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upstart writes in with an IRC submission:

Spreading rock dust on farms could be a major climate action:

Eventually (ideally sooner rather than later), efforts to reduce greenhouse gas emissions are going to have to be joined by a technology that actively removes CO2 from the atmosphere. There are a number of options [...] and a new feasibility study suggests that one of them—spreading crushed rock on farm fields—deserves serious consideration.

[...] Using crushed rocks isn't a new idea. Some common minerals react with water and CO2 as they weather, converting CO2 from the air into bicarbonate dissolved in water. That bicarbonate (along with some calcium and magnesium) may hang out in groundwater or make its way into the ocean. And along the way, it can also turn into solid carbonate. Whatever route it takes, it's no longer a greenhouse gas in the air.

Over hundreds of thousands or millions of years, this process has an important stabilizing influence on Earth's climate. Warmer climates encourage more weathering, pulling greenhouse gas out of the atmosphere.

[...] One way to accelerate weathering is to grind up that rock into small particles. Just as powdered sugar dissolves in water much more quickly than a large solid candy would, these small particles will weather much faster. Spreading that crushed rock over farm fields not only nicely exposes it to the elements but can also be beneficial for the soil, replenishing nutrients and counteracting pH changes in heavily farmed soils.

[...] Globally, the researchers estimate that this process could be used to capture 500 million to 2 billion tons of CO2 per year in 2050. For comparison, scenarios that limit global warming to 2°C generally involve capturing something like 2 to 10 billion tons per year in a few decades from now.

[...] In the US, EU, and Canada, the researchers estimate that all this would cost about $160 to 190 per ton of CO2 captured, while China, India, and Brazil could do it for $55 to 120 per ton. That's in the same ballpark as other some options for atmospheric CO2 removal..

Journal Reference:
David J. Beerling, Euripides P. Kantzas, Mark R. Lomas, et al. Potential for large-scale CO 2 removal via enhanced rock weathering with croplands, Nature (DOI: 10.1038/s41586-020-2448-9)

Additional Information:
Johannes Lehmann, Angela Possinger. Removal of atmospheric CO2 by rock weathering holds promise for mitigating climate change, Nature (DOI: 10.1038/d41586-020-01965-7)

Original Submission