Emissions Scenarios - IPCC

244 Emission Scenarios
О
о
•3
3000
2500
2000
1500
« 1000
-А1ВЛ1М
-AlBASF
- AJE [M tót
-AIB MESSAGE
-AlBMfî^lCAM
-AIB MARJA
-Aie AIM
-Л)С MESSAGE
AIC MINICAM
-AIGAIM
- MÛMES'ÎAGE
-AtGMINlC\M
AlVl \I[NICAA1
- A1V2M[NICAjvl
- ^ITAJM
- \1T MESSAGE
- AITMARJA
"A2ASF
MM
A:ÎO IMAGE
^2 MESSAGE
A2 MINICAM
A2-\I MINICAM
-Bl IM\GE
- Bl MM
-Bl \SF
-Bl MESSAGE
Bl MARIA
- Bl MIMIC AM
-BIT MESS \GE
-BIHIGH MESSAGE
BIHIGH MINICAM
- B2 MESSAGE
- B2 MM
- 02 \3F
- B2 IMAGE
-B2 MARIA
- B2 MINICAM
- B2HIGH MINICAM
-B2C MARIA
Figure 5-1: Global cumulative CO, emissions in the 40 SRES scenarios, classified into four scenario families (each denoted by
a different 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 lines. Black lines show
percentiles, means, and medians for the 40 SRES scenarios. For numbers on the two additional illustrative scenarios AlFI and
AIT see Appendix VII.
energy consumption is driven by population size, level of
affluence, technological development, environmental concerns,
and other factors. The composition of energy supply is
determined by estimated reserves of fossil fuel and the
availability, relative efficiency, and cost of supply technologies.
Emissions from gas flaring and industrial emissions are much
lower in comparison with energy-related emissions; for
simplification, in this discussion they are added to the latter In
1990, the global emissions from cement made up about 2.5%
of the total global COj emissions (Houghton et al., 1995).
Figure 5-2 shows standardized carbon emissions from fossil
energy and industry for the 40 SRES scenarios. Sample statistics
(in terms of percentiles, means, and medians) are indicated
against the background of 40 individual scenarios that make up
the SRES scenario set. The figure also presents emissions ranges
spanned by each of the four scenario famiUes in 2100.
SRES scenarios cover a wide range of annual emissions, and
the uncertainties in future emission levels increase with time.
Up to about the 2040s and the 2050s, emissions tend to rise in
all scenarios, albeit at different rates. Across scenarios this
reflects changes in the underlying driving forces, such as
population, economic output, energy demand, and the share of
fossil fuels in energy supply. By 2050, the emissions range
covered by the 40 SRES scenarios is from about 9 to 27 GtC,
with the mean and median values equal to about 15 GtC. The
range between the 25* and 75* percentiles of emissions (the
"central tendencies") extends from 12 to 18 GtC (i.e. from
twice to thrice that in 1990). Within this interval lie three of the
four marker scenarios. However, a fair number of scenarios
(eight out of 40) also indicate the possibility of much higher
emissions (in the 18 to 27 GtC range) that reflect an increase
by a factor of up to 4.5 over 60 years (1990 to 2050). Another
eight SRES scenarios have 2050 emissions below the 25*
percentile (Figure 5-2).
Beyond 2050, the uncertainties in energy and industrial COj
emissions continue to increase. By 2100, the range of
emissions across the 40 SRES scenarios is between 3 and 37
GtC, which reflects either a decrease to half the 1990 levels or
an increase by a factor of six. Emissions between the 25* and
75* percentiles range from 9 to 24 GtC, while the range of the
four marker scenarios is even wider, 5 to 29 GtC. The 2100
median and mean of all 40 scenarios are 15.5 and 17 GtC,
respectively.
As time passes in the scenarios, uncertainties not only increase
with respect to absolute levels of COj emissions, but also with