Emissions Scenarios - IPCC

312 Summary Discussions and Recommendations
1930 I960 1990 2020 2050 2080 2100
Figure 6-10: Global anthropogenic SOj emissions (MtS) - historical development from 1930 to 1990 and (standardized) in the
SRES scenarios. The dashed colored time-paths depict individual SRES scenarios, the solid colored lines the four marker
scenarios, the solid thin curves the six IS92 scenarios, the shaded areas the range of 81 scenarios from the literature, the gray
shaded area the sulfur-control and the blue shaded area the range of sulfui-non-control scenarios or "non-classified" scenarios
from the literature that exceeds the range of sulfur control scenarios. The colored veitical bars indicate the range of the SRES
scenario families in 2100. Database source: Grübler (1998).
SRES scenarios and the four markers against the emissions
range of the IS92 scenarios, more than 80 scenarios from the
literature, and the historical development.
A detailed review of long-term global and regional sulfur
emission scenarios is given in Grübler (1998) and summarized
in Chapter 3. The most important new finding from the
scenario literature is recognition of the significant adverse
impacts of sulfur emissions on human health, food production,
and ecosystems. As a result, scenarios published since 1995
generally assume various degrees of sulfur controls to be
implemented in the future, and thus have projections
substantially lower than previous ones, including the IS92
scenario series. Of these, only the two low-demand scenarios
IS92c and IS92d fall within the range of more recent longterm
sulfur emission scenarios. A related reason for lower
sulfur emission projections is the recent tightening of sulfurcontrol
policies in the Organization for Economic Cooperation
and Development (OECD) countries, such as the Amendments
of the Clean Air Act in the USA and the implementation of the
Second European Sulfur Protocol. Such legislative changes
were not reflected in previous long-term emission scenarios,
as noted in Alcamo et al. (1995) and Houghton et al. (1995).
Similar sulfur control initiatives due to local air quality
concems are beginning to impact sulfur emissions also in a
number of developing countries in Asia and Latin America
(see lEA, 1999; La Rovere and Americano, 1998; Streets and
Waldhoff, 2000; for a more detailed discussion see Chapter 3).
As a result, the median from recent sulfur scenarios (see
Chapter 3) is consequently significantly lower compared to
IS92, indicating a continual decline in global sulfur emissions
in the long-term. The median and mean of sulfur control
scenarios are almost identical. As mentioned above, even the
highest range of recent sulfur-control scenarios is significantly
below that of comparable, high-demand IS92 scenarios
(IS92a, IS92b, IS92e, and IS92f). The scenarios with the
lowest ranges project stringent sulfur-control levels that lead
to a substantial decline in long-term emissions and a retum to
emission levels that prevailed at the beginning of the 20*
century.
Reflecting recent developments and the literature (reviewed in
Chapter 3), it is assumed that sulfur emissions in the SRES
scenarios will also be controlled increasingly outside the
OECD. As a result, both long-term trends and regional patterns
of sulfur emissions evolve differently from carbon emissions m
the SRES scenarios. As a general pattern, global sulfur
emissions do not rise substantially, and eventually decline,
even in absolute terms, during the second half of the 21'
century (see also Chapters 2 and 3). The spatial distribution of
emissions changes markedly. Emissions in the OECD
countries continue their recent declining trend (reflecting the