The journal Biochar recently published a perspective by authors Robert W. Brown, David R. Chadwick, and Davey L. Jones that addresses a critical misunderstanding in the burgeoning carbon removal industry. As carbon dioxide removal technologies become central to global net-zero goals, biochar has emerged as a dominant force, accounting for 94% of delivered carbon credits globally in 2023 despite receiving only a small fraction of total funding. However, the authors argue that the scientific community and policymakers frequently conflate two distinct properties: the stability of the carbon stored in the biochar and the secondary benefits it provides to the soil. This conflation risks misrepresenting what specific biochar products can actually achieve in different environments.

The fundamental findings of the study center on a significant trade-off driven by production temperatures. Biochar produced at high temperatures, typically exceeding 700°C, develops a dense network of stable polycyclic aromatic carbon structures. This molecular arrangement makes the material incredibly resistant to decay, allowing it to remain in the soil for more than a millennium. While this makes high-temperature biochar the gold standard for long-term carbon sequestration, the intense heat strips away the surface functional groups that allow the material to interact with water and nutrients. Consequently, the most stable forms of biochar are often the most chemically inert, providing fewer immediate advantages for soil fertility or pollutant management.

In contrast, biochar produced at lower temperatures, ranging from 350°C to 500°C, retains a higher proportion of oxygen-containing functional groups. These groups are essential for soil conditioning because they enable the biochar to hold onto nutrients and improve water retention through cation and anion exchange. While these varieties are far more effective at boosting crop yields and stabilizing heavy metals or organic pollutants, they are significantly less durable. The research indicates that these less stable biochars may only persist in aerobic soil environments for 100 to 300 years. This shorter residence timeResidence time refers to the duration that the biomass is heated during the pyrolysis process. The residence time can influence the properties of the biochar produced.   More reduces their overall potential for permanent carbon sequestration compared to their high-heat counterparts.

The effectiveness of these different biochar types is also highly dependent on the location and condition of the soil where they are applied. Highly productive soils in temperate climates, which already possess high fertility and buffering capacity, are less likely to show significant yield increases from any biochar application. On the other hand, degraded or tropical soils often respond dramatically to the co-benefits of lower-temperature biochar, as the added nutrient retention and liming effects have a greater impact on productivity. The authors emphasize that while carbon storage should be pursued in all climates, the choice of biochar must be tailored to the specific goals of the end user, a concept they refer to as designer biochar.

To bridge the gap between stability and soil benefits, the study explores several activation methods that can enhance the functionality of high-stability biochar. Techniques such as co-composting or coating the material with nutrient-rich substances like slurry or manure can create a biological scaffold for microbial colonization. These treatments introduce organic acids and microbial communities to the chemically inert surface of high-temperature biochar, potentially allowing for both permanent carbon storage and meaningful soil improvement. However, these extra steps often involve higher production costs and require careful matching with local soil conditions to be successful.

Moving forward, the researchers advocate for much greater transparency and clarity in how biochar properties are reported. Markets and policies must recognize that not all biochars are created equal. Oversimplifying the benefits of biochar could lead to a misallocation of resources and a loss of confidence in voluntary carbon markets. By decoupling carbon durability from soil co-benefits, the industry can better design products that meet specific environmental and agricultural needs. Ensuring that the inherent trade-offs between permanent storage and soil functionality are clearly communicated is vital for the long-term integrity of biochar as a climate solution.

Source: Brown, R. W., Chadwick, D. R., & Jones, D. L. (2026). Clarifying the conflation of biochar carbon stability and its soil co-benefits. Biochar, 8(67).