Analysis finds gaps in forest carbon offset projects, with most overstating climate impacts

Most Reducing Emissions from Deforestation and forest Degradation (REDD+) forest carbon offset projects significantly overstate their climate benefits, according to a new study published in Science.

The findings come from an international team of researchers, primarily based at the Guangdong Laboratory of Artificial Intelligence and Digital Economy (SZ), China, with contributions from Prof. Dr. Jonathan Chase of the German Center for Integrative Biodiversity Research (iDiv) and the Martin Luther University Halle-Wittenberg (MLU).

The study analyzed 52 REDD+ initiatives, a total of 66 project units (some initiatives included multiple units), certified under Verra’s Verified Carbon Standard. It follows a 2023 study also published in Science, together with major media investigations, that raised questions about the credibility of carbon credits issued under the same standard. While not directly linked, the new research corroborates those concerns, confirming that only a minority of projects achieved meaningful reductions in deforestation, and just 19% met their reported emissions targets.

How REDD+ impact was measured

To evaluate REDD+ effectiveness, the researchers used so-called synthetic control methods—a statistical approach that compares what actually happened in a project area to what would likely have happened without intervention. This “counterfactual baseline” is built by selecting nearby areas with similar environmental and socioeconomic conditions but without REDD+ implementation. The project sites span 14 tropical countries across Latin America, Africa, and Southeast Asia.

These matched control sites act as a stand-in for a REDD+ project’s alternate reality, allowing researchers to estimate the true impact of forest protection efforts. By comparing forest loss in REDD+ areas to these controls, the researchers assessed whether the projects actually reduced deforestation and how many of the resulting carbon credits were backed by real climate benefits.

“Our analysis shows the problem is real, but not hopeless,” says co-author Dr. Jonathan Chase, head of the Biodiversity Synthesis research group at iDiv and MLU professor. “By building transparent counterfactuals, we can see which projects deliver and which do not.”

Partial gains signal promise

About one-third (32%) of the project units (21/66) showed significantly less deforestation than expected, with some Brazilian projects achieving dramatic reductions. However, nearly one-fifth (17%) of the units (11/66) experienced more deforestation than their matched controls, and about 35% of initiatives (18/52) reported deforestation baselines that were far higher than what the data supported. In Colombia, for example, most projects claimed deforestation risks more than ten times greater than the study’s estimates, suggesting substantial overcrediting.

To quantify the scale of the issue, the team examined 48 of the 52 projects with publicly available carbon credit data. By the end of 2022, up to 228 million credits had been issued, with 127 million used by companies or individuals to offset their greenhouse gas emissions, yet only about 35 million were likely to represent real emissions reductions. That amounts to only an estimated 13.2% of tradable credits being backed by evidence of avoided deforestation. This discrepancy raises major concerns about the reliability of current offset practices, according to the authors.

“The market needs credits that mean what they claim. We estimate that only about one in eight tradable credits represents real emissions reductions today. Stronger baselines, independent evaluation, and diversified portfolios can raise that number and restore confidence,” Chase adds.

Rethinking REDD+

Despite the challenges, the authors believe that REDD+ remains a promising tool for climate mitigation. Even among underperforming projects, the researchers found many projects delivered partial climate gains.

When implemented carefully and evaluated robustly, these projects can deliver climate benefits under the right conditions. According to the authors, the aim is not to abandon REDD+, but to fix it so that every credited ton reflects real climate benefit.