On January 18, 2023 three newsrooms reported that most rainforest offsets certified by Verra were worthless, and Verra answered within hours that the claim was incorrect. A peer-reviewed study later put the additional share near 6 percent, and the Kariba project in Zimbabwe unraveled. The studies disagree by a factor of four, so the honest conclusion is a range. The voluntary market lost about three-quarters of its value.
Who's who
- Patrick GreenfieldGuardian reporter who led the January 2023 investigation
- Heidi BlakeNew Yorker writer who investigated Kariba and the cash-for-carbon trade
- Thales West+1 more episodeVrije Universiteit Amsterdam lead author of the PNAS and Science studies
- Barbara Haya+4 more episodesBerkeley researcher and co-author of the cookstove and meta-analysis papers
- Benedict ProbstLead author of the 2024 meta-analysis of 2,346 projects
- David AntonioliVerra chief executive who resigned in May 2023
- Renat HeubergerSouth Pole chief executive who stepped down in November 2023
- Mandy RambharosVerra chief executive from August 2024
Where it happens
- Kariba, ZimbabweFlagship forest project later found heavily over-credited
- Brazilian AmazonSetting for the 2020 and 2023 studies of REDD+ projects
- Washington, D.C.+31 more episodesHeadquarters of the registry Verra
- Zurich, SwitzerlandHome of consultancy South Pole, Kariba's seller
Timeline
- January 18, 2023The Guardian, Die Zeit, and SourceMaterial publish the investigation; Verra rejects it the same day.
- May 17, 2023Zimbabwe declares existing carbon agreements null and void.
- August 24, 2023Science publishes a study finding about 6 percent of credits additional.
- October 17, 2023Verra opens a formal review of Kariba and freezes issuance.
- November 2024A meta-analysis estimates fewer than 16 percent of credits represented real reductions.
- September 2025Verra finds 15.2 million Kariba credits excess, 10.3 million already retired by buyers.
Still debated
Verra objects that studies used too few controls and coarse satellite pixels, and that extrapolating from a quarter of the portfolio is unwarranted. Estimates of real credits range from about 6 percent to 25 percent for REDD+ and under 16 percent market-wide, and Kariba's bad-credit count has not been reconciled.
