I just deleted a post that may have been wrong. It seems there might be limits to how much CO2 the ocean can trap by the particular geoengineering approach I was discussing, which is using ground up alkaline rock at about $10 per ton CO2. The limit is primarily about the amount of shipping we have – and using the ballasts to spread the solution around the world’s oceans.
The bottom line is the following paper seems to suggest the ocean might be limited to absorbing only 9% of our annual emissions this way. This is still being explored by other scientists – and there might be other approaches.
Our results show that enhanced weathering might help to reduce atmospheric CO2. However, with a carbon uptake rate of 0.28 g carbon per g of olivine (neglecting reduced efficiency as discussed above) the recent fossil emissions of about 9 Pg C yr−1 (Peters et al 2012) are difficult if not impossible to be reduced solely based on olivine dissolution. An upper limit for the open ocean distribution of olivine is difficult to estimate, but such a limit certainly depends on shipping capacities, exploitation of olivine, and low distribution rates to prevent particle aggregation. In our STANDARD scenario (3 Pg of olivine dissolution per year) about 9% of the anthropogenic CO2 emissions would be compensated. This is slightly higher than the compensation rate of about 7% after ten years of implementation for the ongoing surface ocean acidification of nowadays 0.1 pH-units (Doney et al 2009).