PCS CN 003 Biochar Stability Metrics_v1.0

Document Control

Document identification

• Document code: PCS-CN-003

• Title: Biochar Stability Metrics

• Applies to: Biochar methodologies and tools under PCS (including relevant durability/stability determinations)

• Purpose: Clarifies acceptable metrics and evidence expectations for quantifying and demonstrating biochar stability

Version history and change log

Table DC-1. Revision history

Version	Date	Status	Summary of changes	Issued by	Approved by
v1.0	TBD	Draft	Release for public consultation	PCS	TBD

Governance note on versioning and archiving

Only the latest approved version of this Clarification Note shall be used. Superseded versions shall be archived and retained for traceability and audit purposes, consistent with PCS governance rules.

Chapter 1 - Purpose and Regulatory

1.1 Purpose of this Clarification Note

1. This clarification note provides authoritative guidance on the interpretation and application of biochar stability requirements under the Planetary Carbon Standard (PCS). Its purpose is to ensure consistent, conservative, and scientifically defensible treatment of biochar stability across all projects applying the Biochar Carbon Removal and Storage Methodology.

2. Biochar stability plays a central role in determining which fraction of measured biochar carbon may be credited as durable atmospheric carbon removal. Differences in interpretation of stability indicators, laboratory evidence, and conservative application of stability fractions can materially affect crediting outcomes. This clarification addresses such interpretive risks by providing explicit guidance on how existing methodological requirements are to be applied in practice.

3. This document does not introduce new eligibility criteria, alter quantification equations, or modify permanence obligations. It clarifies how stability-related provisions already embedded in PCS-MT-003 and operationalized through PCS-TA-010 are to be interpreted and implemented.

1.2 Regulatory Role within the PCS Framework

1. Within the PCS documentation hierarchy, clarification notes serve as interpretative regulatory instruments. They are intended to resolve ambiguity, harmonize application across projects, and provide predictable expectations for project proponents and validation and verification bodies.

2. This clarification note sits:

• Below PCS core standards and methodologies, and

• Above project-specific interpretation and discretion

1. All projects applying PCS-MT-003 are expected to follow this clarification where relevant. Validation and verification bodies must apply this clarification when assessing compliance with stability-related requirements.

2. Where any inconsistency is perceived between this clarification note and PCS core standards or methodologies, the higher-order PCS documents prevail.

1.3 Relationship to PCS-MT-003 and PCS-TA-010

1. This clarification directly supports:

• PCS-MT-003, by elaborating how biochar stability requirements are to be interpreted and applied, and

• PCS-TA-010, by explaining the rationale and correct use of the stability-related inputs, caps, and QA/QC safeguards embedded in the tool.

1. The clarification is particularly relevant to:

• Chapter 5 (Biochar Production and Characterization)

• Chapter 6 (Quantification of Net Carbon Removal)

• Chapter 7 (Permanence and Reversal Risk), insofar as stability is distinct from permanence

1. This document must be read alongside those chapters.

1.4 Intended Audience

1. This clarification is intended for:

• Project proponents designing and operating biochar projects

• Validation and verification bodies assessing biochar stability claims

• PCS Secretariat and registry reviewers evaluating project documentation

1. It assumes a technically competent audience familiar with carbon accounting, laboratory analysis, and negative emissions methodologies.

1.5 Nature and Legal Effect of the Clarification

1. This clarification is interpretative, not constitutive. It does not create new obligations beyond those already established under PCS-MT-003 and PCS governance documents. However, once issued, it represents the authoritative interpretation of stability-related requirements and must be applied accordingly.

2. Failure to apply this clarification where relevant may result in findings of non-conformance during validation or verification.

1.6 Entry into Force

1. This clarification enters into force on the date of its publication.

2. It applies to:

• All new biochar project submissions from that date onward, and

• All registered biochar projects at their next verification event, unless otherwise specified by PCS governance decisions.

Chapter 2 - Scope of Application

2.1 Applicability of this Clarification

1. This clarification applies to all projects that quantify carbon removal using biochar under the Planetary Carbon Standard and that rely on biochar stability as a determining factor for credit eligibility or credit quantity.

2. Specifically, this clarification applies to any project that:

• Applies the Biochar Carbon Removal and Storage Methodology, and

• Uses stability indicators to determine the fraction of biochar carbon eligible for crediting, whether through direct calculation or through the PCS-approved quantification tool.

1. The clarification applies irrespective of project scale, technology configuration, feedstock type, or biochar application pathway.

2.2 Project Types Covered

1. This clarification applies to biochar projects using:

• Residual biomass feedstocks,

• Dedicated biomass feedstocks, or

• A combination of residual and dedicated biomass.

