Fig. 1: Two examples of how a one-time projected baseline (proposed – no activity) can overestimate a project’s additionality claims.

a In a conservation project, the one-time projected baseline predicts an approximate loss of 60% of the biodiversity in 30 years due to deforestation, and thus claims a large additionality by protecting a threatened area. But if a control, properly matched to the drivers of change in the project, had been monitored where no conservation actions were taken (i.e. counterfactual) and there was much less deforestation and loss of biodiversity, the project should claim much less additionality. b In a restoration project, the one-time projected baseline predicts a small increase in biodiversity recovery (proposed – no activity) during the first 30 years of the project, and thus claims large additionality because the restoration activities of the project (project) greatly increased forest cover and biodiversity. But if a well-matched control had been monitored where no restoration actions was taken (i.e. counterfactual), they would have documented significant biodiversity recovery due to secondary succession, thus greatly reducing the actual additionality that could be claimed by the project. The trajectory of the Best on offer (i.e. intact reference site) is included as a reference for deciding the proportion of biodiversity recovery.