665-13684. Link to source: https://acp.copernicus.org/articles/23/13665/2023/acp-23-13665-2023.pdf

Cohen, S. L., Hurrell, J. W., & Lombardozzi, D. L. (2025). The impact of stratospheric aerosol injection: a regional case study. Frontiers in Climate, 7, 1582747. Link to source: https://www.frontiersin.org/journals/climate/articles/10.3389/fclim.2025.1582747/ful

Foley, J.A. (2021). Solar Geoengineering: Ineffective, Risky, and Unnecessary, Medium. Link to source: https://globalecoguy.org/solar-geoengineering-ineffective-risky-and-unnecessary-2d9850328fab

Harvey, C. (2023). Geoengineering is not a quick fix for the climate crisis, new analysis shows. Scientific American. ​​Link to source: https://www.scientificamerican.com/article/geoengineering-is-not-a-quick-fix-for-the-climate-crisis-new-analysis-shows/

Lawrence, M.G., Schafer, S., Muri, H., Scott, V., Oschlies, A., Vaughan, N.E., Boucher, O., Schmidt, H., Haywood, J. and Scheffran J. (2018). Evaluating climate geoengineering proposals in the context of the Paris Agreement temperature goals, Nature, 9, 3734. Link to source: https://www.nature.com/articles/s41467-018-05938-3

Martin, S., Sevestre, H., Bentley, M. J., & 39 others (2025). Safeguarding the polar regions from dangerous geoengineering: a critical assessment of proposed concepts and future prospects. Frontiers in Science, Vol. 3. Link to source: https://www.frontiersin.org/journals/science/articles/10.3389/fsci.2025.1527393/full

National Oceanic and Atmospheric Administration (NOAA) (nd). Layers of the atmosphere. Link to source: https://www.noaa.gov/jetstream/atmosphere/layers-of-atmosphere

Rasch, P. J., Crutzen, P. J., & Coleman, D. B. (2008). Exploring the geoengineering of climate using stratospheric sulfate aerosols: The role of particle size. Geophysical Research Letters, 35(2). Link to source: https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2007GL032179

Samset, B. H., Wilcox, L. J., Allen, R. J., Stjern, C. W., Lund, M. T., Ahmadi, S., ... & Westervelt, D. M. (2025). East Asian aerosol cleanup has likely contributed to the recent acceleration in global warming. Communications Earth & Environment, 6(1), 543. Link to source: https://www.nature.com/articles/s43247-025-02527-3

Shepherd, J. G. (2009). Geoengineering the climate: science, governance and uncertainty. Royal Society. Link to source: https://royalsociety.org/-/media/policy/publications/2009/8693.pdf

Smith, W. (2020). The cost of stratospheric aerosol injection through 2100. Environmental Research Letters, 15(11), 114004. Link to source: https://iopscience.iop.org/article/10.1088/1748-9326/aba7e7/pdf

Tracy, S. M., Moch, J. M., Eastham, S. D., & Buonocore, J. J. (2022). Stratospheric aerosol injection may impact global systems and human health outcomes. Elem Sci Anth, 10(1), 00047. Link to source: https://online.ucpress.edu/elementa/article/10/1/00047/195026/Stratospheric-aerosol-injection-may-impact-global

Union of Concerned Scientists (2020). What is Solar Geoengineering? Link to source: https://www.ucs.org/resources/what-solar-geoengineering

Wagner, G., & Zizzamia, D. (2022). Green moral hazards. Ethics, Policy & Environment, 25(3), 264-280. Link to source: https://www.tandfonline.com/doi/pdf/10.1080/21550085.2021.1940449

NASA Earth Observatory (nd). Global Effects of Mount Pinatubo. Link to source: https://earthobservatory.nasa.gov/images/1510/global-effects-of-mount-pinatubo

Credits

Lead Author

  • Jonathan Foley, Ph.D.

Internal Reviewer

  • Christina Swanson, Ph.D.
Speed of Action
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Caveats
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Additional Benefits
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Risks
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Consensus
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Trade-offs
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Action Word
Deploy
Solution Title
Stratospheric Aerosol Injection
Classification
Not Recommended
Updated Date

Deploy Direct Air Capture

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An image of large fans used for direct air capture of carbon dioxide
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Summary

Direct air capture (DAC) is an industrial process that captures CO₂ from the air and then injects it deep underground for permanent, geologic storage. This process is energy-intensive. Therefore, DAC can only be effective for net carbon removal if it does not generate high levels of emissions during the process. This requires that DAC be powered by zero- or low-carbon energy sources and that the captured carbon is permanently stored rather than used for emission-generating applications. Unlike the situation for many other carbon removal methods, the amounts of CO₂ captured and stored using DAC can be reliably measured, which is an advantage in the carbon marketplace. However, the effectiveness of DAC has been extremely low so far. DAC is also expensive, up to US$1,000/t CO₂ removed and stored. Substantial funding to support DAC development has come from fossil-fuel interests or their government proxies, which view carbon capture as a strategy to extend society’s use of fossil fuels. Therefore, there is a risk that DAC could be used to delay or avoid emissions reductions and perpetuate or even expand fossil-fuel production and use. Based on this risk, as well as the functional and financial challenges for scaling this technology to remove globally meaningful amounts of CO₂, we conclude that DAC is “Not Recommended” as a climate solution.

Description for Social and Search
Direct air capture (DAC) is an industrial process that captures CO2 from the air and then injects it deep underground for permanent, geologic storage.
Overview

What is our assessment?

Based on the difficulty of capturing low concentrations of CO₂ from the air and the associated technological, energy consumption, and financial challenges facing DAC, it is unlikely that this climate technology can be scaled up to remove globally meaningful amounts of CO₂. Furthermore, based on the current financial and policy support for DAC from fossil-fuel interests, there is a clear risk that the technology will be used to enable and perpetuate the production and use of fossil fuels, which is antithetical to solving the climate crisis. Therefore, we conclude that deployment of DAC is “Not Recommended” as a climate solution.

Plausible Could it work? Yes
Ready Is it ready? No
Evidence Are there data to evaluate it? Yes
Effective Does it consistently work? No
Impact Is it big enough to matter? No
Risk Is it risky or harmful? Yes
Cost Is it cheap? No

What is it? 

DAC is a suite of engineered technologies that remove CO₂ directly from the atmosphere, concentrate it, and then inject it underground for permanent storage. CO₂ is captured from the atmosphere by moving large volumes of air, usually with large fans, past a reactive material that selectively binds CO₂, either a solid sorbent (referred to as solid-DAC or S-DAC) or a liquid solvent (referred to as liquid-DAC or L-DAC). The captured CO₂ is recovered from the reactive material by applying heat, pressure, or chemical reactions, and collected and compressed for transportation and storage. The concentrated CO₂ is then injected deep underground into geological formations, such as saline aquifers or basalt formations, where it can be permanently stored. 

Does it work?

