Aerosol and Non-Aerosol Drivers of Regional Trends in Top-of-Atmosphere Albedo over 2002–2020 in Satellite Observations and Climate Models

Climate change responds to, and in turn modifies, trends in the Earth’s top-of-atmosphere albedo.

These trends are caused by anthropogenic aerosol–radiation and aerosol–cloud interactions, as well as by non-aerosol feedbacks involving cloudiness and surface albedo.

To separate those contributions, we identify periods of higher and lower albedo and aerosol optical depth in CERES and MODIS satellite retrievals from 2002–2020 over Europe, Eastern North America, Northeastern Asia, and India. Albedo and aerosol optical depth decrease over 2002--2020 in all regions except India, where both increase. We then apply a Gradient Boosting regression to retrieval differences between periods to decompose regional albedo trends into aerosol, aerosol–cloud, and non-aerosol contributions. According to this regression, these trends are explained by changes in cloud fraction (partially aerosol-related), cloud droplet number, aerosol optical depth, and surface albedo, and by climate feedbacks as well. We also calculate sensitivities of top-of-atmosphere albedo to aerosol optical depth, cloud fraction, liquid water path, droplet number, surface albedo, and surface temperature regionally and seasonally. These sensitivities are compared to those obtained from the same Gradient Boosting regression applied to CMIP6 simulations highlighting limitations in aerosol-cloud representation in some CMIP6 models