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.