Environmental awareness campaigns disseminate information about the state of the natural environment, aiming to affect public attitudes and encourage pro-environmental behavior. I test the influence of awareness days on the general public’s environmental and climate change attitudes and concern, focusing on the case of the Earth Hour, an international campaign organized annually by the World Wide Fund for Nature. The Earth Hour highlights environmental consequences of human activity and encourages
sustainable behavior, culminating with a call to mass action. To assess the Earth Hour’s effect, I use longitudinal data from Germany and the UK, exploiting the orthogonality of the Earth Hour observance to the timing of data collection, to estimate models comparing individual attitudes and concern before and after the event. I find no evidence of an Earth Hour effect on environmental and climate change attitudes and concern. Results suggest that more research is needed to assess the influence of environmental advocacy campaigns and awareness days on the general public.