Leibniz Open Science Day 2025

I Spoke at the Open Science Day 2025 on our latest large-scale many-designs project on support for carbon pricing. Global society needs to reduce carbon emissions quickly to limit the damages caused by climate change. Most economists agree that a carbon price is an effective and cost-efficient policy to mitigate emissions, yet low public acceptance and limited political support remain major barriers to its widespread implementation. This crowd-sourced many-designs project reports results from 55 behavioral interventions on real-world support for carbon pricing, independently developed by international research teams randomly selected from an initial pool of 135 applications. By implementing the interventions simultaneously with almost 20,000 U.S. residents, this pre-registered study ensures comparability of results, accelerates scientific knowledge generation, and reduces risks of scientific malpractices. Results show very small (Cohen's $d$ from 0.04 to 0.07) and statistically significant positive effects of behavioral interventions on real-world support, stated support, and willingness to endorse a carbon price that internalizes social costs of $120 per ton of CO2 emissions. This entails an increase in support for carbon pricing across measures of around two percentage points. We find low-to-medium between-study heterogeneity (tau from 0.07 to 0.12, I2 from 32.4% to 57.8%), indicating that behavioral interventions in this domain are not vastly different in their effectiveness. Lastly, we identify strong overconfidence among research teams regarding the expected effects of their interventions and those of other RTs, highlighting the need to recalibrate expectations.