Almost 11 times more REDD+ carbon credits were issued than the underlying forest protection actually justified, but four in five of the projects assessed still measurably cut tropical deforestation, with a small cluster of high-issuing schemes responsible for the bulk of the over-crediting now at the centre of the credibility crisis sweeping the wider voluntary carbon market. That is according to Dr Tom Swinfield, a researcher in the University of Cambridge’s Department of Zoology and lead author of a major new synthesis published in Nature, which pooled six independent evaluations of 44 REDD+ projects representing nearly half of all schemes producing REDD+ carbon credits by 2020.
“We found that many REDD+ projects were at far lower risk of deforestation than anticipated by project-led evaluations. Credits were issued based on predictions that these forests were at imminent risk of deforestation, but in reality, this risk was often lower,” Swinfield said.
Wood Central understands that REDD+, the Reduced Emissions from Deforestation and Degradation framework, generates carbon credits by comparing anticipated deforestation in a region before protection against projected deforestation once a project is in place, with credits representing the carbon that would otherwise be released through clearance.
The integrity of the credit depends on proving “additionality” — that forest protection would not have occurred without the REDD+ intervention — which in turn depends on the selection of unprotected reference forests against which robust comparisons can be drawn, and the Cambridge synthesis found those reference areas were typically more exposed to deforestation than the project sites would have been, systematically inflating the apparent climate benefit and the volume of credits issued.
The over-crediting has crashed the wider voluntary carbon market from its 2022 peak of US$2 billion to around US$500 million as buyers walked back from credits whose climate claims could not be defended. Cambridge argues that the proper response is not to abandon the framework but to tighten the issuance rate, raise the per-credit price, and bring in independent data providers to strip bias from the valuation step, alongside retrospective checks of project performance to validate whether credits issued matched the actual forest protection delivered.
“A key take-home message is that bad credits do not necessarily mean bad projects. Many projects have successfully slowed deforestation, even if more credits were sold than are justified,” Professor Julia Jones at Bangor University and a co-author of the study said.
The original generation of REDD+ valuation methods has now largely been retired, although the next generation has yet to be fully implemented, with delays the team attributes to concerns about getting the rebuilt system right. The first-generation methodologies failed because project proponents chose reference forests that were more exposed to deforestation than the protected areas, creating a systematic bias that inflated both the apparent threat and the volume of credits justified. Jones said the over-crediting controversy had wrongly tarnished tropical-forest carbon finance as a whole — an unhelpful outcome given the role forest conservation plays in tackling climate change.
For more information: Swinfield, T., Williams, A., Coomes, D. et al. Learning lessons from over-crediting to ensure additionality in forest carbon credits. Nat Commun (2026). https://doi.org/10.1038/s41467-026-71552-3
