Martin Wild reviews the evidence for global dimming and brightening, which refers to decadal variations in surface solar radiation. Observational studies show a widespread decrease in solar radiation between the 1950s and 1980s ("global dimming"), followed by partial recovery ("brightening") in recent decades. These variations are supported by independent observations of sunshine duration, diurnal temperature range, and satellite data. Climate models generally do not simulate these decadal variations well. The causes are likely internal to the Earth's atmosphere, influenced by anthropogenic factors such as aerosol emissions. The relative importance of aerosols, clouds, and aerosol-cloud interactions varies by region and pollution level. Dimming and brightening have potential implications for climate change, including global warming, the hydrological cycle, the carbon cycle, and the cryosphere. Evidence for dimming includes studies showing a decline in solar radiation at various sites, while brightening is supported by recent data showing increases in solar radiation. Satellite-derived products also show a trend of brightening since the mid-1980s. Indirect evidence from sources like planetary albedo, sunshine duration, and diurnal temperature range supports the existence of large-scale decadal variations in solar radiation. The reliability of satellite-derived trends depends on the accuracy of input data and radiative transfer algorithms. Discrepancies between surface and satellite data may arise from differences in aerosol effects and other factors. Overall, the evidence suggests that global dimming and brightening are significant phenomena with potential impacts on climate systems.Martin Wild reviews the evidence for global dimming and brightening, which refers to decadal variations in surface solar radiation. Observational studies show a widespread decrease in solar radiation between the 1950s and 1980s ("global dimming"), followed by partial recovery ("brightening") in recent decades. These variations are supported by independent observations of sunshine duration, diurnal temperature range, and satellite data. Climate models generally do not simulate these decadal variations well. The causes are likely internal to the Earth's atmosphere, influenced by anthropogenic factors such as aerosol emissions. The relative importance of aerosols, clouds, and aerosol-cloud interactions varies by region and pollution level. Dimming and brightening have potential implications for climate change, including global warming, the hydrological cycle, the carbon cycle, and the cryosphere. Evidence for dimming includes studies showing a decline in solar radiation at various sites, while brightening is supported by recent data showing increases in solar radiation. Satellite-derived products also show a trend of brightening since the mid-1980s. Indirect evidence from sources like planetary albedo, sunshine duration, and diurnal temperature range supports the existence of large-scale decadal variations in solar radiation. The reliability of satellite-derived trends depends on the accuracy of input data and radiative transfer algorithms. Discrepancies between surface and satellite data may arise from differences in aerosol effects and other factors. Overall, the evidence suggests that global dimming and brightening are significant phenomena with potential impacts on climate systems.