The technology and chemistry for the selective capture of CO₂ from air are effective, although the CO₂ capture efficiency varies with the reactive material and other factors. A variety of solid and liquid reactive materials have been developed, along with material-specific processes for recovering captured CO₂ and regenerating the sorbents. This process is very energy-intensive and, for liquid-DAC, water-intensive. To capture and recover 1 t CO₂, solid-DAC uses about 1,100 kWh, while liquid-DAC uses about 2,500 kWh and consumes as much as 7 t of water. Most of the energy for DAC (70–90%) is used to generate heat for recovery of the captured CO₂ and regeneration of the sorbent material. Liquid-DAC requires temperatures up to about 900 °C (1,652 °F), while solid-DAC requires temperatures of only about 100 °C (212 °F). Because the process is so energy intensive, DAC achieves net carbon removal – capturing and sequestering more CO₂ than it emits – only if it is powered by zero or low-carbon energy sources and/or uses waste heat. For example, recent reporting showed that the amount of CO₂ captured and stored by Climeworks, the largest commercial DAC company currently in operation, was insufficient to offset the facility’s operational GHG emissions. CO₂ captured by a DAC facility can also be used for other purposes, such as enhanced oil recovery or production of algae biofuels. However, life cycle analyses conducted by the National Energy Technology Laboratory show that these pathways do not result in net carbon removal due to the emissions from production and/or use of these other products. Therefore, in addition to its requirements for zero or low-carbon energy, DAC can only be an effective method for net carbon removal if the CO₂ it captures is permanently stored deep underground. With appropriate pre-injection site selection, geologic testing, and post-injection monitoring, underground storage of CO₂ is safe and effectively permanent.

Why are we excited about it?

Unlike some other carbon removal technologies and practices, a DAC facility has a relatively small footprint and can be located anywhere there is sufficient low-carbon energy and infrastructure and capacity to transport or store captured CO₂. In addition, the amount of CO₂ removed from the atmosphere can be directly measured by monitoring the flow and concentration of captured CO₂ at the point of storage. Compared to many other carbon removal approaches, this method provides a higher level of confidence in the amount of CO₂ being removed for investors and carbon credit purchasers. The geological sequestration of captured CO₂ has high permanence, effectively removing CO₂ from the atmosphere for thousands of years with a low risk of reversal. There are numerous research and pilot projects underway to improve CO₂ capture efficiency, reduce energy use, and reduce costs, which may improve the effectiveness and cost of this technology. 

Why are we concerned?

The concentration of CO₂ in the atmosphere is small, currently about 420 parts per million, or about 0.04%. This means that a DAC facility must process huge amounts of air – more than 1,600 t by one estimate – and consume more energy than a typical U.S. household uses in a month to capture 1 t CO₂. Scaled up to remove a globally meaningful amount of CO₂ (>0.1 Gt CO₂ /yr), DAC would consume more energy than the annual energy consumption of 10 million U.S. households. In addition, removing and storing CO₂ using DAC is very expensive, costing up to US$1,000/t CO₂ stored. This is more than twice the cost per t for all other commercially available carbon removal technologies and practices. 

For these reasons, the technical and financial feasibility of scaling DAC to remove globally meaningful amounts of CO₂ from the atmosphere is low. Despite these challenges, as of September 2025, more than 30 companies have sold more than 2.4 million t of future carbon removal credits. However, less than 1,300 t CO₂ has actually been removed so far – or only 0.05% of these promised credits. To put this in perspective, despite spending billions of dollars, DAC has removed about as much CO₂ as would be saved by keeping 250-300 cars off the road for a single year.

There is also an opportunity cost for DAC. Even if a DAC facility is powered by solar, wind, geothermal, or nuclear energy, that carbon-free energy could have been used to displace coal- and gas-powered electricity instead, reducing emissions by far more than a DAC facility can capture and store. Similarly, the large amounts of public and private sector funding going to DAC could be more cost-effective and carbon-effective if used for other, more effective actions to cut emissions or remove CO₂. There is also the risk that DAC will be used to delay or avoid emissions reduction actions or for greenwashing by fossil fuel companies and other emitters. Substantial amounts of the funding supporting the development of DAC are coming from fossil fuel companies, which have publicly stated that they view carbon capture as a strategy to extend society’s use of fossil fuels. Finally, unlike most other emissions reduction or carbon removal actions, DAC provides no obvious other benefits to nature or human well-being.

Solution in Action

Alexandersson, B. O. P and Grettisson, V. (2025) Climeworks’ capture fails to cover its own emissions. Heimildin. Link to source: https://heimildin.is/grein/24581/

Bashir, A., Ali, M., Patil, S., Aljawad, M. S., Mahmoud, M., Al-Shehri, D., Hoteit, H., & Kamal, M. S. (2024). Comprehensive review of CO2 geological storage: Exploring principles, mechanisms, and prospects. Earth-Science Reviews249, 104672. Link to source: https://www.sciencedirect.com/science/article/pii/S0012825223003616

Bindl, M., Edwards, M. R., & Cui, R. Y. (2025). Risks of relying on uncertain carbon dioxide removal in climate policy. Nature Communications16(1), 5958. Link to source: https://www.nature.com/articles/s41467-025-61106-4

Bisotti, F., Hoff, K. A., Mathisen, A., & Hovland, J. (2023). Direct air capture (DAC) deployment: National context cannot be neglected. A case study applied to Norway. Chemical Engineering Science282, 119313. Link to source: https://www.sciencedirect.com/science/article/pii/S0009250923008692

Calma, J. (2023) To capture CO2 in the US, climate tech startups partner with oil and gas. The Verge. Link to source: https://www.theverge.com/2023/4/21/23690040/climeworks-direct-air-carbon-capture-oil-gas

CDR.fyi. (2025) Keep Calm and Remove On - CDR.fyi 2024 Year in Review Link to source: https://www.cdr.fyi/blog/2024-year-in-review

Chatterjee, S., & Huang, K. W. (2019). Unrealistic energy and materials requirement for direct air capture in deep mitigation pathways. Nat. Commun. 11, 3287. Link to source: https://www.nature.com/articles/s41467-020-17203-7

Chen, S. (2025) Energy and water use for DAC. Carbon180. Link to source: https://carbon180.org/blog/energy-and-water-use-for-dac/#:~:text=To%20estimate%20the%20amount%20of%20energy%20consumed%20by,%3D%20%28Energy%20per%20tCO2%29%20%2A%20%28Total%20DAC%20capacity%29

Eke, V., Sahu, T., Ghuman, K. K., Freire-Gormaly, M., & O'Brien, P. G. (2025). A comprehensive review of life cycle assessments of direct air capture and carbon dioxide storage. Sustainable Production and Consumption. Link to source: https://www.sciencedirect.com/science/article/pii/S2352550925000399

Gulden, L. E., & Harvey, C. (2025). Tracing sources of funds used to lobby the US government about carbon capture, use, and storage. Environmental Science & Policy, 171, 104171. Link to source: https://www.sciencedirect.com/science/article/pii/S146290112500187X

