From a struggling family tea estate to an innovative climate venture, Alt Carbo has raised $12 million in a seed round as it plans to scale its carbon dioxide removal work in the South Asian nation. The climate tech startup, which locks away carbon for thousands of years through enhanced rock weathering on farmlands, attracted investment led by Lachy Groom, the co-founder of the robotics AI company Physical Intelligence.
The journey began in May 2020 with a bittersweet homecoming. Siblings Shrey and Sparsh Agarwal drove 16 hours from the eastern state of Kolkata to Darjeeling — a city known for tea farming in the leafy foothills of the Himalayas — expecting to bid farewell to their family’s tea estate, Salem Hill, which was facing bankruptcy. Instead, that farewell visit planted the seeds for Alt Carbon, which they officially launched in late 2023.
Initially, they explored carbon markets as a way to revive their family business and support other tea estates in the region by generating supplementary income. But during their exploration, they discovered enhanced rock weathering as an approach that could transform Darjeeling’s legacy from being at risk of climate change impact to a frontier of climate action.
“Within carbon markets, our realization was that a lot of the projects in India, which are more avoidance-based, are of very low quality, and they produce junk credits,” Sparsh said in an exclusive interview.
Last year, Alt Carbon started its pilot around the Agarwals’ family tea estate on about 500 acres of land, which they later scaled up in North Bengal, expanding their scope from tea farms to those of rice and bamboo. The startup aims to expand to 500,000 hectares of land.
By 2030, the startup aims to remove 5 million tons of carbon from the region, Sparsh told TechCrunch.
Alt Carbon deploys enhanced rock weathering using waste basalt rock dust from mines and quarries in the volcanic igneous province of Rajmahal Traps, located in eastern India. The rock dust, a waste product from the construction industry, is spread on farm fields, where it reacts naturally with rainwater to remove carbon dioxide and add micronutrients to the soil to improve its fertility and health and enhance crop yields. When rainwater containing carbon dioxide interacts with basalt dust, it forms stable bicarbonate ions. These are stored in the soil and eventually flow through rivers to the ocean, where they settle as calcium carbonate, locking away carbon for over 10,000 years.
For transporting the specialized dust from source locations to farm fields, the startup relies on rails and diesel trucks and pays for one-way fares as these sources are part of the tea industry’s freight transportation system. The startup also avoids emissions from dedicated rock processing by relying on the waste basalt from existing mining and crushing operations.
Instead of using the basalt dust alone, the startup has developed a proprietary combination of basalt and other organic ingredients, which it calls Hari Maati (green soil in Hindi), to convince farmers to spread it on their farmlands.
Alt Carbon estimates its carbon credits at $270 per metric ton, which Sparsh said is significantly cheaper than direct air capture credits that, he believes, cost roughly $800 a ton. However, he expects the startup to reduce costs within 36 to 48 months.
The startup relies on three layers of measurements to understand how much rock is getting weathered and how much carbon is being removed, Shrey told TechCrunch. It begins with measurements to track weathering progress and then moves to measuring water within the soil, groundwater sampling, and river monitoring. The third layer uses proprietary reactive transport models that help track ions transported from the soil to water bodies. The startup also uses machine learning-driven modeling to get carbon-removal numbers.
Alt Carbon says its models adhere closely to methodologies set by carbon removal registries, including Isometric and Puro.earth. They have also received approvals from intergovernmental organizations, including SBTi, ICVCM, and CORSIA.
The startup has its labs in Darjeeling and Bengaluru and employs 8 to 10 PhDs, with an overall headcount of 25 employees. It aims to scale these labs and expand its work by doing more soil sample analysis and even setting up a hardware studio for better, high-quality data collection on the ground, using remote sensing. The startup also plans to deploy sensors on the ground to get more insights at a lower cost and in a faster time. All this will come through that seed round led by Groom.
Last year, the startup secured a $500,000 pre-purchase by Frontier and a $1 billion advanced market commitment led by Stripe, Alphabet, Meta, Shopify, and McKinsey. It also recently signed a strategic partnership with a buyer coalition, NextGe , started by South Pole and Mitsubishi Corporation, to scale its enhanced rock weathering. The group also included BCG Group, Swiss RE, LGT, and UBS among its members. Last month, the startup signed an offtake agreement with Japan’s shipping company, MOL Group, to purchase 10,000 tons of carbon removal credits.
Alt Carbon will deliver its first carbon credits in less than a month through Isometric, Sparsh said.