Emissions Scenarios - IPCC

An Overview of the Scenario Literature 89
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Figure 2-le: Global energy-related and industrial COj emissions for 43 scenarios that could not be classified as intervention or
non-intervention scenarios from the SRES database. Historical development and future scenarios are shown as absolute values
in GtC. Median (50*), 5*, 25*, 75*, and 95* percentiles of the frequency distribution are shown. The statistics associated with
scenarios from the literature do not imply probability of occurrence. The emissions paths for the "non-classified" scenarios
indicate a wide range of future emissions. The actual coverage of CO2 emissions sources may vary across the 43 scenarios
from the database included in the figure. The scenario samples used vary across the time steps (for 1990 43 scenarios; for 2100
40 scenarios were analyzed). Data sources: Morita and Lee, 1998; Nakicenovic et a/.,1998a.
modeling groups in a number of scenario evaluation and
comparison activities. Figure 2-If shows the set of 35 IS92a-like
scenarios that could be classified from the set of non-intervention
scenarios. As these scenarios appeal" to emulate IS92a, they show
httle variation around the median of 20.3 GtC, which is about the
emission level in that scenario (20.4 GtC) in 2100.
The analyses in the following sections focus on the total set of
scenarios in the database only. The distinction between
intervention and non-intervention scenarios applies only to
analyses of COj emissions.
2.4.2. Carbon Dioxide Emissions Histograms
The first two histograms (Figures 2-2a and 2-2b) give the
global CO2 emissions ranges for 2050 and 2100.^ The total
range from the highest to the lowest scenario in 2100 is
between 59 and 2 GtC,^ from about seven times the current
Not all 256 scenarios that report global CO^ emissions cover the
whole period to the year 2100.
* Carbon sequestration exceeds carbon emissions in the negative
emission scenarios.
emissions to below zero. For about 10% of the scenarios,
emissions in the year 2100 are half the current emissions or
below this level. Presumably, some of the scenarios that have
low future emissions include some policy interventions to
reduce GHG emissions.
The distribution of emissions in 2050 is asymmetric; most of the
scenarios cluster in the range between 20 to 6 GtC. The thin tail
that extends above this emissions level includes only 46 of a total
of 211 scenarios. Altogether, the distribution implies a substantial
increase in global CO2 emissions during the next 50 years.
The distribution of emissions in 2100 is even more asymmetric
than that in 2050. The emissions portray a structure that
resembles a trimodal distribution: those that show emissions of
more than 30 GtC (20 scenarios), those with emissions
between 12 and 30 GtC (88 scenarios), and those that show
emissions of less than 12 GtC (82 scenarios). That this is quite
similar to the structure of primary energy consumption
distribution for 2100 is not by chance. The lowest cluster may
have been influenced by many analyses of stabilization of
atmospheric concentrations at levels of 450-550 parts per
million (10^) by volume (ppmv). The middle cluster appears to
echo the many analyses that took IS92a as a reference scenario;
it indicates the possible influence of IS92 scenarios on other
scenarios in the literature. It is very likely that the majority of