1. It applies to projects producing biochar via controlled thermochemical processes, including but not limited to pyrolysis and gasification systems, provided that biochar is intentionally recovered and stored or applied for long-term carbon retention.

2. The clarification applies equally to biochar intended for:

• Soil application,

• Construction or composite materials,

• Land rehabilitation or reclamation, or

• Dedicated storage systems.

2.3 Stability-Related Decisions Covered

1. This clarification governs the interpretation and application of requirements related to:

• Selection of biochar stability indicators,

• Interpretation of laboratory or analytical results used to demonstrate stability,

• Assignment and application of stability fractions in quantification,

• Conservative treatment of uncertainty in stability evidence, and

• Use of automated safeguards and caps in the PCS quantification tool.

1. Any decision that affects the fraction of biochar carbon considered stable for crediting purposes falls within the scope of this clarification.

2.4 Exclusions from Scope

1. This clarification does not apply to:

• Biochar permanence obligations related to storage, custody, or reversal risk, which are governed separately under the methodology;

• Quantification of project emissions, leakage, or baseline scenarios, except where such elements interact indirectly with stability treatment;

• Projects that do not claim carbon removal through biochar carbon stabilization.

1. This clarification also does not establish or modify eligibility rules for biomass sourcing, technology selection, or sustainability safeguards, which remain governed by the applicable methodology and PCS core standards.

2.5 Relationship to Other PCS Documents

1. This clarification must be applied in conjunction with the applicable methodology and any associated tools. It does not operate independently and must not be interpreted in isolation.

2. Where guidance in this clarification overlaps with provisions in the methodology or tool documentation, this clarification provides the authoritative interpretation of how those provisions are to be applied in practice.

3. In the event of a direct conflict between this clarification and a higher-order PCS document, the higher-order document prevails.

2.6 Binding Nature within the PCS System

1. Once issued, this clarification represents the official interpretation of stability-related provisions for all affected projects. Validation and verification bodies are expected to apply this clarification consistently when assessing project documentation, calculations, and evidence.

2. Project proponents are expected to align stability assessment approaches with this clarification from the point of entry into force.

Chapter 3 - Entry into Force and Transitional Application

3.1 Entry into Force

1. This clarification enters into force on the date of its official publication by the Planetary Carbon Standard Secretariat.

2. From the date of entry into force, the provisions of this clarification constitute the authoritative interpretation of biochar stability requirements for all projects applying the Biochar Carbon Removal and Storage Methodology.

3.2 Application to New Projects

1. All biochar projects submitted for validation after the entry into force of this clarification must apply its provisions in full. Project documentation, stability assessments, laboratory evidence, and quantification outputs must be consistent with the guidance provided in this document.

2. Failure to apply this clarification at the project design or validation stage may result in requests for corrective action or findings of non-conformance.

3.3 Application to Registered and Ongoing Projects

1. For biochar projects that are already registered or under implementation at the time this clarification enters into force, the clarification applies at the next verification event following publication.

2. Such projects are not required to retroactively reassess or revise stability determinations for monitoring periods that have already been verified and credited, unless a material misapplication of stability requirements is identified.

3.4 Transitional Treatment of Stability Evidence

1. Where ongoing projects rely on stability evidence generated prior to the publication of this clarification, such evidence may continue to be used provided that it is consistent with the principles set out herein.

2. If previously submitted stability evidence does not meet the representativeness, conservativeness, or documentation expectations clarified in this document, project proponents must update or supplement the evidence prior to the next verification.

3.5 Treatment of Tool Updates and Versions

1. Where stability-related safeguards are implemented through updates to the PCS biochar quantification tool, projects must use the tool version applicable to the monitoring period, in accordance with PCS versioning rules.

2. Projects may not mix stability treatment approaches across tool versions within a single monitoring period. Any transition between tool versions must be clearly documented in the monitoring report.

3.6 Avoidance of Retroactive Reinterpretation

1. This clarification is not intended to create retroactive obligations or to reinterpret previously verified results unless there is clear evidence of misapplication, material error, or non-compliance with the methodology as it stood at the time of verification.

2. PCS governance bodies retain discretion to require corrective actions in cases where environmental integrity may have been compromised.

3.7 Authority and Future Consolidation

1. This clarification may be superseded, consolidated, or integrated into future revisions of the biochar methodology or related PCS documents. Until such consolidation occurs, this clarification remains in force and must be applied as a standalone interpretative document.

Chapter 4 - Conceptual Basis for Biochar Stability

4.1 Role of Biochar Stability in Carbon Removal Accounting

1. Under the Planetary Carbon Standard, carbon removal is credited only where atmospheric carbon is converted into a form that is demonstrably resistant to re-emission over climate-relevant time horizons. In biochar-based pathways, this resistance is provided by the chemical and structural properties of biochar carbon.

