Negligible global but substantial regional effect of vegetation greening on the 21st century permafrost

Vegetation, as a key component of terrestrial ecosystems, influences surface energy, carbon and water balances, and indirectly affects permafrost dynamics. However, under the background of climate warming, the potential impact of future vegetation greening on permafrost remains unclear. This study employs a well-trained ensemble machine learning model to assess the effect of vegetation greening on permafrost ground temperature and extent throughout this century. The results show that, overall, vegetation greening in permafrost regions over the Northern Hemisphere will lead to a warming in mean annual ground temperature (MAGT) of permafrost by 0.01‒0.02 °C, and a reduction in the area of permafrost by 2.5 × 10 4 ‒6.7 × 10 4 km 2 by the end of the 21st century, compared to a scenario without increases in leaf area index (LAI) under four shared socioeconomic pathways. This finding indicates that the impact of vegetation greening on permafrost at global scale is negligible. However, the impact at regional or local scales is substantial and depends on both the magnitude of LAI change and vegetation type. Under both SSP1-2.6 and SSP5-8.5 scenarios, the heating effect is dominated in most shrub‒tundra areas averaging 0.2 ± 0.1 °C and potentially reaching up to 0.8 °C. In contrast, the effect in grassland tundra areas is predominantly cooling, with an average of 0.1 ± 0.05 °C (potentially reaching up to 0.6 °C), and only occurring under SSP5-8.5. The results provide a more comprehensive perspective on how future vegetation greening influences permafrost dynamics, highlighting its multi-scale effects and offering critical implications for understanding the permafrost response to climate change, the carbon cycle, and ecological-hydrological effects.