[GWSG] New National Academies report on carbon sequestration

[Tilley, Al]

The National Academies Press has just published a report, A Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration. You may obtain a free PDF of the 301-page report by registering with the press at https://www.nap.edu/catalog/26278/a-research-strategy-for-ocean-based-carbon-dioxide-removal-and-sequestration

Because the report may be of interest to list members and is unlikely to be treated in detail in online accounts, I am supplying more than the usual information here.

The twelve members of the drafting committee were drawn from a variety of fields appropriate to their task, which was to assess ocean-based sequestration strategies for practicality as well as efficacy. In 2015 the Academies published a report Climate Intervention: Carbon Dioxide Remove and Reliable Sequestration,  which led to their 2019 study Negative Emissions Technologies and Reliable Sequestration: A Research Agenda, dealing with terrestrial technologies. The current report is meant to complete the base for proceeding toward implementation of proper strategies.

Six technologies are discussed: nutrient fertilization, artificial upwelling and downwelling, seaweed cultivation, recovery of marine ecosystems, ocean alkalinity enhancement, and electrochemical engineering. The six are discussed in terms of our knowledge base for pursuing them, their efficacy, their durability (that is, how long their effects will last), their scalability, and their environmental risk. Two of the technologies emerge as showing special promise: ocean nutrient fertilization and seaweed cultivation. The other four should also be pursued until their potential is more fully weighed but look weaker at this point.

Nutrient fertilization adds such nutrients as iron, phosphorus, and nitrogen to the surface to promote growth of phytoplankton. When they die, they can take their embodied carbon to deep waters where it will remain sequestered for a century or more. How efficiently the technique works, and the amounts of carbon stored for long periods, remains something of a question. The technology promises to be cheap but difficult to assess. Its undesirable side-effects are uncertain.

Seaweed cultivation involves growing algae such as kelp close to the surface on frames and towing it to deep water where it is cut free to sink, taking its embodied carbon to the bottom where it can lie for centuries. The farms would have to be quite large. Availability of necessary nutrients and their removal from coastal systems may be a problem, and the length of sequestration can be uncertain even in deep water. (Much of the discussion involves sequestration in shallower waters, which is more short term and more uncertain.)

The carbon sequestration of ecosystem recovery is likely to be a welcome side-effect rather than a motivating target. It may be difficult to predict the degree and durability of the effects, though as time goes on we ought to be restoring ecosystems anyway and their additional effect of lowering carbon in the water will become increasingly significant as the big guns of sequestration are allowed to fall silent.

Artificial upwelling and downwelling is more apt to be used in support of aquaculture and ecosystem recovery than as a technology on its own, though it, along with the others, may see independent development.

Ocean alkalinity enhancement and electrochemical processes involve altering the pH of seawater to remove carbon or to lead it to pull more into solution. We are not so far along in our knowledge of these as we are of the others, though they could have high potential once we come to understand them better.

I found it exciting to see us moving toward implementation of effective ways to remove carbon from our atmosphere and our oceans. We have been talking about these possibilities for years, and now we can see the practices themselves taking shape. The report provides estimated research budgets and an outline for a package of projects in the coming decade. We have much to learn, and much to do.

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