How spreading rocks on fields could combat climate change
Rocks have been helping to draw CO₂ out of the atmosphere for billions of years, but the process is too slow to keep up with our current rate of emissions. Start-ups backed by companies including Microsoft and JPMorgan are trying to accelerate this natural geological activity by spreading finely crushed rocks across farmers’ fields in a technique known as “enhanced rock weathering”.
Around a third of the world’s total land area is dedicated to agriculture, according to the UN. Proponents of enhanced rock weathering hope to leverage this vast available space to capture and remove carbon — and simultaneously benefit farmers. But it remains difficult to measure accurately the impact of their efforts, which could impede wider adoption.
How does it work?
The premise is fairly simple. Silicate rocks, such as basalt and olivine, that naturally absorb CO₂ are crushed and spread over farmland, thereby increasing their surface area for maximum contact with precipitation. The alkaline material in the rocks then reacts with dissolved CO₂ in rainwater to form stable carbonate minerals, such as calcite or dolomite, which do not easily break down.
These carbonates filter down through soils until they are eventually washed into rivers and oceans, where the carbon can be sequestered in rocks and corals for millennia.
What are the pros and cons?
The process itself does not require any new infrastructure or technology, making it technically cheaper and less energy-intensive than other forms of carbon capture. As it can be applied directly to agricultural land, it is both cheaper and faster to scale, advocates argue.
“There’s no new infrastructure to build and no permitting,” says Jim Mann, founder and chief executive of UK-based enhanced weathering start-up Undo. “All those things that slow down other innovations aren’t here.”
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Moreover, promoters say that enhanced weathering could support crop production, because alkaline rocks can de-acidify soils as they break down.
“It offers an exciting opportunity for sustainable agriculture — improving food security while at the same time capturing carbon,” says David Beerling, director of the Leverhulme Centre for Climate Change Mitigation at the University of Sheffield.
But there are also drawbacks. Tracking the amount of carbon dioxide that has been captured and stored through enhanced weathering currently requires extensive soil sampling, which makes it time-consuming and expensive to calculate the impact of an application, thus raising the cost of carbon credits.
It’s also hard to assess how much carbon dioxide is re-released as the stable carbonates produced through the weathering process flow through to the rivers and oceans.
Moreover, scaling up the process could have its own ecological footprint. At present, companies such as Undo typically make use of leftover rock supplies at existing quarries — but they would likely need to find vast new quantities of rock at sites close to agricultural land if the process is widely adopted.
“It’s a question of, are you sacrificing the cost of transport for waste rock, or are you sacrificing the cost of quarrying new rock,” says Hugo Lakin, carbon dioxide removal (CDR) lead at specialised ratings provider Sylvera.
Will it save the planet?
Simulations of widespread adoption suggest that enhanced weathering could sequester as much as 4 gigatonnes of CO₂ per year.
It’s not a silver bullet — the International Energy Agency estimates that energy-related CO₂ emissions hit an all-time high of 37.8 gigatonnes in 2024 — but the process could contribute to mitigating the climate-related harms of industries that cannot easily reduce their emissions, such as aviation and steel production.
Still, some fear that carbon capture methods like enhanced weathering may be used to justify the continued use of fossil fuels. “I’m anxious it could be another vessel for greenwashing,” said Beerling.
Has it arrived yet?
Yes. The first independently verified enhanced weathering carbon credits were issued through Isometric, a carbon credits registry, in January.
Spreading natural materials on to farmers’ fields is nothing new. The latest innovations are in the measurement of the process’s carbon removal benefits, rather than the actual technique itself.
Lakin, from Sylvera, says the costs of this measurement will need to be lowered in order to drive more purchases of carbon credits — but he is optimistic that this can be achieved “fairly quickly”.
Who are the winners and losers?
If the costs of measurement can be reduced, enhanced weathering could ultimately offer a lower-cost way for companies to offset their emissions. Farmers could also benefit from improved soil health without any additional cost, because the process would be funded by the companies buying carbon credits.
There are no obvious corporate losers — but local communities may oppose new quarrying projects that might be required to supply a wider rollout of enhanced weathering.
Who is investing in it?
Companies including British Airways, McLaren, and Microsoft have already committed to buying enhanced rock weathering credits from start-ups such as San-Francisco-based Terradot and UK-based Undo.
The Microsoft Climate Innovation Fund participated in a $54mn funding round for Terradot, while the Elon Musk Foundation-backed XPrize this May awarded $50mn and $5mn, respectively, to Mati Carbon, which also has funding from JPMorgan, and Undo.
Governments, universities, and climate-focused funding bodies have also invested in early-stage research into the process. UK Research and Innovation, the state funding agency, is backing a multiyear “enhanced rock weathering demonstrator” to assess the process’s longer-term effectiveness, as well as the social and ethical acceptability of local deployment.