Hager, B. & MIT Climate Portal Writing Team (2024) What is the risk that CO2 stored underground after carbon capture will escape again? MIT Climate Portal. Link to source: https://climate.mit.edu/ask-mit/what-risk-co2-stored-underground-after-carbon-capture-will-escape-again

Hiar, C. (2023) Oil companies want to remove carbon from the air — using taxpayer dollars. Climatewire, E&E News. Link to source: https://www.eenews.net/articles/oil-companies-want-to-remove-carbon-from-the-air-using-taxpayer-dollars/

International Energy Agency (no date) Direct Air Capture. Website. Link to source: https://www.iea.org/energy-system/carbon-capture-utilisation-and-storage/direct-air-capture

Isometric (2025) Direct Air Capture explained: Understanding the process, benefits and cost of DAC. Link to source: https://isometric.com/writing-articles/direct-air-capture-explained

Jacobson, M. Z. (2019). The health and climate impacts of carbon capture and direct air capture. Energy & Environmental Science12(12), 3567-3574. Link to source: https://web.stanford.edu/group/efmh/jacobson/Articles/Others/19-CCS-DAC.pdf

Jacobson, M. Z., Fu, D., Sambor, D. J., & Muhlbauer, A. (2025). Energy, health, and climate costs of carbon-capture and direct-air-capture versus 100%-wind-water-solar climate policies in 149 countries. Environmental Science & Technology59(6), 3034-3045. https://pubs.acs.org/doi/10.1021/acs.est.4c10686?ref=pdf

Lebling, K., Leslie-Bole, H., Byrum, Z., Wilcox, J. & Riedl, D. (2025) 6 Things to Know About Direct Air Capture. World Resources Institute. Link to source: https://www.wri.org/insights/direct-air-capture-resource-considerations-and-costs-carbon-removal

Mackler, S., Fishman, X., & Broberg, D. (2021). A policy agenda for gigaton-scale carbon management. The Electricity Journal34(7), 106999. Link to source: https://www.sciencedirect.com/science/article/pii/S1040619021000907

Maloney, C. B. and Khanna, R. (2022). Memorandum: Investigation of Fossil Fuel Industry Disinformation. U.S. House of Representatives, Committee on Oversight and Reform. Link to source: https://oversightdemocrats.house.gov/sites/evo-subsites/democrats-oversight.house.gov/files/2022.09.14%20FINAL%20COR%20Supplemental%20Memo.pdf

Martin, P. (2023) Why Direct Air Capture Sucks (and not in a good way!). LinkedIn.Link to source: https://www.linkedin.com/pulse/why-direct-air-capture-sucks-good-way-paul-martin/

Milman, O. (2023) The world’s biggest carbon capture facility is being built in Texas. Will it work? The Guardian. Link to source: https://www.theguardian.com/environment/2023/sep/12/carbon-capture-texas-worlds-biggest-will-it-work

National Academies of Sciences, Medicine, Division on Earth, Life Studies, Ocean Studies Board, Board on Chemical Sciences, ... & Reliable Sequestration. (2019). Negative emissions technologies and reliable sequestration: A research agenda. Link to source: https://nap.nationalacademies.org/read/25259/chapter/7#203

OPIS and CDR.fyi. (2025) Bridging the Gap: Durable CDR Market Pricing Survey: Purchaser and Supplier Expectations in 2025 and 2030. Link to source: https://www.cdr.fyi/reports/pricing-survey-jan-2025.pdf

Ozkan, M. (2025). Atmospheric alchemy: The energy and cost dynamics of direct air carbon capture. MRS Energy & Sustainability, 12(1), 46-61. Link to source: https://link.springer.com/content/pdf/10.1557/s43581-024-00091-5.pdf

Pett-Ridge, J., Ammar, H., & Aui, A. (2023). Roads to Removal. Options for Carbon Dioxide Removal in the United States. Chapter 7. Direct Air Capture with Storage (DACS) and Renewable Energy. Link to source: https://roads2removal.org/wp-content/uploads/07_RtR_Direct-Air-Capture.pdf

Scott, M. and T. Slavin (2023) Fossil-fuel industry embrace raises alarm bells over direct air capture. Reuters. Link to source: https://www.reuters.com/sustainability/climate-energy/fossil-fuel-industry-embrace-raises-alarm-bells-over-direct-air-capture-2023-10-10/

Skone, T. J. (2021) Life Cycle Greenhouse Gas Analysis of Direct Air Capture Systems. National Energy Technology Laboratory. Link to source: https://netl.doe.gov/sites/default/files/netl-file/21DAC_Skone.pdf  

Terlouw, T., Treyer, K., Bauer, C., & Mazzotti, M. (2021). Life cycle assessment of direct air carbon capture and storage with low-carbon energy sources. Environmental science & technology55(16), 11397-11411. Link to source: https://pubs.acs.org/doi/10.1021/acs.est.1c03263

U. S. Department of Energy, Fossil Energy and Carbon Management (2024) Direct Air Capture Explained. https://www.energy.gov/sites/default/files/2024-08/Direct%20Air%20Capture%20Factsheet_August%202024.pdf

Wang, J., Li, S., Deng, S., Zeng, X., Li, K., Liu, J., ... & Lei, L. (2023). Energetic and life cycle assessment of direct air capture: a review. Sustainable Production and Consumption36, 1-16. Link to source: https://www.sciencedirect.com/science/article/abs/pii/S2352550922003384

World Resources Institute. (no date) U.S. Climate Policy Resource Center, Direct Air Capture. Link to source: https://www.wri.org/us-climate-policy-implementation/sectors/direct-air-capture

Young, J., McQueen, N., Charalambous, C., Foteinis, S., Hawrot, O., Ojeda, M., ... & Van Der Spek, M. (2023). The cost of direct air capture and storage can be reduced via strategic deployment but is unlikely to fall below stated cost targets. One Earth 6, 899–917Link to source: https://www.sciencedirect.com/science/article/pii/S2590332223003007?ref=pdf_download&fr=RR-2&rr=96c1a3aebb261758

Credits

Lead Fellows

  • Jonathan Foley, Ph.D.
  • Christina Swanson, Ph.D.

Internal Reviewer

  • Sarah Gleeson, Ph.D.
Speed of Action
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Caveats
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Additional Benefits
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Risks
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Consensus
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Trade-offs
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Action Word
Deploy
Solution Title
Direct Air Capture
Classification
Not Recommended
Updated Date

Advance Artificial Upwelling

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Peatland
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Description for Social and Search
The Advance Artificial Upwelling solution is coming soon.
Solution in Action
Speed of Action
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Caveats
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Additional Benefits
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Action Word
Advance
Solution Title
Artificial Upwelling
Classification
Not Recommended
Updated Date

Deploy Ocean Fertilization

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An aerial view of the Earth with colorful plankton blooms in the ocean off the coast of a landmass
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Summary

Ocean fertilization uses nutrients to enhance photosynthesis by marine phytoplankton, which remove CO₂ and convert it into biomass that can sink to the deep ocean. This practice is a carbon removal technology that could achieve Gt-scale CO₂ removal annually. Potential advantages of ocean fertilization include localized reduction of ocean acidification and low costs. Disadvantages include high and uncertain risks of altering ecosystems both near dispersal sites and farther away, unclear but probably low effectiveness, potentially difficult operational upscaling, and challenges with monitoring and verification. We conclude that Deploy Ocean Fertilization is “Not Recommended” as a climate solution given its likely low effectiveness, technical challenges, and high environmental risks.

