This presentation reports on a study of how discourses of environmental citizenship, sustainability and climate change are communicated and mediated in a global media event. "Earth Hour" began in 2007 in Sydney, Australia, and in 2009 it was proclaimed a successful global event. The event focused primarily on citizen awareness, participation and solidarity in mitigating climate change. In its sister campaign ("Vote Earth"), the discourse of representative democracy was deployed to constitute an imaginary global electorate. The analysis focuses on (a) the intense drive to visualise and spectacularise (mediational means) the simple act of switching off the lights and the consequences of such an act; (b) the massive infrastructure of communication to synchronise the collective performance of a global 'climate public'; (c) the discursive 'memory work' to archive and memorialise the hour, eg. on YouTube; and (d) the attempt to inculcate a 'global citizen' who is concerned with the environment/climate and whose anticipatory mediated actions in relation to it are prefigured by this communicative event, and (e) the resistance to the circulation of this 'new' mediated discourse. The presentation will also reflect on developments that arise as a result of Earth Hour 4 in March 2010.