Opportunities for Abiotic, Ocean-based Carbon Dioxide Management

Greg H Rau, University of California Santa Cruz, Institute of Marine Sciences, Santa Cruz, CA, United States
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.