Environmental predictors
Environmental predictors were generated using a paleoclimate emulator22. The method applies Gaussian process emulation of the singular value decomposition of ensembles of runs from the intermediate complexity atmosphere-ocean GCM PLASIM-GENIE with varied boundary-condition forcing (CO2, orbit and ice-volume). Spatial fields of i) minimum seasonal temperature (hereafter, “MinTemp”) , ii) maximum seasonal temperature (hereafter, “MaxTemp”), iii) minimum seasonal precipitation (hereafter, “MinPrec”), iv) maximum seasonal precipitation (hereafter, “MaxTemp”), and v) net primary productivity (hereafter, “NPP”) are then emulated at 1,000 year intervals, driven by time-series of scalar boundary-condition forcing, and assuming the climate is in quasi-equilibrium. The emulator uses CO2 from Antarctic ice cores for the last 800,000 years46. Prior to 800 ka, and for the entire sea-level record, it uses the CO2and sea-level reconstructions in ref. 47. Contemporary values of the four bioclimatic variables were derived from WorldClim25, while NPP observations were derived from MOD17A3H (MODIS; https://lpdaac.usgs.gov/products/mod17a3hv006/). Current bioclimatic variables and the NPP were interpolated onto the same 0.5° grid and combined with emulated anomalies. Temperature anomalies were additively combined with current temperatures, while precipitation and NPP anomalies were combined with current precipitations using a hybrid additive/multiplicative approach22.
The native-resolution (5°) emulations were extensively validated against model inter-comparisons of the mid-Holocene, the Last Glacial Maximum, the Last Interglacial and the mid-Pliocene warm period. Glacial-interglacial variability was validated against the observationally based global temperature reconstructions48. Paleoclimate anomalies at climate model resolution (5°) were downscaled onto the observed modern climatology at 0.5° spatial resolution using bilinear interpolation. We used the entire bioclimatic predictors in order to consider the last 5 million years of human evolution.