#ManyDesignsCarbon

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 presents 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. The results show very small positive but statistically significant effects of behavioral interventions on real-world support, and stated support, including the willingness to endorse a carbon price that internalizes social costs of \$120 per ton of CO\textsubscript{2} emissions (Cohen's $d$'s range from 0.04 to 0.07). Put differently, this entails an increase in support for carbon pricing across measures of around two percentage points. We find low-to-medium between-study heterogeneity (τ from 0.07 to 0.12, I² from 32\% to 57\%). Lastly, we identify strong overconfidence among research teams regarding the expected effects of their interventions as well as those of their peers, pointing to a potential miscalibration of community expectations.