Nevertheless, substantial progress has been achieved in better
defining the direct effect of a wider set of different aerosols.
The SAR considered the direct effects of only three
anthropogenic aerosol species: sulphate aerosols, biomass-
burning aerosols, and fossil fuel black carbon (or soot).
Observations have now shown the importance of organic materials
in both fossil fuel carbon aerosols and biomass-burning carbon
aerosols. Since the SAR, the inclusion of estimates for the
abundance of fossil fuel organic carbon aerosols has led to an
increase in the predicted total optical depth (and consequent
negative forcing) associated with industrial aerosols. Advances
in observations and in aerosol and radiative models have allowed
quantitative estimates of these separate components, as well as
an estimate for the range of radiative forcing associated with
mineral dust, as shown in Figure 9. Direct radiative forcing is
estimated to be -0.4 Wm-2 for sulphate, -0.2 Wm-2 for biomass-
burning aerosols, -0.1 Wm-2 for fo