Climate change is ushering in a new era across the circumpolar region, affecting all aspects of Arctic life, including conditions of security across the circumpolar Arctic. This article argues that the intersection of human-caused climate change, particularly the warming of the Arctic Ocean, and renewed great power competition are causing the Arctic regional security complex (RSC) that emerged in the post-Cold War period to fragment into distinct sub-regions. Rather than a single region characterized by common environmental and human security challenges, security in the Arctic is increasingly shaped by geopolitical factors related to the North American, European, and Eurasian regions, respectively. The result is the end of the Arctic as a holistic security region and the emergence of distinct sub-regional security challenges across different parts of the circumpolar world. This variation in conditions of security will contribute to the erosion of the circumpolar Arctic as a single, coherent region over the course of this century, and will strain the region’s governance architecture. The result is a circumpolar region that will be less distinctly ‘Arctic’ than in the past, as the cooperative nature of recent Arctic politics is replaced by adjacent security sub-regions characterized by great power competition and differing geopolitical and ecological considerations.