Clear Sky Visibility Has Decreased over Land Globally from 1973 to 2007
Kaicun Wang,1*
Robert E. Dickinson,2
Shunlin Liang1
Visibility in the clear sky is reduced by the presence of aerosols,
whose types and concentrations have a large impact on the amount
of solar radiation that reaches Earth's surface. Here we establish
a global climatology of inverse visibilities over land from
1973 to 2007 and interpret it in terms of changes in aerosol
optical depth and the consequent impacts on incident solar radiation.
The aerosol contribution to "global dimming," first reported
in terms of strong decreases in measured incident solar radiation
up to the mid-1980s, has monotonically increased over the period
analyzed. Since that time, visibility has increased over Europe,
consistent with reported European "brightening," but has decreased
substantially over south and east Asia, South America, Australia,
and Africa, resulting in net global dimming over land.
2 Department of Geological Sciences, University of Texas, Austin, TX 78712, USA.
* To whom correspondence should be addressed. E-mail: kcwang{at}umd.edu
