Emissions Scenarios - IPCC

Emission Scénarios 261
The range of emissions across all 40 SRES scenarios increases
continuously over the 2P' century (Figure 5-7). By 2100, Щ0
emissions range between 5 and 20 MtN. Emission ranges also
tend to be comparable across the four scenario storylines, an
indication of the decisive impact of uncertainty in the modeling
(mentioned above). Future N2O emissions in the SRES
scenarios tend to cluster into two broad groups - those that
project relatively flat, even slightly declining, emissions and
those that indicate continuously rising trends toward high
emission levels. Some other scenarios (e.g. AlB-ASF, Bl-ASF,
and Bl-IMAGE) indicate the possibility of transitional
emission pattems in which N2O emissions peak around 2050
and decline thereafter, more or less in step with the population
size. As a result of differences in modeling approaches, no
individual scenario tracks the mean or median across all 40
scenarios of the SRES set.
5.4.2.1. Al Scenario Family
The Al family of scenarios covers close to the full range of
N,0 emissions from the SRES scenarios (Figure 5-7). The
AlG-MiniCAM scenario is at the high end of the Al range
(Figure 5-8a). Most of the emissions increase in this scenario
is associated with the agriculture sector, primarily with animal
manure management. Emissions are driven by a rapid increase
in income that induces steep increases in meat and dairy
consumption. The AlB-AIM marker scenario has emissions
near the low end of the range. This scenario assumes that
fertilizer use in developing countries is nearly saturated and
that increased productivity comes from better management. A
portion of nitrogen from fertitizers is also assumed to be stored
indefinitely in underground water. However, the emissions
from energy use in AlB-AIM increase until the third quarter of
the 2V century, and reach a level about three times the 1990
volume. In the middle of the Al family range lie emissions
from the AlB-ASF and AlB-IMAGE scenarios (Figure 5-8a).
In these scenarios, emissions growth to the 2050s is driven by
growth in the agricultural and transportation sectors.
Thereafter, emissions decline, primarily because of declining
population levels and increases in agricultural productivity
(lower production factor input per unit of output).
As suggested by Figure 5-8a, differences in the energy supply
system reflected by the four Al scenario groups (AIG, AlC,
AIT, and Al or "balance") are only partially translated into
differences in N^O emissions. For example, scenarios that rely
on coal as the primary energy source span the range from 6
MtN (AlC-MESSAGE) to 16 MtN (AlC-MiniCAM). At the
same time, trajectories of AIT "technology" scenarios are
located in the lower end of the emissions range.
5.4.2.2. A2 Scenario Family
N,0 emission trajectories of the A2 scenario family fall into
two major groups. The first group includes the A2-AIM and
A2-MESSAGE scenarios, and the rest of scenarios fomi the
second group. The A2-AIM NjO emissions increase at a
relatively low rate and do not exceed 10 MtN in 2100 (Figure
5-8b), because of a relatively slow increase in nitrogen
fertilizer input and omission of N,0 sources associated with
animal wastes. N2O emissions in the second group of scenarios
(which includes the family marker A2-ASF) grow steadily
throughout the 2U' century, driven by an increased demand for
food and associated increases in the animal waste and nitrogen
fertilizer use (Table 5-6). In 2100 the emissions from this group
of scenarios range from 15 to 20 MtN.
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Figure 5-8a: Standardized global emissions in the Al 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). In the SPM, AlC and AIG scenarios are merged into one fossil-intensive AlFI scenario group (see also footnote 2).