2. Biochar stability therefore functions as a gatekeeping criterion within carbon removal accounting. It determines whether measured biochar carbon can be considered durable and, if so, what fraction of that carbon may be credited. Stability does not represent a guarantee of permanence, but rather a conservative classification of intrinsic material resistance to degradation.

4.2 Stability as an Intrinsic Material Property

1. Stability is defined as an intrinsic property of biochar that reflects its resistance to biological, chemical, and thermal oxidation under typical environmental conditions. This resistance arises primarily from the transformation of biomass carbon into condensed aromatic structures during thermochemical conversion.

2. Because stability is tied to material properties rather than site conditions, it must be assessed through characterization of the biochar itself, rather than through assumptions about the storage or application environment.

3. Accordingly, stability assessment focuses on measurable indicators that correlate with the degree of carbon condensation and aromaticity achieved during production.

4.3 Distinction Between Stability and Permanence

1. It is essential to distinguish between stability and permanence, as the two concepts serve different roles within the PCS framework.

2. Stability relates to the intrinsic resistance of biochar carbon to degradation, independent of where or how the biochar is stored or applied. Permanence, by contrast, relates to the continued retention of biochar carbon in situ, including protection against disturbance, relocation, or misuse.

3. This clarification addresses stability only. Permanence obligations, monitoring, and reversal risk management are governed separately under the biochar methodology and related PCS documents.

4.4 Stability Assessment as a Conservative Classification

1. PCS does not treat stability as a precise prediction of long-term carbon residence time. Instead, stability assessment functions as a conservative classification mechanism that determines eligibility and creditable fractions at the time of quantification.

2. This approach avoids speculative modeling of long-term decay processes and reduces uncertainty in crediting outcomes. It ensures that only carbon with a high likelihood of long-term retention is credited, while remaining agnostic to exact degradation rates over extended periods.

4.5 Avoidance of Decay Curve Modeling

1. The PCS framework intentionally avoids the use of forward-looking decay curves or probabilistic lifetime estimates for biochar carbon. While such models exist in the scientific literature, their application in crediting frameworks introduces significant uncertainty and scope for inconsistent interpretation.

2. By applying conservative stability fractions up-front, PCS ensures that:

• Credited removals are not dependent on unverifiable future assumptions

• Quantification remains transparent and reproducible

• Verification focuses on evidence rather than model selection

4.6 Implications for Quantification and Verification

1. The conceptual treatment of stability has direct implications for both quantification and verification. Stability indicators are used to assign conservative fractions of biochar carbon as creditable, and these fractions are applied consistently across the monitoring period.

2. Verification bodies are expected to assess whether the selected stability indicators and resulting fractions align with this conceptual framework and whether conservative interpretation has been applied where uncertainty exists.

4.7 Boundary Conditions for Stability Claims

1. Stability claims must be grounded in material characterization and must not be extended to imply permanence guarantees or avoided emission outcomes. Stability classification applies solely to determining the fraction of biochar carbon eligible for crediting and must not be used to justify additional claims beyond the scope of carbon removal accounting.

Chapter 5 - Acceptable Stability Indicators

5.1 General Principles for Stability Indicators

1. Biochar stability under the Planetary Carbon Standard must be demonstrated using indicators that are scientifically defensible, empirically measurable, and directly linked to resistance against biological and chemical degradation. Because long-term stability cannot be observed directly within project timeframes, PCS relies on proxy indicators that reflect the degree of carbon transformation achieved during thermochemical conversion.

2. Stability indicators must therefore serve as conservative proxies, not as precise predictors of residence time. Their role is to support classification decisions regarding the fraction of biochar carbon that may be considered durable for the purposes of carbon removal accounting.

5.2 Scientific Basis for Proxy Indicators

1. Thermochemical conversion of biomass results in progressive dehydration, dehydrogenation, and aromatization of organic carbon. As these processes advance, carbon structures become increasingly condensed and resistant to microbial and oxidative attack.

2. Indicators that capture the extent of this transformation are appropriate for stability assessment. Indicators that do not reflect changes in carbon structure or resistance to degradation are not suitable for crediting purposes.

5.3 Elemental Ratio Indicators

1. Elemental ratios provide a widely accepted proxy for biochar stability. In particular, the ratio of hydrogen to organic carbon reflects the degree of aromatic condensation achieved during production.

2. Lower hydrogen-to-organic-carbon ratios indicate a higher proportion of condensed aromatic structures and, consequently, greater resistance to degradation. Elemental analysis used to derive such ratios must be conducted using recognized laboratory methods and reported on a dry, ash-free basis where applicable.

