Fifty-five crowd-sourced designs assessing carbon pricing support in the U.S.

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 crowdsourced “many-designs” project presents results from 55 behavioral interventions on real-world support for carbon pricing, independently developed by international research teams. By implementing all designs simultaneously with almost 20,000 U.S. residents, this pre-registered study shows very small positive but statistically significant effects of behavioral interventions on a set of design-specific proxies of real-world support (Cohen’s d: 0.06; 99.5% CI: [0.001, 0.124]), and on four out of five common measures of stated support (Cohen’s ds: 10 0.06–0.08; 99.5% CIs: [0.006, 0.112]–[0.020, 0.133]; between 1.7–2.4 percentage points in increased support across outcomes), including the willingness to endorse a carbon price that internalizes the social costs of $120 per ton of CO2 emissions (d: 0.06; 99.5% CI: [0.012, 0.118]). Furthermore, the results reveal low-to-medium between-study heterogeneity (Tau : 0.07–0.12). Lastly, we identify strong overconfidence among research teams regarding the expected effects of their interventions and those of their peers, indicating a miscalibration of community expectations.