The article reviews the origins, precursors, and main proponents of climate change tipping points, and the debates that the tipping point concept has occasioned. The importance of dynamical systems theory, GAIA theory, and abrupt climate change to the main proponents of tipping point warning systems is noted and situated in historical context. The 'semantic confusion' that animates contemporary debates, it is suggested, results not simply from a narrow conception of tipping points, but from inattention to the way metaphor was used to reshape climate policy.