3. Elemental ratios must be interpreted conservatively, taking into account measurement uncertainty and sample representativeness.

5.4 Aromaticity and Structural Indicators

1. Indicators that directly or indirectly measure aromatic carbon content or structural condensation may also be used, provided that their relevance to long-term stability is supported by scientific evidence.

2. Such indicators must be derived from laboratory analysis or standardized testing methods and must be demonstrably linked to resistance against oxidation or biological breakdown. Where multiple structural indicators are available, the most conservative interpretation must be applied.

5.5 Use of Multiple Indicators

1. Projects may apply more than one stability indicator where appropriate. In such cases, stability classification must be based on the most conservative outcome derived from the available indicators.

2. Averaging or weighting of indicators to increase the credited stability fraction is not permitted where indicators yield materially different results. Where indicators are broadly consistent, conservative alignment may be demonstrated through documentation.

5.6 Indicator Applicability and Limitations

1. Not all indicators are applicable to all biochar types or production conditions. Projects must demonstrate that selected indicators are appropriate for the specific biochar produced and that laboratory methods are suitable for the material characteristics.

2. Indicators that are sensitive to short-term surface properties, moisture content, or non-carbon fractions must be interpreted cautiously. Where indicator applicability is uncertain, conservative assumptions must be applied.

5.7 Ineligible Indicators and Claims

1. Indicators that are qualitative, non-reproducible, or not directly linked to carbon stability are not acceptable for determining creditable fractions. Claims based solely on production temperature, reactor type, or residence time, without supporting material characterization, are insufficient.

2. Similarly, claims based on theoretical residence times, modeled decay curves, or analogies to unrelated materials do not constitute acceptable stability indicators under PCS.

5.8 Documentation Requirements for Indicators

1. All stability indicators used for quantification must be fully documented. Documentation must identify the indicator used, the analytical method applied, the sampling basis, and any assumptions or limitations.

2. Indicator documentation must allow independent verification and must be consistent with data entered into the PCS biochar quantification tool.

5.9 Conservative Interpretation Requirement

1. Where indicator results are near eligibility thresholds or subject to uncertainty, projects must apply conservative interpretations that reduce credited quantities rather than increase them. This requirement applies irrespective of project scale or claimed innovation.

2. Conservative interpretation is a core principle underpinning the use of stability indicators within PCS.

Chapter 6 - Laboratory Evidence and Representativeness

6.1 Role of Laboratory Evidence

1. Laboratory analysis provides the empirical basis for demonstrating biochar stability under the Planetary Carbon Standard. Because stability is an intrinsic material property, laboratory evidence is required to substantiate claims regarding the fraction of biochar carbon that may be considered durable.

2. Laboratory evidence serves two functions: it supports eligibility determinations for biochar carbon, and it informs the conservative application of stability fractions used in quantification.

6.2 Acceptable Analytical Methods

1. Laboratory analyses used to support stability assessment must employ recognized analytical methods that are appropriate for biochar materials. Methods must be capable of reliably measuring the parameters relevant to the selected stability indicators.

2. Analytical methods must be documented in sufficient detail to allow independent assessment. This includes identification of the method standard, instrumentation used, and any deviations from standard protocols.

3. Where multiple analytical methods exist for a given indicator, projects must demonstrate that the selected method is suitable for the biochar produced and that results are comparable to established benchmarks.

6.3 Sampling Representativeness

1. Sampling procedures must ensure that laboratory results are representative of biochar produced during the relevant monitoring period. Representativeness must be demonstrated with respect to feedstock variability, production conditions, and batch or continuous production characteristics.

2. Where production occurs in discrete batches, samples must be taken at a frequency sufficient to capture variability. Where production is continuous, sampling must reflect typical operating conditions and must be repeated when material changes occur.

3. Sampling strategies that selectively target favorable batches or conditions are not acceptable.

6.4 Treatment of Feedstock and Process Variability

1. Variability in feedstocks or operating conditions can materially affect biochar stability. Projects must assess whether such variability exists and, where it does, ensure that sampling and analysis capture its effects.

2. If biochar is produced from multiple feedstocks or under varying conversion conditions, laboratory evidence must either demonstrate that stability outcomes are consistent across these conditions or apply conservative assumptions that reflect lower-bound performance.

3. Failure to account for variability must result in conservative treatment of stability fractions.

6.5 Frequency of Testing

1. Laboratory testing must be conducted at a frequency sufficient to maintain confidence in stability classifications. At a minimum, testing must be performed when:

• A project is initially validated,

• Feedstock types change materially,

• Production conditions change materially, or

• Significant process modifications are implemented.

