Microsoft has taken another significant step toward its carbon-negative goals by signing a five-year agreement with Carba, a Minnesota-based climate tech startup. Under the agreement, Microsoft will purchase and retire 44,000 tonnes of carbon removal credits between 2025 and 2030. The credits are generated through Carba’s proprietary pyrolysis technology, which converts organic waste into stable biochar that is then securely stored underground.

The deal reinforces Microsoft’s commitment to long-duration carbon removal and signals confidence in biochar burial as a viable and scalable solution.

A new path for permanent carbon storage

Carba’s solution centers around its patented autothermal pyrolysis reactor, which transforms biogenic waste—such as wood chips and agricultural residues—into biochar. This carbon-rich substance is highly stable and resistant to decomposition. Once produced, the biochar is buried in landfills as alternate daily cover in low-oxygen environments, drastically reducing the risk of carbon re-entering the atmosphere.

This approach not only locks carbon away for centuries but also takes advantage of existing waste management infrastructure, reducing the need for additional land or facilities. For Microsoft, this form of durable carbon sequestration aligns with its goal to remove more carbon than it emits by 2030 and to erase its historical carbon footprint by 2050.

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Integrated climate tech with co-benefits

According to Carba’s CEO Andrew Jones, the company’s vertically integrated model—from feedstock collection to processing and burial—offers speed, control, and traceability. “We’re thrilled to contribute to Microsoft’s portfolio by providing high-quality carbon removal credits that will be retired starting in 2025,” said Jones. “Our fully integrated approach enables us to scale quickly while having the potential to deliver significant community co-benefits.”

These co-benefits may include local job creation, waste stream management, and improved soil health in certain applications. While Carba’s initial focus is on secure landfill storage, future applications could expand biochar use in agricultural or construction contexts.

Government support underscores potential

Carba’s credibility received a further boost when it secured a $7 million grant from the U.S. Department of Energy in 2023, awarded under the Carbon Negative Shot Pilot program. This federal initiative is part of the broader Carbon Negative Shot strategy, which seeks to scale technologies capable of removing gigatons of CO₂ from the atmosphere by mid-century.

The grant provides Carba with the resources to refine its technology, scale its reactor network, and validate long-term carbon storage through rigorous third-party monitoring and verification.

Microsoft’s broader carbon removal strategy

Microsoft has been a leading corporate buyer of carbon removal credits, backing a diverse range of solutions including direct air capture, enhanced weathering, ocean alkalinity enhancement, and now biochar burial. The company has emphasized the importance of durability, transparency, and co-benefits when evaluating removal partners.

“By co-locating biomass supply chain delivery, pyrolysis, and end-use & storage, Carba’s biochar burial offers the potential to become a scalable and cost-effective climate solution,” said Brian Marrs, Senior Director for Energy & Carbon Removal at Microsoft. “This agreement allows us to better explore the future of this biochar end-use while benefiting from near-term credit delivery with straightforward monitoring.”

The deal adds to Microsoft’s growing portfolio of long-term carbon removal contracts, many of which aim to support early-stage technologies that have potential to scale in the decades ahead.

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