Description for Social and Search
Ocean fertilization uses nutrients to enhance photosynthesis by marine phytoplankton, which remove CO₂ and convert it into biomass that can sink to the deep ocean. We conclude that Deploy Ocean Fertilization is “Not Recommended” as a climate solution given its likely low effectiveness, technical challenges, and high environmental risks.
Overview

What is our assessment?

Based on the scientific uncertainties regarding its effectiveness and the potential serious environmental and social risks, we conclude that Ocean Fertilization is “Not Recommended” as a climate solution.

Plausible Could it work? Yes
Ready Is it ready? No
Evidence Are there data to evaluate it? Limited
Effective Does it consistently work? No
Impact Is it big enough to matter? Yes
Risk Is it risky or harmful? Yes
Cost Is it cheap? ?

What is it?

Ocean fertilization involves adding nutrients, such as iron, to seawater to promote photosynthesis in the surface ocean. As phytoplankton draw in seawater CO₂ and convert it into biomass, the ocean can absorb more CO₂ from the atmosphere. Some of the carbon eventually sinks or is transported to the deep sea or seafloor, where it can be stored for decades or centuries. Most ocean fertilization efforts are focused on iron because it is a micronutrient already required in small amounts for photosynthesis and because iron limitation is common in many global ocean regions. The Southern Ocean, in particular, has been highlighted as a potential target due to its widespread iron limitation.

Does it work?

As a carbon removal technique, ocean fertilization requires that the nutrient addition enhances phytoplankton uptake of seawater CO₂ and subsequent absorption of additional CO₂ from the atmosphere, and that the carbon is transported and durably stored in the deep sea. Research since the 1990s has shown that ocean iron fertilization does lead to increased seawater CO₂ uptake due to enhanced photosynthesis. However, the ultimate fate and durability of that carbon are less well understood. To be sequestered, carbon must be transported below water depths where annual mixing occurs, often considered to be ~1,000 m, but research suggests that, on average, 66% of carbon at these depths can be re-exposed to the atmosphere in less than 40 years. Ocean fertilization might also increase production of GHGs, such as nitrous oxide and methane, which could impact the effectiveness of this practice, although these effects remain understudied. In places like the Southern Ocean, sunlight and changes in the availability of other nutrients, such as silicate, can also limit the effects of iron addition. Additionally, nutrients such as iron can have high loss rates, up to 75%, after dispersal into seawater due to conversion into forms inaccessible to phytoplankton, potentially further reducing the effectiveness of nutrient addition.

Why are we excited?

If ocean fertilization were broadly deployed and functioned as intended, its global climate impact could reach 0.1–1.0 Gt CO₂ /yr. Ocean fertilization is expected to increase surface water pH, which could help temporarily reduce ocean acidification locally. However, some studies suggest this benefit will come at the cost of increased acidification of deeper ocean regions. While costs remain highly uncertain, estimates of ocean fertilization range between US$80/t CO₂ and US$457/t CO₂, suggesting this practice might also be relatively inexpensive compared to other marine CO₂ removal practices.

Why are we concerned?

Ocean fertilization poses several technical challenges, along with significant environmental and social risks. Tracking the amount of carbon sequestered from ocean fertilization is difficult because carbon export efficiencies – the amount of carbon produced in surface waters that makes its way to the deep sea – can be low and highly variable in time and space. Addressing this will require both field studies and models capable of capturing global and multi-decadal changes in carbon cycling due to fertilization, given the long time scales and large spatial areas involved. Implementing ocean fertilization at globally meaningful carbon removal levels could raise additional feasibility concerns, given the potential difficulty of dispersing sufficiently large quantities of nutrients across vast areas and the need for fertilization to be done continuously to minimize carbon returning to the atmosphere. 

Beyond these technical challenges, ocean fertilization also poses several potentially severe, environmental risks. Enhancing primary production could disrupt existing nutrient pools in the ocean, reducing the nutrients available for ecosystems far from dispersal sites. Another consequence of ocean fertilization is that increased organic carbon supply can enhance microbial processes that consume dissolved oxygen, potentially impairing respiration in marine organisms and leading to mortality. Other unintended consequences of nutrient fertilization include promoting harmful algal blooms that can release toxins that negatively impact a wide array of life, from shellfish to marine mammals to humans. Ocean fertilization also carries significant social risks, as global-scale modification of marine ecosystems is likely to create inequities in environmental and economic impacts.

Solution in Action

Aumont, O., & Bopp, L. (2006). Globalizing results from ocean in situ iron fertilization studies. Global Biogeochemical Cycles20(2). Link to source: https://doi.org/10.1029/2005GB002591

Bakker, D. C. (2004). Storage of carbon dioxide by greening of oceans. In C. B. Field & M. R. Raupach (Eds.), The global carbon cycle: Integrating humans, climate, and the natural world (pp. 453–469). Island Press.

Boettcher, M., Chai, F., Canothan, M., Cooley, S., Keller, D. P., Klinsky, S., ... & Webb, R. M. (2023). A code of conduct for marine carbon dioxide removal research. Aspen Institute. Link to source: https://www.aspeninstitute.org/publications/a-code-of-conduct-for-marine-carbon-dioxide-removal-research/

Boyd, P. W. (2008). Implications of large-scale iron fertilization of the oceans. Marine Ecology Progress Series, 364, 213–218. Link to source: https://www.int-res.com/articles/theme/m364p213.pdf

Boyd, P. W., Jickells, T., Law, C. S., Blain, S., Boyle, E. A., Buesseler, K. O., ... & Watson, A. J. (2007). Mesoscale iron enrichment experiments 1993-2005: synthesis and future directions. Science, 315(5812), 612–617. Link to source: https://doi.org/10.1126/science.1131669

Buesseler, K. O., & Boyd, P. W. (2003). Will ocean fertilization work?. Science, 300(5616), 67–68. Link to source: https://doi.org/10.1126/science.1082959

Cao, L., & Caldeira, K. (2010). Can ocean iron fertilization mitigate ocean acidification? A letter. Climatic Change99(1), 303–311. Link to source: https://link.springer.com/article/10.1007/s10584-010-9799-4

Emerson, D., Sofen, L. E., Michaud, A. B., Archer, S. D., & Twining, B. S. (2024). A cost model for ocean iron fertilization as a means of carbon dioxide removal that compares ship‐and aerial‐based delivery, and estimates verification costs. Earth's Future, 12(4), e2023EF003732. Link to source: https://doi.org/10.1029/2023EF003732

