A new report from the National Academies of Sciences, Engineering, and Medicine suggests that the United States should invest heavily in research into how oceans could be artificially harnassed to remove carbon dioxide from the air. 

Scientists are increasingly agreeing that lowering carbon emissions alone may not be enough to stabilize the climate and that technologies to actively extract carbon from the atmosphere may be required.

The new report builds on a 2019 National Academies study that found that, in addition to reducing emissions, the world's nations would need to remove roughly 10 billion tons of CO2 from the air every year by 2050 to meet internationally agreed-upon climate goals—nearly a quarter of current annual emissions.

While certain land-based techniques, such as storing carbon in agricultural soil or altering forest management, may be ready for implementation now, the authors claim that little is understood about the risks, benefits, and trade-offs of ocean-based strategies.

According to the report, the study should begin now and continue for the next ten years.

How could the project be approached? 

Some prospective methods could include cultivating seaweed on vast scales, manipulating seawater nutrients, or even passing electrical currents through the water.

Nutrient fertilization

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This would entail introducing nutrients to the ocean surface, such as phosphorus or nitrogen, to boost phytoplankton photosynthesis. Because a portion of phytoplankton sinks when it dies, this would boost carbon transport to the deep ocean, where it can last a century or longer. According to the analysis, there is a medium to a high likelihood that this technique would be effective and scalable, with medium environmental hazards and minimal scale-up costs beyond environmental monitoring expenditures.

The report estimates $290 million would be needed for research, including field experiments and tracking the amount of carbon sequestered as a result.

Seaweed cultivation  

According to the analysis, large-scale seaweed farming that carries carbon to the deep ocean or into sediments would remove CO2 from the atmosphere with medium effectiveness and medium to high durability. However, there would be moderate to severe environmental dangers.

The report estimates $130 million would be needed for research to understand technologies for efficient large-scale farming and harvesting, the long-term fates of seaweed biomass, and the environmental impacts.

Ecosystem recovery

Protecting and rebuilding coastal habitats, as well as the subsequent reintroduction of fish, whales, and other marine organisms could help with carbon sequestration. It offered the lowest environmental risks of all the choices assessed, as well as significant co-benefits, according to the scientists. It has a low to medium efficacy, according to the analysis.

It estimates $220 million would be needed for research, including the study on effects of macroalgae, marine animals, and marine protected areas.

Ocean alkalinity enhancement

This method involves chemically altering ocean water to improve alkalinity and hence boost reactions that absorb CO2 from the atmosphere. According to the report, there is a high level of confidence in its efficacy. Enhancing ocean alkalinity poses moderate environmental concerns and has medium to high scale-up costs.

The report estimates $125 million to $200 million would be needed for research, including field and laboratory experiments to explore the impact on marine organisms.

Electrochemical processes

Passing an electric current through water could either increase the acidity of seawater, allowing it to release CO2, or increase its alkalinity, allowing it to retain it more effectively. Its efficacy has a high level of confidence, and its scalability has a medium to a high level of confidence. This strategy, on the other hand, has the largest scale-up cost of any of the approaches evaluated, as well as medium to severe environmental risks.

The report estimates $350 million required for research, including for demonstration projects and the development and assessment of the improved materials that would be needed.

Artificial upwelling and downwelling

Upwelling brings cooler, nutrient, and CO2-rich deep water to the surface, promoting phytoplankton growth. Surface water and carbon are transported to the deep ocean by downwelling. According to the paper, there is little trust in the efficacy and scalability of these systems, and they come with medium to high environmental hazards, as well as high prices and carbon accounting issues.

The report estimates $25 million would be needed for research, such as technological readiness and limited and controlled ocean trials.