Microsoft has signed a multi-year agreement to purchase up to 36,920 metric tonnes of verified carbon dioxide removal from Alt Carbon’s Enhanced Rock Weathering operations in India.

Announced on 11 June 2026, the agreement will source carbon dioxide removal credits from the Darjeeling Revival Project in West Bengal. According to Alt Carbon, it is Microsoft’s first Asian purchase of carbon credits generated through Enhanced Rock Weathering, commonly abbreviated as ERW.

The agreement is significant for both India’s emerging carbon removal sector and the wider corporate climate market. It places a major global technology buyer behind a project that combines geochemical carbon removal, agricultural land management, laboratory analysis and rural employment.

Alt Carbon reports that it has onboarded more than 80,000 acres of agricultural land, works with over 35,000 farmers across more than 60 gram panchayats and has created over 250 jobs in field operations, logistics and laboratory monitoring. Its Isometric registry currently shows 9,566.66 Enhanced Weathering certificates issued across three active projects.

For corporate sustainability and procurement teams, however, the transaction should not be assessed solely by its headline volume. The credibility of Enhanced Rock Weathering depends on how the basalt is sourced, how its environmental impact is controlled and how the resulting carbon removal is measured, reported and independently verified.

Microsoft and Alt Carbon Agreement at a Glance

The principal elements announced for the agreement are:

• Up to 36,920 metric tonnes of carbon dioxide removal
• A multi-year purchasing arrangement
• Credits generated through Enhanced Rock Weathering
• Removal activity based in India
• Supply from the Darjeeling Revival Project
• Verification before delivery to Microsoft
• The possibility of additional purchases subject to delivery and verification milestones

The commercial value and price per tonne were not disclosed in Alt Carbon’s announcement. The absence of published pricing is common in corporate carbon removal contracts, particularly when pricing may vary according to delivery year, verification costs, scientific uncertainty and contracted volume.

The deal is an offtake agreement rather than an immediate transfer of 36,920 already-issued credits. Alt Carbon must carry out the physical project activity, quantify the resulting net carbon removal and complete the required validation and verification procedures before the contracted credits can be issued and delivered.

This distinction is important. A carbon removal purchase agreement represents a commitment to future delivery, while an issued certificate represents removal that has passed the applicable monitoring and verification process.

What Is Enhanced Rock Weathering?

Enhanced Rock Weathering accelerates a natural geochemical process through which certain rocks react with carbon dioxide and water.

The process normally involves crushing silicate-rich rock, such as basalt, into a fine material and applying it to agricultural soil. Crushing increases the available surface area, allowing chemical weathering to occur faster than it would with larger pieces of rock.

Atmospheric carbon dioxide dissolves in rainwater and soil water, creating a weak carbonic acid. This reacts with minerals in the applied rock, releasing base cations and increasing alkalinity. Part of the carbon can then be transported through soil water as dissolved bicarbonate before moving into groundwater, rivers and potentially the ocean.

The intended result is the transfer of atmospheric carbon into a more durable dissolved inorganic form.

Independent scientific reviews estimate that terrestrial Enhanced Weathering could eventually have the technical potential to remove approximately 0.5 to 2 gigatonnes of CO₂ annually by 2050. This is a potential range rather than a deployment forecast, and achieving it would require large-scale mining or by-product supply, processing, transport, agricultural participation and reliable monitoring.

Does the Carbon Become Corals and Seashells?

The chemistry is more complex than the simplified claim that captured carbon automatically becomes corals or seashells.

Bicarbonate can remain dissolved in water for long periods and may eventually reach the ocean. Some of that carbon can participate in carbonate chemistry or mineral formation, but the exact outcome depends on water chemistry, biological processes, transport pathways and the location at which mineral precipitation occurs.

In some circumstances, carbonate precipitation can also release part of the carbon back as CO₂. High-quality carbon accounting must therefore consider the complete pathway from rock application and soil weathering to downstream storage.

The durability of Enhanced Rock Weathering may extend beyond 1,000 years, but that durability must be supported by project-specific evidence rather than assumed from the underlying chemistry alone. Microsoft classifies mineralisation-based removals among high-durability pathways and prioritises projects with appropriate monitoring, responsible storage and full lifecycle assessment.

