Last month, I led the inaugural Climate @ Work Employee Training, a new workshop by Project Drawdown designed to help non-sustainability employees understand the role of businesses – and most importantly, their employees – in scaling climate action.
Improving aquaculture involves reducing CO₂ and other GHG emissions during the production of farmed fish and other aquatic animals through better feed efficiency and the decarbonization of on-farm energy use. Advantages include reduced demand for feedstocks produced from both wild capture fisheries and terrestrial sources, which benefits marine and terrestrial ecosystems. Disadvantages include the costs of transitioning to fossil-free energy sources. While these interventions are unlikely to lead to globally meaningful emissions reductions (>0.1 Gt CO₂‑eq/yr ), we consider Improve Aquaculture as “Worthwhile” given the rapid and ongoing expansion of the industry, its potential to replace higher-emission protein sources, and the ecosystem benefits of reducing feedstock demand.
While Improve Aquaculture is unlikely to have a major climate impact, our assessment concludes that it is “Worthwhile” due to its ability to reduce pressure on wild fish stocks and terrestrial biomass, and because efficiency improvements made now are likely to scale into greater climate impact as the sector continues to expand.
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | Yes |
| Impact | Is it big enough to matter? | No |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | ? |
GHG emissions from aquaculture can be reduced by increasing the feed conversion efficiency of the cultured animals and decarbonizing on-farm energy use. Aquaculture – farming aquatic animals or plants for food or other purposes – is rapidly growing and now accounts for over half of the global production of aquatic animals, exceeding wild capture fisheries. Over 7% of human-consumed protein is aquaculture-produced. As this sector has grown, it has become increasingly reliant on external feed sources, with the share of non-fed aquaculture (e.g., bivalves that feed from the water column) dropping from nearly 40% in 2000 to 27% in 2022. Improving feed conversion ratios (FCR) – the amount of feed it takes to produce a given amount of biomass – can lower feed demand and reduce CO₂ and other GHG emissions tied to feed production and transport. FCRs can be improved by feed formulations that increase digestibility, genetic or breeding modifications to improve digestive efficiency in the cultured animal, species-specific feed formulations, and optimizing ration size and feeding frequency. At the same time, decarbonizing on-farm energy use can help reduce CO₂ emissions from common equipment, such as aerators and water pumps.
Interventions to improve feed and energy efficiency can reduce CO₂ emissions from aquaculture operations, although the potential achievable climate impact of these actions is currently unlikely to be globally meaningful (>0.1 Gt CO₂‑eq/yr ). Total annual emissions from aquaculture were estimated to be 0.26 Gt CO₂‑eq/yr in 2017, with nearly 60% of that attributed to feed production. Improving FCR is both plausible and effective, since it directly reduces the amount of food needed to cultivate fish and other species, thereby lowering emissions tied to feed production and transport. Between 1995 and 2007, improvements in FCR have ranged between 5 to 15% for a variety of species, including shrimp, salmon, carp, and tilapia.
Decarbonizing on-farm energy use can reduce equipment-related emissions, particularly in intensive systems that use energy for automated feeding systems, water temperature control, and circulation and aeration systems. In general, the potential impact of decarbonizing varies widely because on-farm energy use differs significantly across species and production systems. For instance, shrimp and prawn farming use nearly 20,000 MJ/t of live weight (LW), with over 75% from electricity, while bivalve production uses around 3,000 MJ/t of LW supplied largely by diesel.
Improving feed efficiency in aquaculture reduces demand for captured wild fish used in feed, reducing pressure on overfished stocks. It also lowers reliance on terrestrial biomass, such as soy, wheat, and rice, which come with additional land-use and emission costs. More efficient feeding can help reduce nutrient pollution, which can be responsible for high methane and nitrous oxide fluxes in some inland aquaculture systems. At the same time, decarbonizing on-farm energy use might ultimately lead to lower long-term operating costs and improved energy reliability.
