Geological archives preserve records of critical climate transitions that allow for constraining interactions between the Earth’s system components. Present-day climatic, biotic and environmental conditions are, at least to some extent, shaped by both deep-time events (e.g., the Great Oxidation Event, the Snowball Earth, the Permian-Triassic Transition, the Cretaceous/Paleogene extinction, the Palaeocene-Eocene Thermal Maximum, and the Eocene-Oligocene Transition) and Quaternary climate variability (e.g., the Early-Middle Pleistocene transition, the glacial/interglacial cycles). Understanding feedback and threshold dynamics associated with geological climate transitions is essential to predict and prevent future impacts of anthropogenic global change. New proxy and modelling advances allow for unprecedently detailed palaeoclimate/palaeoenvironmental reconstructions that enhance our knowledge about the drivers, feedbacks, impacts and timescales of critical transitions. In this session, we welcome (integrated) proxy records from sedimentary archives, climate and biogeochemical modelling and theoretical frameworks to study critical Phanerozoic climate transitions. We invite contributions that assess the triggers, feedbacks and magnitudes of geological climate transitions, and/or document biogeochemical, environmental and/or biotic shifts induced by these events. This session aims to generate a comprehensive discussion in which novel findings, innovative interpretations, and future directions of palaeoclimate/palaeoenvironmental reconstructions are addressed.