How the Darjeeling Revival Project Works

Alt Carbon sources waste basalt rock and applies the processed material to tea estates and neighbouring agricultural land in West Bengal.

The region’s warm conditions and high rainfall may support faster chemical weathering than colder or drier environments. However, weathering performance is also influenced by basalt composition, particle size, soil acidity, water movement, application rate and agricultural practices.

The project’s principal activities include:

• Characterising the basalt feedstock
• Transporting and processing the rock material
• Applying measured quantities to farmland
• Establishing treated and untreated comparison areas
• Collecting soil and porewater samples
• Measuring changes in soil chemistry
• Estimating net carbon removal
• Monitoring environmental safeguards
• Documenting field operations
• Submitting data for independent verification

Alt Carbon describes its project as an effort to restore degraded soils while supporting Darjeeling’s tea-growing communities. Its public project information says it works with farmers and tea estate owners to spread its basalt-based soil amendment, test soil and porewater and measure both carbon removal and agricultural outcomes.

Agricultural Benefits Are Possible but Must Be Verified

Basalt can contain calcium, magnesium, potassium and other elements that may improve some soils. Enhanced Weathering may also help neutralise acidic conditions and reduce dependence on conventional agricultural lime in suitable locations.

Potential agricultural benefits include:

• Improved soil pH
• Replenishment of selected mineral nutrients
• Better nutrient availability
• Reduced soil acidification
• Potential crop-yield improvements
• Improved resilience of degraded agricultural land

These outcomes are not guaranteed on every farm.

The response will depend on the original soil condition, crop type, basalt composition, application rate, rainfall and existing fertiliser programme. A material that benefits one soil may provide little advantage or create unwanted changes in another.

Alt Carbon reports crop-yield improvements from its project, but corporate buyers should distinguish between developer-reported agricultural performance and independently verified carbon removal. Agronomic claims, social benefits and carbon accounting may require different evidence and verification procedures.

Why Microsoft Is Buying Carbon Removal

Microsoft has committed to becoming carbon negative by 2030. Its strategy includes reducing operational and value-chain emissions while building a portfolio of carbon dioxide removal projects intended to address residual emissions.

The company purchases several forms of carbon removal, including biochar, direct air capture, biomass carbon removal and storage, mineralisation, soil-based methods and Enhanced Rock Weathering. Microsoft’s published criteria place particular emphasis on lifecycle accounting, durability, environmental safeguards and measurement.

Technology companies have become some of the largest purchasers of engineered carbon removal because their data centres, construction programmes, hardware supply chains and growing AI workloads create substantial emissions that cannot yet be eliminated immediately.

Carbon removal should not be treated as an alternative to cutting those emissions.

A credible corporate climate strategy should generally follow this hierarchy:

1. Measure direct and value-chain emissions.
2. Improve energy and material efficiency.
3. Replace fossil-fuel electricity with additional carbon-free energy.
4. Electrify suitable processes and transport.
5. reduce supply-chain emissions.
6. Use high-quality carbon removal for residual emissions that remain difficult to eliminate.

Microsoft’s carbon removal programme therefore operates alongside, rather than instead of, its renewable electricity, energy efficiency and supply-chain decarbonisation programmes.

Why This Is Different from a Conventional Carbon Offset

The terms carbon offset, carbon credit and carbon removal credit are often used interchangeably, but they do not necessarily represent the same environmental outcome.

An avoided-emissions credit may claim that a tonne of emissions was prevented compared with a projected baseline. Examples may include preventing deforestation or replacing a fossil-fuel activity with a lower-emission alternative.

A carbon removal credit is intended to represent CO₂ physically removed from the atmosphere and stored for a defined period.

Enhanced Rock Weathering belongs to the removal category because its purpose is to transfer atmospheric carbon into stable dissolved or mineral forms.

This does not automatically make every ERW credit high quality. The project must still demonstrate:

• That the removal would not have occurred without the intervention
• That the carbon quantity has been measured conservatively
• That project emissions have been deducted
• That the same removal is not claimed more than once
• That environmental harm has been avoided
• That storage durability is supported by evidence
• That uncertainty has been quantified
• That verification is independent

The difference between an estimated future removal and an independently issued certificate is therefore commercially important.

