People tend to discount information from sources with obvious persuasive intent.... messages that exist in an online context where explicit persuasive intent may be present are subject to lower credibility assessments, perhaps as a result of higher scrutiny or skepticism.
- Flanagin and Metzger (2007)
Want to convince someone the situation is urgent and immediate action is imperative? Well, you're not going to get very far by laying it on with a sledgehammer. This approach usually backfires by triggering resistance and motivating counterarguments. Repeating the same message with an increasing sense of alarm isn't going to help either. As a voluminous academic literature has already shown, the frequency of persuasive messages is inversely related to their effectiveness at influencing behavior. In the context of getting people to do what you want, that means if at first, you don't succeed, try try again is a tactic that reaps diminishing returns.
These are preliminary thoughts upon reading World Scientists’ Warning to Humanity: A Second Notice (2017) and World Scientists' Warning to Humanity (1992). Much more later.
Reference:
Flanagin, A. J. and M. J. Metzger (2007). "The role of site features, user attributes, and information verification behaviors on the perceived credibility of web-based information." New Media & Society 9(2): 319-342.