While environmental argumentation has recently received much attention from science educators, little consideration has been given to how personal identities and social relationships can either support or constrain student argumentation. This study attends to this issue by examining environmental argumentation as a sociocultural activity (how students implicitly create identities and relationships through environmental warrants and claims). By integrating rhetorical and sociocultural analysis of oral discourse, we examine argumentation about environmental dilemmas (problematic scenarios involving animals and the environment). Although students set forth a variety of warrants (social, economic, contextual, biocentric, and expertise-based), the dilemmas led to distinct forms of argumentation. One dilemma involving a pet iguana fostered non-adversarial argumentation wherein students identified themselves as animal lovers and cooperative discussants. By contrast, the other two dilemmas (the hypothetical encounter with a fawn in the woods and the observation of classroom lights being unnecessarily left on) led to the unexpected emergence of sexual identities, combative disagreement, and conflict resolution on social rather than rational grounds. The main implication of this study is that it highlights the need for educators to pay closer attention to specific textual elements in the design of environmental dilemmas (types of prompts used, decision-makers' identities, statements of intentionality and outcome, moral complexity, values of nature, and social representation or cultural images of animals) in order to foster an appropriate and productive sociocultural classroom context for rational and reasoned environmental argumentation to take place without the constraints of unexpected social complications. (Contains 3 figures, 4 tables and 3 excerpts.)