Increased Freezing Temperature of Clouds Over China Due To Anthropogenic Pollution

The temperature for cloud glaciation importantly determines the initialization of precipitation and lifetime of clouds. The role of anthropogenic pollutants as ice nucleating particles (INPs) to determine the cloud glaciation remains uncertain. In this study, based on satellite radar and lidar observations, the clouds either in pure liquid or mixed‐phase with liquid top were statistically analyzed over China during 2006–2019, to obtain the transition freezing temperature (T*) of cloud top where mixed‐phase becomes more frequent than pure water, with further validation by the aircraft in situ measurements. Anthropogenic pollution was observed to raise T* up to −9°C, significantly increasing it by approximately 5°C per unit of aerosol optical depth. The results provide regional‐scale evidence that anthropogenic pollutants act as efficient INPs, increasing the freezing temperature of mixed‐phase clouds. Plain Language Summary Cloud phase transition (from liquid water to ice) is of great importance to Earth's energy and water cycle. Forming ice crystals in mixed‐phase clouds requires ice nucleating particles (INPs). However, whether the anthropogenic pollution can be efficient INPs remains unclear. In this study, based on satellite and aircraft observations in China, the temperature when clouds start to freeze is estimated by analyzing the frequency of liquid water and glaciated cloud tops, under which the occurrence of glaciated cloud tops started to overtake that of pure liquid water cloud tops. We found that the clouds over the anthropogenically polluted region over China presented higher freezing temperature than other cleaner regions. The results suggest anthropogenic pollution can efficiently control cloud glaciation in regional scale by serving as INPs. Key Points Transition freezing temperature is estimated by analyzing the frequency of mixed‐phase and liquid clouds over China using satellite data Anthropogenic pollution can cause freezing temperature of clouds up to −9°C Anthropogenic pollutants can be efficient ice nuclei and increase the freezing temperature of mixed‐phase clouds