Gattuso, J. P., Williamson, P., Duarte, C. M., & Magnan, A. K. (2021). The potential for ocean-based climate action: negative emissions technologies and beyond. Frontiers in Climate, 2, 575716. Link to source: https://doi.org/10.3389/fclim.2020.575716

Harrison, D. P. (2013). A method for estimating the cost to sequester carbon dioxide by delivering iron to the ocean. International Journal of Global Warming, 5(3), 231–254. Link to source: https://doi.org/10.1504/IJGW.2013.055360

Harvey, J. (2020). 30 years: The iron hypothesis is no more. Moss Landing Marine Laboratories BlogLink to source: https://mlml.sjsu.edu/2020/06/18/30-years-the-iron-hypothesis-is-no-more/

Jin, X., & Gruber, N. (2003). Offsetting the radiative benefit of ocean iron fertilization by enhancing N2O emissions. Geophysical Research Letters, 30(24). Link to source: https://doi.org/10.1029/2003GL018458

Marinov, I., Gnanadesikan, A., Toggweiler, J. R., & Sarmiento, J. L. (2006). The southern ocean biogeochemical divide. Nature, 441(7096), 964–967. Link to source: https://doi.org/10.1038/nature04883

Martin, J. H., Gordon, M., & Fitzwater, S. E. (1991). The case for iron. Limnology and Oceanography, 36(8), 1793–1802. Link to source: https://doi.org/10.4319/lo.1991.36.8.1793

National Academies of Sciences, Engineering, and Medicine. (2021). A research strategy for ocean-based carbon dioxide removal and sequestration. National Academies Press. Link to source: https://www.nationalacademies.org/our-work/a-research-strategy-for-ocean-carbon-dioxide-removal-and-sequestration

Ocean Visions. (2023). Microalgae cultivation. Link to source: https://oceanvisions.org/microalgae-cultivation/

Oschlies, A., Koeve, W., Rickels, W., & Rehdanz, K. (2010). Side effects and accounting aspects of hypothetical large-scale Southern Ocean iron fertilization. Biogeosciences7(12), 4017–4035. Link to source: https://bg.copernicus.org/articles/7/4017/2010/bg-7-4017-2010.pdf

Oschlies, A., Slomp, C., Altieri, A. H., Gallo, N. D., Grégoire, M., Isensee, K., Levin, L. A., & Wu, J. (2025). Potential impacts of marine carbon dioxide removal on ocean oxygen. Environmental Research Letters, 20(1), 011001. Link to source: https://doi.org/10.1088/1748-9326/ade0d4

Robinson, J., Popova, E. E., Yool, A., Srokosz, M., Lampitt, R. S., & Blundell, J. R. (2014). How deep is deep enough? Ocean iron fertilization and carbon sequestration in the Southern Ocean. Geophysical Research Letters, 41(7), 2489–2495. Link to source: https://doi.org/10.1002/2013GL058799

Sarmiento, J. L., Gruber, N., Brzezinski, M. A., & Dunne, J. P. (2004). High-latitude controls of thermocline nutrients and low latitude biological productivity. Nature, 427(6969), 56–60. Link to source: https://doi.org/10.1038/nature02127

Shepherd, J. G. (2009). Geoengineering the climate: science, governance and uncertainty. The Royal Society. Link to source: https://royalsociety.org/-/media/policy/publications/2009/8693.pdf

Strong, A., Chisholm, S., Miller, C., & Cullen, J. (2009). Ocean fertilization: time to move on. Nature461(7262), 347–348. Link to source: https://doi.org/10.1038/461347a

Tagliabue, A., Aumont, O., DeAth, R., Dunne, J. P., Dutkiewicz, S., Galbraith, E., Misumi, K., Moore, J. K., Ridgwell, A., Sherman, E., Stock, C., Vichi, M., Völker, C., & Yool, A. (2016). How well do global ocean biogeochemistry models simulate dissolved iron distributions?. Global Biogeochemical Cycles, 30(2), 149–174. Link to source: https://doi.org/10.1002/2015GB005289

Tagliabue, A., Twining, B. S., Barrier, N., Maury, O., Berger, M., & Bopp, L. (2023). Ocean iron fertilization may amplify climate change pressures on marine animal biomass for limited climate benefit. Global Change Biology, 29(18), 5250–5260. Link to source: https://doi.org/10.1111/gcb.16854

Trick, C. G., Bill, B. D., Cochlan, W. P., Wells, M. L., Trainer, V. L., & Pickell, L. D. (2010). Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas. Proceedings of the National Academy of Sciences, 107(13), 5887–5892. Link to source: https://doi.org/10.1073/pnas.0910579107

Yoon, J. E., Yoo, K. C., Macdonald, A. M., Yoon, H. I., Park, K. T., Yang, E. J., Kim, H. C., Lee, J. I., Lee, M. K., Jung, J., Park, J., Lee, J., Kim, S., Kim, S. S., Kim, K., & Kim, I. N. (2018). Reviews and syntheses: Ocean iron fertilization experiments–past, present, and future looking to a future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) project. Biogeosciences, 15(19), 5847-5889. Link to source: https://doi.org/10.5194/bg-15-5847-2018

Credits

Lead Fellow

  • Christina Richardson, Ph.D.

Internal Reviewer

  • Christina Swanson, Ph.D.
Speed of Action
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Deploy
Solution Title
Ocean Fertilization
Classification
Not Recommended
Updated Date

Deploy Vertical Farms

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Summary

Vertical farms are facilities that grow crops indoors, vertically stacking multiple layers of plants and providing controlled conditions using artificial light, indoor heating and cooling systems, humidity controls, water pumps, and advanced automation systems. In theory, vertical farms could reduce the need to clear more agricultural land and the distance food travels to market. However, because vertical farms are so energy and material intensive, and food transportation emissions are a small fraction of the overall carbon footprint of food, vertical farms do not reduce emissions overall. We conclude that vertical farms are “Not Recommended” as an effective climate solution.

Description for Social and Search
Because vertical farms are so energy and material intensive, and food transportation emissions are a small fraction of the overall carbon footprint of food, vertical farms do not reduce emissions overall. We conclude that vertical farms are “Not Recommended” as an effective climate solution.
Overview

What is our assessment?

Based on our analysis, vertical farms are not an effective climate solution. The tremendous energy use and embodied emissions of vertical farm operations outweigh any potential savings of reducing food miles or land expansion. Moreover, the ability of vertical farms to truly scale to be a meaningful part of the global food system is extremely limited. We therefore classify this as “Not Recommended” as an effective climate solution.

Plausible Could it work? No
Ready Is it ready? Yes
Evidence Are there data to evaluate it? Yes
Effective Does it consistently work? No
Impact Is it big enough to matter? No
Risk Is it risky or harmful? No
Cost Is it cheap? No

What is it?

Vertical farms are facilities that grow crops indoors, with multiple layers of plants stacked on top of each other, using artificial lights, large heating and cooling systems, humidity controls, water pumps, and complex building automation systems. In principle, vertical farms can dramatically shrink the land “footprint” of agriculture, and this could help reduce the need for agricultural land. Moreover, by growing crops closer to urban centers, vertical farms could potentially reduce “food miles” and the emissions related to food transport.

