Amplified Cloud-Phase Responses Over Global Mountain Regions Under Climate Warming

Abstract

Changes in cloud phase can substantially affect cloud radiative feedbacks and precipitation processes, yet their responses to climate warming remain poorly understood, particularly over mountain regions. Using 20 years of satellite observations together with ERA5 reanalysis data, this study investigates changes in cloud fraction (CF), cloud top temperature, and cloud top height across major mountain regions worldwide and their adjacent lowlands. We find that cloud-phase responses to warming are generally amplified over mountains: ice and warm CF increase, while supercooled CF decreases, at rates exceeding those over global land and ocean. These changes are accompanied by ice cloud tops rising and cooling at rates two to four times faster than over lowlands. Over most mountain and lowland regions, supercooled cloud tops warm and descend, indicating suppressed vertical development. In contrast, the Tibetan Plateau and Andes exhibit pronounced cooling and ascent of supercooled cloud tops, suggesting active supercooled-to-ice phase transitions. Over the Tibetan Plateau, this behavior is associated with enhanced thermal destabilization linked to stronger low-level warming than warming aloft. Over the Andes, a moister mid-tropospheric background environment is consistent with colder and higher supercooled clouds. This stands in contrast to the broader tendency toward atmospheric stabilization under global warming, alongside generally limited changes in relative humidity. These findings highlight distinct and amplified cloud-phase and cloud top responses over high-elevation regions and suggest that mountain cloud changes may represent an important but still insufficiently explored pathway affecting regional radiative response.