Under the terms of the agreement, Alt Carbon will utilize its proprietary ERW methodology to sequester atmospheric carbon dioxide while simultaneously revitalizing local agricultural ecosystems. The deal includes provisions for Microsoft to purchase additional volumes of carbon credits in the future, contingent upon the successful delivery of initial volumes and the achievement of rigorous verification milestones. This scalable approach reflects the growing maturity of the voluntary carbon market, where long-term off-take agreements are becoming essential for startups to secure the capital necessary for large-scale operations.
The Mechanics of Enhanced Rock Weathering
Enhanced rock weathering is a geochemical process that accelerates the natural weathering of silicate rocks to capture atmospheric CO2. In its natural state, the weathering of rocks takes place over millions of years as rainwater, which is slightly acidic due to dissolved carbon dioxide, reacts with minerals. Alt Carbon’s approach accelerates this timeline significantly. The company sources basalt rock dust—a byproduct of mining operations—and spreads it across vast agricultural landscapes, including the iconic tea estates of Darjeeling and neighboring rice paddies.
When rainwater hits the basalt dust, a chemical reaction occurs. The CO2 in the rainwater reacts with the silicate minerals in the rock, converting the gas into stable bicarbonate ions. These ions are then stored in the soil or carried by runoff into rivers and eventually the oceans. Once in the marine environment, the carbon resides as calcium carbonate for upwards of 10,000 years, providing a permanent and durable solution for carbon sequestration. Unlike traditional reforestation projects, which are vulnerable to wildfires or disease that can release stored carbon back into the atmosphere, ERW offers a geological storage solution that is effectively irreversible on a human timescale.
The Darjeeling Revival Project: A Dual-Purpose Initiative
The carbon credits for this deal will be generated through Alt Carbon’s flagship "Darjeeling Revival Project" (DRP). Founded in 2023 by brothers Shrey and Sparsh Agarwal, Alt Carbon has designed the DRP to address both the climate crisis and the economic challenges facing India’s agricultural sector. The project focuses on the heritage tea estates of Darjeeling, a region world-renowned for its tea production but currently grappling with soil degradation and declining yields.
By integrating basalt dust into the soil, Alt Carbon provides farmers with a natural soil amendment. Basalt is rich in essential nutrients such as magnesium, calcium, and potassium. The application of this rock dust helps balance soil pH, which is often too acidic in regions with heavy rainfall and intensive farming. Improved soil health leads to more resilient crops and higher yields, providing a tangible economic incentive for local farmers to participate in carbon removal efforts. This synergy between environmental restoration and agricultural productivity is a cornerstone of Alt Carbon’s business model, aiming to remove 5 million metric tons of CO2 by 2030.
Microsoft’s Carbon Strategy and Market Dominance
Microsoft has established itself as the preeminent leader in the global carbon removal market. According to data from the CDR.fyi platform, Microsoft accounted for approximately 90% of the total carbon removal credit purchases globally in 2025. This latest deal with Alt Carbon reinforces the company’s commitment to its 2020 pledge: to be carbon negative by 2030 and to remove from the environment all the carbon the company has emitted either directly or by electrical consumption since it was founded in 1975.
The agreement with Alt Carbon is particularly noteworthy given the recent volatility in Microsoft’s procurement narrative. In April 2026, reports surfaced suggesting that the company was pausing some of its carbon removal purchases. However, Melanie Nakagawa, Microsoft’s Chief Sustainability Officer, later clarified that the program remains a vital pillar of the company’s climate strategy. The Alt Carbon deal serves as a concrete rebuttal to rumors of a retreat, demonstrating that Microsoft is continuing to diversify its portfolio of removal technologies, moving beyond forestry and direct air capture (DAC) to include terrestrial mineral-based solutions like ERW.
Phil Goodman, Program Director for Carbon Removal at Microsoft, emphasized the importance of high-integrity data in this partnership. The project utilizes both primary and secondary quantification methods to ensure that every ton of carbon removed is accurately measured and verified. This focus on "high-integrity" is a direct response to historical criticisms of the voluntary carbon market, which has occasionally struggled with transparency and the actual permanence of carbon offsets.
