Tight Regulation of Phanerozoic Temperatures Revealed by Weathering Proxies and Climate Model Assimilation

Understanding Earth’s long-term temperature evolution is fundamental to constraining the mechanisms that regulate climate and biosphere development. However, the magnitude of Phanerozoic temperature variations remains highly debated, with previous reconstructions—primarily based on oxygen isotope records—suggesting a long-term cooling trend but with substantial uncertainties. Here, we present a new independent reconstruction of Phanerozoic global temperatures based on a large compilation of chemical weathering indices from siliciclastic sedimentary rocks, integrated with simulations from a state-of-the-art general circulation paleoclimate model. By assimilating proxy-derived local temperatures into model simulations, we derive a robust estimate of global mean surface temperature through time. Our results indicate that Phanerozoic temperatures were constrained within a relatively narrow range of ~10–30 °C, and that Paleozoic oceans were not significantly warmer than those of the Mesozoic and Cenozoic. These findings challenge previous interpretations of extreme early Paleozoic warmth and support the operation of long-term stabilizing feedbacks, particularly silicate weathering, in regulating Earth’s climate. This tight thermal regulation may have played a key role in sustaining habitable conditions and facilitating the long-term evolution of the biosphere.