Standard and methodologies

Revising Rainbow Standard Documentation

The Rainbow Standard Rules and the Procedures Manual undergo regular revision to ensure they reflect up-to-date science and best practice in the voluntary carbon market. The revision of the documents shall follow the procedure outlined below.

Major revisions

Major revisions are tracked through the first integer after the standard document name (e.g. Rainbow Standard Rules V1 → V2). Major revisions include three phases: Feedback Collection, Draft Preparation, and Approval.

Feedback Collection Phase

Open external feedback: Any interested party can provide feedback on the Rainbow Standard Rules and methodologies at any time. The latest versions of all documentation are published on Rainbow’s website, enabling continuous input—not just during public consultations.

All interested parties, irrespective of their background or involvement, are encouraged to continuously provide their feedback on the current Rainbow Standard Documentation. They can do so by email at [email protected], or via this form.

Internal planned revisions: Rainbow continuously reviews and updates its Standard documents to reflect new knowledge, market developments, evolving regulations and accreditation requirements. The Rainbow Science team actively monitors all referenced standards and tools (e.g. IPCC, ISO …) to ensure alignment with best practices.

Compilation of feedback: The Secretariat compiles external feedback and internally-identified planned revisions into a Standard Revision Proposal.

Draft Preparation Phase

Evaluation of Revision Proposal: The Secretariat analyzes the suggested changes in the Standard Revision Proposal, and evaluates the changes deemed necessary to the Rainbow Standard Documentation based on the feedback received. Responses to any external feedback, including a decision on whether to incorporate the feedback or not, will be made publicly available with the public consultation feedback responses.

Revision draft: The Secretariat and the Rainbow Science team make the revisions in a draft update to the Standard Documentation.

Submission to SAB and deliberation: The draft update is presented to the SAB for their critical evaluation, highlighting key updates plus providing the full revised text. The SAB provides feedback.

Public Consultation: The Secretariat organizes a public consultation of the proposed revisions (see Public consultation section).

Approval Phase

Integration of Public Feedback: the Secretariat integrates feedback from the public consultation into the draft update to the Standard Documentation.

SAB Review and Approval: The draft update to the Standard Documentation is submitted to the SAB for final approval. The SAB ensures that feedback from the public consultation phase, as well as their own comments, has been appropriately incorporated or that adequate justification is provided for any feedback not adopted.

Implementation: The Science team implements the approved revisions into the Rainbow Standard Documentation and any affiliated documents. All changes are documented in the Version History, previous versions are archived, and changes to certification are implemented.

Minor revisions

Minor revisions may be made by the Rainbow Science Team when they are deemed necessary. Minor revisions are tracked through the second integer after the standard document name (e.g. Rainbow Standard Rules V1.1 → V1.2). Revisions are considered minor if they do not result in widespread material changes affecting the eligibility of projects, such as:

• Updating references to external documents, tools, or standards

• Adjusting procedural and operational steps to improve clarity or efficiency

• Adding or updating examples or case studies to aid understanding

• Simplifying documentation language to improve accessibility

• Formalizing processes that are already implemented in practice

• Making other non-critical changes to requirements.

All changes are documented in the Version History, and previous versions are archived.

Creating new Rainbow Standard Documentation

The creation of new Rainbow Standard Documentation follows the Draft Preparation and Approval phases described in the Revising Rainbow Standard Documentation section, with the following differences:

• All Rainbow Standard Documentation is initially drafted internally by the Rainbow Science team.

• Procedures are tailored to Rainbow’s operations, but shall draw inspiration and guidance from established standards such as ISO 9001 and ISO 31000, ensuring global compliance and recognition.

• Instead of a Revision Proposal as described in the Draft Preparation section, a Creation Proposal is submitted to the Standard Advisory Board for validation.

• A public consultation is conducted for the creation of any new Rainbow Standard Documentation.

Creating a new methodology

Submission

Any interested party may submit a request for a new methodology at any time. The requests are summarized by the Secretariat into a Methodology Creation Proposal (template here).

The Methodology Creation Proposal is reviewed first by the Rainbow Science Team, and if approved then it is reviewed by the SAB for final approval.

The reviews consider factors such as:

• Maturity of the technology

• Number of existing projects

• Scientific consensus of substantial carbon avoidance/removal potential

• Feasibility of MRV

• Feasibility of meeting other Principles and requirements from the Rainbow Standard Rules

If the proposal is validated by the SAB, a Methodology Creation Mandate is granted to the Secretariat and the Rainbow Science Team. This mandate assigns the designated teams to research, develop, and finalize the methodology. The current Methodology Creation Mandates are presented below.

If the proposal is rejected by the SAB, it then decides whether to earmark it for reworking or, based on the gravity of the concerns, abandon it altogether.

Development

The Secretariat gathers a technical working group composed of at least 3 individuals, including members of the Expert Community and at least one independent external expert (i.e. an individual with relevant technical expertise who is not affiliated with Rainbow, its funders, or eligible projects, and who has declared no conflict of interest). The technical working group collaborates with the Rainbow Science Team to develop the methodology.

Members of the technical working group shall be selected based on

• expertise related to e.g. the scientific foundations, sustainability issues, LCA/GHG quantification, policy, or operations of the methodology's subject.

• representation from diverse stakeholders from e.g. researchers/academics, project developers, independent experts, or NGOs.

Members of technical working groups are subject to the relevant provisions of the Terms of Reference - Expert Community, including but not limited to rules on independence, conflict of interest, confidentiality, and conduct.

To research and develop the methodology, the Rainbow Science team gathers and consults the technical working group on a regular basis. Final decisions rest with the Rainbow Science team.