1. Where production conditions remain stable over time, periodic testing may be used to confirm continued representativeness. The frequency of such testing must be justified and documented.

6.6 Use of Historical or Prior Evidence

1. Laboratory evidence generated prior to the current monitoring period may be used where it remains representative of current production conditions and feedstocks. Projects must demonstrate that no material changes have occurred that would invalidate the relevance of prior results.

2. Where uncertainty exists regarding the continued applicability of historical evidence, projects must either conduct new testing or apply conservative stability assumptions.

6.7 Treatment of Measurement Uncertainty

1. Laboratory measurements are subject to uncertainty arising from sampling, analytical precision, and material heterogeneity. Projects must account for such uncertainty by applying conservative interpretations of results.

2. Where uncertainty ranges are reported, projects must use lower-bound values for stability classification where such ranges could materially affect credited quantities.

6.8 Documentation and Traceability of Evidence

1. All laboratory evidence must be fully documented and traceable. Documentation must include sample identifiers, dates, analytical results, and linkage to specific biochar batches or production periods.

2. Evidence must be consistent with data entered into the PCS biochar quantification tool and referenced using the applicable evidence reference structure.

6.9 Inadequate or Insufficient Evidence

1. Where laboratory evidence is incomplete, inconsistent, or insufficient to support stability claims, the affected biochar fraction must not be credited. Projects may not substitute assumptions, literature values, or extrapolations in place of required evidence.

2. In such cases, conservative exclusion of affected quantities is required until adequate evidence is provided.

6.10 Verification Considerations

1. Verification bodies are expected to assess the adequacy, representativeness, and conservative interpretation of laboratory evidence. Where evidence quality is insufficient, verifiers must require conservative treatment rather than expanded crediting.

Chapter 7 - Conservative Application of Stability Fractions

7.1 Purpose of Stability Fractions

1. Stability fractions are applied under the Planetary Carbon Standard to conservatively determine the proportion of measured biochar carbon that may be credited as durable atmospheric carbon removal. The stability fraction represents a classification outcome, not a prediction of exact long-term carbon residence time.

2. The application of stability fractions ensures that only the portion of biochar carbon with a high likelihood of long-term retention is credited, while avoiding speculative or model-based assumptions regarding future degradation.

7.2 Up-Front Application Principle

1. Under PCS-MT-003, stability fractions are applied at the point of quantification, rather than through forward-looking decay or lifetime modeling. This up-front application reflects a deliberate methodological choice to prioritize transparency, conservativeness, and verifiability.

2. Once applied, the credited fraction represents a conservative estimate of durable storage. Subsequent permanence obligations are addressed separately and do not retroactively adjust the applied stability fraction unless a reversal occurs.

7.3 Determination of Stability Fractions

1. Stability fractions must be derived from:

• Laboratory-based stability indicators supported by evidence, and

• Conservative interpretation of those indicators in accordance with this clarification.

1. Projects must not derive stability fractions through averaging, extrapolation, or probabilistic modeling that would increase credited quantities. Where multiple indicators are available, the lowest resulting stability fraction must be applied.

7.4 Use of Conservative Upper Caps

1. To ensure consistency across projects and prevent over-crediting, PCS applies conservative upper caps to stability fractions. These caps reflect a precautionary interpretation of scientific evidence and establish a maximum creditable fraction regardless of measured values.

2. Where a project enters a measured stability fraction exceeding the applicable PCS cap, the capped value must be applied for quantification purposes. Measured values above the cap may be reported for transparency but have no effect on credited quantities.

7.5 Hybrid Input and Safeguard Approach

1. The PCS biochar quantification tool implements a hybrid approach to stability fraction application. Project proponents manually enter stability fractions supported by laboratory evidence, while the tool enforces automatic safeguards, including upper caps and eligibility checks.

2. This approach ensures that project-specific evidence is respected while maintaining standardized conservativeness across all projects. Manual overrides of tool safeguards are not permitted.

7.6 Treatment of Values Near Thresholds

1. Where stability indicator results fall close to eligibility thresholds or cap values, projects must apply conservative interpretations. Marginal exceedances or results subject to measurement uncertainty must not be used to justify higher stability fractions.

2. In such cases, the stability fraction applied must reflect the lower-bound interpretation consistent with conservative accounting principles.

7.7 Treatment of Variability Across Batches

1. Where stability indicators vary across batches or production periods, projects must apply stability fractions that reflect the lowest representative performance for the relevant monitoring period, unless robust evidence demonstrates that higher-stability batches can be clearly segregated and traced.

2. Selective crediting of higher-stability batches is not permitted unless segregation, monitoring, and traceability are demonstrated to a level sufficient for independent verification.

