Global dimming was observed between about 1950 and the 1990s. It describes the decrease of the sun's intensity measured on the earths surface especially near highly populated areas. The main reason for global dimming is seen in aerosols -- particles hovering in the air and reflecting sunlight.
The rise of particle emission and carbon dioxide emissions might have cancelled each other. Global dimming was reduced since air pollution was diminished by law and technologies. During the same period a rising global mean temperature was observed.