Polar dimming and mid-latitude brightening in a warming climate.

Downward surface solar radiation (DSSR) is the dominant energy source for the Earth's surface. It exhibits pronounced spatial heterogeneity and a strong seasonal cycle, yet how these features would evolve under global warming remains poorly understood. Here, we show a pronounced future meridional contrast in DSSR changes, with polar dimming and Northern Hemisphere (NH) mid-latitude brightening. This contrast peaks in local summer, weakening the seasonal cycle of DSSR at high latitudes with a multi-model mean of 14.6% (12.7%-17.6% for the interquartile range; same hereafter) in the Arctic, 7.0% (5.8%-8.1%) in the Antarctic, while slightly strengthening it over NH mid-latitudes by 2.1% (0.7%-3.1%) in the high-emission scenario SSP585. Under global warming, reduced clouds contribute to the mid-latitude brightening, whereas increased cloud liquid water contributes to polar dimming. Instead, increased water vapor under global warming drives the widespread clear-sky DSSR dimming. As a result, cloud-induced and clear-sky effects have comparable contributions to the polar dimming, while the cloud-induced brightening overwhelms the water-vapor-induced dimming in the NH mid-latitudes. The changes in the DSSR would alter the surface energy balance, which may exert significant influences on the polar amplification.