7.8 Prohibited Practices

1. The following practices are not permitted under PCS:

• Increasing stability fractions through averaging across indicators or batches

• Applying modeled decay outcomes to justify higher stability fractions

• Adjusting stability fractions retroactively to increase credited quantities

• Bypassing or overriding tool-enforced caps or safeguards

1. Any such practices may result in findings of non-conformance.

7.9 Documentation and Disclosure

1. Applied stability fractions must be clearly documented in monitoring reports and traceable to supporting laboratory evidence. Where measured values exceed PCS caps, both the measured value and the applied capped value must be disclosed transparently.

2. Documentation must allow verifiers to independently confirm that stability fractions have been applied conservatively and in accordance with this clarification.

7.10 Verification Expectations

1. Verification bodies are expected to confirm that stability fractions:

• Are supported by appropriate evidence,

• Have been conservatively interpreted, and

• Have been correctly applied within the PCS quantification tool.

1. Where uncertainty exists, verifiers must require conservative treatment rather than expanded crediting.

Chapter 8 - Treatment of Data Gaps and Uncertainty

8.1 Principle of Conservative Resolution

1. Where data gaps, limitations, or uncertainty affect the assessment of biochar stability, the Planetary Carbon Standard requires that such uncertainty be resolved conservatively. Conservative resolution means adopting assumptions or values that reduce or do not increase credited carbon removal quantities.

2. Under no circumstances may uncertainty be used to justify higher stability fractions or expanded crediting.

8.2 Types of Data Gaps and Uncertainty

1. Data gaps and uncertainty may arise from, but are not limited to:

• Incomplete or missing laboratory analyses

• Insufficient sampling frequency or representativeness

• Variability in feedstocks or production conditions not fully characterized

• Measurement uncertainty reported by laboratories

• Use of historical evidence with uncertain relevance to current operations

1. Each type of uncertainty must be explicitly identified and assessed for materiality.

8.3 Treatment of Missing Stability Evidence

1. Where stability evidence is missing for a portion of biochar produced during a monitoring period, that portion must not be credited unless conservative assumptions can be applied that demonstrably reduce credited quantities.

2. If minimum eligibility thresholds for stability cannot be demonstrated, the affected biochar fraction is ineligible for crediting until adequate evidence is provided.

3. Projects may not substitute literature values, modeled assumptions, or analogies in place of required stability evidence.

8.4 Limited or Outdated Laboratory Data

1. Laboratory data generated outside the monitoring period may be used only where projects demonstrate that:

• Production conditions and feedstocks remain materially unchanged, and

• The data remain representative of biochar produced during the monitoring period.

1. Where such demonstration is incomplete or uncertain, projects must apply conservative stability fractions or conduct new testing.

8.5 Variability and Inconsistent Results

1. Where laboratory results exhibit variability across samples, batches, or time periods, projects must assess whether the variability is material to stability classification.

2. If variability is material, the stability fraction applied must reflect the lowest representative outcome unless higher-stability batches are clearly segregated, traced, and verifiable. Aggregation or averaging that increases credited quantities is not permitted.

8.6 Measurement Uncertainty and Lower-Bound Application

1. Where analytical uncertainty ranges are reported, projects must apply lower-bound values for stability classification where such uncertainty could materially affect credited quantities.

2. If uncertainty cannot be reasonably bounded, conservative default treatment must be applied or affected quantities excluded from crediting.

8.7 Prohibition of Extrapolation and Backfilling

1. Projects may not extrapolate stability results from limited samples to increase credited quantities without demonstrating representativeness. Similarly, backfilling of missing data using later results or favorable assumptions is not permitted.

2. Where extrapolation is unavoidable for operational reasons, it must be conservative and must not result in higher credited quantities than would be achieved with complete data.

8.8 Documentation of Uncertainty Treatment

1. All instances of data gaps or uncertainty must be clearly documented in monitoring reports. Documentation must describe:

• The nature of the uncertainty

• The affected quantities

• The conservative assumptions applied

1. Such documentation must be sufficient to allow independent verification and reconstruction of quantification outcomes.

8.9 Interaction with Tool Safeguards

1. The PCS biochar quantification tool includes automated safeguards designed to prevent over-crediting where required data are missing or inconsistent. Projects must not bypass or override these safeguards.

2. Where tool flags indicate missing data or potential issues, projects must address the underlying cause or accept conservative exclusion of affected quantities.

8.10 Verification Expectations

1. Verification bodies are expected to:

• Identify unresolved data gaps or uncertainty, and

• Require conservative treatment where uncertainty remains material.

1. Where data gaps cannot be conservatively resolved, verifiers must require exclusion of affected quantities from crediting for the monitoring period.

