Microsoft signs carbon removal deal with India’s Alt Carbon

Microsoft’s agreement with Alt Carbon took more than a year of scientific review and due diligence, a reminder that the carbon-removal market is becoming less about bold promises and more about proof. Alt Carbon said Microsoft required additional verification and data-sharing measures before signing the deal, and the discussions between the two companies began in early 2025 before stretching on for more than a year.

The project behind the deal uses enhanced rock weathering, a technique that spreads basalt from the Rajmahal Traps in eastern India across farmland in West Bengal. Alt Carbon says the rock reacts with rainwater and atmospheric carbon dioxide to form stable bicarbonates, locking away carbon while also improving agricultural land. The company has centered the work in Darjeeling and launched its Darjeeling Climate Action Lab in March 2025, aiming to build a permanent removal model rather than a short-lived offset.

The Microsoft deal lands as Alt Carbon has already begun to scale. In May 2026, the company said it had generated 9,566 tonnes of verified carbon dioxide removal credits, describing that total as the world’s largest enhanced rock weathering issuance by volume. Alt Carbon said those credits had gone to buyers including the Frontier coalition, whose members include Stripe, Google, Shopify and Match Group, working through Watershed. In April 2026, Mitsui O.S.K. Lines said it had received 2,500 tonnes of CDR credits from Alt Carbon’s Darjeeling Revival project.

Alt Carbon’s financing history has also moved quickly. The company raised $12 million in seed funding in May 2025, which it described as the largest seed round to date for climate tech in India. That funding, along with its early buyers, helped turn a regional pilot into a project that is now being watched as a benchmark for durable removal in a country increasingly central to the market.

Microsoft’s latest India deal adds to that shift. In March 2025, the company announced a 30-year agreement to buy 1.5 million tonnes of verified carbon removal credits from the Panna afforestation project, its first carbon removal project in India and its largest in the Asia-Pacific region. That agreement also followed three years of due diligence and pilot activities. Taken together, the Panna and Alt Carbon deals show India moving from a peripheral market for climate claims to a core geography for buyers seeking verified, longer-lasting carbon removal.