How these brothers harnessed the carbon market to rescue India's tea plantations
The Alt Carbon project now offers some of the cheapest CDR credits globally and aims to scale up to gigaton levels by 2050
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Alt Carbon’s story began in a moment of crisis. When the pandemic swept across India in 2020, it plunged many of the Darjeeling tea farms into destitution. The Agarwal brothers Sparsh and Shrey – 4rth generation tea estate owners – travelled for 16 hours from Calcutta to Darjeeling on the day lockdown was lifted in India, to close down the failing family tea plantation. "We wanted to spend a week at the family tea estate before selling it. During that week, we reflected on our situation and realized we had all these fancy degrees. We wondered if we could use them to turn things around. We've been familiar with the area and the local community since childhood—they’ve known our family for generations. So, we thought, 'Can we do something meaningful here?'
“We decided to stay at the tea estate, and we renamed the house ‘Second Chance House’ as a symbol of hope. It became a way to prove our self-worth by making the most of what we had," says Sparsh Agarwal.
The fourth-generation tea farmers devised a plan that transformed their family estate into a climate action frontier. They developed a direct-to-consumer tea brand and launched Alt Carbon to pioneer issuing carbon credits for Enhanced Rock Weathering (ERW) on tea plantations. Their ERW process disperses finely crushed basalt rock over farmland. As the rock particles break down, they bind with COâ‚‚ from the air and soil, forming bicarbonate ions that eventually wash into the oceans, removing carbon from the atmosphere for centuries. In the nutrient-starved soils of Darjeeling, this method also restores essential minerals, helping farmers boost yields by as much as 30-50% for smallholders growing rice and bamboo.
The idea for Alt Carbon had come from Shrey’s engineering degree. He had studied ERW and realised Darjeeling’s geography was ideal for the process. He saw ERW as a way to solve a longstanding issue: acidic soils that had drained the region’s farmlands of productivity. Traditionally, estates had spent up to $40,000 annually on agricultural lime treatments, but with economic downturns in the tea industry, this had become unsustainable. ERW provided a solution: by spreading basalt on farmland soil, they could not only capture carbon, but improve soil quality and crop-yield. If the carbon capture was accredited via the carbon market, it could be offered to farmers at no cost, creating a win-win for crop health, local economies and carbon capture.
ERW accelerates natural rock weathering to remove carbon dioxide from the atmosphere and has the potential to sequester gigatonnes of carbon dioxide. According to The Intergovernmental Panel on Climate Change (IPCC) we need to remove at least 10 billion tonnes of COâ‚‚ from the atmosphere every year by 2050 to avoid the worst impacts of climate change. Enhanced rock weathering, if scaled, holds the promise of removing 4 billion tonnes of CO2 on an annual basis, meeting 40% of this climate target.
Alt Carbon has just signed a deal with NextGen CDR, one of the world’s largest diversified portfolios of permanent carbon dioxide removals (CDRs), becoming the first carbon credit provider outside of Europe and the US on the platform. The Alt Carbon project now offers some of the cheapest CDR credits globally and aims to scale up to gigaton levels by 2050, positioning India as a global hub for carbon removal.
What’s your background and what led you to green techpreneurship?
Sparsh: My younger brother and I are fourth-generation Darjeeling tea farmers. Academically, I studied political philosophy and later worked at a think tank, the Center for Policy Research, as chief of staff. Then I pursued international climate law at Oxford. My brother has a background in chemistry and mechanical engineering from BITS Pilani. We didn’t originally envision careers in climate tech, but the credit goes to my brother. I was focused on climate finance and carbon markets, but my brother’s background in chemistry and engineering led him to study rock weathering, specifically the potential for enhanced weathering to capture CO₂. India’s geography and mineral resources make it particularly suited to this approach, and it just clicked for us.
Rock weathering sounds like a complex process. Can you explain how it works for carbon removal?
Sparsh: In nature, when rainwater containing CO₂ interacts with alkaline minerals in certain rocks, a chemical reaction occurs that converts the CO₂ into stable bicarbonate, which is then transported to the oceans. Normally, this process takes millions of years, but we accelerate it by spreading finely ground basalt rock dust—an abundant resource in India—across the soil.
The increased surface area of the rock dust speeds up the reaction, allowing carbon to be sequestered as bicarbonate in groundwater and eventually deposited in the ocean. Enhanced rock weathering is particularly powerful because it locks CO₂ away for thousands of years in one of Earth’s largest carbon sinks—the ocean.
How does this technique benefit tea farming?
Sparsh: Rock weathering fits well with agriculture, particularly for tea estates, which often have acidic soil. Basalt rock dust neutralizes soil acidity and enriches it with nutrients, improving crop yield by as much as 20–30% in tea and even more for other crops like rice and bamboo.
So, farmers get these benefits for free since we provide them with basalt dust, while we gain a valuable carbon removal solution. It’s a win-win: improved soil health, increased productivity, and stable carbon storage.
What did it take to make the NextGen deal happen and become accredited for carbon credits?
Cost-effectiveness
Being based in India gives us cost advantages in materials, labor, and transport, making us one of the most cost-effective carbon removal providers.
Unique access to scale
As a family with strong community ties, we have access to over 5,000 acres of land and connections across the tea belt, which spans 450,000 hectares in northeastern India. This gives us the capacity to scale and deliver carbon removal on a massive level. Our partnerships are built on community trust, and farmers benefit directly, creating a sustainable cycle of support.
Rigorous scientific measurement of carbon removal
Shrey: Our ERW process itself is simple: spread crushed basalt rock on farmland. Yet, the science behind it is incredibly hard to crack. The real work is in accurately measuring how much carbon is actually removed from the atmosphere, which is a process with many steps. To get precise data, we take soil samples from different depths and at multiple times throughout the year, collecting several samples per acre. These samples undergo chemical preparation and analysis, yielding critical data points. These data points are then fed into advanced geochemical models to calculate accurate carbon removal rates. To do this, we established the Darjeeling Climate Action Lab, a cutting-edge geochemical facility. We collaborate with academic labs at the Indian Institute of Science, but as we grow, we’ll need to expand into commercial labs to scale up our impact.
What does this mean for India’s role in the carbon market?
Sparsh: This partnership signals a big shift. India has been a significant player in carbon markets, but there’s been a trust gap. This deal with NextGen shows that high-quality carbon credits can come from innovative projects in the Global South. We believe India can become the manufacturing hub for global carbon removal.
Why is India especially suited for using EWR for carbon removal?
Shrey: India has the ideal climate, geological resources, and low-cost structure to make carbon removal efficient. Our high temperatures, humidity, and rainfall all accelerate rock weathering, and we have a wealth of basalt rock that we can source affordably. Geologically, we have conditions like the high pH in the Bay of Bengal, which minimises COâ‚‚ degassing. All these factors position India uniquely to lead ERW carbon removal efforts worldwide.
What does the future hold?
Shrey: We want to fulfil our family’s vision for the estate, making it a model of sustainability. Then, we aim to scale this to the entire tea industry, removing 5 million tons of CO₂ per year by 2030. But to truly address climate change, we need to reach gigaton-scale impact. Long-term, we’re working to make India the world’s hub for carbon removal, combining our expertise and India’s climate and cost advantages.
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#SparkTheTransition,
Marianne