Carbon offset projects frequently claim biodiversity “co-benefits”, yet empirical evidence supporting these claims remains scarce. This study provides the first comprehensive empirical investigation of how voluntary carbon offset projects may impact biodiversity. We compile a novel dataset combining hand-collected data on 29,974 voluntary carbon offset projects with finely-resolved data on local ecosystems from satellite measures. Results indicate carbon offset projects are associated with a 3.7% increase in human impact on local ecosystems, as measured by the Human Impact Index (HII). To investigate whether certain types of projects yield biodiversity co-benefits, we analyze heterogeneity across four dimensions: (a) projects located in areas with low initial HII, (b) projects subject to specific biodiversity requirements, (c) projects that disclose biodiversity benefits, and (d) projects located in protected areas. Despite this heterogeneity analysis, we find no evidence of significant biodiversity co-benefits across these dimensions. These findings raise concerns about the additionality and effectiveness of biodiversity claims, suggesting a disconnect between stated goals and actual ecological outcomes. The results highlight potential “biodiversitywashing” in voluntary carbon markets and underscore the need for more rigorous standards to align carbon finance mechanisms with biodiversity conservation objectives.
