Persistent warming of the ground on the Earth’s Third Pole

Abstract. A continuously increasing ground temperature in the Tibetan Plateau (TP) can result in permafrost degradation and impact regional climate through land-atmosphere interactions. However, systematic knowledge of spatiotemporal dynamics and regulatory mechanisms of ground temperature changes in the region is limited. Here, we quantify the thermal status and trends of both soil temperatures measured at depth and typical permafrost profile temperatures. We show that, shallow soil layers (0–40 cm) in most TP regions experienced significant warming from 1981 to 2021, with lower rates at greater depths. Ground surface warming trends aligned with air temperature, but the timing of the maximum warming trend was progressively delayed with depth. Cold seasons exhibited the largest warming trends for air and ground surface, while warm seasons saw greater warming trends at 5–40 cm soil depths. Regionally, warming trends were larger at sites with lower mean annual temperature and higher elevation. Out of the factors tested in addition to air temperature, only snow-cover days and downward longwave radiation were significantly related to the soil warming rate trends. Further analysis reveals that the persistent shallow ground temperature increase over decades is linked to the Atlantic Multidecadal Oscillation's warm phase, impacting near-surface air temperature through teleconnections. Additionally, we present spatially heterogeneous observations of continuous warming in permafrost profiles, which show intense warming in the surface layers, and minimal warming at 40 m depth. Permafrost profile warming magnitude and depth-dependent variation are influenced by local climate and elevation. This study provides a comprehensive view of persistent warming in the Tibetan Plateau across surface and deep layers.