Earth Hour (EH) is a large-scale campaign launched by the World Wide Fund For Nature (WWF) every year to raise awareness about environmental issues. Although the EH campaign is active on social media, there is currently no systematic way of assessing its impact on public engagement and the topics they post about. In this paper we study engagement towards the 2014 EH campaign on Twitter. By analysing more than 35K tweets around the campaign we observed that longer posts, easier to read and with positive sentiment generated higher attention levels. Conversations were driven by the main themes of the campaign (super hero, the panda, etc.), but engagement towards these themes did not always translate in engagement towards environmental issues. Users decreased their engagement towards the topics of the campaign after it finished, but these topics still remained in their conversations one month later
