Who Certifies and Grades Carbon Credits?
Two different jobs get confused constantly: issuing a credit, and grading how good it is. Here's a neutral map of who does each — we don't rank or endorse any of them.
Standards & Registries
Write the methodologies, approve individual projects against them, and issue serialized credits into a public ledger. Think of them as the rulebook-writer and record-keeper.
Independent Rating Agencies
Assess already-issued credits for actual quality — additionality, permanence, over-crediting risk — and publish a letter grade, similar to a bond-rating agency reviewing a bond after it's issued.
Where credits come from
| Registry | Focus | Notes |
|---|---|---|
| Verra (Verified Carbon Standard / VCS) | Broadest project-type coverage; largest voluntary registry | The world's largest voluntary GHG crediting program, with more than 4,000 registered projects across roughly 95 countries — an estimated 70–80% of all voluntary credits ever issued run through Verra. |
| Gold Standard | Sustainable-development co-benefits | Founded in 2003 by WWF and other NGOs; requires mandatory demonstration of co-benefits aligned to the UN Sustainable Development Goals, which often commands a price premium. |
| American Carbon Registry (ACR) | U.S. compliance & voluntary, forestry/agriculture | One of the oldest U.S. registries; methodologies are eligible for California's Cap-and-Trade compliance program. |
| Climate Action Reserve (CAR) | U.S. compliance-grade projects | Strong regulatory acceptance, especially within California's Cap-and-Trade program; often commands premium pricing for that reason. |
| Puro.earth | Engineered carbon removal (biochar, DAC, mineralization) | Helsinki-founded registry issuing CO₂ Removal Certificates (CORCs); operates the leading biochar methodology and focuses exclusively on durable, engineered removal categories. |
Who grades the credits after they're issued
| Agency | Approach | Notes |
|---|---|---|
| BeZero Carbon | Remote sensing + expert analyst review | Rates 900+ projects on an AAA–D scale; publishes headline ratings openly on its platform. |
| Sylvera | Automated data analysis + human analyst review | Rates 680+ projects across carbon delivery, additionality, permanence, and co-benefits, also on an AAA–D scale. |
| Calyx Global | Programme, methodology, and project-level evaluation | Has assessed 940+ projects across 27 project types and 121 methodologies; adopted the common AAA–D scale in 2025. |
ICVCM & the Core Carbon Principles
The Integrity Council for the Voluntary Carbon Market (ICVCM) isn't a registry or a rater — it's an independent governance body that assesses entire methodologies (not individual projects) against a global quality bar called the Core Carbon Principles (CCP). A methodology that passes can carry the "CCP-Approved" label, and registries including Gold Standard, ACR, and Climate Action Reserve have had methodologies approved, with Verra's largest methodologies under active review.
ISO 14064 & third-party verifiers
Separate from registries and raters, bodies like Kiwa Inspecta, SGS, DNV, and TÜV act as independent verifiers/certifiers, auditing a specific project's carbon accounting against international standards such as ISO 14064-2 (quantification and verification of project-level GHG reductions and removals). This is the kind of certification behind, for example, Carboreal's Trammell S. Crow Forest — see our Org of the Month feature.
None of this is an endorsement.
We list these organizations because they are the ones buyers, journalists, and researchers most often need to understand — not because the Carbon Advisory Coalition has vetted, certified, or ranked them ourselves. Always check each organization's current published rules directly before relying on them.