Introduction

Capturing atmospheric carbon dioxide is a strategic priority for slowing the warming of the planet. Photosynthetic organisms naturally capture atmospheric carbon dioxide (CO₂) and, with engineering biology, could potentially become efficient enough at removing CO₂ to slow global warming. Annually, atmospheric carbon dioxide falls during the summer months of the northern hemisphere when most of the landmass on the planet experiences the warmer days and longer sunlight that contribute to photosynthetic biomass growth. Unfortunately, this natural carbon removal process is insufficient to stop the overall rise of atmospheric carbon dioxide.

Engineering plants or other photosynthetic organisms to capture more atmospheric carbon has been suggested as an approach to lower or prevent the rise of atmospheric carbon. One element of such an approach could be to leverage the vastness of Earth’s oceans to capture more atmospheric carbon with marine photosynthetic organisms, for example by distributing engineered algae with increased CO₂ capture capabilities in coastal waters. However, a study by the National Academies of Science, Engineering, and Medicine found that if 63% of global coastlines were used to grow 100-meter-wide belts of seaweed for this purpose, it would still only capture 0.1 gigatons of carbon dioxide each year.¹National Academies of Sciences, Engineering, and Medicine. (2022). A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. View Publication. Engineered algae could potentially improve this trade-off, with less coastline required for more carbon dioxide capture. Assuming that engineering could make this strategy more feasible, high-efficiency carbon capturing algae would still very likely require growth around vast stretches of coastline where a large suite of biotic and abiotic factors could impact or be impacted by its presence. For example, the biomass and excess carbon of the engineered algae could impact marine food webs, including local seafood industries. Alternatively, some scientists are pursuing kelp growth on biodegradable rafts further out in the ocean. This would preserve valued coastlines and increase the likelihood of kelp sinking to leave its carbon on the ocean floor as opposed to washing up on beaches. Furthermore, because oceans are turbulent environments through which biomass can readily be moved, engineered algae is likely to spread beyond the areas where it is seeded or initially anchored, which could have impacts on geopolitical relationships.

Nontechnical considerations and social dimensions

Solutions landscape:

• Ethical / societal – If there is high uncertainty as to the ecosystem impacts of the release of engineered algae, should technologies with similar potential impact but more certain outcomes be preferenced (in terms of funding, research time)?
• Ethical / societal – How does this solution compare to other marine-based solutions like ocean fertilization or ocean alkalinity enhancement?¹

Feasibility:

• Ethical / societal – What scale (algae biomass, area and depth of the ocean) would be required for impact? Can open-air carbon capture systems (as opposed to point-source carbon capture) be sufficiently efficient?
  • Can contained test environments be created and/or used that accurately predict impact on an environmental scale?
• Economic – Would the algae need to be biomanufactured? Or would small quantities successfully grow to relevant scale in situ? In either case, how would it be distributed?
• Economic – Who would pay for the production, distribution, maintenance, monitoring, etc., of engineered algae, especially considering the global movement of ocean water and its inhabitants.
  • What is the economic value of environmental carbon sequestration?

Benefits and consequences:

• Ethical / societal – How would coastal ecosystems be affected?
  • How do those effects compare to the impacts of higher atmospheric carbon levels if the technology is not used?
• Ethical / societal – Can engineered algae be used at a density that significantly lowers atmospheric carbon without compromising local ecosystems?
• Security, Policy / regulatory – How might the larger ocean ecosystem be impacted?

Implementation:

• Policy / regulatory – What existing policy and regulatory frameworks might impact the use of this technology?
  • Which treaties/international agreements would govern this release? What precedents exist for considering how the actions of one country impact the air, water, and/or organisms in another (e.g., nuclear power plants near international borders, dam construction on rivers that flow into other countries, genetically engineered mosquitos).
• Policy / regulatory – Are regulators aware of and considering their regulatory approach to using engineered organisms in the ocean?
• Policy / regulatory, Ethical / societal – Do relevant regulatory bodies require proof of safety? Or require that certain tests and experiments do not show evidence of harm?

Micro-level impacts:

• Economic – How would the use of engineered coastal algae for carbon capture impact coastal economic activities such as fishing and tourism?
• Ethical / societal – How would the algae affect the relationship of coast communities with the ocean?

Macro-level impacts:

• Ethical / societal – How could engineered algae alter the balance of marine food webs? What positive or negative effects could that have?
  • Could concerns about human health – regardless of the legitimacy of those concerns – ultimately lower global seafood consumption?
• Security, Policy / regulatory – Could the spread of engineered algae into the ocean food web and ecosystems foment international conflict based on real or perceived damages?

Competing values and priorities:

• Ethical / societal – If coastal engineered algae could capture significant atmospheric carbon, but would also cause ecological changes and/or economic damage to tourism communities, would it be worth it? How can all interests be represented and incorporated into decision-making and benefits-sharing?

Footnotes

1. National Academies of Sciences, Engineering, and Medicine. (2022). A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278