The minimum requirements for a Rainbow methodology include the following:

Minimum requirements for a methodology

Scope/general

• Eligible technologies and activities, description of the practices and processes covered

• Scope/delineation of a project (e.g. number of sites can be included in one project)

• Minimum requirements for a monitoring plan

• Maximum duration of the crediting period

• Maximum duration of the monitoring period/frequency of credit issuance

• Glossary with definitions of technical terms

• Requirements for project compliance with methodology revisions

• Requirements for site audits to be on-site or remote

Baseline scenario

• Justification of the pre-defined/standardized baseline scenario, or guidance for defining an activity-specific baseline scenario

• Frequency of updating the baseline scenario

Principles and requirements

• Any standardized calculations for co-benefits

• Durability (for removal RCCs)

  • durability threshold, in years

  • technology/methodology level reversal risk assessment

  • post-crediting monitoring requirements for reversals

  • liability and compensation requirements

  • minimum buffer pool contribution (if higher than the Standard default of 2%)

• Technology/methodology-specific leakage assessment and if applicable, further requirements

• Reversal and ESDNH Risk assessment template

GHG quantification

• Assumptions

• Secondary data sources

• Description of processes, GHG sinks, and GHG sources to include in the project and baseline scenario

• Uncertainty assessment and minimum discount factor

• Approaches to account for uncertainties in a conservative matter

• All equations and rules needed to calculate, where relevant in the applicable methodology:

  • project and baseline induced emissions

  • project and baseline removals,

  • LULUCF soil emissions,

  • agricultural soil emissions, and

  • total GHGs avoided and/or removed

Review and acceptance

Once the initial methodology draft is complete, the Secretariat launches a public consultation for a minimum of 30 days, following the Public consultation procedures outlined below.

The Secretariat and the Rainbow Science team then assess all feedback, deciding and justifying whether to incorporate each feedback into the final methodology draft. This draft is validated by the SAB, which verifies that input from the Expert Community, other experts, and the public consultation has been fully integrated.

Current Methodology Creation Mandates

The following Methodology Creation Mandates have already been approved by the SAB as of November 2025, and may be created by Rainbow at any time:

• Low carbon cement

• BiCRS carbon storage modules on geologic storage, and biomass sinking

• BiCRS carbon capture modules on biogenic CO$_2$

• Distributed biochar production

• Ocean alkalinity enhancement

• Reuse of building materials

• Textile second life

• Direct Air Capture

Revising a methodology

Methodologies are revised regularly based on external feedback and internally planned updates. The Rainbow Science team manages two types of revisions:

• Major updates involve substantive changes and undergo a rigorous vetting process, following the Rainbow Standard Documentation Major revision procedure and the technical working group requirements described the Creating a new methodology section, including a public consultation. These updates are indicated by changes to the first number after the methodology name (e.g. BiCRS methodology V1 → V2). Major updates include:

  • Changes to eligible project types, technologies, or geographies

  • Revisions to Principles & requirements that could disqualify previously validated projects (compliance procedures apply as outlined in the Versioning and project compliance section

  • Adjustments to quantification methodologies, such as scope reviews or database updates, that result in at least a 20% average change in avoided or removed emissions

  • Any changes deemed as major by the SAB

• Minor updates and clarifications are published regularly and remain open for continuous public feedback on the Rainbow website. These updates are tracked by changes to the second number after the methodology name (e.g. BiCRS methodology V1.1 → V1.2).

All methodologies shall be reviewed and undergo public consultation at least every three years.

Project requirements for updating and complying with methodology revisions during the crediting period are detailed in the Versioning and project compliance section.

Modules follow the same creation and revision requirements as methodologies.

Discontinuing a methodology

A methodology may be discontinued if:

• shifts in scientific consensus indicate it no longer aligns with best practices

• it fails to achieve measurable carbon avoidance/removal

• it is no longer additional

• it consistently overestimates credits and cannot be revised to ensure conservativeness

• projects under that methodology consistently fail to meet the Principles and requirements outlined in the Rainbow Standard Rules

Methodologies are evaluated against these criteria at least once every three years during the mandatory major revision process, though they can also be reviewed and discontinued at any time if necessary.

Projects already validated under a discontinued methodology may continue using it until their next verification. After that, they must transition to a new methodology or become ineligible for new RCCs. Previously issued RCCs remain valid and tradable.

Public consultation

Criteria for Public Consultation

Public consultations are mandatory for:

• major revisions of the Rainbow Standard Documents

• major revisions of a methodology and module and

• creation of new methodologies and modules.

For minor revisions, the Rainbow Science team shall decide whether to launch a public consultation, based on the complexity and the impact of the changes on projects.

Publishing the Call for Consultation

The Secretariat initiates the public consultation through a Call for Consultation. This call is widely broadcasted through relevant channels to ensure maximum outreach, inviting Project Developers; carbon credit resellers, brokers, and marketplaces; net-zero engaged corporates; VVBs; climate and environmental scientists; and the general public to provide their insights and feedback on the topic. The minimum duration of the consultation is 30 days.

Rainbow shall provide an accessible mode of comment submission, through e.g. a dedicated platform or form. Stakeholders may also provide feedback via email, during a webinar, or in one-on-one meetings with the Rainbow Science team.

For the creation of new methodologies, the Secretariat should organize a webinar to explain the rationale of the methodology and an overview of its requirements.

Compilation and integration of feedback

After the the public consultation period, the Secretariat compiles all feedback, suggestions, and perspectives collected. The Rainbow Science team assesses and responds to each feedback, deciding and justifying whether to incorporate the feedback or not.

This collective feedback and the Rainbow Science team responses are summarized and published on the Rainbow Documentation Hub under the Closed public consultations section.

The Rainbow Science team integrates relevant feedback into the methodology or Rainbow Standard Documents draft, finalizing the process and publishing the document for use.