A Cost Model for Ocean Iron Fertilization as a Means of Carbon Dioxide Removal That Compares Ship‐ and Aerial‐Based Delivery, and Estimates Verification Costs.

We present a cost model for implementing a deployment scale effort for conducting ocean iron fertilization (OIF) for marine‐based carbon dioxide removal (CDR). The model incorporates basic oceanographic parameters critical for estimating the effective export of newly fixed CO2 into biomass that is stimulated by Fe addition to an Fe‐limited region of the Southern Ocean. Estimated costs can vary by nearly 100‐fold between best‐case and worst‐case scenarios, with best‐case values of $7/net tonne C captured versus worst‐case $1,500/net tonne C captured, without accounting for verification costs. Primary oceanographic factors that influence cost are the net primary productivity increases achieved via OIF, the amount of C exported into the deep ocean, and the amount of CO2 ventilated back to the atmosphere. The model compares ship‐based versus aerial delivery of Fe to the ocean, and estimates aerial delivery can be 30%–40% more cost effective; however, the specific requirements for aerial delivery require additional research and development. The model also estimates costs associated with verification and environmental monitoring of OIF. These costs increase $/net tonne C captured by 3–4‐fold. Best, intermediate, and worst cases for aerial delivery and ship delivery are $21, $83, $2,033, and $24, $94, $4,691, respectively, inclusive of verification costs. The primary goal of this model is to demonstrate the variability in cost of OIF as a CDR method, and to better understand where additional research is needed to determine the major factors that may make OIF a tractable, nature‐based CDR method. Plain Language Summary: This paper presents a basic cost model for undertaking ocean iron fertilization (OIF) as a means of removing carbon dioxide from the atmosphere. It presents a simple application scenario that compares two different modes for delivering iron to the ocean, plane‐based and ship‐based, and estimates costs associated with verification of carbon export into the deep ocean, as well as assessing the environmental changes that may occur as result. Key findings are that, in terms of USD/tonnes carbon exported, OIF can be at the lower cost end (<S10/tonne) of methodologies for carbon dioxide removal, and that aerial delivery is likely to be at least 30% less than ship‐based delivery. However, uncertainties pertaining to how quickly this carbon dioxide may return to the atmosphere, and the impacts of other off‐setting greenhouse gases could push these costs up by 50‐fold or more. Furthermore, verification costs may increase the costs substantially. The primary goal of this work is to place some dollar values on the uncertainties that underlie OIF as a means of marine carbon dioxide removal that can help guide much‐needed research into its ultimate efficacy. Key Points: Variability in key oceanographic parameters can impact predicted costs of ocean iron fertilization by 100‐foldThe model finds aerial‐based delivery of iron may reduce costs by 30%–40% compared to ship‐based deliveryThe cost of verification and environmental monitoring may increase overall costs of ocean iron fertilization by 3–4 fold [ABSTRACT FROM AUTHOR]