Synergies of interventions to promote pro-environmental behaviors – A meta-analysis of experimental studies

Addressing the threat of climate change requires effective environmental regulation to induce pro-environmental behavior. While various policy interventions already exist, combining different policies may offer greater effectiveness in dealing with market failures, multiple environmental objectives, and mitigating the regressive effects of single policies. In this meta-study, we investigate the potential synergies between policy interventions by rigorously assessing their comparative effectiveness when used individually versus in combination. We focus on experimental studies providing comparable findings from controlled settings to facilitate an empirically grounded understanding of climate policy synergies. Our analysis reveals negative synergy effects, indicating that, on average, the analyzed policy mixes are less effective than the sum of their individual intervention effects. However, we also find that policy mixes can offset the negative effects of single policies. Notably, combinations involving nudges and monetary incentives prove particularly effective in promoting pro-environmental behavior. Lastly, behavioral changes induced by policy mixes tend to wane faster compared to single interventions once the policies are removed. Our study provides important scientific and policy-relevant insights regarding the performance of policy mixes.