Microsoft just made its first bet on enhanced rock weathering in Asia — and it's betting on an Indian startup to pull it off.
The tech giant signed a three-year agreement to buy nearly 37,000 metric tons of carbon removal credits from Alt Carbon, an Indian company running the Darjeeling Revival Project in eastern India. Under the deal, Alt Carbon will deliver 36,920 metric tons of carbon dioxide removal credits by 2029. Microsoft also has an option to buy more if Alt Carbon hits delivery and verification milestones.
Enhanced rock weathering works by spreading crushed silicate rocks on farmland. The rocks react with CO₂ in the air and lock it away in solid minerals. It's one of several carbon removal methods companies like Microsoft are betting on to offset emissions they can't cut directly.
This deal is small compared to Microsoft's overall carbon removal portfolio — the company has bought millions of tons of credits from projects around the world. But it's a big deal for Alt Carbon and for India's carbon removal scene. India has the geology and agriculture to host large-scale enhanced rock weathering projects, but the sector is still early-stage. A commitment from a buyer like Microsoft gives Alt Carbon credibility and a revenue stream to scale up.
The Darjeeling Revival Project is located in the Darjeeling district of West Bengal, a region known for tea plantations and steep hills. Alt Carbon hasn't disclosed how much Microsoft is paying per ton, but enhanced rock weathering credits typically sell for anywhere from $100 to $300 per ton, depending on verification and co-benefits.
Microsoft has been one of the most aggressive corporate buyers of carbon removal credits. In 2024, it signed a deal with Stockholm Exergi for 3.3 million tons of bioenergy carbon capture and storage credits. It also has agreements with direct air capture companies like Climeworks and 1PointFive. The Alt Carbon deal is the company's first for enhanced rock weathering in Asia, and it comes as Microsoft pushes toward its goal of being carbon negative by 2030.
The deal also signals growing interest in nature-based and geological carbon removal methods in developing countries. Enhanced rock weathering has the added benefit of improving soil health — the crushed rock releases nutrients that can boost crop yields. That dual benefit makes it attractive for countries like India, where agriculture is a major part of the economy.
Alt Carbon was founded in 2022 by a team of Indian scientists and entrepreneurs. The company sources basalt rock from quarries, crushes it, and spreads it on farmland. It monitors carbon removal using soil sampling and modeling. The Darjeeling Revival Project is its first commercial-scale project.
For Microsoft, the deal is a test. If Alt Carbon delivers on time and verifies the carbon removal, Microsoft will likely expand its enhanced rock weathering investments in Asia. If not, the option to buy more credits expires. Either way, the deal puts Indian startups on the map in a market dominated by US and European companies.