Quantifying baseline costs and cataloging potential optimization strategies for kelp aquaculture carbon dioxide removal

Abstract

To keep global surface warming below 1.5°C by 2100, the portfolio of cost-effective CDR technologies must expand. To evaluate the potential of macroalgae CDR, we developed a kelp aquaculture bio-techno-economic model in which large quantities of kelp would be farmed at an offshore site, transported to a deep water “sink site”, and then deposited below the sequestration horizon (1,000 m). We estimated the costs and associated emissions of nursery production, permitting, farm construction, ocean cultivation, biomass transport, and Monitoring, Reporting, and Verification (MRV) for a 1,000 acre (405 ha) “baseline” project located in the Gulf of Maine, USA. The baseline kelp CDR model applies current systems of kelp cultivation to deep water (100 m) exposed sites using best available modeling methods. We calculated the levelized unit costs of CO2eq sequestration (LCOC; $ tCO2eq-1). Under baseline assumptions, LCOC was $17,048 tCO2eq-1. Despite annually sequestering 628 tCO2eq within kelp biomass at the sink site, the project was only able to net 244 C credits (tCO2eq) each year, a true sequestration “additionality” rate (AR) of 39% (i.e., the ratio of net C credits produced to gross C sequestered within kelp biomass). As a result of optimizing 18 key parameters for which we identified a range within the literature, LCOC fell to $1,257 tCO2eq-1 and AR increased to 91%, demonstrating that substantial cost reductions could be achieved through process improvement and decarbonization of production supply chains. Kelp CDR may be limited by high production costs and energy intensive operations, as well as MRV uncertainty. To resolve these challenges, R&D must (1) de-risk farm designs that maximize lease space, (2) automate the seeding and harvest processes, (3) leverage selective breeding to increase yields, (4) assess the cost-benefit of gametophyte nursery culture as both a platform for selective breeding and driver of operating cost reductions, (5) decarbonize equipment supply chains, energy usage, and ocean cultivation by sourcing electricity from renewables and employing low GHG impact materials with long lifespans, and (6) develop low-cost and accurate MRV techniques for ocean-based CDR.

Seaweed afforestation at large-scales exclusively for carbon sequestration: Critical assessment of risks, viability and the state of knowledge

“…Recently Coleman et al (2022) provided the first detailed published estimates on the costs of a potential ocean afforestation via a bio-techno-economic model. They found that there would be a cost of $17,048 tCO 2 eq -1 , but by optimising parameters on ocean afforestation this could be reduced to $1,257 tCO 2 eq -1 .…”

“…boat fuel emissions and construction of aquaculture infrastructure) of the operation of any ocean afforestation project should be subtracted from any potential carbon sequestration via ocean afforestation (Coleman et al, 2022). Coleman et al (2022) calculated that potential CO 2 sequestration was reduced from 638 tons to 244 tons of net emissions once operational emissions were subtracted and that did not include boat emissions to transport to the sink site [Figure 5 in Coleman et al (2022)]. This suggests operational emissions may be considerable for some types of ocean afforestation operations.…”

“…Several studies have considered seaweed cultivation in the context of geoengineering (Aldridge et al, 2012;Chung et al, 2017;Wood et al, 2017), and a small but increasing number of papers have mentioned the possibility of new seaweed-based carbon capture and storage projects, or ocean afforestation, as they relate to the sale of carbon credits (Chung et al, 2013;N'Yeurt et al, 2012;Chung et al, 2017;Sondak et al, 2017;Coleman et al, 2022;Troell et al, 2022). Several businesses have recently proposed ocean afforestation as a carbon sequestration strategy (eg.…”

An Estimate of Carbon Storage Capabilities from Wild and Cultured Shellfish in the Northwest Atlantic and Their Potential Inclusion in a Carbon Economy

“…No set CO 2 emission cap. The carbon offset market price is predefined Ton Metric ton (1,000 kg) $ (or dollar) US Dollar (USD; unless otherwise noted) Coleman et al 2022, Daneshvar et al 2022. Concurrently, shellfish production has been suggested as a sustainable form of protein, due to their low associated GHG emissions (Ray & Fulweiler 2020, Gephart et al 2021, Naylor et al 2021, and oyster aquaculture has been estimated to have less than 0.5% of the GHG cost of other animal protein sources (Ray et al 2019).…”

“…To address these challenges, multiple industries have been developing green technologies to reduce (e.g., green energy, electric vehicles) and remove CO 2 via storage or chemical weathering (de Lannoy et al 2018, Bach et al 2019, Kazemifar 2021, Galimova et al 2022, Raza et al 2022), effectively sequestering atmospheric CO 2 over long (geological) timescales. In addition, proposed ocean-based removals of emissions include bio fixation by algae and kelp (Chung et al 2013, Coleman et al 2022, Daneshvar et al 2022). Concurrently, shellfish production has been suggested as a sustainable form of protein, due to their low associated GHG emissions (Ray & Fulweiler 2020, Gephart et al 2021, Naylor et al 2021), and oyster aquaculture has been estimated to have less than 0.5% of the GHG cost of other animal protein sources (Ray et al 2019).…”