The last two decades have seen the emergence of discourses that depict climate change as a major threat to security. This thesis seeks to explore the consequences of using security narratives to speak about climate change. Focusing on the EU as a case study, the thesis aims to answer two central questions. First, has the climate change and international security discourse become dominant in the way climate change is conceptualised in the EU? Second, has this discourse solidified in concrete policies or institutional arrangements? To this end, I use Maarten Hajer’s framework for discourse analysis, which enables the uncovering of the narratives, metaphors and storylines through which climate change is being constructed as a security problem, but also the institutional consequences following from such discourse. I argue that, in the EU, the storyline that depicts climate change as a ‘threat multiplier’ has managed to gain considerable influence in the EU climate change, and security discursive spaces. While other conceptualisations of the climate problem co-exist, EU climate actors now accept that climate change should be viewed as a security issue. At the same time, EU security actors now include climate change in their comprehensive definition of security. Regarding the policy consequences of the discourse, I contend that these are mainly visible in the context of external climate policies, as the security dimension of climate change is now part of EU climate diplomacy strategies. In addition, climate change considerations have been increasingly included in the EU’s comprehensive approach to external conflicts and crises. These findings, I argue, can shed some light on the normative debate over the securitisation of climate change as a positive or negative concept.