Spare the details, share the relevance: The dilution effect in communications about carbon dioxide capture and storage

The mitigation of climate change may require the implementation of carbon dioxide capture and storage technology (CCS). Both proponents and opponents of CCS will try to convince the public of the (dis)advantages of this technology. This research examines the relative persuasiveness of communications that only contain highly relevant information (e.g., the argument that the implementation of CCS would have important climate benefits) or combine highly relevant with irrelevant or moderately relevant information. The results of three experiments consistently show that adding irrelevant information dilutes the impact of highly relevant information: Irrelevant information reduced the persuasiveness of communications (Experiments 1 and 2) and weakened people's beliefs about the issue (Experiment 3). This dilution effect occurred with both positive (pro-CCS) information and negative (con-CCS) information, but the effect was stronger with positive information. Awareness of the source of the communications moderated the dilution effect. Implications for public communications about CCS are discussed.