There are relatively few drawbacks associated with improving aquaculture. In the case of decarbonizing on-farm energy use, upfront costs could be high. For instance, installing solar panels or upgrading pumps can be financially challenging for small-scale operations. Energy use on farms can also vary throughout the day and night, which might not always align with renewable energy sources, like solar, without storage.
Badiola, M., Basurko, O. C., Piedrahita, R., Hundley, P., & Mendiola, D. (2018). Energy use in recirculating aquaculture systems (RAS): a review. Aquacultural Engineering, 81, 57-70. Link to source: https://doi.org/10.1016/j.aquaeng.2018.03.003
Boyd, C. E., McNevin, A. A., & Davis, R. P. (2022). The contribution of fisheries and aquaculture to the global protein supply. Food Security, 14(3), 805-827. Link to source: https://doi.org/10.1007/s12571-021-01246-9
Food and Agriculture Organization of the United Nations. (2018). The state of world fisheries and aquaculture. Food and Agriculture Organization of the United Nations. Link to source: https://openknowledge.fao.org/handle/20.500.14283/i9540en
Food and Agriculture Organization of the United Nations. (2024). The State of World Fisheries and Aquaculture 2024 – Blue Transformation in action. Food and Agriculture Organization of the United Nations. Link to source: https://openknowledge.fao.org/handle/20.500.14283/cd0683en
Henriksson, P. J. G., Troell, M., Banks, L. K., Belton, B., Beveridge, M. C. M., Klinger, D. H., ... & Tran, N. (2021). Interventions for improving the productivity and environmental performance of global aquaculture for future food security. One Earth, 4(9), 1220-1232. Link to source: https://doi.org/10.1016/j.oneear.2021.08.009
Jones, A. R., Alleway, H. K., McAfee, D., Reis-Santos, P., Theuerkauf, S. J., & Jones, R. C. (2022). Climate-friendly seafood: the potential for emissions reduction and carbon capture in marine aquaculture. BioScience, 72(2), 123-143. Link to source: https://doi.org/10.1093/biosci/biab126
MacLeod, M. J., Hasan, M. R., Robb, D. H., & Mamun-Ur-Rashid, M. (2020). Quantifying greenhouse gas emissions from global aquaculture. Scientific Reports, 10(1), 11679. Link to source: https://doi.org/10.1038/s41598-020-68231-8
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Naylor, R. L., Hardy, R. W., Buschmann, A. H., Bush, S. R., Cao, L., Klinger, D. H., ... & Troell, M. (2021). A 20-year retrospective review of global aquaculture. Nature, 591(7851), 551-563. Link to source: https://doi.org/10.1038/s41586-021-03308-6
Scroggins, R. E., Fry, J. P., Brown, M. T., Neff, R. A., Asche, F., Anderson, J. L., & Love, D. C. (2022). Renewable energy in fisheries and aquaculture: Case studies from the United States. Journal of Cleaner Production, 376, 134153. Link to source: https://doi.org/10.1016/j.jclepro.2022.134153
Shen, L., Wu, L., Wei, W., Yang, Y., MacLeod, M. J., Lin, J., ... & Zhuang, M. (2024). Marine aquaculture can deliver 40% lower carbon footprints than freshwater aquaculture based on feed, energy and biogeochemical cycles. Nature Food, 5(7), 615-624. Link to source: https://doi.org/10.1038/s43016-024-01004-y
Stentiford, G. D., Bateman, I. J., Hinchliffe, S. J., Bass, D. 1., Hartnell, R., Santos, E. M., ... & Tyler, C. R. (2020). Sustainable aquaculture through the One Health lens. Nature Food, 1(8), 468-474. Link to source: https://doi.org/10.1038/s43016-020-0127-5
Tacon, A. G., & Metian, M. (2008). Global overview on the use of fish meal and fish oil in industrially compounded aquafeeds: Trends and future prospects. Aquaculture, 285(1-4), 146-158. Link to source: https://doi.org/10.1016/j.aquaculture.2008.08.015
Vo, T. T. E., Ko, H., Huh, J. H., & Park, N. (2021). Overview of solar energy for aquaculture: The potential and future trends. Energies, 14(21), 6923. Link to source: https://doi.org/10.3390/en14216923
Zhang, Z., Liu, H., Jin, J., Zhu, X., Han, D., & Xie, S. (2024). Towards a low-carbon footprint: Current status and prospects for aquaculture. Water Biology and Security, 3(4), 100290. Link to source: https://doi.org/10.1016/j.watbs.2024.100290
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.
