Through natural processes, rocks currently absorb about 1.1 gigatons (Gt) of CO2 per year, by reacting with CO2 in the air and converting into solid carbonates, where most of it ends up eventually being permanently stored as bicarbonate in the oceans.

Currently, humans emit about 37 Gt of CO2 from fossil fuels, according to data collected by Our World In Data. So the amount that's naturally sequestered by rocks is only a small percentage of overall global carbon emissions, and there have been proposals for enhanced rock weathering to speed up the process, with the potential for up to 2 Gt of CO2 to be removed each year, according to one study.

One such method of enhanced rock weathering involves crushing a mineral-rich rock such as basalt or olivine and spreading the powder into fields or other areas it can be put to efficient use, reacting with CO2 to form solid carbonates. The physics of this are similar to granulated sugar compared with sugar cubes -- with the granulated sugar dissolving faster in water do to having higher surface area compared with volume. The process works similarly with CO2-absorbing rocks, where, as the Head of Science of InPlanet, a start-up working on the issue, puts it:

It is a natural process, and instead of happening over hundreds of thousands to millions of years, we speed it up to happen in less than a decade. And we do this by taking rock from the earth, crushing it, grinding it to small particle size, and then spreading it on farmland, where this process will happen much more quickly.

Another method is to use additives on rocks to speed up their chemical reactions, especially if it can be done on a large scale, at a low cost per unit. Please see the related Metaculus question, Will a bio additive for accelerating mafic rock weathering by at least 30%, which enhances its CO2 sequestration, be available before 2030 and cost less than $20 per ton of rock?

See Also

• Scientific Reports: The environmental controls on effciency of enhanced rock weathering in soils

• Environmental Science and Pollution Research: A state of the art of review on factors affecting the enhanced weathering in agricultural soil: strategies for carbon sequestration and climate mitigation

• Biology Letters: Climate change mitigation: potential benefits and pitfalls of enhanced rock weathering in tropical agriculture

• Earth's Future: Impact of Climate on the Global Capacity for Enhanced Rock Weathering on Croplands