Changing Regional Land Surface Albedos Alter the Planetary Albedo During the Twenty-First Century

The top-of-atmosphere (TOA) albedo controls the amount of solar energy absorbed by Earth and is influenced by the reflectivity of both the atmosphere and surface. With considerable changes in land use over the past few decades it is reasonable to question whether a perturbed surface albedo has influenced TOA albedo over the corresponding period. Here, we identify regions for which surface albedo changes have been the dominant driver of TOA albedo trends from 2001 to 2020 and examine the degree to which this relates to changes in snow cover, surface soil moisture, and vegetation density and greenness. We show that land surface albedo changes have been the dominant driver of TOA albedo trends in 10.0% of the global land area, within which surface albedo decreases have led to increases in absorbed solar radiation of 0.737 ± 4.984 Wm⁻² from 2001 to 2020. This corresponds to global change in absorbed solar radiation of 0.019 ± 0.812 Wm⁻², which is equivalent to approximately 7.0% of the radiative forcing from anthropogenic CO₂ emissions from 2011 to 2019 (IPCC, 2021, https://doi.org/10.1017/9781009157896.009). Net TOA darkening above tundra and deserts constitutes 38.6% and 21.4%, respectively, to the radiative feedback identified, whereas temperate biomes induced net TOA brightening, corresponding to 22.3%. Collectively, changes in snow cover, vegetation density and greenness, and surface soil moisture drive 68.5% of the surface albedo changes. The importance of surface albedo in explaining TOA albedo trends for parts of the globe highlights the relevance of land surface changes in understanding Earth's energy imbalance.