Climate changes across the last 24,000 years provide key insights into Earth system responses to external forcing. Climate model simulations and proxy data have independently allowed for study of this crucial interval; however, they have at times yielded disparate conclusions. Here, we leverage both types of information using paleoclimate data assimilation to produce the first observationally constrained, full-field reanalysis of surface temperature change spanning the Last Glacial Maximum to present. We demonstrate that temperature variability across the last 24 kyr was linked to two modes: radiative forcing from ice sheets and greenhouse gases; and a superposition of changes in thermohaline circulation and seasonal insolation. In contrast with previous proxy-based reconstructions our reanalysis results show that global mean temperatures warmed between the early and middle Holocene and were stable thereafter. When compared with recent temperature changes, our reanalysis indicates that both the rate and magnitude of modern observed warming are unprecedented relative to the changes of the last 24 kyr.