Paleolatitude bias in reconstructions of Cenozoic greenhouse climates

Cenozoic greenhouse climates offer important insights into Earth’s climate system and carbon cycle under elevated CO₂ conditions. A major challenge in simulating these warm intervals lies in the accurate reconstruction of the paleogeography, yet its impact on modeled climates and their agreement with proxy data remains poorly quantified. In this study, we systematically assess the sensitivity of fully coupled climate simulations to alternative paleogeographic reconstructions for the Paleocene, early Eocene, and middle-late Eocene. Using the IPSL-CM5A2 Earth System Model, we find that regional climates are particularly sensitive to the paleolatitudinal position of landmasses and ocean basins. Latitudinal shifts of more than 5°, arising from the choice of mantle versus paleomagnetic reference frame, significantly alter modeled regional temperature and precipitation patterns, as well as ocean circulation patterns. Moreover, we demonstrate that reconciling simulated climates with temperature proxy data depends strongly on the reconstructed paleolatitude of the proxy sites. In regions such as the southwest Pacific, correcting for paleolatitude bias induced by a mantle frame reduces model-data temperature misfits by up to 5°C. Our results further show that the regional climatic impact of paleogeography can equal or even exceed that of a doubling of atmospheric CO₂, particularly at mid-latitudes. These findings highlight the importance of using accurate paleogeographic reconstructions and an appropriate reference frame for improving paleoclimate simulations and their integration with proxy data.