Microsoft has signed a three-year deal to buy almost 37,000 tonnes of carbon removal credits from an Indian startup All carbonmarking the tech giant’s first enhanced rock weathering deal in Asia.
Under the agreement, Alt Carbon will deliver 36,920 metric tons of carbon dioxide removal credits by 2029 from its Darjeeling Revival Project in eastern India. Microsoft also has the option to purchase additional volumes if the startup meets delivery and verification milestones.
The agreement follows reports that suggested Microsoft, the world’s largest buyer of carbon removal credits, had paused parts of its carbon removal procurement program. The company rejected those claimssaying it remained committed to its climate goals even as it refined its sustainability strategy.
The deal is a potential boon for Alt Carbon, a Bengaluru-based startup founded in 2023 that focuses on carbon removal projects, including improving rock erosion. This technique involves spreading crushed basalt and other silicate rocks on farmland to speed up natural chemical reactions that help store carbon dioxide. Alt Carbon sources basalt from Rajmahal traps in eastern India and deploys it on farmland in West Bengal, where the rock reacts with rainwater and atmospheric carbon dioxide to form stable bicarbonates.
Talks with Microsoft began in early 2025 and culminated more than a year later, after extensive scientific review, due diligence and contract negotiations, Alt Carbon co-founder and president Sparsh Agarwal told TechCrunch. Microsoft also required additional monitoring, reporting and verification (MRV) measures beyond the registration requirements, including expanded carbon quantification and data sharing protocols, it said.
The deal comes as buyers increasingly seek proven carbon removal projects in a market where verified supply remains scarce. Hundreds of new companies have emerged promising to remove carbon dioxide from the atmosphere. However, only a small fraction have provided verified credit on a commercial scale.
“The problem now is that there are many suppliers, but there are very few verified deliveries,” Agarwal said. “When companies are able to deliver, everyone wants to make sure they get a share of the supply.”
Alternative carbon has issued almost 10,000 carbon removal credits thanks to enhanced rock erosion to date, making it the largest such credit issuance in the world, according to Agarwal. The startup hopes to issue another 15,000 credits before the end of the year.
Alt Carbon operates two carbon removal projects in North Bengal, including one dedicated to Japanese shipping giant Mitsui OSK Lines and a broader program from which Microsoft credits will be sourced, Agarwal said. The startup has expanded beyond tea plantations into rice-growing areas and now works with more than 35,000 farmers on approximately 80,000 acres.
Credits under the deal with Microsoft will be issued through Isometric, a carbon removal registry that developed an improved rock weathering methodology.
The deal also reflects the growing role of emerging market suppliers in carbon removal. Developers from the Global South now account for about 26% of carbon removal credit emissions, up from about 2% in 2022, Agarwal said. He added that international buyers were often skeptical of Indian carbon projects when Alt Carbon was launched more than two years ago, but rising emission volumes and stricter verification standards have helped improve market confidence.
The Alt Carbon deal is not Microsoft’s first investment for carbon removal in India. In January, the company signed an agreement with another Indian startup, Varahato purchase more than 100,000 tons of carbon dioxide removal credits generated through biochar over three years.
Microsoft joins a list of buyers of Alt Carbon credits that includes procurement coalitions such as Borderwhose members include Google, Stripe and Shopify, and Next generationbacked by companies such as UBS, Swiss Re and Boston Consulting Group, according to registry data.
Agarwal said Alt Carbon plans to expand its deployment footprint approximately five-fold in the next four to five years from approximately 80,000 acres currently, as demand for verified carbon removal credits grows.
Alt Carbon, which last year raised $12 million in seed funding round led by technology investor Lachy Groom, has built its own MRV infrastructure, including laboratories in Bengaluru and Darjeeling that it uses to analyze soil and water samples and quantify carbon removal. Agarwal said improving verification capabilities and reducing measurement costs will be critical to scaling up enhanced rock weathering projects in India and beyond.
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