Measurement, Reporting and Verification Determine Credit Quality

Enhanced Rock Weathering is attractive partly because the physical deployment can use existing agricultural and quarrying infrastructure. Measuring the resulting carbon removal is much more difficult.

A direct air capture facility can measure the quantity of concentrated CO₂ passing through industrial equipment. ERW occurs across large areas of heterogeneous soil, where weathering rates vary with rainfall, soil depth, mineral composition and biological activity.

A reliable monitoring, reporting and verification programme may need to track:

• Basalt mineralogy and chemical composition
• Particle-size distribution
• Quantity applied to each field
• Treatment and control plots
• Soil elemental changes
• Porewater chemistry
• Bicarbonate formation
• Carbon movement below the root zone
• Crop uptake
• Potential carbonate formation
• Nitrous oxide effects
• Grinding and transport emissions
• Uncertainty ranges

Isometric’s Enhanced Weathering protocol requires representative sampling in treated and control areas and chemical analysis of soil and porewater. Its stated objective is to issue certificates only after durable removal has occurred rather than issuing credits solely from predicted future performance.

Independent Verification and Public Records

Alt Carbon’s first verified credits were issued under Isometric’s Enhanced Weathering in Agriculture Protocol and independently validated and verified by 350Solutions.

Isometric states that the measurement data and calculations supporting issued credits are available through its public registry, creating an audit trail that can be independently reviewed.

The registry currently records:

• 9,566.66 certificates issued
• 919 certificates retired
• Three active projects
• 191.335 certificates allocated to the supplier buffer pool
• No recorded buffer-pool reversals

A buffer pool reserves a proportion of certificates to address uncertainty or potential reversals. It is one risk-management mechanism, although it does not replace conservative measurement or project-level environmental safeguards.

Alt Carbon’s Laboratory and Field Infrastructure

Alt Carbon operates internal scientific and laboratory infrastructure to support its ERW projects.

Shonku Labs carries out research and development at the company’s Bangalore headquarters within the Indian Institute of Science environment. Its Darjeeling Climate Action Lab supports sample preparation and geochemical analysis for field operations in West Bengal.

Laboratory work can include:

• Soil preparation
• Elemental analysis
• Mineral identification
• Isotope analysis
• Porewater testing
• Basalt characterisation
• Environmental safeguard monitoring
• Data quality control

The company’s June 2026 announcement states that its Darjeeling laboratory is intended to process up to 100,000 samples annually. An earlier 2024 announcement cited a substantially higher target capacity, so buyers assessing laboratory scale should request the latest operational throughput, equipment list and quality-assurance records rather than relying only on headline capacity figures.

For ERW, laboratory capacity is a central part of the business model. If every tonne of removal requires extensive manual sampling and expensive chemical analysis, monitoring costs can restrict commercial scale.

Developers are therefore working to combine physical measurements with models, remote sensing and improved sampling design. Any cost reduction must preserve confidence in the issued removal quantity.

What Corporate Carbon Removal Buyers Should Check

A carbon removal contract should be evaluated with the same discipline as a long-term energy, infrastructure or technology procurement agreement.

Delivery Structure

The buyer should establish:

• The contracted quantity
• Expected delivery years
• Minimum annual delivery
• Conditions for additional purchases
• Remedies for under-delivery
• Substitution rights
• Verification deadlines
• Registry used for issuance

A large headline contract may contain conditional volumes that depend on future milestones.

Net Removal Accounting

The project should deduct emissions associated with:

• Rock crushing
• Screening and processing
• Road or rail transport
• Application machinery
• Sampling
• Laboratory operations
• Fertiliser interactions
• Changes in other greenhouse gases

Gross weathering estimates should not be sold as net carbon removal.

Feedstock Quality

Not every rock is suitable for agricultural application.

Procurement due diligence should examine:

• Mineral composition
• Weathering potential
• Nickel, chromium and other trace metals
• Asbestos-form mineral presence
• Particle size
• Dust exposure
• Agricultural safety
• Source traceability
• Whether the material is genuinely a waste stream

Using quarry waste may lower costs and reduce the need for new extraction, but waste status does not remove the need for chemical and environmental testing.

