Emissions Scenarios - IPCC

Technical Summary 35
regrouped into tlieir respective scenario families and four Al
scenarios groups (three in the SPM) that explore different
technological developments in the energy systems. The SRES
scenarios cover a wider range of energy structures than the
previous IS92 scenario series, which reflects advances in
knowledge on the uncertainty ranges of future fossil resource
availability and technological change.
In a clockwise direction, AlB, AIT, and Bl scenario groups
map the structural transitions toward higher shares of nonfossil
energy in the future, which almost closes the historical
"loop" that started in 1850. The B2 scenarios indicate a more
"moderate" direction of change with about half of the energy
coming from non-fossil sources and the other half shared by
coal on one side and oil and gas on the other. Finally, the A2
scenario group marks a stark transition back to coal. Shares of
oil and gas decline while non-fossils increase moderately.
What is perhaps more significant than the diverging
developments in these three marker scenarios is that the whole
set of 40 scenarios covers virtually all possible directions of
change, from high shares of oil and gas to high shares of coal
and non-fossils. In particular, the Al scenario family covers
basically the same range of structural change as all the other
scenarios together. In contrast, the IS 92 scenarios cluster into
two groups, one of which contains IS92c and IS92d and the
other the four others. In all of these the share of oil and gas
declines, and the main structural change occurs between coal
on the one hand and non-fossils on the other. This divergent
nature in the structural change of the energy system and in the
underlying technological base of the SRES results in a wide
span of future GHG and sulfur emissions.
20% л 40%
Cropland + Energy Biomass
( \ 20%
Other (incl. grasslands)
Figure TS-5: Global land-use patterns, shares (%) of croplands and energy biomass, forests, and other categories including
grasslands - historical development from 1970 to 1990 (based on В1-IMAGE) and in SRES scenarios. As for the energy
triangle in Figure 6-3, each comer coiTcsponds to a hypothetical situation in which land use is dedicated to a much greater
extent than today to one category - 60% to cropland and energy biomass at the top, 80% to forests to the left, and 80% to
other categories (including grasslands) to the right. Constant shares in total land area of cropland and energy biomass, forests,
and other categories are denoted by their respective isoshare lines. For 1990 to 2100, alternative trajectories are shown for the
SRES scenarios. The three marker scenarios AlB, Bl, and B2 are shown as thick colored lines, and other SRES scenarios as
thin colored lines. The ASF model used to develop the A2 marker scenario projects only land-use change related GHG
emissions. Comparable data on land cover changes are therefore not available.The trajectories appear to be largely model
specific and illustrate the different views and interpretations of future land-use patterns across the scenarios (e.g. the scenario
trajectories on the right that illustrate larger increases in grasslands and decreases in cropland are MiniCAM results).