Mitigating climate change requires mass behavior change. However, individuals may fail to act because they perceive climate change as a threat that is distant or not personally relevant, or believe their actions are not impactful. To address these barriers, we conducted an “intervention tournament.” In Phase 1 (N=7,473), we tested 17 interventions that targeted psychological mechanisms under three themes: Self-and Social-Relevance, Future Thinking, and Action Impact. The most effective interventions for motivating action involved imagining the future, paired with appeals to self-or social-relevance. The most effective interventions for motivating information sharing involved reflecting on self-and social-relevance of climate change. Importantly, these interventions were substantially more effective than prevalent existing strategies (e.g., carbon footprint feedback). In Phase 2, we will conduct a pre-registered replication of the leading interventions identified in Phase 1. Insights from our tournament could be applied to communication campaigns and online interventions for behavior change.