Calyx Global has rated credits from 700 projects and with this milestone comes new learnings. Read on to discover why engineered removals are far from straightforward, how ICVCM-approved cookstove and biodigester projects could improve quality and what the latest data tells us about the relationship between price and quality.

#1 – Engineered removals are not always a slam dunk

Calyx Global has expanded its selection of biochar ratings and added bio-oil and concrete projects to our platform. With new removal-based credits rated, we’ve learned that size matters when project activity centers on energy-intensive equipment or facilities. 

This pattern occurs because accounting for embodied emissions (lifecycle emissions from building and maintaining removal infrastructure​) is easier for projects that deliver a high volume of removals. Not all registries require accounting for embodied emissions, and those that do may allow the accounting to stretch over many years, leading to increased over-crediting risk. Nevertheless, some engineered removal projects can deliver relatively high integrity even if they fail to account for embodied emissions. Embodied emissions accounting is sometimes the difference between very good and excellent GHG integrity.

#2 – Cookstoves can be high quality if they fix over-crediting

We recently wrote about how the ICVCM approved several cookstove and household biodigester methodologies. These approvals come with conditions that require all such projects to revise their approach to claiming emission reductions. The ICVCM’s conditions may not resolve all the ways cookstoves may be over-crediting, though they tackle three key sources. In particular, they take a cautious stance on the most significant one: the fraction of non-renewable biomass (fNRB) value applied by projects. However, as noted by Barbara Haya and Annelise Gill-Wiehl at the Berkeley Center for Environmental Public Policy (CEPP), while this represents an important step for higher quality credits, no cookstove or biodigester projects meet those criteria so far. 

To date, we have rated credits from 234 cookstove and biodigester projects. We’ve found that if cookstove and biodigester projects were to make more accurate claims on their emission reductions, they could be among the higher-quality projects in the voluntary carbon market (VCM) (see image below). 

Typically, credits from cookstove and biodigester projects score highly in other components of their overall rating, such as additionality, but are only over-crediting. As such, a downward adjustment of claimed emission reductions can have a drastic positive impact on the ratings. If this were to occur – and cookstoves claimed a reasonable amount of reductions – credits from multiple projects could be rated in our Tier 1 (i.e., A, AA, or AAA) category. 

That said, in some cases, this could mean reducing the number of credits claimed by as much as 85%, while in others the adjustment might be relatively small – around 5%. Ultimately, it’s a trade-off between credit volume and credit quality.

#3 – Pricing is (finally) reflecting higher quality

Price has not always been a good indicator of greenhouse gas (GHG) integrity in the VCM. Throughout our years of analyzing quality, we’ve found highly rated, bargain-priced carbon credits and ones that pull a premium for characteristics unrelated to quality. 

However, the new Calyx-ClearBlue Carbon Price-Integrity Index™ shows that by around March 2024 this began to change and, on average, higher-rated credits were receiving higher prices. As of February 2025, the Calyx-ClearBlue Carbon Price-Integrity Index™ showed that Tier 1 credits (those receiving the highest Calyx Ratings, AAA-A) commanded a 24% price premium over Tier 2 (those receiving BBB-B ratings) or Tier 3 credits (those receiving C-D ratings). 

What is driving this shift? Buyers are starting to recognize that quality risks aren’t just abstract – they translate into reputational, legal and even climate risks. We expect pricing signals to sharpen as the marketplace and brokers begin to differentiate products.

However, the gap needs to widen. A 24% premium is encouraging, but not yet sufficient to consistently shift supply-side incentives. In many cases, projects that make conservative assumptions or adopt latest benchmarks see their credit volumes drop, but without a proportionate price boost.

What is needed: Buyers should prioritize integrity over volume and sellers need to be more transparent about what lies beneath the label. Valuing higher integrity through higher price signals is key to improving the quality of the VCM. Ideally this dynamic acts as a flywheel, attracting investment to projects that have the most positive impact on our planet, ultimately bringing back confidence to the VCM.

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More from this series:

600 Calyx Ratings: What have we learned?
500 Calyx Ratings: What have we learned?
400 Calyx Ratings: What have we learned?
300 Calyx Ratings: What are we learning?