Global dimming is the hypothesised gradual reduction in the amount of sunlight reaching the Earth's surface measured since the 1950s, as first reported by Atsumu Ohmura in the 1980s.
A number of studies have estimated the rate of dimming at around 3% per decade, but it is difficult to make an exact measurement because of the slow rate of change and large timescale involved for comparisons.
The cause is not known, although it has been hypothesized that the effect may be due the increased presence of aerosols and other particulates in the atmosphere.
- Stanhill, G. & Cohen, S. 2001. Global Dimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences. Agricultural and Forest Meteorology 107, 255-278.