Plio–Pleistocene Paleoclimate Insights into Alpine Permafrost Stability and Ice-Age Megafaunal Dispersal in Asia

As the largest elevated plateau on Earth, the Tibetan Plateau has played a pivotal role in shaping both global and regional climate as well as mammalian dispersal. Yet how paleoclimate and biome shift in and around the Plateau responded to Plio–Pleistocene cooling, marked by a ~3–4 °C global temperature drop at ~2.7 million years ago (Ma) and the intensification of Northern Hemisphere glaciation, remains to be further investigated. Here we integrate novel climate and biome simulations with new carbonate stable and dual clumped isotope analyses to reconstruct past climate and ecosystems across the Tibetan Plateau and its surroundings. Our clumped-isotope temperatures indicate warmer mean annual air temperatures prior to 2.7 Ma, supporting a permafrost-free northern Plateau under climates warmer than today. Combined with climate modeling and global permafrost distribution, these results suggest that under conditions similar to the mid-Pliocene Warm Period (3.3–3.0 Ma), ~60% of alpine permafrost, containing ~85 petagrams of carbon—may have been vulnerable to thaw, compared to only ~20% of circumarctic permafrost. This implies that up to ~25% of global permafrost carbon, and associated permafrost–climate feedbacks, could originate in alpine regions. In addition, our results show the emergence of cold steppe–tundra habitats suitable for woolly rhinoceroses during Plio–Pleistocene cooling, forming plateau–circumarctic dispersal corridors. The ~3–4 °C cooling around 3.0–2.7 Ma along these corridors coincided with ~8 °C cooling on the Plateau. A >30% decline in plateau habitat suitability, alongside a ~23-fold corridor expansion, points to temperature decline as the primary driver of poleward megafaunal dispersal. Taken together, our findings highlight the amplified temperature sensitivity of high-elevation regions and underscore the central role of global temperature change in shaping the past, present, and future dynamics of cold-adapted mammals across the cryosphere.