Tyler Rohr: Modelling Requirements for Ocean Alkalinity Enhancement
Meeting Paris-targets will require gigatonne-scale carbon dioxide removal (CDR). Ocean alkalinity enhancement (OAE) is one of the most actively investigated marine CDR approaches, with dedicated field trials, emerging carbon-crediting protocols, and over $40 Million in credits already sold. However, unlike more expensive (direct air capture) and less durable (forestry) offsets, the amount of carbon sequestered by OAE cannot be measured. Once added to the ocean, alkalinity is rapidly diluted, with most carbon sequestered many miles and years from the initial deployment. Meanwhile, biogeochemical feedbacks that could reduce the additionality cannot be easily distinguished from counterfactual baselines. As such, carbon credits must be quantified with models. But which models? And how skillful must they be?
In July 2026, Carbon to Sea funded 30 global experts to convene in Germany and develop the guidelines. Myself and 3 co-authors were asked to lead the synthesis of this document across five working groups focused on 1) the nearfield delivery of alkalinity, 2) physical transport, 3) air-sea gas exchange and biogeochemical feedbacks in 4) the water column and 5) sediments. With representatives from the leading OAE companies and CDR registries, it is likely these guidelines become industry standard – setting the baseline model requirements for credible carbon accounting. From large eddy simulations to particle dissolution dynamics to advanced mixing schemes to a whos-who of biogeochemical feedbacks, this talk is for anyone who loves COSIMA and/or wants to understand how rigorous modelling might be before we start paying people for OAE.