Does it work? 

The technology of growing some kinds of crops – especially greens and herbs – in indoor facilities is well developed, but there is no evidence to show that doing so can reduce GHG emissions compared to growing the same food on traditional farms. Theoretically, vertical farms could reduce emissions associated with agricultural land expansion and food transportation. However, the operation and construction of vertical farms require enormous amounts of energy and materials, all of which cause significant emissions. Vertical farms require artificial lighting (even with efficient LEDs, this is a considerable energy cost), heating, cooling, humidity control, air circulation, and water pumping – all of which require energy. Vertical farms could be powered by renewable sources; however, this is an inefficient method for reducing GHG emissions compared to using that renewable energy to replace fossil-fuel-powered electricity generation. Growing food closer to urban centers also does not meaningfully reduce emissions because emissions from “food miles” are only a small fraction of the life cycle emissions for most farmed foods. Recent research has found that the carbon footprint of lettuce grown in vertical farms can be 5.6 to 16.7 times greater than that of lettuce grown with traditional methods.

Why are we excited?

While vertical farms are not an effective strategy for reducing emissions, they may have some value for climate resilience and adaptation. Vertical farms offer a protected environment for crop growth and well-managed water use, and they can potentially shield plants from pests, diseases, and natural disasters. Moreover, the controlled environment can be adjusted to adapt to changing climate conditions, helping ensure continuous production and lowering the risks of crop loss.

Why are we concerned?

Vertical farms use enormous amounts of energy and material to grow a limited array of food, all at significant cost. That energy and material have a significant carbon emissions cost, no matter how efficient the technology becomes. On the whole, vertical farms appear to emit far more GHGs than traditional farms do. Moreover, vertical farms are expensive to build and operate, and are unlikely to play a major role in the world’s food system. At present, they are mainly used to grow high-priced greens, vegetables, herbs, and cannabis, which do not address the tremendous pressure points in the global food system to feed the world sustainably. There are also concerns about the future of the vertical farming business. While early efforts were funded by venture capital, vertical farming has struggled to become profitable, putting its future in doubt.
 

Solution in Action

Blom, T. et al.., (2022). The embodied carbon emissions of lettuce production in vertical farming, greenhouse horticulture, and open-field farming in the Netherlands. Journal of Cleaner Production, 377, 134443. Link to source: https://www.sciencedirect.com/science/article/pii/S095965262204015X 

Cornell Chronicle, (2014). Indoor urban farms called wasteful, “pie in the sky.” Link to source: https://news.cornell.edu/stories/2014/02/indoor-urban-farms-called-wasteful-pie-sky

Cox, S., (2012). The vertical farming scam, Counterpunch. Link to source: https://www.counterpunch.org/2012/12/11/the-vertical-farming-scam/ 

Cox, S., (2016). Enough with the vertical farming fantasies: There are still too many unanswered questions about the trendy practice, Salon. Link to source: https://www.salon.com/2016/02/17/enough_with_the_vertical_farming_partner/ 

Foley, J.A. et al., (2011). Solutions for a cultivated planet, Nature. Link to source: http://doi.org/10.1038/nature10452

Foley, J.A., (2018). No, vertical farms won’t feed the world, Medium. Link to source: https://globalecoguy.org/no-vertical-farms-wont-feed-the-world-5313e3e961c0 

Hamm, M., (2015). The buzz around indoor farms and artificial lighting makes no sense. The Guardian. Link to source: https://www.theguardian.com/sustainable-business/2015/apr/10/indoor-farming-makes-no-economic-environmental-sense 

Peters, A., (2023). The vertical farming bubble is finally popping, Fast Company. Link to source: https://www.fastcompany.com/90824702/vertical-farming-failing-profitable-appharvest-aerofarms-bowery

Ritchie, H., (2022). Eating local is still not a good way to reduce the carbon footprint of your diet, Sustainability by the numbers. Link to source: https://www.sustainabilitybynumbers.com/p/food-miles 

Tabibi, A. (2024). Vertical farms: A tool for climate change adaptation, Green.org. January 30, 2024. Link to source: https://green.org/2024/01/30/vertical-farms-a-tool-for-climate-change-adaptation/   

Credits

Lead Author

  • Jonathan Foley, Ph.D.

Internal Reviewer

  • Christina Swanson, Ph.D.
Speed of Action
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Caveats
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Additional Benefits
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Risks
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Consensus
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Action Word
Deploy
Solution Title
Vertical Farms
Classification
Not Recommended
Updated Date

Use Corn-Based Ethanol

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Peatland
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The Use Corn-Based Ethanol solution is coming soon.
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Use
Solution Title
Corn-Based Ethanol
Classification
Not Recommended
Updated Date

Use Carbon Capture & Storage on Fossil Fuel Power Plants

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Electricity
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Power plant emissions
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Summary

Carbon capture and storage (CCS) reduces the operational GHG emissions from fossil fuel power plants by selectively capturing CO₂ from the plant’s exhaust flue, preventing it from entering the atmosphere. The captured CO₂ is then concentrated, compressed, and permanently stored underground. The carbon capture technology is effective and available, but it is expensive and energy-intensive. Globally, emissions from coal and gas power plants are still increasing, potentially making retrofitting newer plants with CCS an appealing emissions reduction strategy. However, despite 30 years of pilot and commercial projects, most power plant CCS projects have failed. While CCS can cut CO₂ emissions, large-scale deployment of this technology on fossil-fueled power plants will likely drive continued production and use of coal and gas. Based on this risk, as well as the availability of cheaper, clean energy alternatives for power generation, we conclude that using CCS on fossil fuel power plants is “Not Recommended” as a climate solution.

Description for Social and Search
Using carbon capture and storage on fossil fuel power plants is not recommended for myriad reasons, including costs and risks.
Overview

What is our assessment?

Using CCS on fossil-fueled power plants will reduce electricity production emissions, but it is more expensive, more energy-intensive, and more polluting than readily available, cheaper, and cleaner alternatives like wind, solar, and geothermal. Based on this, and the risk that large-scale deployment of CCS on fossil-fueled power plants could drive continued production and use of coal and gas, we conclude that using CCS on fossil fuel power plants is “Not Recommended” as a climate solution.

Plausible Could it work? Yes
Ready Is it ready? Yes
Evidence Are there data to evaluate it? Yes
Effective Does it consistently work? No
Impact Is it big enough to matter? Yes
Risk Is it risky or harmful? Yes
Cost Is it cheap? No

What is it?

