Professor Ove Hoegh-Guldberg discovered the molecular mechanism behind coral bleaching during his PhD and early career. He also pioneered our understanding of endosymbiosis between invertebrates such as reef-building corals and dinoflagellates (Symbiodinium), particularly the flow of energy and carbon and its breakdown during ecosystem-level mass-coral bleaching events. Hoegh-Guldberg’s discoveries have directly influenced global policy through their integration of the thermal physiology of corals with projections of future sea temperatures. His research was one of the first to demonstrate the extreme sensitivity of ecosystems to increases in anthropogenic CO2, emphasising the need for a 2°/450 ppm 'guardrail' in climate policy.