Planetary albedo change exacerbates surface warming: a perspective from cloud-type changes

Abstract. Persistent global warming is modulated by cloud changes, yet the specific contributions and associated controlling factors remain inadequately quantified. Using CERES radiation data with a surface energy-balance framework, we quantify the contribution of cloud radiative changes to decadal surface temperature trends over 2002–2023. Cloud changes exert a weak net effect on global mean warming due to near-cancellation between shortwave warming and longwave cooling, but strongly modulate the meridional pattern of zonal-mean warming. Specifically, clouds enhance warming in low- and mid-latitudes while mitigating warming at high latitudes. This pattern is associated with a systematic redistribution of cloud occurrence from low-/mid-level cloud types to high-level optically thin clouds, which reduce planetary albedo and weaken cloud longwave emission. These changes exhibit hemispheric difference. In 30–60° N, the region contributing most to global warming, the decline in the cloud-reflected solar radiation is mainly driven by decreased cloud fraction, linked to elevated sea surface temperatures, aerosol reductions, and mid-tropospheric drying. In 30–60° S, reduced cloud reflectivity resulting from decreased cloud optical thickness and increased liquid droplet radius dominates. However, at high latitudes in both hemispheres, increased mid-/high-clouds and enhanced cloud reflectivity, driven by enhanced moisture, upper-tropospheric static stability and increased cloud optical thickness, lead to greater reflected solar radiation and reduced downwelling longwave radiation, thereby attenuating local warming. Our results establish a direct observational link between cloud-type changes, planetary albedo decline, and contrasting warming across latitude zones, characterizing the cloud-radiative changes in recent climate change.