How Enhanced Rock Weathering Works

It’s wild to think that the same process that created the eerie and otherwordly Carlsbad Caverns National Park in New Mexico, is at the heart a carbon removal and storage method now expected to play an important role in helping restore our climate.  

This natural process is called chemical weathering and it causes the breakdown of rocks and minerals, storing carbon dioxide along the way. Chemical weathering occurs naturally when rain, which has absorbed carbon dioxide from the atmosphere on its way to Earth, reacts with rocks and soils on the ground. The rain-soaked rocks and soils then break down, forming tiny rock grains and bicarbonates. These bicarbonates eventually wash into the ocean where the carbon is stored for thousands of years.

Carlsbad Caverns National Park (United States of America) © Evergreen

Scientists are perfecting ways of speeding up this process - enhancing it -  by spreading fast-weathering, naturally-occurring, minerals on agricultural lands. As enhanced weathering makes water more alkaline, it can also help counteract ocean acidification. Countries such as the United States, China, India and Russia, which have very large areas of farmland, are excellent candidates for using enhanced weathering to help absorb and store carbon dioxide. On farmlands, minerals and particles slowly sift through the topsoil and into the waterways below the soil layer on their way to the ocean. 

Farmers have been adding rocks such as phosphate, potash, gypsum, and limestone to their soils for centuries. Scientists and farmers working together to support climate goals are testing the use of silicate rocks such as olivine which is a type of mineral that weathers very quickly on the surface of the Earth.

Photo by Federico Respini

Below, learn about a few companies in the community of carbon removal innovators exploring enhanced rock weathering for carbon removal. 

Eion applies crushed silicate rock - olivine - to soil. The use of Eion’s product, whose founder has a background in soil management and crop production, can replace the agricultural lime farmers currently use in amounts ranging from 25 to 30 million tons per year.  

Through existing moisture and acidity in the soil, the crushed rock dissolves, resulting in carbon dioxide being pulled from the atmosphere into the solution. The bicarbonate ions that are formed as part of the process over time make their way to the ocean. Once they reach the ocean, they improve ocean alkalinity and remain at the bottom of the ocean for 500,000 years. Eion has also developed a verifiable tracer that allows it to return to a field several years after its product has been applied to the soil and see which minerals were applied in which quantities, and verify the carbon removal.

Similar to Eion,  Lithos is spreading a different kind of silicate rock, in this case basalt, on croplands to increase dissolved inorganic carbon with eventual storage as ocean bicarbonate. Lithos’ technology uses novel soil models and machine learning to maximize carbon dioxide removal while boosting crop growth. One estimate holds that “applying 50 tonnes of basalt powder per hectare per year to 70m hectares of the corn belt of North America might sequester as much as 1.1billion tonnes of carbon dioxide – equivalent to 13% of the global annual emissions from agriculture.”

And then there’s Vesta, which is combining olivine with beach sand. Vesta launched its first demonstration project in Southampton, where it is adding a small amount of olivine sand mixed with beach sand to remove carbon dioxide from the atmosphere and restore the eroding coastline. 

Natural rock weathering already absorbs approximately 0.3% of global fossil fuel emissions; the IPCC has estimated that at scale it could capture 2 and 4 billion metric tons (at a cost of between $50 and $200 per metric ton). 

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Physical Geology, 2nd Edition, by Steven Earle

Carbon Brief: How ‘enhanced weathering’ could slow climate change and boost crop yields

National Geographic Resource Library: Weathering

Negative Emissions and Technologies You Need to Know About at Drax

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