Who gets credit for reduced deforestation? Evaluating additionality in subnational jurisdictional REDD+ under national policy reforms in Indonesia

Forest carbon offsets have been criticised for overstated impacts, encouraging a shift from project-level schemes to jurisdictional programs intended to address deforestation drivers at scale. We evaluate the additionality of one of the first subnational initiatives to receive results-based payments: East Kalimantan's jurisdictional REDD+ program in Indonesia. Using remotely sensed data and the synthetic control method, we estimate counterfactual trends in deforestation and forest degradation over a two-year anticipation period and the full crediting period (2019–2024) and detect no statistically significant effects. These results suggest that observed declines in East Kalimantan reflect a broader nationwide reduction in deforestation plausibly driven by post-2015 policy reforms, with which the program's theory of change is intertwined. Consistent with this interpretation, complementary Bayesian structural time-series models, which do not rely on external controls and estimate the combined trajectory of deforestation under observed drivers, indicate that the intervention was associated with significant reductions in deforestation and forest degradation concentrated in the early years of the crediting period, but that these effects were not sustained. Together, these findings suggest that subnational jurisdictional programs operating in highly centralized governance systems may struggle to demonstrate additionality and claim credit at the subnational level, particularly when their theory of change is closely aligned with national policy reforms. Methodologically, our study demonstrates how combining counterfactual approaches with distinct comparison strategies can strengthen evaluation of large-scale climate policies and improve understanding of underlying impact mechanisms.