Chapter 9 - Interaction with the PCS Biochar Quantification Tool

9.1 Purpose of Tool-Based Implementation

1. The PCS biochar quantification tool operationalizes the stability-related requirements of the biochar methodology and this clarification note. Its purpose is to translate methodological rules into a structured, auditable calculation framework that minimizes interpretation risk, user error, and over-crediting.

2. The tool does not create new requirements. It enforces existing methodological rules and this clarification through automated calculations, caps, and quality-control safeguards.

9.2 Role of Manual Inputs

1. Project proponents are required to manually input stability-related values that are supported by laboratory evidence. These inputs represent the proponent’s interpretation of measured indicators, subject to conservative treatment.

2. Manual inputs must:

• Be directly traceable to documented laboratory evidence

• Reflect conservative interpretation of results

• Be representative of the biochar produced during the monitoring period

1. Manual inputs must not incorporate assumptions that are not supported by evidence.

9.3 Automated Safeguards and Caps

1. The tool applies automated safeguards to ensure conservative application of stability fractions. These safeguards include:

• Enforcement of upper caps on stability fractions

• Automatic selection of the lower value where entered fractions exceed PCS-defined limits

• Eligibility checks that prevent crediting where stability requirements are not met

1. These safeguards are integral to the PCS framework and must not be overridden, disabled, or bypassed.

9.4 Hybrid Stability Application Model

1. The tool applies a hybrid model in which:

• Stability fractions are entered manually based on evidence, and

• Final applied stability fractions are determined automatically through conservative caps and validation logic.

1. This model balances flexibility for project-specific evidence with standardization and environmental integrity across projects. The applied stability fraction used in quantification is always the most conservative value resulting from this interaction.

9.5 Treatment of Multiple Batches and Aggregation

1. Where multiple biochar batches are produced within a monitoring period, stability inputs must be provided at a level of granularity sufficient to ensure representativeness.

2. The tool aggregates stability-adjusted carbon quantities across batches only after stability fractions have been conservatively applied at the batch or representative level. Aggregation must not mask variability that would otherwise reduce credited quantities.

9.6 Quality-Control Flags Related to Stability

1. The tool includes quality-control checks that flag potential issues related to stability inputs. These may include:

• Entered stability fractions exceeding PCS caps

• Missing or incomplete evidence references

• Stability inputs inconsistent with characterization data

1. Quality-control flags are intended to alert users and verifiers to issues requiring review. Flags indicating non-compliance must be resolved prior to credit issuance.

9.7 Transparency and Auditability

1. All stability-related calculations within the tool are transparent and traceable. Applied stability fractions, capped values, and eligibility outcomes are visible and auditable.

2. Projects must not obscure, hide, or alter stability-related calculations. Any manual adjustments outside the tool framework are not permitted.

9.8 Treatment of Tool Errors or Inconsistencies

1. If errors or inconsistencies are identified in tool outputs related to stability application, projects must investigate and resolve the root cause. Resolution must prioritize conservative treatment and must be documented.

2. Where tool limitations or updates affect stability treatment, projects must apply the tool version specified by PCS and document any transition between versions.

9.9 Verification Expectations for Tool Use

1. Verification bodies are expected to:

• Confirm that stability inputs are supported by evidence

• Confirm that automated safeguards have been correctly applied

• Review tool flags and confirm appropriate resolution

• Ensure that reported stability fractions match tool-applied values

1. Any discrepancy between reported values and tool outputs must be resolved conservatively.

9.10 Prohibited Tool Practices

1. Projects may not:

• Override protected cells or formulas

• Disable automated safeguards

• Input values designed to circumvent caps or eligibility checks

• Modify the tool to increase credited quantities

1. Such actions may result in findings of non-conformance and potential credit invalidation.

Chapter 10 - Verification Expectations

10.1 Purpose of Verification Guidance

1. This chapter clarifies how validation and verification bodies are expected to assess biochar stability claims under the Planetary Carbon Standard. The purpose is to ensure consistent, conservative, and predictable verification outcomes across projects and verifiers.

2. Verification of stability claims is evidence-based and focuses on whether stability has been demonstrated and applied conservatively, rather than on optimizing or maximizing credited quantities.

10.2 Scope of Stability Verification

1. Verification bodies must assess stability-related elements within the scope of verification for biochar projects, including:

• Appropriateness of selected stability indicators

• Quality and representativeness of laboratory evidence

• Conservative interpretation of indicator results

• Correct application of stability fractions and caps

• Consistency between tool outputs and reported values

1. Verification must cover all biochar quantities for which credit issuance is requested.

10.3 Assessment of Stability Indicators

1. Verification bodies must confirm that stability indicators used by the project are:

• Scientifically defensible and relevant to biochar stability

• Empirically measurable using recognized analytical methods

• Appropriate for the biochar produced and production conditions

1. Indicators that are qualitative, unverifiable, or unrelated to carbon structure must not be accepted for crediting purposes.

