Orbital and millennial-scale climate forcing of the Northern Hemisphere aridity and its influence on human evolution over the past 3.6 Myr

Arid regions in the Northern Hemisphere significantly influence global terrestrial biogeography, yet systematic research on their orbital-to-millennial-scale aridity dynamics remains limited. Here, we analyze orbital-to-millennial-scale climate fluctuations using dust flux records from two marine sediment cores reflecting the evolution of the Sahara-Arabian Desert and two terrestrial sediment cores recording hydroclimate changes in Central Asia. Our results reveal that the expansion of Northern Hemisphere ice sheets and shifts in glacial boundary conditions (i.e. marine ice-sheet expansion) drive orbital-scale aridification climate variability through atmospheric-ocean circulation. Millennial-scale climate fluctuations in these regions are persistently influenced by changes in obliquity and eccentricity-modulated precession amplitude, further highlighting the regulatory role of high-latitude ice sheets and sea ice on millennial climate variability. A re-examination of existing fossil records from East Africa demonstrates that periods of shifts in the dominant climate cyclicity and changes in obliquity sensitivity of marine dust fluxes coincide temporally with the major stages of hominin evolution. This suggests that periods of instability in Earth's climate system were a critical trigger for hominin evolution.