In July 2025, we published an article summarizing the evolution of biochar persistence science over the past four decades and called for a cross-standard workshop to align scientific and methodological approaches. Now, a few months later, we are pleased to share that this workshop has taken place. 

In October 2025, Puro.earth organized a Biochar Persistence Workshop which brought together Carbon Standard International, Isometric, Puro.earth, Rainbow, and Verra, alongside a group of leading academic researchers in the field of biochar persistence. Held under the Chatham House Rule, the workshop fostered open dialogue on  science and methodologies. Participants exchanged recent insights and agreed to continue collaboration toward greater consistency and transparency in biochar carbon persistence quantification. 

In this article, we share Puro.earth’s key takeaways from the discussions, grouped around five themes. We hope these reflections help inform ongoing conversations and future collaborations among standards and the wider biochar research community. Note: in line with the workshop’s confidentiality principle, takeaways are not attributed to any specific participant and only represent Puro.earth’s views. 

1. Encouraging signs of alignment among standards 

Alignment between standards on biochar persistence is both needed and progressively taking shape. For instance, Puro.earth’s open-source persistence equations are now being reviewed and considered by others. Publishing these equations in a fully reproducible and open-source manner, is valuable to the entire ecosystem. 

There is also growing consensus that certain simplified approaches, such as globally applicable default persistence values, are not suitable for the voluntary carbon market. Project-specific quantification remains essential to ensure integrity and accuracy. 

2. Constructive exchanges between researchers and standards 

The workshop highlighted the value of dialogue across science and practice, fostering genuine learning in all directions. Mutual understanding helps spark new ideas and strengthens methodology development and research agendas. 

Researchers expressed interest in better understanding the commercial realities of carbon removal projects and buyer expectations, which can help shape more market-relevant scientific work. Conversely, standards learned the importance of careful interpretation and translation of early research findings, given the diversity of scientific fields involved and the risks of misinterpretation of research statements. 

New research findings are emerging and incorporated into methodologies at an unprecedented pace. While this potentially accelerates diffusion of progress, it can create integrity risks if results are applied before sufficient validation. Ensuring that methodological updates keep pace with science, yet remain grounded in robust evidence and clear communication, is essential to Puro.earth’s philosophy. 

3.  A conservative approach to durability builds confidence 

Some question the need for 1,000 year biochar durability labels in the voluntary carbon market. The time horizons for climate action is not purely a scientific matter, but also a political one, shaped by frameworks such as  UNFCCC and IPCC. 

Given that the scientific evidence for 1,000 year biochar persistence has not yet reached strong consensus, we believe that issuing biochar removals with durability labels of at most several centuries represents a credible and conservative approach aligned with the current state of knowledge and agreement. This approach is for instance reflected in the latest draft documents of the EU CRCF, which proposes that all biochar removal units carry the same durability label, irrespective of the quantification method applied. 

4. Persistence equations are evolving 

Persistence equations currently used in the voluntary carbon market are multiple and evolving. This evolution affects both main quantification approaches, although in different ways. 

For equations derived from decomposition experiments (type A), updates tend to be gradual and continuous, reflecting deliberate efforts to integrate new data and refine modelling while maintaining conservativeness. A series of recent publications illustrate this steady progress, with broad awareness that no model is perfect and has limitations, but that models must be useful for their intended purpose. 

For equations based on compositional characterization methods (type B), change has been fast since their emergence: equations introduced less than two years ago are already being revised or replaced, sometimes producing substantially different results. However, limited theoretical justification and scarce public data make it difficult to assess these shifts and their implications for market integrity. This is exemplified by the recent evolution of random reflectance methods. Initially, the approach considered the fraction of the reflectance distribution exceeding 2% as representing permanent carbon storage. More recent proposals, however, suggest adjusting this fraction by multiplying it with the proportion of non-reactive carbon determined through thermogravimetric analysis (TGA), followed by the application of uncertainty deductions to each parameter. This change can in practice lead to markedly different persistence estimates, underscoring the sensitivity of results to methodological assumptions. 

Such evolution is natural and valuable within the scientific domain, but premature implementation in market methodologies risks undermining transparency and confidence. Biochar remains a sound and well-recognized climate investment, there is no debate about that in the academic community, yet it is normal and healthy for scholarly discussions to continue on the finer scientific details. Scholarly testing and debate should precede adoption, while the market, for its part, should continue to enable and support scientific advancement.

Table 1. Non-exhaustive list of biochar persistence approaches currently in use or suggested for use in the voluntary carbon market, grouped between approaches derived from decomposition experiments and compositional characterization methods.

5. More funding is needed to keep the science strong 

Research remains essential to strengthen the scientific foundation for biochar carbon removal, particularly as novel approaches emerge and integrate with established ones. 

To confirm novel approaches and strengthen established ones, more research is needed particularly on the persistence of specific carbon fractions (e.g., inertinite, semi-inertinite, SPAC), reconciling discrepancies in field decay data, and developing reliable molecular- or reflectance-based indicators of long-term stability. Addressing these gaps will require a combination of laboratory and field studies using isotopic tracing and direct CO2 flux measurements, re-characterisation of archived biochar samples, and inter-laboratory validation to ensure analytical consistency. 

Some of these research areas are already being explored, but long-term funding remains scarce. Advancing the science of biochar persistence will require sustained support and collaboration across sectors. Puro.earth stands ready to facilitate and contribute to efforts that strengthen the research ecosystem and advance understanding of durable biochar carbon removal. 

Looking ahead 

These discussions reinforce Puro.earth’s determination to apply science where it is strong, and remain transparent where uncertainty persists. We will continue to monitor research developments and, in coordination with our independent scientific Advisory Board, we are ready to update our Edition 2025 Biochar Methodology through minor revisions whenever new evidence justifies it.