Winter greening on the Tibetan Plateau induced by climate warming over 2000-2021

Climate warming is expected to increase growth and expansion of evergreen vegetation in many cold regions, with substantial influences on ecological and atmospheric processes. Nevertheless, the direction and magnitude of changes in productivity (greenness) of evergreen vegetation, as well as their potential drivers, remain unclear in many parts of the world. The woody evergreen vegetation on the Tibetan Plateau influences ecosystems and land surface processes, affecting regional and continental weather and climate through regulating land-air interactions. Here, we show that the remotely-sensed winter greenness of evergreen vegetation increased by 9.8% over 2000–2021 on the Tibetan Plateau, with significant (P < 0.05) greening across 55.8% of the areas with evergreen vegetation, which is more widespread than the increase of summer peak greenness, suggesting upslope shifts in treelines and shrublines and encroachment by evergreen woody plants. While our results show that warming was the principal climate driver of greening, the spatial pattern of greening was more related to the temperature sensitivity of greenness rather than temperature trends. Positive impacts of increasing precipitation on greenness were observed in a few areas classified as grasslands. Moreover, the magnitude of winter greening on the plateau was larger than that of the greening in the Arctic, where warming was faster, which indicates higher level of sensitivity of greenness to temperature of evergreen vegetation on the Tibetan Plateau. Our results highlight the high sensitivity of evergreen vegetation to climate warming and provide a new foundation for improving the understanding the responses and feedbacks of the Tibetan Plateau ecosystem to climate change.