Background
As the world races to find new, cutting-edge solutions to our climate crisis, one piece of ancient wisdom has been re-emerging as a ready-to-deploy option with multiple benefit streams. Biochar, a term derived from "biological charcoal,” is the result of heating biomass (such as wood, crop residues, or animal manure) to between 400-800°C in an oxygen-limited environment through a process called pyrolysis. This method prevents the biomass from combusting, leaving behind a gas (syngas), a liquid (bio-oil), and a solid (biochar). The resulting solid, which contains the carbon from the biomass in a highly permanent form, can be used to improve soil health. Note that there are many other use cases for biochar, such as a sand replacement in concrete, but these are not the focus of this article. While the end product looks similar to common charcoal, the burning method ensures that biochar is distinct in its carbon density, chemical composition, and ability to lock carbon away for hundreds to thousands of years.
Biomass pyrolysis uses converts organic biomass into a series of outputs, including biochar, bio-oil, gas, and heat/electricity1
Biochar and Soil Health
Interestingly, the concept of biochar is not new; its roots date back to ancient agricultural practices from over 2,500 years ago. Indigenous communities across the world, from the Amazon Basin to sub-Saharan Africa, have historically used biochar as a soil amendment to improve fertility and crop yields. When biochar is incorporated into soil, it enhances the soil's nutrient-holding capacity and promotes microbial activity, which in turn increases crop yields. Studies have shown that soils amended with biochar exhibit higher levels of essential nutrients crucial for plant growth, leading to materially higher crop yields.2 Biochar also acts as a powerful adsorbent, effectively capturing and immobilizing pollutants in both soil and water. By reducing contaminants such as heavy metals and organic pollutants, biochar helps purify water sources and prevents their leaching into groundwater, thus improving overall environmental quality. Another significant benefit of biochar is its impact on soil structure. The microstructure of the biochar, as shown in the image below, increases soil porosity, creating spaces that enhance water infiltration and retention. This property is particularly beneficial in arid and semi-arid regions where water availability is limited, as it helps plants access water more efficiently during dry periods.
Biochar's spongy microstructure helps soil absorb and retain water3
Carbon Credits
Beyond its agricultural benefits, biochar has emerged as a leading method to capture and sequester carbon dioxide. In fact, pyrolysis of biomass to create biochar is currently the most effective method of carbon sequestration, according to the voluntary carbon markets: in 2023, 94% of deliveries of carbon removal credits (in which a given unit of carbon has been sequestered and verified by an agency such as Puro.Earth) were from biochar production.4 The dominance of biochar in deliveries of carbon credits indicates how far ahead biochar is in real impact as compared to recently introduced technologies that are still struggling to scale, such as direct air capture, enhanced rock weathering, and point source capture.
The permanence of carbon credits generated from biochar production has at times been called into question. However, recent research has indicated that biochar produced at high enough temperatures sequesters the majority of its carbon content for thousands of years. This is due to the graphitic microstructure of carbon that is formed at high temperatures. Simply put, microbial enzymes are unable to break down the graphitic carbon because each carbon atom is bonded to multiple neighboring atoms, creating large structures that the enzymes cannot cleave. These carbon structures are referred to as polycyclic aromatic carbon, and they are stable for thousands of years.
Most of the carbon locked up via biochar remains sequestered for 1000+ years5
Challenges
While biochar offers substantial benefits, its production presents several challenges. Achieving high-quality biochar requires precise control over pyrolysis conditions to maximize carbon retention and minimize emissions. The decentralized nature of biomass sources (which often include farm waste or dispersed woody biomass in a forest) further complicates production logistics, as transporting biomass to centralized facilities can introduce costs and emissions. To address this, mobile pyrolysis units have emerged as a practical solution by processing biomass on-site. However, ensuring consistent quality and verifying carbon sequestration outcomes remain ongoing challenges that will require more production capacity and further technological innovation in the future.
Additional Case Studies
Wildfire Risk Mitigation
In California, utility companies are exploring biochar as a solution to manage wildfire risks exacerbated by overgrown forests and the accumulation of biomass waste from routine maintenance of power lines. Instead of allowing this biomass to decompose, or worse, become fuel for wildfires, biochar offers a closed-loop, climate-positive disposal method. Moreover, as mentioned earlier, biochar enhances soil water retention, thereby fortifying the forest against future fires. Despite this potential, implementing biochar faces practical challenges. The dispersed nature of the waste biomass suggests that a mobile pyrolysis unit is the most viable option. However, limited production capacity means few units are currently available, with extensive waiting lists among the handful of companies producing these units. Furthermore, California's stringent fire regulations restrict the operational window for mobile pyrolysis units to just a few months each year. Addressing these issues necessitates a fully trained and scaled workforce capable of efficiently managing large volumes of biomass within a limited timeframe. Despite these challenges, the potential benefits of biochar in mitigating wildfire risks in California make it a promising avenue for further exploration and implementation.
Agricultural Efficiency
Across the world, biochar production has the potential to fundamentally change how crop waste is disposed of and to create a circular farming system. In Louisiana, a sugarcane farm that has operated for over 150 years is setting up biochar production as a solution to its multi-million ton piles of sugarcane waste (aka bagasse) that have built up over their many years of operation. Once the sugarcane waste has been turned into biochar, it will be sold to compost producers and used as an input for other farms across the state. Similarly, in Kenya, sugar producers are moving toward creating biochar from their massive piles of bagasse which they will provide to their raw sugarcane suppliers upstream, in order to increase crop yields. This will free up acres of land that are currently filled with bagasse, lock away the carbon that would have otherwise been released as the bagasse decomposes over time, improve the health of the soil in the fields where the sugarcane is grown, and provide an additional revenue stream from the sale of carbon credits.
Multi-million ton pile of sugarcane bagasse at a sugar mill in Kenya.
Conclusion
In sum, biochar represents a convergence of ancient agricultural wisdom and modern environmental science, offering a pathway to sustainable agriculture and proven carbon sequestration. While challenges in production and scalability persist, the growing recognition of biochar's benefits underscores its potential as a pivotal tool in mitigating climate change impacts and fostering resilient ecosystems. As we navigate the complexities of a changing climate, biochar stands out as a testament to the enduring relevance of indigenous practices in shaping sustainable solutions for the future.
Sources
1https://spacebakery.be/en/basics-biochar
2https://www.sciencedirect.com/science/article/pii/S2666049024000070
3https://www.researchgate.net/publication/317185366_Biochar_characteristi...
4https://www.cdr.fyi/blog/2023-year-in-review
5https://www.biochar-journal.org/en/ct/109-Permanence-of-soil-applied-bio...