Regime shift to extensive valley glaciations over High Mountain Asia during the Early-Middle Pleistocene.

In contrast to the well-established onset of Northern Hemisphere high-latitude glaciation at 2.7 Ma, the timing and drivers of the intensified glaciation over High Mountain Asia (HMA) remain elusive, as glacial geologic evidence within this region is inherently fragmentary. Here, we offer a spatiotemporally complete view of glacier behavior over HMA spanning the last 3 Ma using transient climate-glaciation simulations to address this challenge. We illustrate that intensified glaciations with expanded ice caps and widespread valley glaciation began at ~0.9 Ma over the monsoonal-influenced southern HMA confirmed by the glacial sediments, whereas the intensification started earlier (1.5 Ma) over the westerly-influenced western HMA, with a further intensification at ~1.0-0.9 Ma, supported by paleoenvironmental proxies. The intensification of glaciation masks obvious shifts in the amplitude and pacing of glacier variability (e.g., the establishment of the 100-ka cycle) and induces larger environmental perturbations, which are in line with geologic evidence and largely linked with the long-term global cooling during the mid-Pleistocene transition.