Emissions Scenarios - IPCC

308 Summary Discussions and Recommendations
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1990 2010 2030 2050 2070 2090
Figure 6-7: Global CO2 emissions (GtC, standardized) from all sources for the four scenario families from 1990 to 2100.
Scenarios are also presented for the four constituent groups of the Al family (high-coal AIC, high oil and gas AIG, high nonfossil
fuel AIT, and the balanced AIB) and for the other three families (A2, Bl, and B2), forming seven scenario groups
altogether. The emissions of AIC and AIG scenario groups are combined into AlFI (see footnote 2). Each colored emission
band shows the range of the harmonized scenarios within one group that share common global input assumptions for
population and GDP. The scenarios remaining outside the seven groups adopted altemative interpretations of the four scenario
storylines.
structure similar to the distribution of cumulative emissions
from the scenarios in the literature. The groups of SRES
scenarios span the whole range of cumulative emissions from
the scenarios in the literature. The range of the four markers is
from 1000 to 1900 GtC. In comparison, the IS92 cumulative
emissions range from 700 GtC for IS92c to 2140 GtC for
IS92e.
The SRES emissions scenarios encompass emissions of other
GHGs and chemically active species such as carbon
monoxide, nitrogen oxides, and non-methane volatile organic
compounds. The emissions of other gases follow dynamic
patterns much like those shown in Figures 6-5 and 6-6 for
CO2 emissions. Further details of GHG emissions are given in
Chapter 5.
6.3.2. Other Greenhouse Gases
Of the GHGs, CO2 is the main contributor to anthropogenic
radiative forcing because of changes in concentrations from
pre-industrial times. According to Houghton et al. (1996) wellmixed
GHGs (COj, CH4, NjO, and the halocarbons) induced
additional radiative forcing of around 2.5 W/m^ on a global and
annually averaged basis. COj accounted for 60% of the total,
which indicates that the other GHGs are significant as well.
Whereas COj emissions are by-and-large attributable to two
major sources, energy consumption and land-use change, other
emissions arise from many different sources and a large
number of sectors and applications (e.g. see Table 5-3 in
Chapter 5).
The SRES emissions scenarios also have different emissions
for other GHGs and chemically active species such as carbon
monoxide, nitrogen oxides, and non-methane volatile organic
compounds. The uncertainties that surround the emissions
sources of these gases, and the more complex set of driving
forces behind them aie considerable and unresolved. Hence,
model projections of these gases are particularly uncertain and
the scenarios presented here are no exception. Improved
inventories and studies linking driving forces to changing
emissions in order to improve the representation of these gases
in global and regional emission models remain an important
future research task. Therefore, the models and approaches