Consistent Elevation-Dependent Permafrost Changes Despite Variable Elevation Dependence of Atmospheric Warming

The elevation dependence (ED) of atmospheric warming in mountain regions is debated, with studies showing varying trends due to data, spatial, and temporal differences. Permafrost, a critical component of alpine environment, also exhibits elevation dependent changes in response to climate change. This study investigated the ED of permafrost changes on the Qinghai-Tibet Plateau, the world’s largest alpine permafrost region, using multi-forcing ensemble simulations with a numerical model. We analyzed the ED of ground temperature (GT) at various depths and active layer thickness (ALT) changes over recent decades.

Three gridded meteorological datasets from reanalysis and remote sensing consistently show a negative ED of air warming (i.e., its trend decreases with increasing elevation) in permafrost regions (primarily above 3800m). Our ensemble simulations reveal that the ED of ALT and surface GT (GT0m) is consistently negative. However, interestingly, below 5000m elevation, the ED of GT at deeper depths (e.g., GT3m) becomes positive. This apparent discrepancy can be explained by the sensitivity of GT3m to air warming: in warmer permafrost (lower elevations), the increase in GT3m per unit of air warming is smaller compared to colder permafrost (higher elevations). This sensitivity is fundamentally linked to the soil freezing characteristic curve, which governs how heat is partitioned between temperature increases and ice melting. Similarly, the sensitivity of ALT to air warming is larger in warmer permafrost regions. Consequently, the consistently negative ED of ALT is a result of the combined influence of air warming ED and ALT sensitivity.

Under Coupled Model Intercomparison Project 6 (CMIP6) scenarios, we projected future permafrost changes by using the sensitivities of GT3m and ALT derived from historical simulations. Despite variations in air warming ED across scenarios and periods, the ED of GT3m and ALT changes remained consistent with historical period, demonstrating that air warming ED alone does not solely determine the ED of permafrost changes. Our findings were further corroborated by analysis of additional gridded dataset and in-situ observations. This study highlights the consistent ED of permafrost changes despite the variability in atmospheric warming trends across elevations, advancing our understanding of the diverse responses of ground temperature and ice to climate change in permafrost regions.