Hotspots of Aerosol Pollution Identified in Satellite Climatologies of Clouds

Anthropogenic aerosols offset a poorly quantified fraction of greenhouse gas warming. Moreover, poorly understood aerosol impacts on clouds limit our ability to better constrain the sensitivity of Earth’s climate to anthropogenic radiative forcing. Recently, natural experiments have become a state-of-the-art approach for studying the causal impacts of aerosols on clouds. Here, we identify localised anomalies in cloud properties as recorded in long-term satellite climatologies from MODIS, AVHRR and SEVIRI satellite instruments. We identify aerosol-impacted cloud areas around megacities, near volcanoes and near shipping corridors as regions with reduced cloud droplet size in satellite climatologies of liquid-water clouds. The contrast in cloud properties between the polluted hot spot and the nearby unpolluted area depends on the horizontal resolution of a cloud climatology. Such resolution-dependence highlights the need to analyse localised cloud property anomalies in high-resolution climatologies of clouds. The natural experiments of aerosol impacts on clouds documented here can be used to better understand cloud responses to aerosols.