Planetary Albedo Change Exacerbates Surface Warming: A Perspective From Cloud Transition

Abstract. Persistent global warming is modulated by cloud changes, yet the specific contributions and mechanisms 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 its spatial pattern. Specifically, clouds enhance warming in low- and mid-latitudes while mitigating warming at high latitudes. This pattern is driven by systematic transitions from low-/mid- 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, partly offset by shifts from cumulus to stratocumulus. 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 transitions, planetary albedo decline, and spatially heterogeneous warming, providing a constraint on cloud feedbacks in recent climate change.