Emissions Scenarios - IPCC

278 Emission Scénarios
subsequent decline in emissions is less pronounced. The
MiniCAM model has a higher level of controls, but also a
greater fossil fuel use, resulting in slightly higher SO,
emissions in 2100.
The AIT, AIG, and AlC scenario groups assume various roles
for the development of energy resources and technologies (the
coal-intensive AIC scenario group, the oil- and gas-intensive
AIG group, and the AIT scenaiio group with accelerated nonfossil
technology diffusion). Consequently, they span a very
wide range of future sulfur emissions, ranging from 20 MtS by
2100 in the AIT-MESSAGE scenario to 83 MtS in the AlC­
AIM scenario.
5.5.2.2. A2 Scenario Family
Sulfur emission trajectories in all the A2 family scenarios,
except A2-AI-MiniCAM with its much lower energy
consumption, have the same general convex shape (Figure 5-
13b). However, the rime when maximum emissions are
attained varies quite widely across the scenarios. Emissions
peak in the A2-ASF marker scenario in 2030, in A2-
MESSAGE in 2040, in A2G-IMAGE in 2050, in A2-
MiniCAM in 2060, and in A2-AIM not until 2070. These
differences are explained primarily by different assumptions
about the mechanisms of SOj reduction adopted in different
models. For example, the SOj reduction in A2-MESSAGE is
explained by fundamental structural changes in the electricity
generation technologies, while the A2-ASF scenario assumes a
rapid introduction of inexpensive end-of-the-pipe sulfur
scrubbers and shifts to low-sulfur fuel qualities.
The A2-A1-MiniCAM scenario yields a nearly flat sulfur
emission profile, explained by a relatively slow growth in
population and GDP in the first half of the 2P' century
(compared to other scenarios of the A2 family) and by
expedited technological progress in the second half
Numeric estimates of SOj emissions developed by different
models ушу substantially, especially in the middle of the
modeling period (Figure 5-13b). Emissions are largest in the
A2-AIM scenario, exceeding 160 MiS in 2070. From 2020 to
2060 the lowest emissions are produced by the A2-A1-
MiniCAM scenario, while after 2070 the lowest emissions are
achieved in the A2-ASF scenaiio.
5.5.2.3. ВI Scenario Family
Sulfur emissions in the ВI family scenarios fall within the
lower third of the full range of emissions from the SRES
scenarios (Figure 5-12). The BI-IMAGE trajectory is generally
posifioned in the middle of the Bl family range in the first
decades of the 2P' century, which corresponds to a 75%
reducüon of emissions in industrialized countries between
2000 and 2050. The near-term increase in emissions in Bl-
IMAGE occurs predominantly in developing countries and is
associated with increases in fossil fuel use in those regions,
combined with relafively low levels of emission controls. After
2040, increased emission controls and declines in fossil fuel
use result in decreasing SQ2 emissions.
Emissions in other В1 family scenarios decline even faster than
in Bl-IMAGE. In Bl-AIM, a decline in emissions is directiy
related to per capita incomes. As developing countries reach
levels of US$3500 per capita in 1990 dollars, they start to apply
more stringent SO, controls that lead to quickly dropping
emission levels (Figure 5-13c).
5.5.2.4. 82 Scenario Family
Emissions in the B2 family scenarios cover close to the full
range of SO2 emissions (Figure 5-12). The B2-MESSAGE
scenario yields steadily declining global emissions from 1990.
This overall trajectory includes a tripling of emissions from
non-energy sources by 2050, with subsequent stabilization and
eventual decline after that (Figure 5-13d). The increase in
emissions from non-energy sources is more than offset by very
rapid reductions in emissions from energy sources between
2015 and 2050. Developing countries have rising emissions
through to 2025, which stabilize by 2050, and decfine
thereafter. This increase in emissions in developing countries is
offset by reductions in developed countries. These results are
explained largely by regional measures and technological
changes to minimize critical loads of acidic deposition (see
Box 5-4). The B2-ASF scenario projects very rapid growth in
emissions from energy use through 2025, primarily from
increases in fossil fuel use in developing countries. After 2025,
the growth in fossil fuel declines and developing countries
become wealthier and are more aggressive on SOj emission
controls, which in the ASF model are directiy linked to
GDP/capita levels. Emissions from other industrial sources
increase steadily throughout the period as economic activity
increases.
5.5.2.5. Inter-Family Comparison
The relatively rapid desulfurization in the AlB-AIM marker
compared to the other SRES markers mainly results from high
capital turnover rates and, therefore, rapid diffusion of new and
clean technologies combined with high income levels in the
developing world by the middle of the 2P' century (Figure 5-
12). The structure and pattems of sulfur emissions for the two
illustrative scenarios in the two scenario groups AlFI and AIT
are similar to those of the AIB and Bl marker scenarios,
respectively, and are therefore not discussed separately here.
As technological progress and income growth are the slowest
in A2 among all the SRES scenario families, the primary
energy mix in the A2-ASF marker by 2100 is still dominated
by fossil fuels, with about 50% of the primary energy supplied
by coal. Although measures are adopted to limit local and
regional environmental damages, sulfur-mitigation measures in
the A2 world are less pronounced than in the other SRES
scenarios. Therefore, global sulfur emissions in the A2 marker
are highest as compared to the other markers (Figure 5-12).