This study investigated a new direction for improving the decision making of populations at risk in the context of uncertain environmental events, such as volcanic hazards. According to the risk as feelings theory and dual process models, situations with certain outcomes do not necessarily require the use of affect heuristics (e.g., experienced feelings, anticipated emotions) as valid information in the decision‐making process. In the case of difficult decisions with moral dilemmas, certainty could even improve decisions. Thus, using an ecological design with various scenarios depicting upcoming volcanic hazards, we examined whether reducing the uncertainty of lethal threat by conveying certainty in an information campaign could influence decision making and promote a better quality of choice (correct application of the recommendations from the competent authorities). We focused specifically on two populations composed of local people living in the vicinity of an active volcano (Tungurahua volcano, Ecuador) and local scientists. We also examined whether a difficult decision involving a moral dilemma (e.g., leaving people behind so as not to jeopardize one's own life) potentiated this effect, compared to a less difficult situation without a dilemma. We demonstrated that, for local people facing a moral dilemma (difficult decision), the reduction of uncertainty of lethal threat involved a better application of the actual recommendations. These outcomes provided perspectives on improving the applications of the recommendations among local populations at risk in the context of a real risk exposure.