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Fig. 5.15 Globally and annually averaged temporal evolution of the instantaneous all-sky RF
(a) and surface forcing (b) due to various agents, as simulated in the IROC+SPRINTARS model
(Watanabe et al. 2011; Takemura et al. 2005). This is an illustrative example of the forcings as
implemented and computed in one of the climate models participating in the AR4. Note that there
could be differences in the RFs among models. Most models simulate roughly similar evolution of
the LLGHGs
'
RF
estimates of future concentrations of LLGHGs and other radiatively active species
are clearly subject to signi
cant uncertainties. The evolution of these species is
governed by a variety of factors that are dif
cult to predict, including changes in
population, energy use, energy sources and emissions. For these reasons, a range of
projections of future climate change has been conducted using coupled AOGCMs.
The future concentrations of LLGHGs and the anthropogenic emissions of sulphur
dioxide (SO
2
), a chemical precursor of sulphate aerosol, are obtained from several
scenarios considered representative of low, medium and high emission trajectories.
These basic scenarios and other forcing agents incorporated in the AOGCM pro-
jections, including several types of natural and anthropogenic aerosols, are discussed
in IPCC (2007).
Crowley (2000) estimated the contribution of various factors to climate forma-
tion (SAT change) for the last 1,000 years using the energy-balance climate model.
According to the results obtained:
(1) Changes of global mean SAT during the last 1,000 years may be explained as
a result of the combined impact of the known RFs (in the pre-industrial epoch
41
64 % of SAT changes had taken place due to the extra-atmospheric
insolation and volcanic activity).
(2) Global warming observed in the 20th century was mainly of anthropogenic
(
-
) origin, substantially exceeding the internally caused variability
of the climate system.
“
greenhouse
”
Unfortunately, the argumentation contained in the study of Crowley (2000) is
unconvincing even from the viewpoint of explanation of the centennial change of
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