Emissions Scenarios - IPCC

260 Emission Scénarios
significantly (Table 5-5). In the A2 (A2-ASF) and B2 (B2-
MESSAGE) markers, emissions increase throughout the whole
time horizon to the year 2100. This increase is most
pronounced in the A2 marker scenario, in which emissions
reach about 900 MtCH^ by 2100 (about a three-fold increase of
1990 levels). The emission level by 2100 for the B2 marker,
600 MtCH^, is about twice as high as in 1990.
fossil fuel production and agricultural animals (Table 5-5).
Agricultural animals are the major source of emissions in the
A2 marker, with fossil fuels being second, and landfills and
sewage third in importance. In the Bl marker, fossil fuels
produce the largest volumes of CH^, followed by agricultural
sources (Table 5-5). Finally, the B2 marker emissions originate
primarily from landfills and sewage, followed by fossil fuels
The four SRES marker scenarios illustrate a complexity of
relative impacts of technology, GDP, and population on CH^
emissions. In 2050 and 2100 the A2 and B2 markers have very
similar per capita emissions, which indicates a certain
similarity between the cumulative impact of economic,
technological, and structural changes on emissions in both of
these scenarios (in spite of significant differences in the global
average per capita incomes). Hence, differences in the absolute
emission levels in these scenarios can be explained primarily
by differences in population trajectories, with the A2
population in 2100 being 1.5 times larger than the B2
population. At the same time, differences in the absolute
emissions between the AlB and Bl markers cannot be
explained by population size (both markers have the same
population trajectory), but instead result from the greater
emphasis on "dematerialization" and "sustainability" in the В1
storyline. The two illustrative scenarios AlG-MiniCAM and
AIT-MESSAGE display similar pattems of methane emissions
as the A2 and Bl marker scenarios respectively and are
therefore not discussed separately here.
At the sectoral level, CH^ emissions in the AlB marker
originate primarily from landfills and sewage followed by
5.4.2. Nitrous Oxide
Uncertainties in the estimates of current N,0 emissions (Table
5-3) are also reflected in base-year 1990 differences, between
4.8 and 6.9 MtN across the six models used to develop the
SRES scenarios. The range across the four markers (Table 5-3)
is not as wide, between 6.0 and 6.9 MtN, and leans more toward
the higher end of the uncertainty range reported in Houghton et
al. (1995). After standardization, 1990 N^O emissions in the
SRES scenarios were set to 6.7 MtN, well within the IPCC
WGI SAR range (Table 5-3). Even more so than for CH^, food
supply is assumed to be a key determinant of future N2O
emissions. Size, age structure, and regional spread of the global
population are likely to affect future emission trajectories,
together with diets and rates of improvement in agricultural
productivity. The representation of how these driving forces
translate into NjO emissions varies across the models because
of differences in both sectoral coverage and emission factors.
As a result, differences in emission trajectories are not only
scenario dependent, but also model dependent, which illustrates
additional uncertainties in our understanding and representation
of driving forces and their influence on N2O emissions.
-ЛШ MAGE
— A В MESSAGE
-AlB MIMCAM
— A(G MESSAGE
\1V MIVICSM
Л2 » MimeAM
Ü
О B2 !4i,GF
аз мпяслм
о- - вгнюнMLNiCAM
2010 2030 2050 2070 2090
Figure 5-7: Standardized global NjO emissions for SRES scenarios, classified into four scenario families (each denoted by a
difterent color code - Al, red; A2, brown; Bl, green; B2, blue). Marker scenarios are shown with thick lines without ticks,
globally harmonized scenarios with thin lines, and non-harmonized scenarios with thin, dotted tines (see Table 4-3). Black lines
show percentiles, means, and medians for SRES scenarios. For numbers on the two additional illustrative scenarios AlFI and
AIT see Appendix VII.