Emissions Scenarios - IPCC

208 An Overview of Scenarios
new renewable sources of energy are dependent on ongoing
technological development and cost reductions.
The conventional oil industry is relatively mature and the
question is at what point in the 2P' century will the current
reserves start to run out. However, unconventional resources
are also available - shale oil, bitumen, and heavy oil. These are
starting to be exploited and they will extend current
conventional oil i-eserves. The gas industry is less mature and
much more remains to be discovered, particularly in areas that
do not currently have the infrastructure to utilize gas and
consequently exploration has been unattractive. Additionally,
large amounts of unconventional gas have been identified,
some of which are already in commercial production (e.g., in
the US). Also, huge quantities of natural gas are believed to
exist as methane hydrates on the ocean floor (see Chapter 3)
and it is possible that technology to exploit these will be
developed at some stage. For uranium and thorium, the
amount of exploration to date has been very limited, and hence
the possibilities of discovering new deposits are enormous. It
is likely that even a major expansion of the nuclear industry
will not be limited by the amount of available uranium or
thorium. With coal, the question is not one of discovery but
one of economics, accessibility, and environmental
acceptability.
To consider future resource availability as a dynamic process,
however, does not resolve the inherent uncertainties in terms of
future success rates of hydrocarbon exploration, technology
development for either non-conventional fossil resources or
non-fossil alternatives, or future energy prices. Therefore, these
uncertainties are explored by adopting different scenario
assumptions that range from low to (very) high resource
availability (see Table 4-4), consistent with the interpretation of
the various scenario storylines presented in Section 4.3. This
scenario approach is especially important given that
hydrocarbon occurrences are the largest storage of carbon.
IPCC WGII SAR (Watson et al., 1996) estimates the size of the
total carbon "pool" in the form of hydrocarbon occurrences to
be up to 25,000 GtC. How much of this eventually could
become atmospheric emissions is at present unknown, and
depends on the future evolution of technology, prices, and
other incentives for future hydrocarbon use and their
alternatives.
Given that long-term emission scenarios invariably rely on
quantification by formal models, an important distinction
needs to be made between assumptions concerning the ultimate
resource base and projected actual resource use. Typically,
assumptions on the ultimate resource base enter models as
exogenously specified constraints - cumulative future
production simply cannot exceed values specified as the
resource base. Actual resource use, or what is frequently
termed the "call on resources" conversely depends on
numerous other factors represented in models, such as:
• Future price levels (either assumed as exogenous inputs
or determined endogenously in the model).
• Assumptions on future technology improvements that
either enable unconventional hydrocarbons to be
"mined" economically or, conversely, that draw on nonfossil
alternatives and/or non-climate environmental
and social constraints (e.g., limits on particulates and
sulfur emissions or on land degradation and mining
accidents).
Their complex interplay results in scenarios of future
cumulative resource use being the most appropriate indicator,
as opposed to exogenously pre-specified resource-base
constraints, especially in view of the multi-model approach
adopted to develop the SRES scenarios. Table 4-10 and Figures
4-8 to 4-10 summarize the results for the four SRES marker
scenarios and of the ensemble of SRES scenarios for their
respective scenario families and scenario groups (in the case of
the Al scenario family). It is evident that, in the absence of
climate policies, none of the SRES scenarios depicts a
premature end to the fossil-fuel age. Invariably, cumulative
fossil-fuel use to 2050 (not to mention 2100) exceeds the
quantities of fossil fuels extiacted since the onset of the
Industrial Revolution, even though the "call on" fossil
resources differs significantiy across the four marker scenarios.
This increase is higher in the scenarios that explore a wider
domain of uncertainty on future fossil-resource availability.
For non-fossil resources, like uranium and renewable energies,
future resource potentials are primarily a function of the
assumed rates of technological change, energy prices, and
other factors such as safety and risk considerations for nuclear
power generation. Generally, absolute resource constraints do
not become binding in the marker scenarios or other scenarios.
The contribution of these resources is substantially below the
physical flows identified in Section 3.4, and therefore resuhs
mainly from scenario-specific assumptions concerning
technology availability, performance, and costs. These are
summarized in Section 4.4.7.
4.4.6.1. Al Scenarios
Energy resources are taken to be plentiful by assuming a large
future availability of coal, unconventional oil, and gas as well
as high levels of improvement in the efficiency of energy
exploitation technologies, energy conversion technologies, and
transport technologies. The grades of energy resources used in
the model differ on the basis of extraction costs. When
combined witl; the level of improvement in efficiency of
exploitation technology (expressed as the rate of improvement
in marginal production costs), the graded costs of energyresource
exploitation determine the energy production costs
(prices) and hence the ultimate resource extraction quantities.
For AI, large amounts of unconventional oil and natural gas
availability were assumed. Cumulative (1990 to 2100)
extraction of oil ranges between 15 and 30 ZJ in the Al
scenarios (AIB marker, 17 ZJ); for gas the range is between 23
and 48 ZJ (AIB marker, 36 ZJ) and for coal the range is
between 8 and 50 ZJ (AIB marker, 12 ZJ). Resource
availability and reliance uncertainties are also explored through