Global warming has led to permafrost degradation worldwide. The Qinghai-Tibet Plateau (QTP) hosts most of the world's alpine permafrost, yet its impending changes remain largely unclear, thereby affecting regional hydrological and ecological processes and the global carbon budget. By employing a land surface model adapted to simulate frozen ground, and using state-of-the-art multi-model and multi-scenario data from the Coupled Model Intercomparison Project Phase 6, changes in permafrost distribution and its thermal regimes on the QTP are systematically predicted under various shared socioeconomic pathways (SSPs). Projections for SSP2-4.5, SSP3-7.0, and SSP5-8.5 show that most of the continuous permafrost region of the QTP will persist through 2050. Much of the permafrost is likely to degrade in the late 21st century, with projected area losses of 44 +/- 4%, 59 +/- 5%, and 71 +/- 7%, respectively, by 2100. In particular, the Three Rivers Source region in the central eastern part of the QTP is a key area of permafrost degradation, where permafrost is most vulnerable and degradation occurs earliest. The mean annual ground temperature of QTP permafrost will increase by 0.8 +/- 0.2 degrees C, 2.0 +/- 0.3 degrees C, and 2.6 +/- 0.3 degrees C under SSP2-4.5, SSP3-7.0, and SSP5-8.5, respectively, and the active layer thickness will increase by 0.7 +/- 0.1 m, 1.5 +/- 0.3 m, and 3.0 +/- 1.0 m, respectively. The surviving permafrost under SSP3-7.0 and SSP5-8.5 will be thermally unstable, which is a clear warning sign of complete disappearance. The analysis of permafrost sensitivity to climate change signifies that alpine permafrost on the QTP has low resilience to climate change, in contrast to permafrost in pan-Artic high latitudes.

Frozen ground degradation plays an important role in vegetation growth and activity in high-altitude cold regions. This study estimated the spatiotemporal variations in the active layer thickness (ALT) of the permafrost region and the soil freeze depth (SFD) in the seasonally frozen ground region across the Three Rivers Source Region (TRSR) from 1980 to 2014 using the Stefan equation, and differentiated the effects of these variations on alpine vegetation in these two regions. The results showed that the average ALT from 1980 to 2014 increased by 23.01 cm/10a, while the average SFD decreased by 3.41 cm/10a, and both changed intensively in the transitional zone between the seasonally frozen ground and permafrost. From 1982-2014, the increase in the normalized difference vegetation index (NDVI) and the advancement of the start of the vegetation growing season (SOS) in the seasonally frozen ground region (0.0078/10a, 1.83d/10a) were greater than those in the permafrost region (0.0057/10a, 0.39d/10a). The results of the correlation analysis indicated that increases in the ALT and decreases in the SFD in the TRSR could lead to increases in the NDVI and advancement of the SOS. Surface soil moisture played a critical role in vegetation growth in association with the increasing ALT and decreasing SFD. The NDVI for all vegetation types in the TRSR except for alpine vegetation showed an increasing trend that was significantly related to the SFD and ALT. During the study period, the general frozen ground conditions were favorable to vegetation growth, while the average contributions of ALT and SFD to the interannual variation in the NDVI were greater than that of precipitation but less than that of temperature.