“Fake news” on global warming is widely disseminated via social and partisan media. Scientists worry about its effect, because fake news may hurt public support and change policy on climate change. The current study tested the roles of cultural constructs (individualism, collectivism, and uncertainty-avoidance) in predicting the presumed effect of fake news on global warming. Based on 770 answers in four countries, the study found that individualism and collectivism influenced the presumed media effect on others and the third-person effect (self-other disparity of media effect). Moreover, the presumed media effect contributed to both preventive actions such as support for regulation on fake news and corrective actions such as a willingness to donate money. Likewise, the study found that collectivism positively predicted a willingness to donate money, while uncertainty-avoidance predicted support for regulation.