Emissions Scenarios - IPCC

An Overview of Scenarios 211
availability might be much larger than assumed a decade ago.
This finding also reflects the results of IPCC WGII SAR
(Watson etal., 1996).
4.4.6.5. Bl Scenarios
Assumpfions on the fossil fuel resource-base used in the Bl
marker scenario quantification are based on the estimates of
ultimately recoverable conventional and unconventional fossil
resources described in Rogner (1997). The capital output ratio
of resource exploitation is assumed to rise with progressive
resource depletion, but this is counteracted by learning curve
effects in the marker scenario quantification provided by the
IMAGE model. Regional estimates of the exploitation costs of
conventional and unconventional resources of Rogner (1997)
were used to construct long-term supply cost curves as of 1971.
These values, rather than absolute upper bounds on resource
base availability, define future resource availability in the
IMAGE model. The supposed availability of huge nonconventional
occurrences of oil and natural gas, with a
geographic distribution markedly different from the distribution
of conventional oil and gas, has significant implications for fuel
supply and trade patterns in the long term. For coal resources,
Rogner's (1997) estimates were also adopted; of the total of 262
ZJ, 58 ZJ belong to the categories of proved recoverable,
additional recoverable, and additional identified coal resources.
The production costs of coal were assumed to rise with
increasing depth and rising labor wages, but these costs are
largely offset by mechanization (in underground mining) and
economies of scale (in surface mining).
4.4.6.6. Harmonized and Other Bl Scenarios
The call on oil resources in the scenarios that comprise the В1
scenario family ranges between 11 and 20 ZJ, with a median of
17 ZJ (Bl marker, 20 ZJ). For gas the range is 15 to 33 ZJ
(median, 20 ZJ; Bl marker, 15 ZJ), and for coal the
corresponding range is between 3 and 27 ZJ (median, 11 ZJ;
Bl marker, 13 ZJ). An overview is given in Figures 4-8 to 4-
10.
4.4.6.7. B2 Scenarios
The availability of fossil energy resources in the B2 marker
scenario is assumed to be conservative, in line with the gradual,
incremental change philosophy of the B2 scenario storyline.
Consequentiy, oil and gas availability expands only gradually
while coal continues to be abundant. Assumed oil and gas
resource availability does not extend much beyond current
conventional and unconventional reserves. Through gradual
improvements in technology, a larger share of unconventional
resei-ves and some additional resource categories are assumed
to become available at improved costs over the 21" century.
The availability of oil and gas, in particular, is Umited
compared to the estimated magnitude of global fossil resources
and occurrences (Watson et ai, 1996). This translates into
relatively limited energy options in general and extends also to
non-fossil energy options.
4.4.6.8. Harmonized and Other B2 Scenarios
Altemative B2 scenario implementations assumed similar order
of magnitudes of resource availability as the B2-marker scenario,
except for B2High-MiniCAM. The resultant cumulative resource
use (1990-2100) ranged between 9 and 23 ZJ (median, 17 ZJ; B2
marker, 19 ZJ) for oil, between 18 and 27 ZJ (median, 21 ZJ; B2
marker, 27 ZJ) for gas, and between 12 and 55 ZJ (median, 21
ZJ; B2 marker, 13 ZJ) for coal (see Figures 4-8 to 4-10). The
largest uncertainties relate to different inteipretations of the more
gradual changes under a "dynamics-as-usual" philosophy that
characterizes the B2 scenario storyline. One group of scenarios
(including the B2 marker) assumed a gradual expansion in the
availability of conventional and unconventional oil and gas,
whereas another group of scenarios adopted more conservative
assumptions (akin to the A2 and В1 scenario families).^'' All else
being equal, lower resource-availability assumptions for oil and
natural gas lead to a higher reliance on coal and non-fossil
altematives and explain, together with technology assumptions,
the differences in emissions between altemative В 2 scenario
quantifications discussed in Chapter 5.
4.4.7. Technological Change
Chapter 3 highlights the importance of technological change in
long-run productivity growth, but also for the historical
transformations of energy end-use and supply systems. The
importance of technological change in explaining wide-ranging
outcomes in future emissions has been highlighted by Alcamo
et al., (1995) and Grübler and Nakicenovic (1996), among
others. The latter reference also provides a critical assessment
of the previous IS92 scenario series and its comparison to the
literature. Prominent scenario studies of possible technological
change in future energy systems in the absence of climate
policies include Ausubel et al. (1988), Edmonds et al. (1994,
1996a), IIASA-WEC (1995), and Nakicenovic et al. (1998).
Future technology characteristics must therefore be treated as
dynamic, with future improvement rates subject to considerable
uncertainty. This is reflected in the SRES scenarios that adopt a
wide range of improvement rates for energy extraction,
conversion, and end-use technologies (Table 4-11). The actual
representation of technological change in the six SRES models
ranges from exogenously prescribed availability, through cost
and performance profiles (which in some cases also include
consumer or end-use costs for technology use), to stylized
representation of leaming processes.^' Yet, as summarized in
Chapter 3, model representations of technological change are
poorly developed, although evolving rapidly.
^" Resource availability assumptions also appear to be rather model
specific in this scenario family. For instance, in many scenarios
pattems of resource availability resemble the hypotheses retained by
a particular model used for quantification of a marker scenario in one
of the other three scenario families.
'^ Roehrl and Riahi (2000) provide a description of the methodology
of representing technological change in MESSAGE as used here in
the SRES scenarios.