qThe major sources of anthropogenic
aerosols are fossil fuel and biomass burning. These sources are also linked to degradation of air quality and
acid deposition.
qIn
general, the direct radiative forcing of aerosols is negative (except
for black carbon fossil).
qThere
is much less confidence in the ability to quantify the total aerosol direct
effect, and its evolution over time.
qAerosols
also vary considerably by region and respond quickly to
changes in emissions.
qIn addition to their direct radiative
forcing, aerosols have an indirect radiative forcing through their effects on clouds.
qThere
is now more evidence for this indirect effect, which is negative,
although of very uncertain magnitude.