10.4 Review of Laboratory Evidence

1. Verification bodies must review laboratory evidence supporting stability claims to confirm:

• Representativeness of samples relative to the monitoring period

• Adequacy of sampling frequency and coverage

• Proper documentation of analytical methods and results

1. Where laboratory evidence is incomplete, inconsistent, or insufficiently representative, verification bodies must require conservative treatment or exclusion of affected quantities.

10.5 Evaluation of Conservative Interpretation

1. Verification bodies must assess whether stability results have been interpreted conservatively. This includes confirming that:

• Lower-bound values are applied where uncertainty exists

• No averaging or extrapolation has increased credited quantities

• Variability across batches has been treated conservatively

1. Where interpretation appears optimistic or unsupported, verification bodies must require downward adjustment of stability fractions.

10.6 Verification of Tool-Based Application

1. Verification bodies must confirm that stability fractions have been correctly applied within the PCS biochar quantification tool. This includes checking that:

• Manual stability inputs match documented evidence

• Automated caps and safeguards have been applied

• Tool-generated eligibility flags have been appropriately addressed

1. Verification bodies must not accept results derived from modified or bypassed tool logic.

10.7 Treatment of Non-Conformities

1. Where stability-related non-conformities are identified, verification bodies must classify them in accordance with PCS procedures and require corrective action prior to credit issuance.

2. Material non-conformities affecting credited quantities must result in exclusion or downward adjustment of affected biochar fractions.

10.8 Resolution of Interpretive Disputes

1. Where disagreements arise regarding the interpretation of stability evidence or indicators, verification bodies must apply this clarification note as the authoritative interpretation.

2. In cases of unresolved uncertainty, conservative treatment must prevail.

10.9 Documentation of Verification Findings

1. Verification reports must clearly document:

• Stability indicators reviewed

• Evidence assessed

• Stability fractions applied

• Any conservative adjustments required

1. Documentation must allow independent reviewers to understand how stability-related conclusions were reached.

10.10 Independence and Consistency

1. Verification bodies must apply stability requirements consistently across projects and must avoid project-specific reinterpretation that would undermine standardization.

2. Consistency across verification outcomes is a core objective of this clarification.

Chapter 11 - Final Provisions and Boundary Conditions

11.1 No Expansion of Methodological Scope

1. This clarification note does not expand the scope of the Biochar Carbon Removal and Storage Methodology. It does not introduce new project eligibility criteria, quantification pathways, or crediting mechanisms beyond those already defined under PCS-MT-003.

2. In particular, this clarification does not permit:

• Avoided emission claims associated with alternative biomass treatment pathways

• Credit differentiation based on speculative longevity or residence time claims

• Use of modeled decay curves or probabilistic lifetime estimates

1. All crediting remains strictly limited to conservative classification of durable biochar carbon.

11.2 Boundary Between Stability and Permanence

1. This clarification addresses biochar stability only. It does not modify or reinterpret permanence obligations, reversal risk management, or long-term monitoring requirements established elsewhere in the PCS framework.

2. Stability classification determines the fraction of biochar carbon eligible for crediting at the time of quantification. Permanence obligations govern the continued retention of that credited carbon and are assessed independently.

3. Stability must not be used to justify reduced permanence obligations or altered reversal treatment.

11.3 No Precedent for Future Methodological Claims

1. Application of this clarification does not create precedent for future methodological claims or for the acceptance of alternative stability indicators outside those described herein.

2. Future updates to stability treatment, indicators, or caps may only be introduced through formal methodology revision or PCS governance decisions.

11.4 Treatment of Innovation and Novel Indicators

1. Projects proposing novel stability indicators or analytical approaches must demonstrate equivalence or conservativeness relative to recognized indicators. Such approaches do not fall within the scope of this clarification and must be assessed separately through methodology approval or revision processes.

2. Until formally approved, novel indicators must not be used to increase credited quantities beyond conservative defaults.

11.5 Authority and Supersession

1. This clarification represents the authoritative interpretation of biochar stability requirements under the PCS framework from the date of entry into force.

2. It may be superseded, amended, or consolidated into future revisions of PCS methodologies or regulatory documents. Until such action occurs, it remains applicable and binding for all affected projects and verification activities.

11.6 Final Statement

1. This clarification is issued to support consistent, conservative, and transparent application of biochar stability requirements across all PCS biochar projects. Its objective is to safeguard environmental integrity while providing predictable and defensible implementation pathways for project proponents and verification bodies.