Axel Timmermann, Sun-Seon Lee, Jung-Eun Chu, Eui-Seok Chung, June-Yi Lee

The COVID-19 pandemic has led to massive disruptions of public life on a global scale. To halt the spread of the disease, China temporarily shut down parts of the manufacturing and transportation sectors. Associated anthropogenic aerosol emissions in February 2020 plunged to record lows, causing a temporary improvement of air quality with uncertain effects on cloud formation, atmospheric radiation and climate. To determine the regional and remote climatic impacts of a wide-spread reduction of anthropogenic aerosol emissions in China in early 2020, we conduct a series of sensitivity experiments with a state-of-the art Earth System Model. By reducing February anthropogenic aerosol emissions by 65%, we find evidence for a substantial increase in cloud droplet size and a corresponding enhancement of low cloud cover over Eastern China which intensifies longwave downwelling radiation at the surface but reduces incoming shortwave fluxes, in accordance with observational data. Remote climatic effects of the improvement in air quality can be further identified over the Korean Peninsula and southern Japan. Even though regional climatic responses were only short-lived, the COVID-19-related human interference with earth’s radiation balance may hold important clues on how the climate system will respond to the implementation of future long-term air-pollution mitigation strategies.