Timeline and Project Milestones
The collaboration between Alt Carbon and Microsoft is the result of several years of foundational work by the startup. Since its inception, Alt Carbon has invested heavily in laboratory capabilities and field operations to advance the science of rock weathering.
- 2023: Alt Carbon founded by Shrey and Sparsh Agarwal; initial pilot studies launched in Darjeeling.
- 2024-2025: Expansion of farmer networks and establishment of a supply chain for basalt sourcing from regional mines.
- Early 2026: Implementation of advanced Monitoring, Reporting, and Verification (MRV) protocols to track soil chemistry changes and bicarbonate runoff.
- June 2026: Formal announcement of the multi-year deal with Microsoft for 36,920 tons of CDR.
- 2027-2030: Planned scaling phase, aiming to reach the 5-million-ton cumulative removal target.
The delivery of these credits is subject to strict verification. Alt Carbon must demonstrate that the basalt application has resulted in the net removal of CO2 after accounting for the emissions generated during the mining, grinding, and transportation of the rock dust.
Implications for the Indian Climate Tech Sector
India is increasingly being viewed as a critical hub for technology-based carbon removal. With its vast agricultural land, extensive mining infrastructure, and a growing pool of scientific talent, the country is uniquely positioned to lead in ERW and other nature-based climate solutions. Shrey Agarwal, CEO and Co-founder of Alt Carbon, noted that India has the potential to become a global leader in tech-based carbon removal, bridging the gap between Global North capital and Global South climate action.
The success of the Darjeeling Revival Project could serve as a blueprint for similar initiatives across South Asia. By leveraging existing agricultural networks, these projects can scale rapidly without the need for the massive energy inputs required by mechanical solutions like Direct Air Capture. Furthermore, the deal highlights the role of private sector investment in achieving India’s national climate goals, including its target of reaching Net Zero by 2070.
Analysis of Global Carbon Removal Trends
The Microsoft-Alt Carbon deal reflects broader trends in the ESG (Environmental, Social, and Governance) and climate tech landscapes. First, there is a clear shift toward "durable" carbon removal. While nature-based solutions like tree planting remain popular, corporate buyers are increasingly willing to pay a premium for solutions that guarantee carbon storage for centuries or millennia.
Second, the deal highlights the importance of "co-benefits." In the modern carbon market, a credit is more valuable if it also supports biodiversity, improves local livelihoods, or enhances food security. The agricultural benefits of ERW make it an attractive option for companies looking to fulfill their ESG mandates while also contributing to the United Nations Sustainable Development Goals (SDGs).
Finally, the geographical diversification of Microsoft’s portfolio is significant. By moving into the Asian market for ERW, Microsoft is helping to build the necessary infrastructure and expertise in a region that is both highly vulnerable to climate change and essential to any global mitigation strategy.
Challenges and Future Outlook
Despite the promise of ERW, challenges remain. The primary hurdle is the complexity of measurement. Unlike a machine where you can meter the gas captured, ERW occurs in open environments. Scientists must use complex models and soil sampling to estimate the amount of carbon sequestered. Alt Carbon’s commitment to using field deployments and primary data collection is a vital step in overcoming these scientific uncertainties.
As the partnership progresses, the focus will shift to scalability. Removing 36,920 tons is a significant start, but it represents only a fraction of what is needed to move the needle on global temperatures. The ability of Alt Carbon to scale its operations to 5 million tons will depend on maintaining the integrity of its MRV processes and ensuring that the logistical chain—from mine to field—remains carbon-efficient.
For Microsoft, this deal is another step toward a future where carbon removal is a standard part of corporate operations. By supporting early-stage innovators like Alt Carbon, the tech giant is not just buying credits; it is helping to mature an industry that the Intergovernmental Panel on Climate Change (IPCC) suggests will be necessary to limit global warming to 1.5 degrees Celsius. The eyes of the climate tech world will be on Darjeeling as this project unfolds, testing whether the ancient hills of India can provide a modern solution to the world’s most pressing environmental challenge.
