The coral reef hypothesis asserts that carbonate production on newly flooded shelves contributes importantly to the rise of atmospheric carbon dioxide during deglaciation. We seek to constrain the timing and strength of such carbon dioxide flux by re-assessing reef and platform distribution in the world ocean. The pattern of reef growth that emerges suggests that emission of CO2 resulting from carbonate production was important particularly during the late stages of deglaciation. The effect peaked during the early Holocene and presumably contributed to the warming in the climatic optimum.