Farmer Participation and Land Rights

Large agricultural projects require clear agreements with farmers, tea estates and local institutions.

Buyers should assess:

• Informed participation
• Land-use permissions
• Compensation or benefit-sharing
• Complaint procedures
• Worker health and safety
• Community consultation
• Long-term monitoring access
• Protection of existing agricultural livelihoods

Alt Carbon says it conducts agricultural meetings in collaboration with women’s self-help groups and local panchayats and has created an Association of Responsible Deployers involving estate management and labour organisations. These structures may support community participation, but their effectiveness should be assessed through project evidence and stakeholder feedback.

Double Counting and Credit Ownership

The contract should clearly establish who owns the environmental claim.

A single tonne of removal must not be simultaneously:

• Sold to two corporate buyers
• Counted by both the farmer and the credit purchaser
• Used for more than one climate target
• Claimed under overlapping registries
• Included in a national accounting mechanism without appropriate adjustment where required

Registry serial numbers, retirement records and contractual language are essential for avoiding duplicate claims.

The Scientific Limitations of Enhanced Rock Weathering

ERW is promising, but it remains an emerging carbon removal pathway.

A major scientific review published in 2025 identified several outstanding challenges, including the need to follow carbon from soil to downstream storage, quantify delays, standardise methodologies and complete long-duration field trials. The authors also identified initial credit prices, lifecycle emissions and inconsistent methodologies as barriers to scaling.

Weathering Can Take Time

Applying basalt does not create an immediate tonne of carbon removal.

The reaction rate depends on:

• Climate
• Soil moisture
• Soil acidity
• Mineral composition
• Particle size
• Root activity
• Drainage
• Application depth

Some carbon transformations may occur relatively quickly, while movement through deeper soil and groundwater can take much longer.

Carbon Can Be Difficult to Track

Carbon does not remain in one easily measured container. It moves through soil water, groundwater, rivers and potentially the ocean.

Monitoring must determine whether measured chemical changes represent new atmospheric CO₂ removal or are caused by existing soil minerals, fertilisers, liming or other processes.

Project Emissions Can Reduce the Benefit

Grinding rock into fine particles requires energy. Transporting large quantities of dense mineral material can also create significant emissions.

Projects located close to suitable waste basalt and agricultural land may have a stronger lifecycle profile than projects requiring long-distance transport or purpose-mined feedstock.

Environmental Effects Require Monitoring

Rock application may alter:

• Soil pH
• Nutrient availability
• Trace-metal concentrations
• Water chemistry
• Soil organisms
• Crop uptake
• Downstream ecosystems

Responsible scaling requires feedstock screening, conservative application rates and continued environmental monitoring.

Why India Could Become an Important ERW Market

India offers several conditions that could support Enhanced Rock Weathering deployment:

• Large agricultural areas
• Warm and seasonally wet climates
• Existing mineral and quarrying industries
• Extensive farming networks
• Lower field and laboratory costs than several developed markets
• Strong scientific and engineering capabilities
• Growing climate-technology investment

Tropical and subtropical conditions can accelerate chemical weathering, while existing agricultural spreading equipment may reduce deployment costs.

These advantages do not apply uniformly across the country. Local soil chemistry, groundwater conditions, rainfall, crop selection and basalt availability must be assessed for each region.

The Microsoft agreement gives India greater visibility within the engineered carbon removal market, but long-term leadership will depend on consistent verification, transparent data and responsible community participation rather than low cost alone.

What the Deal Means for Solar and Energy Companies

Carbon removal is becoming relevant to companies throughout the renewable energy supply chain.

Solar panels, solar inverters, solar batteries and energy storage systems help customers avoid future emissions by replacing fossil-fuel energy and improving system flexibility. Manufacturing and transporting those products still creates residual emissions.

A solar PV supplier, solar distributor or solar wholesaler may encounter emissions from:

• Module and battery manufacturing
• Aluminium frames
• Glass production
• Semiconductor components
• International freight
• European warehousing
• Business travel
• Packaging
• Product installation
• End-of-life treatment

The first priority should be to reduce those emissions through cleaner production, renewable electricity, lower-carbon transport and more efficient logistics.