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? | ? |
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.
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.
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.
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.
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
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In a study published today in Nature Geoscience, an international team of researchers from the University of Minnesota, Project Drawdown, and several other institutions elucidate and quantify a worrying climate feedback loop in which global warming hampers crop efficiency, leading to more land use for comparable amounts of food, which then releases yet more greenhouse gas emissions.
Food and agriculture account for around one-quarter of global greenhouse gas emissions, primarily due to land use. Meanwhile, millions of people around the world live without enough to eat. To feed the planet without destroying it will require remarkable efficiency – growing as much food as possible on as little land as possible. Unfortunately, as the planet warms, global food systems seem to be getting less efficient.
“Agricultural efficiency is the invisible lever that determines how much land we need to feed the world,” says University of Minnesota research scientist Jessica Till, Ph.D., who co-led the study. “Our study shows that improvements in agricultural efficiency can be a powerful buffer against cropland expansion. But climate change is eroding that buffer, partially reversing the progress that made modern agriculture more sustainable.”
Across the 110 countries analyzed for the study, the researchers found that croplands have expanded by 3.9% over the last three decades. Absent climate change, however, total croplands could have actually shrunk by roughly 2% while maintaining current production levels, as improved farming practices led to greater efficiency.
This reduced land use and increased efficiency would have spared 88 million hectares – twice the size of California – from being cleared for agriculture worldwide. It would have also prevented 22 gigatons of CO₂ from entering the atmosphere, enough to offset the annual emissions from more than five billion fossil-fueled cars.
“When climate change slows productivity gains, it pushes more land into cultivation, often at the expense of forests and carbon-rich ecosystems,” says study author and University of Minnesota Associate Professor Zhenong Jin, Ph.D. “Clearing land for cultivation changes the local temperature and rainfall patterns, and also releases carbon, which worsens climate change, creating a runaway feedback loop.”
To uncover their findings, the researchers applied two models: one looking at how temperature changes between 1992 and 2020 have impacted total factor productivity (TFP), a measure of farming efficiency that compares inputs to outputs, and another that estimates TFP over the same timeframe, but without human-caused warming. They then incorporated land-use responses to international trade patterns to determine how much less land would have been used due to greater efficiency, and finally, how much emissions would have been reduced through undisturbed biomass and soil carbon if that land was still covered with natural vegetation.
Although this feedback loop is likely to continue as long as planet-warming greenhouse gas emissions continue to pollute the atmosphere, the researchers say that solutions in the food and agriculture sectors can help intervene.
“Climate change is hurting farmland productivity, and emissions from clearing natural ecosystems exacerbate that problem,” says study co-author and Project Drawdown Senior Scientist Paul West, Ph.D. “Fortunately, we have everything we need to break out of this downward spiral. By changing our diets, preventing food waste, and improving farming practices, we can start to reduce the demand for land that’s feeding this destructive feedback loop.”
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Project Drawdown is the world’s leading resource for climate solutions. By advancing science-based climate solutions, fostering bold climate leadership, and promoting new narratives and voices, we are helping the world stop climate change as quickly, safely, and equitably as possible. A 501(c)(3) nonprofit organization, Project Drawdown is funded by individual and institutional donations.
Farmers require 88 million hectares more land to grow current levels of food than they would have absent global warming