Emissions Scenarios - IPCC

264 Emission Scenarios
о I . . , . , . . , .
1990 2010 2030 2050 2070 2090
Figure 5-8d: Standardized global emissions in the B2 family scenarios. The marker scenario is shown with a thick line
without ticks, the globally harmonized scenarios with thin lines, and the non-harmonized scenarios with thin, dotted lines (see
Table 4-3).
while it is useful to discuss emissions from the marker
scenarios individually, clearly differences in modeling
approaches and model assumptions have a particularly strong
effect on future emissions.
Agricultural emissions in the AlB-AIM marker scenario
decrease over the 21'^' century, with increased productivity
offsetting additional food demand. Agricultural emissions in
the A2-ASF marker scenario increase substantially because of
the food demands of a large population, coupled with less
technological change. Emissions in the Bl-IMAGE marker
scenario increase and subsequently fall. In the B2-MESSAGE
marker, agricultural emissions of N-,0 increase steadily
throughout most of the 2P' century, with a decrease between
2000 and 2010. These patterns differ because of the different
driving forces (population and demand), model assumptions,
and modehng approaches.
Emissions from the categories "Industry/Fossil Fuels" and
"Other" show a monotonie rise in the A2-ASF marker, while
emissions in the Bl-IMAGE marker rise and subsequently fall.
Industry and fossil fuel emissions fall and then increase
slightly in the B2-MESSAGE marker scenario, while "Other"
emissions, which largely arise from land-use changes, fall.
Industry and fossil fuel emissions in the AlB-AIM marker
scenario increase through the 21" century, but are countered by
a decrease in emissions from the "Other" category.
The combined dynamics of NjO emissions in the Al, В1, and
B2 markers leads to nearly stable or declining emissions
during most of the 2P' century (Figure 5-7). The B2 marker
shows the lowest emission level (from the year 2010 to 2080),
despite a larger population than in AI and Bl. One possible
reason is inter-model differences in treatment of land-use
changes. Unlike the other markers, the A2-ASF scenario
yields a continuous growth in emissions, which corresponds to
its assumptions of high population and slow technological
change.
5.4.3. Halocarbons and Other Halogenated Compounds
Emissions of halocarbons (CFCs, HCFCs, halons, PFCs, and
HFCs) and other halogenated compounds (SFg) on a substanceby-substance
basis are described in detail in Fenhann (2000). A
list of the substances covered, together with their GWPs and
lifetimes (as in IPCC SAR; Houghton, et al. 1996), is given in
Table 5-7.
Importantly, future emissions of halocarbons and other
halogenated compounds strongly depend on the technologies
involved in their production and use. New uses for these
substances may arise or new products or technologies may
replace current uses. It is assumed here that the current mix of
products continues to exist for the next 100 years to 2100, with
some generic technological improvements as described below.
This assumption, however, means that emissions projections
for industrial gases discussed in this section carry a substantial
uncertainty.
Halocarbons are carbon compounds that contain fluorine,
chlorine, bromine, and iodine. Halocarbons that contain
chlorine (CFCs and HCFCs) and bromine (halons) cause ozone
depletion, and their emissions are controlled under the
Montreal Protocol and its Adjustment and Amendments.
According to the 1987 Montreal Protocol and its subsequent