Historical and future vegetation changes in the degraded frozen soil and the entire Tibetan plateau and climate drivers

About 99% of the Tibetan Plateau (TP) is covered by frozen soils and degradation of frozen soils will certainly impact TP's ecosystems. Here, we investigate decadal changes of frozen soils and net primary productivity (NPP, representing vegetation) in the degraded frozen soil zones and the TP during 1982-2014 and 2015-2100 using a dynamic vegetation model, historical records and the latest CMIP6 projections, as well as observation-based soil temperature thresholds. In 1982-2014, degraded permafrost soil zones were in the range of 316,975-455,402 km(2), with mean annual NPP staying around 84.9 gCm(-2) and annual NPP showing a significant reduction at -1.71 gCm(-2)/year due primarily to warming air. Seasonally frozen soil also degraded by 15,636 km(2) in the southeast TP, with mean annual NPP staying around 620.0 gCm(-2) and annual NPP showing a significant increase at 11.00 gCm(-2)/year. In the future, frozen soil continues to degrade and the degradation accelerates toward the end of the century such that only 2.7% of permafrost soil in 2014 is left by 2080-2100 under the shared socioeconomic pathway SSP5-8.5. Mean annual NPP in the permafrost soil degraded zones in 2015-2100 is about half of that for 1982-2014, with spatially mixed decrease and increase trends in the near-, mid-, and long-term periods. Over the seasonally frozen soil degraded zones and the entire TP, more positive than negative annual NPP changes are seen in 2015-2100, especially in the southeast of the TP, due to improved growing conditions and the expansion of primarily subtropical and temperate scrubland.