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Tech companies, banks and shipping groups are investing in a method of carbon dioxide removal that promises to speed up the chemical reaction between absorbent rocks and rainfall.
The natural geological process is accelerated by spreading crushed silicate rock onto farm land to increase the surface area of the rock and its contact with CO₂, its promoters say. The alkaline materials can also be added to the ocean floor.
The notion is growing in popularity, with polluters betting on a variety of technologies to hit “net zero” goals as cheaply as possible in coming decades.
Microsoft agreed last month to buy 12,000 tonnes of so-called Brazilian “enhanced rock weathering” carbon credits between 2026 and 2029, from San-Francisco-based Terradot, which sources basalt from quarries in southern Brazil and transports it to nearby farms. The Microsoft Climate Innovation Fund participated in a $54mn funding round for the company.
The Elon Musk Foundation-backed XPrize recently awarded $5mn and $50mn respectively to two companies promoting enhanced weathering: London-based start-up company Undo, from which Microsoft has also committed to buying credits, and Mati Carbon, which has funding from JPMorgan and has trialled the spread of powder on rice fields.
Using a separate technology that relies on similar chemical reactions, the Abu Dhabi National Oil Company has backed the start-up 44.01 to pilot technology that injects dissolved CO₂ into rocks found in the Emirate of Fujairah.
Initial trials for enhanced rock weathering have shown that around 4 tonnes of CO₂ could be captured from 1ha of land. Once the rock is spread, the ions can take a few years to release deep enough into the soil, a few months to be exported into groundwater and the ocean, and tens of thousands of years to turn into a solid calcium carbonate.
“We’re in the business of creating corals from clouds,” said Sparsh Agarwal, a fourth-generation tea-planter in India and co-founder of Alt Carbon, a start-up with a project in Darjeeling which is planning to deliver its first carbon credits in June. It has previously sold credits at $270 a tonne.
Alt Carbon last year signed an offtake agreement with the NextGen coalition of buyers, which is led by Mitsubishi Corporation and includes UBS and Swiss Re. It has also signed a similar deal with a coalition called Frontier, involving a commitment by companies including Stripe, Alphabet and Meta to buy at least $1bn worth of permanent carbon removals by the end of the decade.
The company operates in the Himalayan foothills, where it spreads finely ground basalt rock on fields.
Frontier has spent more than $150mn on agreements for future carbon credits from this process. Other start-ups with which Frontier has signed deals spread rock on Brazilian sugarcane plantations and maize farms in Cameroon.
The extensive sampling needed to check on ions’ progression through the soil still make it “commercially and operationally quite a challenge,” said Simon Manley, head of carbon dioxide removal for specialised ratings provider Sylvera.
At the moment, getting to the stage of being able to issue credits requires “lots of very diligent scientists crawling around on their hands and knees” to collect samples from fields, he noted.
Japanese shipping companies NYK and Mitsui OSK Lines both recently agreed to buy enhanced weathering credits to cancel out some of their emissions — in NYK’s case from burning shipping fuel.
Ships entering and leaving the European Economic Area were each responsible for more than 10,000 tonnes of greenhouse gas emissions on average in 2023, the European Commission estimated.
Nan Ransohoff, the Frontier coalition’s founder, said the natural interactions between rocks and the CO₂ in rainwater already help planetary systems absorb around 1GT a year of CO₂. Specialised enhanced rock weathering techniques mean “you’re just trying to speed that process up.” This means it is “less a question of if it’s happening but when.”
Enhanced weathering had the potential to be a relatively low-cost process by “piggybacking” on existing industrial and agricultural processes, Ransohoff said. Projects use byproducts of quarrying, and encourage farmers to spread the rock as they would their fertiliser.
However, it is more expensive to measure accurately than other carbon removal technologies such as direct air capture, where machines suck CO₂ directly out of the atmosphere and sequester it underground.
Prices for enhanced weathering credit deals have so far ranged widely from as little as $75 to a steep $500 per tonne, according to MSCI Carbon Markets data.
Lukas May, chief commercial officer at Isometric, a registry for carbon credits, said the cost could drop as standard-setters developed methodologies that could predict CO₂ storage, rather than only being able to measure it through soil samples. But the costs could, in theory, also rise.
The market is still in its infancy. Isometric in January announced the first delivery of independently verified credits. Investments so far account for about 7 per cent ($53mn) of total investments into permanent carbon removal, MSCI said.
Recent research from MIT noted that enhanced rock weathering had the benefit of requiring less dedicated land than bioenergy with carbon capture and sequestration, a popular type of carbon removal which stores the CO₂ emitted when biomass is burned for power.
These techniques are all however considered more expensive or energy-intensive than cutting emissions in the first place by burning fewer fossil fuels.
Illustration by Bob Haslett, graphic by Janina Conboye
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