Observations indicate that the amount of solar radiation reaching the surface of the Earth has varied significantly over decadal timescales during the past half century. A workshop of the Israel Science Foundation evaluated the observational evidence for global dimming and brightening (GDB), its possible causes, and its implications for the Earths climate, hydrology, agriculture, and land use. The workshop also identified gaps in our knowledge and made recommendations to fill these gaps.
Speakers at the workshop reviewed current understanding of GDB. Surface observations indicate that widespread global dimming (reduced solar radiation) at a rate of about 2–3 watts per square meter per decade occurred between the late 1950s and the late 1980s over midlatitude land surfaces of the Northern Hemisphere. These records also show a reversal of this trend over many land areas in the past two decades— brightening of the order of 2 watts per square meter per decade. Satellite estimates of solar radiation reaching the surface and aerosol trends, only available since the early 1980s, are generally consistent with these findings. Some analyses of the surface observations indicate that the rates of dimming and brightening are highest in major population centers and fall off significantly in areas with lower population densities.