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Quality & IntegrityLesson 4 of 47 min readICVCM Assessment Framework, Section 7

Ratings & Due Diligence: BeZero, Calyx, Sylvera

Ratings and Due Diligence: BeZero, Calyx, and Sylvera

The voluntary carbon market has long suffered from information asymmetry: project developers know far more about their projects than buyers do, and the registry label on a credit - "VCS registered" or "Gold Standard certified" - tells a buyer relatively little about the actual quality of the underlying emission reduction. Into this gap have stepped a new breed of market infrastructure providers: independent carbon credit rating agencies. BeZero Carbon, Calyx Global, and Sylvera are the three dominant players, each offering systematic, independent assessments of carbon credit quality.

Why Rating Agencies Exist

The existence of registry certification does not guarantee that a credit is high quality. Registry standards set minimum thresholds, but project quality varies enormously within any methodology category. A REDD+ project with a conservatively set baseline in a low-deforestation region differs fundamentally from one with an aggressive baseline in a historically deforested landscape - both may receive VCS certification, but their actual credit integrity is very different.

Rating agencies bridge this quality information gap by conducting project-level analysis that goes beyond registry compliance, incorporating scientific literature, satellite data, political risk assessments, local knowledge, and methodology critique.

Analogy: Credit Ratings in Financial Markets

The parallel to financial credit rating agencies (Moody's, S&P, Fitch) is intentional and instructive. A bond issued by a sovereign government is not automatically safe just because it cleared the issuance process; ratings assess the probability of default based on economic and political factors. Similarly, a carbon credit is not high quality just because it passed registry validation; rating agencies assess the probability that the emission reduction it represents is real, additional, and permanent. Both markets benefit from independent quality signals that reduce information asymmetry.

BeZero Carbon

BeZero Carbon was founded in London in 2020 and has built the largest portfolio of rated carbon projects. BeZero's rating scale runs from AAA (highest quality) to D (lowest), with letters in between (AA, A, BBB, BB, B, C). Projects are assigned a "risk of non-delivery" score - the probability that one credit from this project does not represent one tonne of CO2e in emission reductions or removals.

BeZero's methodology incorporates six risk factors:

  • Additionality: How confident are we that the emission reductions are additional?
  • Overcrediting: Are the baseline and emission factor assumptions conservative, or is the methodology likely producing more credits than actual reductions?
  • Permanence: What is the risk of reversal, and are buffer mechanisms adequate?
  • Project design: Are the monitoring protocols and project safeguards robust?
  • Political and regulatory: Is the project in a stable jurisdiction with supportive policy?
  • Macro: Does the project face systemic risks from market, climate, or technology change?

BeZero publishes ratings publicly and updates them when new information becomes available - a project that previously rated A might be downgraded to BBB following new research on baseline overcrediting in its methodology category.

Calyx Global

Calyx Global focuses on project-level quantitative analysis with an emphasis on the probability distribution of credit quality rather than a single point estimate. Rather than assigning a letter grade, Calyx models the statistical range of likely actual emission reductions given uncertainty in baseline assumptions, monitoring data quality, and permanence risk. This probabilistic approach is valuable for buyers who want to understand not just whether a credit is likely good or bad, but how confident they should be in that assessment.

Calyx also provides analysis specifically focused on methodology risk - their assessments highlight when systemic overcrediting is likely across an entire VCS methodology category, not just a single project. This was particularly valuable in the wake of the 2023 REDD+ investigations, when Calyx produced analysis showing that specific baseline methodologies had structural tendencies toward over-crediting.

Sylvera

Sylvera was founded in 2020 and emphasises nature-based solution projects, particularly REDD+ and ARR, where satellite data can provide independent validation of forest carbon stocks and deforestation rates. Sylvera's platform integrates satellite monitoring data, geospatial analysis, and financial modelling to produce project ratings alongside detailed project reports.

Sylvera uses a five-level rating scale: AAA, AA, A, B, and C. Their published research on REDD+ project quality has been widely cited in the mainstream press and has influenced buyer behaviour. A Sylvera B or C rating on a REDD+ project is often cited in journalistic investigations as evidence of integrity concerns.

