Global warming is thought by many to be caused by rising CO2 levels in the atmosphere. This proposal deals with the possibility to sequester large volumes of CO2 from the atmosphere by spreading fine-grained olivine in coastal waters in order to adsorb CO2, and counteract the expected acidification of the sea water caused by the rising CO2 concentration in the atmosphere.
Olivine is a very abundant magnesium silicate that weathers easily. Olivine is definitely not in equilibrium with sea water. During a test in which fine-grained olivine was added to a bottle of sea water, closed and shaken, the pH of the sea water had increased from 8.4 to 9.1 in 24 hours only. This makes the sea water strongly undersaturated with respect to CO2. If the system is open to the atmosphere this deficit of CO2 will be quickly compensated by the uptake of CO2. This opens the way to use the sea as a huge sink for CO2 without causing any acidification, and thus to sustainably remove large volumes of this greenhouse gas from the atmosphere.
Mg2SiO4 + 4 CO2 + 4 H2O -> 2 Mg2+ + 4 HCO3– + H4SiO40
In addition to the storage of organic carbon through deposition under anoxic conditions and burial into the fossil rock record, weathering of silicates is the major pathway by which nature removes CO2 from the atmosphere. Indeed, the start of glaciations during the Tertiary has been attributed to enhanced weathering due to the uplift and erosion of the Himalaya and the consequent increased exposure of silicates to, and the withdrawal of CO2 from the atmosphere. This proposal introduces a simple technique for such enhanced weathering and CO2 consumption on a global scale.