High-quality carbon removal may then be considered for emissions that cannot yet be eliminated economically or technically. It should not be used to market a poorly designed or carbon-intensive product as environmentally neutral.

Questions for Renewable Energy Procurement Teams

A B2B solar webshop, EPC company or European solar wholesaler considering carbon removal should ask:

• Does the project remove atmospheric CO₂ or only claim avoided emissions?
• Is the removal already issued or contracted for future delivery?
• Which registry and methodology are used?
• Who performs independent verification?
• Are lifecycle emissions deducted?
• How long is the carbon expected to remain stored?
• How is uncertainty treated?
• Are the underlying data publicly available?
• What environmental and social safeguards apply?
• How will the certificate be retired?
• Which corporate claim will be made?

These questions help distinguish procurement-ready carbon removal from a general environmental marketing claim.

Carbon Removal Does Not Replace Solar Deployment

The Microsoft–Alt Carbon deal illustrates an important distinction between emissions reduction and carbon removal.

Renewable electricity prevents emissions that would otherwise be produced by fossil-fuel generation. Carbon removal addresses CO₂ that is already in the atmosphere.

Both may be required in a credible long-term climate strategy, but the order matters.

For most organisations, installing solar panels, procuring additional renewable electricity, improving efficiency and using battery energy storage will avoid more emissions at a lower cost than purchasing engineered removal credits.

Carbon removal is most credible when applied to the remaining emissions after practical reductions have been implemented.

For energy-intensive companies, the complete strategy may therefore combine:

• Commercial or utility-scale solar PV
• Renewable power purchase agreements
• Solar inverter and energy-management upgrades
• Solar battery and C&I energy storage
• Fleet electrification
• Lower-carbon logistics
• Supplier emissions reductions
• Verified carbon removal for residual emissions

A carbon credit cannot compensate for a lack of operational decarbonisation planning.

Frequently Asked Questions About the Microsoft and Alt Carbon Deal

How much carbon removal will Microsoft purchase from Alt Carbon?

Microsoft has agreed to purchase up to 36,920 metric tonnes of verified carbon dioxide removal through a multi-year agreement.

Where will the carbon removal take place?

The credits will be generated through the Darjeeling Revival Project in West Bengal, India.

What is Enhanced Rock Weathering?

Enhanced Rock Weathering involves applying finely crushed silicate rock, such as basalt, to soil. The minerals react with CO₂ dissolved in water, increasing alkalinity and converting part of the carbon into durable dissolved inorganic forms.

Have all 36,920 credits already been issued?

No. The agreement covers future verified delivery. Alt Carbon’s Isometric registry currently records 9,566.66 certificates issued across its active projects.

Who verifies Alt Carbon’s carbon removal credits?

Alt Carbon’s first credits were independently validated and verified by 350Solutions under Isometric’s Enhanced Weathering in Agriculture Protocol. Future credits must follow the applicable validation, verification and registry procedures.

How long can Enhanced Rock Weathering store carbon?

The pathway may provide storage lasting more than 1,000 years, but actual durability depends on chemical conditions, downstream transport and project-specific monitoring.

Does basalt improve agricultural soil?

It may improve pH and provide selected mineral nutrients in suitable soils. Results depend on the feedstock, soil, crop, rainfall and application rate, so benefits should be measured rather than assumed.

Is carbon removal a substitute for renewable energy?

No. Companies should first reduce their energy and supply-chain emissions through efficiency, solar power, clean electricity and electrification. Carbon removal is intended mainly for residual emissions that remain difficult to eliminate.

Microsoft’s agreement with Alt Carbon provides commercial support for one of the carbon removal market’s most promising but scientifically demanding pathways. The project combines Indian agricultural networks, waste basalt, laboratory analysis and independent credit verification in an attempt to deliver durable atmospheric carbon removal at scale.

Its success will depend on more than the contracted number of tonnes. Alt Carbon must demonstrate that the weathering occurred, that the carbon has been conservatively quantified, that lifecycle emissions have been deducted and that local environmental and social safeguards remain effective as deployment expands.

For clean energy businesses, the lesson is equally clear. Solar PV, electrification and energy storage remain the primary tools for avoiding new emissions. High-integrity carbon removal can support those measures, but it cannot replace them.