Example: Rating Divergence

It is not unusual for BeZero and Sylvera to reach different ratings for the same project. Rating differences typically reflect different analytical frameworks, different weights applied to specific risk factors, or different access to project-level data. A project rated A by BeZero might receive a B from Sylvera if the two agencies apply different assumptions about baseline deforestation rates. This divergence, while sometimes confusing for buyers, is actually informative: it highlights the uncertainty inherent in carbon credit quality assessment and signals that the buyer should investigate further before purchasing at scale.

Buyer Due Diligence: A Framework

Rating agency assessments are a starting point, not a complete due diligence process. Sophisticated buyers combine external ratings with their own analysis. A practical buyer due diligence checklist includes:

  • Registry verification: Confirm the credit is registered on the relevant registry (Verra, Gold Standard, ACR, CAR), has a unique serial number, and has not been retired.
  • Methodology review: Identify the specific methodology used. Review the ICVCM's assessment status for that methodology category. Avoid methodologies flagged for systemic overcrediting concerns.
  • Rating agency check: Review BeZero, Calyx, or Sylvera ratings if available. Note any rating divergence and understand the key risk factors identified.
  • Vintage consideration: Older vintages (pre-2016 credits in particular) may have been issued under less stringent methodology versions. More recent vintages under revised methodologies typically carry lower baseline risk.
  • Project-level review: Review the project description document (PDD) and most recent verification report on the registry. Look for any corrective action requests (CARs) or clarification requests (CLs) from the auditor.
  • Broker or intermediary due diligence: If purchasing through a broker, confirm the broker's sourcing practices, whether they have independent access to project-level data, and what warranties they provide on credit quality.

The "A-Rated" Benchmark

Many institutional buyers have established internal policies requiring carbon credits to meet a minimum rating threshold from at least one or two recognised rating agencies. A common benchmark is BeZero A or above, or Sylvera A or above. This does not guarantee perfect quality - rating agencies can be wrong, and ratings are backward-looking assessments based on currently available information - but it provides a systematic filter that reduces the risk of purchasing credits whose quality is already known to be compromised. For large-volume purchases, multi-agency ratings provide more confidence than a single-agency assessment.

Limitations of Rating Agencies

Rating agencies are not infallible. Their assessments depend on the quality and completeness of the data available to them - project developers are not required to disclose all project-level data to third-party raters. Ratings also reflect the analytical frameworks and assumptions of each agency, which may not perfectly capture every dimension of project risk.

There are also commercial incentive questions. BeZero, Calyx, and Sylvera generate revenue primarily from buyer subscriptions and data licensing, creating potential incentives to be responsive to buyer feedback. Unlike regulated financial rating agencies, carbon rating agencies operate without government oversight or legally defined fiduciary responsibilities. The market is young and regulatory frameworks for rating agency accountability are still being debated.

One of the most significant developments shaping future rating methodology is the growing integration of high-resolution satellite data and digital monitoring into project-level MRV. Companies like Planet Labs provide daily satellite imagery at resolutions sufficient to detect individual tree crown changes. AI-enabled analysis of this imagery can independently validate or challenge the forest inventory surveys that underpin credit issuance for REDD+ and ARR projects. Sylvera and others are integrating these satellite datasets into their rating models, creating an ongoing digital audit layer that supplements periodic verification visits. As this technology matures, it should significantly reduce the information asymmetry between project developers and external analysts.

Key Takeaways

  • 1BeZero Carbon, Calyx Global, and Sylvera are the three dominant independent carbon credit rating agencies, providing project-level quality assessments that go beyond registry compliance
  • 2BeZero uses a letter scale (AAA to D) measuring risk of non-delivery; Calyx focuses on probabilistic quantification of credit quality ranges; Sylvera emphasises satellite-based validation for nature-based projects
  • 3Ratings from different agencies can diverge for the same project; divergence is informative and should trigger deeper investigation before large purchases
  • 4A practical buyer due diligence process combines registry verification, methodology review, rating agency checks, vintage assessment, and project document review
  • 5Rating agencies are valuable but not infallible: they depend on available data, apply their own analytical assumptions, and operate without formal regulatory oversight

Knowledge Check

1.BeZero Carbon's rating scale measures what specific risk for carbon credits?

2.When BeZero and Sylvera assign different ratings to the same carbon credit project, what does this divergence typically indicate?

3.Which element of a buyer's carbon credit due diligence process specifically helps identify credits that may have been issued under methodologies now known to produce systemic overcrediting?

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