The microvideo platform TikTok has emerged as a popular hub for self-expression and social activism, particularly for youth, but use of the platform’s affective affordances to spread awareness of important issues has not been adequately studied. Through an exploratory multimodal discourse analysis of a sample of popular climate change-hashtagged TikTok videos, we examine how affordances of visibility, editability, and association facilitate the formation of affective publics on TikTok. We describe how TikTok’s features allow creators to construct and propagate multi-layered, affect-laden messages with varying degrees of earnestness, humor, and ambiguity. Finally, we identify recurring affective themes in popular climate change messages by studying not just in-frame content but also the discursive, intertextual, and memetic linkages that propagate affective publics. Collectively, these audiovisual expressions of personal engagement and awareness demonstrate how media affordances can abet, amplify, and confuse discussions of global issues online. These affordances facilitate a unique kind of activism by helping non-expert users intervene in a discussion that generally takes place among scientists and journalists: the question of how serious a problem climate change is and what to do about it.