Enhanced weathering refers to chemical approach to geoengineering involving land or ocean based techniques. Examples of land based enhanced weathering techniques are in-situ carbonation of silicates. Ultramafic rocks, for example, have the potential to store 500 years worth of CO2 production according to one estimate. Ocean based techniques involve alkalinity enhancement, such as, grinding, dispersing and dissolving limestone, silicates, or calcium hydroxide to address ocean acidification and CO2 sequestration. Enhanced weathering is considered as one of the least expensive of geoengineering options.