It is important to understand how persuasive the most-cited climate change messaging strategies are. In five replication studies, we found limited evidence of persuasive effects of three highly cited strategies (N = 3,216). We then conducted a registered report megastudy (N = 13,544) testing the effects of the 10 most-cited climate change messaging strategies on Americans’ pro-environmental attitudes and behaviour. Six messages significantly affected multiple preregistered attitudes, with effects ranging from 1 to 4 percentage points. Persuasiveness varied little across party lines, inconsistent with theories predicting heterogeneous effects for targeted messages. No message increased pro-environmental donations, suggesting costly behaviours are difficult to influence with messaging alone. Inference of mechanisms driving effects was limited as the most impactful messages influenced multiple mediating variables. Taken together, these results identify several persuasive strategies, while also highlighting the limits of short-form messages for increasing Americans’ support for action to address climate change.

Vaccination is a cost-effective strategy for reducing morbidity and mortality among children under 5 years old. To be fully protected from diseases such as tuberculosis, diphtheria, pertussis, and polio, children must receive all recommended vaccinations in a timely manner. In many countries, including Tanzania, high overall vaccination rates mask substantial regional variation in vaccination coverage and low rates of vaccination timeliness. This study evaluates the efficacy of mobile phone-based (mHealth) reminders and incentives for improving vaccination timeliness in the first year of life.