In a recent commentary in GCB Bioenergy, lead author Hans-Peter Schmidt and colleagues address the evolving scientific and policy debate regarding biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More durability. While biochar serves as a verifiable carbon dioxide removal pathway with mean residence times often exceeding 1,000 years, the authors argue against emerging proposals to classify specific types of biochar as completely inert.  

The commentary challenges the “inertinite” concept, which suggests that biochar meeting a specific reflectance benchmark (Ro ≥ 2%) remains 100% persistent in soil for millennia. Schmidt and his co-authors contend that declaring any soil-applied carbon to be fully resistant to degradation is inconsistent with current scientific understanding. No carbonaceous material is completely inert, and field studies utilizing isotopically labeled biochar reveal measurable decay rates ranging from 0.8% to 7.0% per year. These losses occur even in materials with properties that would otherwise classify them as stable inertinite.  

Biochar aging involves complex interactions between intrinsic material properties and environmental factors. Rather than remaining static, biochar undergoes both decomposition and stabilization processes driven by soil mineralogy, biological activity, and climatic conditions. For example, biochar decomposes more rapidly in biologically active soils compared to those with lower activity, demonstrating that persistence is relative rather than absolute. However, aging also fosters stabilization; biochar interacts with minerals and organic matter to form aggregates that protect it from rapid mineralization.  

Consequently, the authors recommend that policy definitions for biochar carbon removal reflect climate-relevant timescales on the order of centuries rather than millennia. They suggest that durability claims should be supported by registered material properties, traceable application data, and conservative modeling. By acknowledging that biochar persists for hundreds of years but eventually degrades, the scientific community can ensure that carbon accounting remains credible and robust.  

SOURCE: Schmidt, H.-P., Abiven, S., Cowie, A., Glaser, B., Joseph, S., Kammann, C., Lehmann, J., Leifeld, J., Pan, G., Rasse, D., Rumpel, C., Woolf, D., Zimmerman, A. R., & Hagemann, N. (2025). Biochar permanence: A policy commentary. GCB Bioenergy, 17(e70092). https://doi.org/10.1111/gcbb.70092