Emissions Scenarios - IPCC

Emission Scenarios 279
Box 5-4: Future Sulfur Dioxide Emissions in tlie B2 Marker Scenario
Future global emissions of SOj are generally lower across the SRES emissions scenarios compared to most earlier projections,
because of three factors:
• Switch to cleaner fuels, such as natural gas and renewable sources.
• Transition to cleaner, more efficient coal technologies, such as IGCC generation and pressurized FBC.
• Utilization of direct emissions-reduction technologies, such as FGD.
The scope of reductions from fuel switching is illustrated by the following. At present, 60% of anthropogenic SO, emissions in
developing regions are from the direct use of fossil fuels in buildings and industry (Smith et al., 2000). Reductions in these
emissions will be realized by shifting from an energy stmcture that relies on the direct use of solid fuels to one that increasingly
relies on distributed energy grids (electricity, natural gas, etc.). This shift, and a resultant decrease in SO^ emissions, has already
occurred m Europe and North America. Further reductions are expected m the future as more efficient, and inherently low
emission, fossil fuel technologies (such as IGCC) become commercialized. Explicit policies for sulfur emissions reductions,
such as the use of FGD devices, will be needed to meet emissions targets in the near term, but are likely to be less necessary in
the longer term.
To illustrate these trends and the resultant decrease in SOj emissions over the 2P' century, emissions in the B2-MESSAGE
scenario (Riahi and Roehil, 2000) are analyzed. Global energy-related SO^ emissions m this B2 scenario decline from 59 MtS
in 1990 to about 12 MtS in 2100. The primaiy causes for this reduction are the transition to more advanced coal technologies
and desulfurization. Consistent with the characteristics of gradual change in the B2 storyline, the aggregated emissions
coefficient'^ for power production from coal declmes from about 5.3 kgS/MWh in 1990 to 0.04 kgS/MWh in the year 2100.
The latter emissions intensity is similar to that of the most advanced current technologies, for example, the Siemens IGCC98
power plant featuring 0.032 kgS/MWh (Baumann et al., 1998). In the second half of the 2P' century, desulfurization of the
energy system also takes place because of the production of methanol from coal. Sulfur removal is a process-inherent featare.
Methanol is mainly used in the transport sector as a substitute for оП products that become scarce after 2050.
The percentage reductions m energy-related SO2 emissions in the B2 scenaiio are shown in Table 5-12 as a function of time for
five technologies. These percentages were obtained by re-calculating the B2-MESSAGE emissions scenario with the energy
structure and emissions coefficients held constant in time at those of 1990. In this hypothetical case, SOj emissions in 2100
would be 227 MtS. Accordingly, energy-related SO^ emissions in 2100 are reduced by about 215 MtS in the B2 scenario, 68%
of which results from technological change and 32% from fuel switchmg. By the year 2100 the contribution to these emissions
reductions by flue-gas scrubbing (FGD) is negligible by the year 2100, because more-advanced coal technologies eliminate any
need for it. Furthermore, a shift m refining technology to lighter oil products, currently underway worldwide, contributes to a
reduction m SO, emissions, particularly in the early part of the 2P' century.
Table 5-12: Sources of energy-related SO2 emissions reductions in the B2 marker scenario.
Year Scrubbing IGCC Synfuel Light oil shift Fuel switching Total reduction
(%) (%) (%) (%) (%) (MtS)
1990 100 0 0 0 0 5.1
2020 26 16 0 24 33 58.6
2050 11 15 2 17 54 128.9
Following the Bl storyline, in the Bl-IMAGE marker the
emphasis is on global solutions to environmental sustainability
and improved welfare and development equity. High
technological development rates in the renewable energy sector
result in a continued structural shift away from fossil fuels.
All emissions coefficients were calculated with the MESSAGE
model.
Combined with dematerialization of the economy and with the
most pronounced sulfur mitigation measures assumed among the
SRES scenarios, this results in emissions that peak around 2020
and subsequentiy decline continuously to 2100 (Figure 5-12).
In the B2 scenario family, and thus in the B2-MESSAGE
marker, strong emphasis is placed on regional environmental
protection. Dynamics of technological change continue along
historical trends ("dynamics as usual"), which are slower than