By employing historical institutionalism, this article argues that anthropogenic risks (i.e., climate change and the COVID-19 pandemic) serve as a critical juncture for NATO in reorienting its sustainability strategies in response to climate fluctuations and potential insecurity arising from resource depletion. During the Cold War, NATO’s main objective was to deter threats from states, mainly the Soviet Union. At the beginning of the twenty-first century, the Alliance turned to non-state actors (e.g., Al-Qaida, Somali pirates, and Russian hackers). Then, climate change and COVID-19 emerged as global security risks from natural, environmental phenomena. NATO had incrementally sought to address the threats from climate change, but COVID-19 served as an impetus to acknowledge insecurity caused by neither states nor non-state actors. The pandemic represented the Alliance’s first significant mobilization of military assets on a regional (i.e., European level), for a sustained period, in response to a unique risk. Based on this experience, NATO needs a sustainable strategy to acknowledge anthropogenic risks and to prepare for future climate-related fluctuations and insecurity.