Opportunities for Abiotic, Ocean-based Carbon Dioxide Management

Recent modeling and analysis (IPCC, etc.) has concluded that remaining below critical climate thresholds (e.g., below 1.5ºC warming) now requires both a drastic reduction in GHG emissions plus pro-active removal of CO₂ from the atmosphere. To date land-based methods have dominated the proposed CO₂ management responses. This could prove risky and inadequate given that such actions would compete with growing demands for land-based food, fiber, and fuel production. The oceans could help relieve such land limitations via harnessing a portion of its: 1) vast, renewable energy potential (marine wind, wave, solar, thermal, etc. sources) as well as 2) very large CO₂ uptake and storage capacity. Exploitable ocean energy is estimated to be on the order of 2 EWh/yr or some 12X that of current, land-based energy production. Further R&D on cost-effective marine energy generation and delivery could greatly alleviate pressures on land use and resources in reducing energy-related GHG emissions. Secondly, ocean uptake and storage of CO₂, currently about 9 Gt/yr., could be biologically enhanced via fertilization, aquaculture, permaculture, Blue Carbon, etc. Yet issues such as ecological impact, cost, and environmental safety could affect scales of deployment. Alternatively, direct alteration of surface ocean chemistry, e.g. alkalinity addition or CO₂ stripping, have been proposed as methods of increasing atmospheric CO₂ removal, storage and/or acidity reduction. Reaction of excess CO₂ with natural (Earth-abundant alkaline rocks) or synthetic chemical bases (e.g., hydroxides) converts CO₂ to dissolved mineral bicarbonates and carbonates (seawater alkalinity), already the dominant carbon reservoir on the Earth's surface. Indeed, the consumption of excess CO₂ by alkaline rock weathering and the resulting ocean alkalinity increase is a primary way that CO₂ is naturally consumed and sequestered, and ocean chemistry restored, on geologic time scales. Various methods of accelerating this process will be reviewed. Given that failure is not an option regarding staying below CO₂ and climate thresholds, the very large potential for the ocean to help abiotically manage atmospheric CO₂ should not be ignored.