Emissions Scenarios - IPCC

Technical Summary 45
in tlie hiigiiest emission scenarios (tlie fossil fuel intensive
scenarios within the Al scenario family and the high
population, coal intensive A2 scenario family) do emissions
rise continuously throughout the 2P' century. In the AIB
("balanced") scenaiio group and in the B2 scenario family,
NOjj emission levels rise less. N0^^ emissions tend to increase
up to 2050 and stabilize thereafter, the result of a gradual
substitution of fossil fuels by alternatives as well as of the
increasing diffusion of N0,^ control technologies. Low
emission futures are described by various ВI family scenarios,
as well as in the AIT scenario group, that describe futures in
which NOj^ emissions are controlled because of either local air
quality concerns or rapid technological change away from
conventional fossil technologies. Overall, the SRES scenarios
describe a similar upper range of NO^^ emissions as the
previous IS92 scenarios (151 MtN versus 134 MtN,
respectively, by 2100), but extend the IS92 uncertainty range
toward lower emission levels (16 versus 54 MtN by 2100 in the
SRES and IS92 scenarios, respectively).
9.4.2. Volatile Organic Compounds, Excluding Methane
NMVOCs arise from fossil fuel combustion (as with NO^^,
wide ranges of emission factors are typical for internal
combustion engines), and also from industrial processes, fuel
storage (fugitive emissions), use of solvents (e.g., in paint and
cleaners), and a variety of other activities. In this report
NMVOCs are discussed as one group. As for N0^^ emissions,
not all models include the NMVOCs emissions category or all
of its sources.
A relatively robust trend across all 40 scenarios (see Chapter 5)
is a gradual increase in NMVOC emissions up to about 2050,
with a range between 190 and 260 Mt. Beyond 2050,
uncertainties increase with respect to both emission levels and
trends. By 2100, the range is between 58 and 552 Mt, which
extends the IS92 scenario range of 136 to 403 Mt by 2100
toward both higher and lower emissions (see Table TS-4). As
for N0^ emissions, the upper bounds of NMVOC emissions
are formed by the fossil fuel intensive scenarios within the Al
scenario family, and the lower bounds by the scenarios within
the Bl scenario family. Characteristic ranges are between 60
and 90 Mt NMVOC by 2100 in the low emissions cluster and
between 370 and 550 Mt NMVOC in the high emissions
cluster. All other scenario families and individual scenarios fall
between these two emissions clusters; the B2 marker scenario
(B2-MESSAGE) closely tracks the median of global NMVOC
emissions from all the SRES scenarios (see Chapter 5).
9.4.3. Carbon Monoxide Emissions
The same caveats as stated above for N0,^ and NMVOC
emissions also apply to CO emissions - the number of models
that represent all the emission source categories is limited and
modeling and data uncertainties, such as emission factors, are
considerable. As a result, CO emission estimates across
scenarios are highly model specific and future emission levels
overlap considerably between the four SRES scenario families
(see Table TS-4). Generally, emissions are highest in the high
growth fossil fuel intensive scenarios within the Al scenario
family. Lowest emission levels are generally associated with
the Bl and B2 scenario famiUes. By 2100, emissions range
between 363 and 3766 Mt CO, a considerably larger
uncertainty range, particularly toward higher emissions, than in
IS92, for which the 2100 emission range was between 450 and
929 Mt CO (see Table TS-4).
9.5. Emissions Overview
Table TS-4 (see later) summarizes the emissions of GHGs,
sulfur dioxide and other radiatively active species by 2100 for
the four markers and the ranges for other 36 scenarios.
Combined with Tables TS-2 and TS-3, the tables provide a
concise summary of the new SRES scenarios. Data are given
for both the harmonized and all scenarios.
10. Summary, Conclusions, and Recommendations
In summary, the SRES scenarios lead to the following findings:
• Alternative combinations of driving forces can lead to
similar levels and structure of energy and land-use
patterns, as illustrated by different scenarios and
groups. Hence, even for a given scenario outcome (e.g.,
in terms of GHG emissions) there are alternative
combinations of driving forces and pathways that could
lead to that outcome. For instance, significant global
changes could result from a scenario of high population
growth, even if per capita incomes rise only modestly,
as well as from a scenario in which a rapid
demographic transition (to low population levels)
coincides with high rates of income growth and
affluence.
• Important possibilities for further bifurcations in future
development trends exist within one scenario family,
even when particular values are adopted for the
important scenario driving force variables to illustrate a
particular development path. The technology scenario
groups in the Al family illustrate such alternative
development paths with similar quantifications of the
main driving forces.
• Emissions profiles are dynamic across the range of
SRES scenarios. They portray trend reversals and
indicate possible emissions crossover among different
scenarios. They do not represent mere extensions of
continuous increase of GHGs and SOj emissions into
the future. This more complex pattern of future
emissions across the range of SRES scenarios, time
periods, world regions, and sectors reflects recent
scenario literature.
• Describing potential future developments involves
inherent ambiguities and uncertainties. One and only one
possible development path (as alluded to, for instance, in
concepts such as "business-as-usual scenario") simply