This article adapts and applies a securitisation framework to produce an analytical explanation for the heightened geopolitical status of climate change over the past decade, as demonstrated by the breakthrough Paris Agreement of 2015. Rather than speech acts invoking security, the focus of this analysis is on the socio-scientific discourse of global climate crisis that emerged in the several year period leading to the 2009 COP 15 conference in Copenhagen. Two types of experts—contributory and interactional—are identified as the essential and interdependent actors that engaged in ‘crisification’, a novel crisis-based perspective on political agenda setting, in which climate crisis served as a primary discursive device employed by prominent advocates of urgent action. Contributory experts, that is, authoritative climate scientists and their institutions, together with interactional experts—non-scientist social actors who appropriated and mediated scientific data and knowledge in framing climate change as a global crisis—constituted an extended epistemic community of climate advocates. Through an array of speech acts, this extended community effectively co-constructed a convincing climate crisis discourse that consisted of quantitative data artefacts based on CO2 concentration and global mean temperature, and qualitative invocations of existential threat to human civilisation, which contributed to the ascent of climate change on the global political agenda. In proposing crisification as a complement to securitisation, the article offers a theoretical innovation that facilitates constructivist analysis of issues framed as crises, including geopolitical problems in certain non-military sectors where crisis is a favoured label for perceived threats to core values.