As cloud thickness increases, the fraction of incoming solar radiation reflected (cloud albedo) rises relatively quickly and approaches a saturation value at moderate thicknesses, because multiple scattering within the cloud efficiently redirects photons back upward before they can penetrate deeply; in contrast, the fraction absorbed within the cloud increases much more gradually with thickness, since absorption depends on photons traveling a sufficient path length within the cloud, and much of the incoming radiation is already reflected before reaching the deeper, more absorbing portions of a very thick cloud.