Carbon capture and storage (CCS) is a technology that reduces GHG emissions from fossil fuel-powered electricity generation facilities by selectively capturing CO₂ from the power plant’s exhaust flue, preventing it from entering the atmosphere. The captured CO₂ is then concentrated, compressed, and permanently stored underground. There are other commercially available CCS technologies, such as pre-combustion capture and oxy-fuel combustion, but these are used almost exclusively for industrial processes like gas processing and cannot be readily retrofitted to existing power plants. CCS can also be applied to capture CO₂ from other industrial facilities that generate emissions from fuel combustion or production processes, like cement or ethanol production plants, or from biomass energy power plants. Instead of permanent storage, captured CO₂ can also be used as a chemical precursor for the manufacture of other products or for enhanced oil recovery, but, compared to geologic storage, these post-capture uses of CO₂ emit GHGs, thereby reducing or eliminating the emissions reduction efficacy of CCS. 

Does it work?

The technology and chemistry for the selective capture of CO₂ from the exhaust of a power plant are effective. There are numerous chemical, membrane, and cryogenic methods for capturing CO₂, but monoethanolamine (MEA) is the predominant commercially available chemical absorbent currently in use in power plants with CCS. CO₂ capture efficiency varies with the type of reactive absorbent material and plant operations. Most CCS installations target 90% CO₂ capture rates, although actual capture rates are usually lower. CCS infrastructure is large, and the process of capturing CO₂ from power plant exhaust is complex, expensive, and energy-intensive. CCS requires the flue gas to be pumped to different parts of the power plant, the CO₂ to be captured and then separated from the sorbent material, and the concentrated CO₂ to be compressed for transport and storage. Energy for all these processes comes from the power plant. Various studies estimate CCS consumes at least 15–25% of the plant’s total generation capacity, with most of the energy used to separate the CO₂ and regenerate the sorbent material. 

CCS has been used in pilot studies and commercial operations in a few dozen coal and natural gas power plants since the late 1990s. Despite the functional effectiveness of the technology, use of CCS to reduce power plant emissions has not been broadly adopted, and most CCS projects initiated in the past three decades have failed or been discontinued. Based on various assessments and projections, deployment of CCS on power plants has consistently lagged behind its expected contribution to emissions reduction. There are currently only four power plants with CCS in operation in the world, less than 0.05% of the global fossil fuel power plant fleet. According to a 2021 study, only 10% of proposed CCS projects for power plants have actually been implemented. Based on another study, 78% of all power plant and industrial manufacturing CCS pilot and demonstration plants with a project size greater than 0.3 Mt CO₂ /yr have been cancelled or put on hold. 

Why are we excited?

Globally, emissions from coal- and gas-fired power plants are still increasing, primarily in China and India, where large numbers of new thermal power plants have been built in the last two decades. Given the typical 30- to 45-year operational lifespan for coal and gas power plants, retrofitting these newer plants with CCS could substantially reduce their operational emissions while also allowing plant owners and investors to recover their investments. Installation of CCS to reduce emissions can also be prioritized for power plants located near places with geologic storage and where alternative electricity generation options are limited. There is a large amount of active research underway to develop and test alternative carbon capture technologies, most aimed at increasing carbon capture efficiencies and reducing energy demands and costs. Other research on the factors contributing to the failure of most CCS projects to date may lead to the development of regulations and policies that require or incentivize the use of CCS for power plants, which could increase the current low implementation and success rates for this emissions reduction technology. 

Why are we concerned? 

While CCS can reduce the operational CO₂ emissions from fossil-fueled power plants, large-scale deployment of this technology will likely drive continued production and use of coal and gas. Even before fossil fuels are burned, extraction, transport, and processing generate substantial GHG emissions, particularly for gas. Therefore, in addition to perpetuating the fossil fuel industry, even 90% efficient CCS reduces only a fraction of the life cycle emissions from coal and gas. 

Widespread deployment of CCS in the electricity sector could also delay or crowd out deployment of wind, solar, and geothermal energy, slowing the clean energy transition that is already underway. Beyond these risks, the three-decade-long failure of power plant CCS to make the transition from pilot-scale science and technology to large-scale commercial deployment reflects its systemic problems and limitations. Unlike wind and solar energy, which have seen costs decline rapidly with development and deployment, CCS on power plants shows little evidence of a learning curve. It remains very expensive and very energy-intensive. A large-scale CCS demonstration project can cost more than US$1 billion to build and, in addition to its operational costs, CCS consumes at least 15–25% of the energy that the plant could otherwise sell to customers. CCS-related energy requirements could mean that a power company would need to build an additional power plant to compensate for reduced electricity deliveries from every four of its power plants equipped with CCS. 

 

Due to these high project risks and costs, as well as the lack of regulations and policies to require or support CCS on power plants, public and private investments in the technology have been falling. Despite all this, recent research shows that the vast majority of lobbying spending for government support of CCS comes from fossil fuel interests, which have publicly stated that they view the technology as a strategy to extend society’s use of fossil fuels. Finally, in contrast to most other climate solutions that provide other benefits to natural systems or human well-being, CCS on power plants does nothing to address or alleviate the current harm from toxic air pollution produced by fossil-fueled power plants.

Solution in Action

Abdulla, A., Hanna, R., Schell, K. R., Babacan, O., & Victor, D. G. (2020). Explaining successful and failed investments in US carbon capture and storage using empirical and expert assessments. Environmental Research Letters16(1), 014036. Link to source: https://iopscience.iop.org/article/10.1088/1748-9326/abd19e?trk=public_post_comment-text

Caesary, D., Kim, H., & Nam, M. J. (2025). Cost effectiveness of carbon capture and storage based on probability estimation of social cost of carbon. Applied Energy, 377, 124542. Link to source: https://www.sciencedirect.com/science/article/abs/pii/S0306261924019251

Corcuera, E. G. T., & Petrakopoulou, F. (2025). Evaluating the impact of CO2 capture and storage on total efficiency: A lifecycle analysis. Cleaner Engineering and Technology, 101002. Evaluating the impact of CO2 capture and storage on total efficiency: A lifecycle analysis - ScienceDirect

Dabbs, B., Anchondo, C., & Marshall, C. (2023) The complete guide to CCS and the EPA power plant rule. Energywire, E&E News, May 10, 2023. The complete guide to CCS and the EPA power plant rule - E&E News by POLITICO

Drugman, D. (2023) Big Oil’s Been Secretly Validating Critics’ Concerns about Carbon Capture. DeSmog. Big Oil’s Been Secretly Validating Critics’ Concerns about Carbon Capture - DeSmog 

Durmaz, T. (2018). The economics of CCS: Why have CCS technologies not had an international breakthrough?. Renewable and Sustainable Energy Reviews95, 328-340. The economics of CCS: Why have CCS technologies not had an international breakthrough? - ScienceDirect

Gibbons, B. (2024) In Illinois, a massive taxpayer-funded carbon capture project fails to capture about 90 percent of plant’s emissions. Oil and Gas Watch, Environmental Integrity Project. Link to source: https://news.oilandgaswatch.org/post/in-illinois-a-massive-taxpayer-funded-carbon-capture-project-fails-to-capture-about-90-percent-of-plants-emissions 

Gonzales, V., Krupnick, A. and Dunlap, L. (2020) Carbon Capture and Storage 101. Resources for the Future. Link to source: https://media.rff.org/documents/CCS_101.pdf

