Adaptation and mitigation efforts are hampered by multiple obstacles and thus lag behind climate changes' speed and scope. Some of the most powerful obstacles to climate action are the social-psychological factors that influence human thought, preferences, and behaviors. These factors, including those articulated by environmental psychology generally, and Terror Management Theory (TMT) specifically, are neglected within climate response research. TMT underlies an extensive and wellestablished literature; researchers have shown that efforts to repress one's mortality awareness, triggered when people are explicitly or implicitly reminded of their unavoidable death, influences individuals' attitudes and behavior. These psychological defenses, including denial, distraction and worldview defense, sometimes produce counterintuitive and potentially counter-productive outcomes. Meanwhile, the growing global awareness and media coverage of climate change, and much scholarly research, has skewed toward negative "disaster and death" narratives. Exposure to such stimuli, highlighting climate change's potentially life-threatening effects, may exacerbate counter-productive responses. In this thought experiment, we propose that mortality awareness could be a critical variable that helps explain climate action at the individual and societal levels. We survey TMT insights, focusing on the relationship between mortality reminders and human responses. We then identify how climate change may lead to increased mortality awareness and consider the psychological defenses triggered by this awareness. We argue that mortality defenses may both limit and advance climate action. Finally, we set out an agenda for TMT-climate response research and discuss the potential to advance several inquiry lines, including climate change communication, collective action and the capacity for transformational responses.