Yale Program on Climate Change Communication

We are pleased to announce the publication of a new article, “The unique roles of breadth and depth in climate change persuasion” in the Journal of Environmental Psychology.

Climate change message testing often compares the persuasiveness of different climate messages across different audiences. The most rigorous way to evaluate message effectiveness is to use randomized controlled trials, where different groups of people each receive a different message, and then compare the average persuasion effects across the different messages. However, a drawback of comparing the average effects of different messages is that averages do not describe the underlying pattern of belief change. That is, are overall message effects being driven by how many people change their beliefs (i.e., breadth), or how much their beliefs change (i.e., depth)?

To investigate this question, we conducted a meta-analysis of all relevant studies in our experimental data archive (14 unique experiments; 94 messages; total N = 41,265). We found that both breadth and depth are significant predictors of message effect size, but breadth is a much stronger predictor than depth (see figure below). This means that more successful messages tend to convince more people rather than convince a smaller number of people to a larger degree.

It is important to note, however, that breadth and depth are both important and might play different roles depending on your context, goals, and audience. For example, in some cases the goal might be to build public awareness among a broad audience, whereas in other cases the goal might be to engage a select group more deeply. These different goals suggest whether communicators should focus more on breadth or depth in their climate change communication. We discuss these nuances in the full article, which includes three case studies.

The full article is available here to those with a subscription to the Journal of Environmental Psychology. If you would like to request a copy of the published paper, please send an email to climatechange@yale.edu with the subject line: Request breadth vs. depth paper. Or, a preprint version is available here.

Here are three top-performing messages from our study, from Yale Climate Connections:

• Tybee Island residents see more flooding as sea levels rise
• ‘Green Schools Challenge’ teaches Miami kids about climate problem, solutions
• A simple way cities can make it easier for people to go solar