This Milankovic Medalist paper represents a tour de force, addressing a complex yet crucial question: the evolution of global climate over the past 4.5 million years. This paper makes a significant contribution to the geoscience community by providing a self-consistent decomposition of global mean benthic δ18O into its temperature and seawater (ice volume) components. This approach is consistent with independent estimates of global mean sea surface temperature (GMSST) and sea level constraints.The analysis incorporates numerous high-resolution records spanning this period and highlights two distinct climatic regimes: • Before 1.5 million years ago, a warm period characterized by smaller-amplitude ice sheet and sea level cycles, primarily driven by obliquity timescales. • Following the Mid-Pleistocene Transition (MPT), i.e. after 1 million years, a well-documented increase in the amplitude of glacial cycles became evident. The central finding of the study is that, during the MPT, there was a shift in ocean heat storage efficiency (HSE). Prior to this transition, HSE remained low and constant, whereas after the MPT, it doubled and stabilized at a higher value. This finding is supported by the observation of subtle differential changes in global mean SST and mean ocean temperature (MOT), which appear to be time-dependent. These observations suggest a potential fundamental shift in oceanic heat storage dynamics.