Grubert, E., & Sawyer, F. (2023). US power sector carbon capture and storage under the Inflation Reduction Act could be costly with limited or negative abatement potential. Environmental Research: Infrastructure and Sustainability3(1), 015008. Link to source: https://iopscience.iop.org/article/10.1088/2634-4505/acbed9

Gulden, L. E., & Harvey, C. (2025). Tracing sources of funds used to lobby the US government about carbon capture, use, and storage. Environmental Science & Policy, 171, 104171. Link to source: https://www.sciencedirect.com/science/article/pii/S146290112500187X

Guo, J. X., & Huang, C. (2020). Feasible roadmap for CCS retrofit of coal-based power plants to reduce Chinese carbon emissions by 2050. Applied Energy, 259, 114112. Link to source: https://www.sciencedirect.com/science/article/abs/pii/S0306261919317994

Herzog, H. & Krol, A. (2025) Carbon Capture. MIT Climate Portal.  “Carbon Capture” Carbon Capture | MIT Climate Portal 

Herzog, H. & MIT Climate Portal Writing Team. (2024) If a fossil fuel power plant uses carbon capture and storage, what percent of the energy it makes goes to the CCS equipment? MIT Climate Portal. If a fossil fuel power plant uses carbon capture and storage, what percent of the energy it makes goes to the CCS equipment? | MIT Climate Portal

Hiar. C. (2023) Oil companies want to remove carbon from the air — using taxpayer dollars. Climatewire, E&E News, July, 13, 2023. Oil companies want to remove carbon from the air — using taxpayer dollars - E&E News by POLITICO

International Energy Agency (2020) The role of CCUS in low-carbon power systemsThe role of CCUS in low-carbon power systems. subsection How carbon capture technologies support the power transition – The role of CCUS in low-carbon power systems – Analysis - IEA

International Energy Agency (2023). Emissions from Oil and Gas Operations in Net Zero Transitions: A World Energy Outlook Special Report on the Oil and Gas Industry and COP28. Link to source: https://iea.blob.core.windows.net/assets/2f65984e-73ee-40ba-a4d5-bb2e2c94cecb/EmissionsfromOilandGasOperationinNetZeroTransitions.pdf

International Energy Agency (2025) Global Energy Review 2025: CO2 EmissionsCO2 Emissions – Global Energy Review 2025 – Analysis - IEA

Jacobson, M. Z., Fu, D., Sambor, D. J., & Muhlbauer, A. (2025). Energy, health, and climate costs of carbon-capture and direct-air-capture versus 100%-wind-water-solar climate policies in 149 countries. Environmental Science & Technology59(6), 3034-3045. Energy, Health, and Climate Costs of Carbon-Capture and Direct-Air-Capture versus 100%-Wind-Water-Solar Climate Policies in 149 Countries | Environmental Science & Technology 

Jacobson, M. Z. (2019). The health and climate impacts of carbon capture and direct air capture. Energy & Environmental Science12(12), 3567-3574. The health and climate impacts of carbon capture and direct air capture

Liu, S., Li, H., Zhang, K., & Lau, H. C. (2022). Techno-economic analysis of using carbon capture and storage (CCS) in decarbonizing China's coal-fired power plants. Journal of Cleaner Production351, 131384. Techno-economic analysis of using carbon capture and storage (CCS) in decarbonizing China's coal-fired power plants - ScienceDirect

Loria, P., & Bright, M. B. (2021). Lessons captured from 50 years of CCS projects. The Electricity Journal, 34(7), 106998. Link to source: https://www.sciencedirect.com/science/article/abs/pii/S1040619021000890

Ma, J., Li, L., Wang, H., Du, Y., Ma, J., Zhang, X., & Wang, Z. (2022). Carbon capture and storage: history and the road ahead. Engineering14, 33-43. Carbon Capture and Storage: History and the Road Ahead - ScienceDirect

Mackler, S., Fishman, X., & Broberg, D. (2021). A policy agenda for gigaton-scale carbon management. The Electricity Journal34(7), 106999. A policy agenda for gigaton-scale carbon management - ScienceDirect

National Energy Technology Laboratory. (2018). Carbon Capture and Storage Database (Washington, DC: U.S. Department of Energy). Link to source: https://netl.doe.gov/carbon-management/carbon-storage/worldwide-ccs-database

Osman, A. I., Hefny, M., Abdel Maksoud, M. I. A., Elgarahy, A. M., & Rooney, D. W. (2021). Recent advances in carbon capture storage and utilisation technologies: a review. Environmental Chemistry Letters19(2), 797-849. Recent advances in carbon capture storage and utilisation technologies: a review

Patel, S. (2024) Capturing Progress: The State of CCS in the Power Sector. POWER Magazine. Link to source: https://www.powermag.com/capturing-progress-the-state-of-ccs-in-the-power-sector/

Peridas, G., & Schmidt, B. M. (2021). The role of carbon capture and storage in the race to carbon neutrality. The Electricity Journal, 34(7), 106996. Link to source: https://www.sciencedirect.com/science/article/pii/S1040619021000877

Rathi, A. K. A., & Rathi, J. A. (2025). CO2 capture: a concise, comprehensive overview of recent research trends. Academia Environmental Sciences and Sustainability2(2). Rathi and Rathi 2025 CO2_capture_a_concise_comprehensive_overview.pdf

Scott, M. & Slavin, T. (2023)  Fossil-fuel industry embrace raises alarm bells over direct air capture. Reuters, October 10, 2023. Fossil-fuel industry embrace raises alarm bells over direct air capture | Reuters

Singh, S. P., Ku, A. Y., Macdowell, N., & Cao, C. (2022). Profitability and the use of flexible CO2 capture and storage (CCS) in the transition to decarbonized electricity systems. International Journal of Greenhouse Gas Control120, 103767. Profitability and the use of flexible CO2 capture and storage (CCS) in the transition to decarbonized electricity systems - ScienceDirect

Stephens, J. C. (2014). Time to stop investing in carbon capture and storage and reduce government subsidies of fossil‐fuels. Wiley Interdisciplinary Reviews: Climate Change5(2), 169-173. Time to stop investing in carbon capture and storage and reduce government subsidies of fossil‐fuels - Stephens - 2014 - WIREs Climate Change - Wiley Online Library

Wang, N., Akimoto, K., & Nemet, G. F. (2021). What went wrong? Learning from three decades of carbon capture, utilization and sequestration (CCUS) pilot and demonstration projects. Energy Policy158, 112546. What went wrong? Learning from three decades of carbon capture, utilization and sequestration (CCUS) pilot and demonstration projects - ScienceDirect

Credits

Lead Fellow

  • Christina Swanson, Ph.D.

Internal Reviewers

  • Sarah Gleeson, Ph.D.
Speed of Action
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Caveats
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Additional Benefits
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Risks
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Consensus
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Trade-offs
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Action Word
Use
Solution Title
Carbon Capture & Storage on Fossil Fuel Power Plants
Classification
Not Recommended
Updated Date
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