A major analysis led by the University of Cambridge has found that many REDD+ projects achieved meaningful reductions in forest loss – offering real environmental benefits.
This is despite the study confirming that almost eleven times more carbon credits were issued from the REDD+ (Reduced Emissions from Deforestation and Degradation) voluntary carbon market than was justified.
The research, led by Dr Tom Swinfield as part of the Cambridge Centre for Carbon Credits, aims to build a confidence in evaluation of carbon credits to help address the urgent challenge of tropical deforestation. It suggests that improved valuation methods, that better reflect real reductions in deforestation over time, would increase confidence in the critically important market for these credits.
Professor David Coomes, Head of the Forest Ecology and Conservation group at the Department of Plant Sciences, and co-author of the paper said: "Our synthesis shows that while many REDD+ projects do reduce deforestation, credited impacts have often been substantially overstated due to biased baselines and flexible modelling choices. Robust, independent ex post evaluation against credible counterfactuals is essential if carbon credits are to reflect real climate benefits. Encouragingly, several rigorous methods are now available."
The report is published today in the journal Nature Communications.
Improvements needed to ensure credits remain a meaningful solution to deforestation
Tropical forests are an invaluable global asset under increasing threat, and carbon markets have the potential to contribute substantial funds to their protection.
The researchers say future projects must ensure the claimed impacts reflect real reductions in deforestation: the REDD+ carbon credit market should not be abandoned, but far fewer credits should be issued, at a higher price.
Over the last two decades the voluntary carbon market - through which people can buy carbon credits to offset their carbon emissions – has boomed and almost bust. REDD+ schemes use funds from the sale of carbon credits to protect existing forests, but their valuation methods have come under heavy scrutiny leading to a crisis of confidence in the market.
The new study reveals that nine high-issuing REDD+ projects accounted for much of the over-crediting, skewing both market value and public perception. The researchers say that these ‘bad credits’ are not necessarily reflective of bad forest conservation projects.
The synthesis of six independent evaluations of the effectiveness of 44 REDD+ projects, representing almost half of the projects producing REDD+ carbon credits by 2020 – found that four in five projects successfully protected forests.
“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,” said Swinfield, a researcher in the Department of Zoology and first author of the study.
He added: “It’s vital that future forest carbon credits accurately represent their benefits for these schemes to be a meaningful solution to deforestation.”
“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,” said Professor Julia Jones at Bangor University, a co-author of the study.
She added: “The over-crediting scandal in the voluntary carbon market has left many with the unhelpful impression that anything to do with funding tropical forest conservation through carbon finance is a bit dodgy. It is important to set the record straight, as forest conservation is so vital to tackling climate change.”
How are carbon credits generated?
REDD+ schemes generate carbon credits by investing in the protection of the world’s most important forests, from the Congo to the Amazon basin. Credits represent the carbon that is no longer released through deforestation as a result. Organisations and individuals can then offset their own carbon footprint by buying credits equivalent to a given quantity of emissions.
Carbon credits are generated by comparing the anticipated deforestation in a region before protection, with the projected deforestation once areas of forest are protected through a REDD+ project. This depends on accurately selecting other, unprotected areas of forest against which robust comparisons can be made.
The problem many independent evaluators have discovered is that the comparison areas chosen by crediting agencies were often more exposed to deforestation than project areas would have been, so too many credits have been issued.
An evolving market
The value of the carbon market has plummeted to only around one quarter of its 2022 US $2 billion high, following widespread evidence that carbon credits were oversold.
Although the first generation of REDD+ methodologies has largely been phased out, the next generation has yet to be fully implemented – with major delays perhaps driven by concerns about getting the system right.
The researchers say to avoid over-crediting, future REDD+ projects must draw on more representative reference forests to better assess the true contribution of projects to forest protection.
Several improvements – such as using independent data providers to remove any bias in valuing credits - are already helping to make these credits more robust, but researchers say retrospective checking of project performance is also essential.
“This study confirms concerns widespread over-crediting in the carbon market. But despite the challenges, carbon markets remain one of the few mechanisms we have to protect tropical forests while giving organisations and individuals the chance to compensate for their emissions,” said Swinfield.
Reference: Swinfield, T. et al: ‘Learning lessons from over-crediting to ensure additionality in forest carbon credits.’ 'Nature Communications', April 2026. DOI: 0.1038/s41467-026-71552-3
Image: Morning mist lifts from Indonesian forest as it warms. Credit: Tom Swinfield.
Adapted from an article by Jacqueline Garget published on the University of Cambridge research news pages on 30 April 2026. Read the original article.