Seaweed Carbon Credits - Should Or Shouldn’t We?

Currently, to my knowledge, there are two seaweed carbon credits available: both for restoring wild seaweed forests, one run by the Japanese initiative ‘J Blue’ and one in Western Australia run by Canopy Blue (https://canopyblue.co/purchase-kelp-reforestation-credits/). The project in Western Australia uses conservative carbon accounting to estimate carbon removal by seaweed restoration. However, buyers of this carbon credit effectively buy two carbon credits as they must buy another internationally verified carbon credit alongside their seaweed carbon credit which is used for their reporting obligation. However, this is a more expensive approach to carbon crediting for the buyer, which means that the seaweed restoration project does not have to go through international project verification. The J-Blue project in Japan has yet to be approved by other global standards and the methodology remains in Japanese. To my knowledge, there are now over 30 sites where carbon credits are being issued for seaweed restoration in Japan. In countries like New Zealand, where traditional blue carbon (mangroves, saltmarshes and seagrasses) opportunities are limited in scale compared to seaweed restoration, they may look to take similarly pragmatic paths to finance seaweed restoration as Japan. Currently, there are also two carbon credit methodology proposals being assessed by the carbon standard Verra: one for carbon sequestration from seaweed farming (https://verra.org/methodologies/methodology-for-carbon-removals-through-seaweed-aquaculture/) and another one for seaweed restoration (not publicly available yet). 

In the context of the four routes seaweed can potentially contribute to carbon sequestration I found that the only immediately feasible global standardised methodology for carbon credits from seaweed currently is for carbon sequestered in sediment below seaweed farms. However, the maximum current sequestration annually globally for seaweed farming is approximately 3.2 Mt/CO2/yr. The potential costs for administering such a methodology for carbon crediting may be significant in comparison to the scale of opportunity.

Current carbon credit methodology standards require rigorous carbon accounting due to recent controversies in the international carbon market. Validating an international carbon methodology can, in most cases, take several years and incur significant costs. There are often portions of funds when carbon credits are purchased that go towards administration and verification for carbon credits. Due to the many challenges with seaweed carbon accounting (measuring how much seaweed gets to the deep sea, testing nutrient competition with phytoplankton, etc seaweed carbon credits may take more work to implement with existing global standards. In addition, the principle of ‘additionality’ will be difficult to determine for seaweed farming projects. This is where projects must show that the carbon would not have otherwise been sequestered if the project had not gone ahead. However, suppose a more pragmatic approach is taken in a similar way to the two existing seaweed carbon credit methods implemented in Western Australia and Japan. In that case, carbon credits for seaweed aquaculture and seaweed restoration may be possible.

Another way to recognise carbon removal from seaweed aquaculture is through insetting. This is where companies purchasing seaweed products pay a premium for their products because they can claim the carbon sequestered in their supply chain in their company emissions budget. Importantly, robust traceability of seaweed products is required for this. Using insetting, the carbon removal can be quantified, sold and transformed into tradable products, without having to complete the same administrative processes to register carbon credits. Insetting is currently enabled through existing globally recognised standards such as ISO 14064:1. However, some risks to insetting exist around guaranteeing double counting of carbon sequestration and permanence of carbon sequestration. Currently, seaweed is largely a low-value commodity crop which limits its scalability and potential to support developing communities and positively impact the environment. This is partly because there currently needs to be more traceability in the seaweed industry. Suppose improved seaweed traceability is able to occur concurrently with financial recognition of the co-benefits of seaweed production, for example carbon credits or insetting. In that case, seaweed farmers will be able to unlock an additional income source which could expand seaweed farming.  

Another approach to recognise carbon sequestration from seaweed is to reward seaweed restoration based on the carbon stored in the standing stock of seaweed (Qu et al. 2023). While guaranteeing long-term permanence for the standing stock is a challenge, permanence can be protected with buffer and insurance schemes. Such a framework would increase kelp restoration finance and avoid challenges around measuring seaweed carbon export. One disadvantage of this approach would be that the project would be only able to receive credits once, as once the seaweed forest and standing stock are restored there are no more carbon credits received. 

Ultimately, for seaweed carbon crediting projects, it is important that the majority of funding from carbon credit revenue be channelled towards restoring seaweed forests and supporting communities that are farming seaweed. Seaweed projects must balance pragmatism and integrity in their methodology to be successful, using conservative carbon accounting. It remains to be seen if the global markets for carbon credits will accept the unique challenges and complexity of seaweed carbon credit accounting.