Susanne Bauer

Separating direct, indirect, semi-direct and surface albedo effects
from sector contributions of the CMIP 5 emission inventory

The anthropogenic increase in aerosol concentrations since
preindustrial times and its net cooling effect on the atmosphere is
responsible for masking some of the greenhouse gas induced warming of
the Earth. Although the overall effect of aerosols on solar radiation
and clouds is most certainly negative, some individual forcing agents
and feedbacks have positive forcing effects. Recent studies have tried
to identify some of those positive forcing agents and their individual
emission sectors, with the hope that mitigation policies could be
developed to target those emitters. Understanding the net effect of
multi source emitting sectors and the involved cloud feedbacks is very
challenging and this paper will clarify forcing and feedback effects
by separating direct, indirect, semi-direct and surface albedo
effects. For this purpose we apply the GISS climate model including
detailed aerosol microphysics to examine aerosol impacts on climate by
isolating single emission sector contributions as given by the CMIP5
emission datasets.  

Our results point out that each emission sector has varying impacts by
geographical region. For example the single sector most responsible
for a net positive radiative forcing is the transportation sector in
the United States, agricultural burning and transportation in Europe,
and the domestic emission sector in Asia. Aerosol induced changes on
cloud cover often depends on cloud type and geographical
region. Indirect and semi-direct effects can be isolated on the
regional scale, and often have opposing forcing effects, leading to
overall small forcing effects on the global scale of aerosol-cloud
interaction induced climate impacts.