4.4.8.1. A1 Scenarios

The most significant change in the long-term primary energy mix in the A1B-AIM marker scenario is the fast market penetration of (new) renewable energy. Its share increases from a current 3% (excluding traditional non-commercial biomass use) to some 66% by 2100. Given the assumption of rapid technology progress, the costs of modern renewable energy technologies (solar, wind, commercial biomass, etc.) decline significantly in the long-term (see Section 4.4.7). Such low costs could make solar energy the largest primary energy source by 2100. Commercial, "high-tech" biomass also increases substantially, and contributes 18% of primary energy supply by 2100 globally. In the meantime, the shares of coal and oil decrease from 25% and 36% in 1990 to 12% and 15%, respectively, by 2050, and decline thereafter either because of depletion of conventional oil resources or because of fast market penetration of post-fossil technologies (in the case of coal). Gas increases its market share initially (from 20% in 1990 to 33% by 2050) and declines thereafter, but still maintains an important market share (24%) by the end of the 21st century. Nuclear is mainly a transient "backstop" technology - its share increases from 2% in 1990 to some 10% by 2050, and declines to 4% by 2100 because its economics increasingly fall behind those of new renewables. Overall, consistent with the high-income characteristics of the A1 scenario family, the share of traditional, non-commercial biomass use declines. By 2100 its use has virtually disappeared.

4.4.8.2. A1 Scenario Groups

Embedded in the overall storyline of the A1 scenario family are the possible widely ranging technological bifurcations, each of which spans a "corridor" of the future evolution of primary energy shares (see Figure 4-11). The A1C scenario group spans a range of structural change in future energy supply between the extremes of the A2 marker scenario and of the previous coal-intensive IS92 scenarios (IS92a,b,e,f). Conversely, the A1T scenario group spans a range of structural change in future energy systems delineated by the A1B and B1 marker scenarios, respectively. In all of these the global energy system completes a structural shift initiated with the onset of the Industrial Revolution. This could draw to a close more than 100 years from now, around 2100, with an energy system that predominantly relies on non-fossil energy sources, but evidently with a radically different technology portfolio of "high-tech" non-fossil energy compared to the "low-tech" non-fossil energy of 1800. The second major difference is that even with somewhat similar primary energy structures, absolute levels of demand would have increased by a factor 200 - 2000 EJ by 2100 in the A1T scenario, compared to a mere 10 EJ in 1800. Compared to all other scenarios, the A1G scenario group represents a distinct cluster in which the current dominance of oil and gas is perpetuated throughout much of the 21 st century. This scenario cluster is somewhat difficult to discern in Figure 4-11, because of the absence of structural change as a result of which the scenario cluster in terms of primary energy shares moves horizontally along the top part of the energy triangle. The only long-term fuel substitution that takes place is between coal and non-fossil alternatives.

4.4.8.3. A2 Scenarios

Major global trends in the A2 (ASF) marker scenario include an increase in the coal share (from 29% in 1990, through 30% by 2050, to 53% in 2100) and a reduction in the share of conventional oil (from 43% in 1990 to 23% by 2050, from where it declines asymptotically toward zero at the end of the 21st century). The progressive depletion of oil resources in the scenario reflects the prevailing view as to the finiteness of conventional oil resources³⁴, a picture also confirmed by other quantifications of the storyline (see discussion below). Nonetheless, the decline in oil market share should not be interpreted as a physical "running out," but rather as a gradual replacement process via price competition with synfuels and other alternatives as oil prices rise, along with the need to access ever more remote and expensive petroleum deposits. Once oil becomes increasingly expensive (starting from 2030) a substantial proportion of coal is converted into synthetic liquid fuels. Nuclear and renewable energy sources gradually increase in importance from 1990 to 2100, while the share of natural gas remains almost constant. Substantial changes in the primary energy mix also occur at the regional level. Coal shifts from a currently dominant primary energy source only in ASIA and becomes the most important fuel in all the SRES regions. Natural gas remains the second or the third major fuel. Nuclear energy becomes important in OECD90 and ASIA regions, and biomass and other renewables in the ALM region.

4.4.8.4. Harmonized and Other A2 Scenarios

The shares of different fuel types in all the A2 scenarios, except A2-IMAGE, are close to that of the marker scenario. As in the A2 marker, and with the exception of A2-IMAGE, coal becomes a major fuel by 2100 (45 to 50% of primary energy) in all the scenarios, followed by renewables (19 to 31%) and natural gas (9 to 18%). A higher share of renewables (biomass plus other) and a lower share of nuclear is the major difference between the scenarios (e.g., A2-MESSAGE shows the lowest nuclear share in primary energy of 7% in 2100). The A2G-IMAGE scenario has a quite different energy supply structure in which natural gas is the most important source, followed by renewables and coal, as it was designed to explore the implications of larger gas availability in an A2 world. Table 4-15 presents the primary energy structure of different A2 scenarios.

4.4.8.5. B1 Scenarios

The B1 marker scenario in the IMAGE model describes a structural transition in energy systems toward increasing shares of non-fossil energy. This long-term transition features an interim reliance on fossil fuels, in particular with natural gas as the preferred transitional fuel. Structural changes in energy supply are comparatively fast because of both the dynamic outlook on energy-efficiency improvements and structural change and the "dematerialization" of economic activities, characteristic of the B1 world. With lower energy demand than in the other scenarios, technological innovation and diffusion initially translate into slower rates of structural change in primary energy supply (lower demand growth leads to lower investment in capacity expansion and hence fewer opportunities for technological learning). However, once underway, structural change translates into radical systems restructuring in the long term (i.e. post-2050). A persistent long-term trend of B1 is also the continuously declining share of coal in the global primary energy mix, caused by local and regional environmental considerations (airborne emissions, social and environmental impacts from large-scale mining activities, etc.). Until 2050, the global energy system remains fossil-fuel dominated (with an important shift away from coal to gas use within fossil fuels). By 2020, fossils still account for some 79% of global primary energy (23% coal, and 56% oil and gas combined). By 2050, fossils account for 69% (20% coal and 49% oil and gas). By 2100, however, the transition away from fossil fuels is well underway; they only account for some 47% of primary energy use, mostly natural gas. The non-fossil share mirrors in its growth the declining trajectory of fossil fuels. Generally, even this scenario of significant structural change illustrates the long lead times needed for an "orderly" transition away from the current dominance of fossil fuels. Energy efficiency and "dematerialization" of the economy are integral parts of this transition in the B1 scenario.

A distinguishing feature of the IMAGE model used to develop the B1 marker scenario is the generic treatment of non-fossil fuel alternatives, which recognizes that the technology portfolio is particularly diverse and that numerous combinations are possible because of regional resource endowments, economics, technology policies, etc. A second important characteristic of the IMAGE modeling approach is the link between energy sector investments with future improvements in the form of a learning-curve approach. The model structure and methodology is described in more detail in Alcamo et al. (1998) and de Vries et al. (1994, 1999, 2000), (see also Appendix IV).

4.4.8.6. Harmonized and Other B1 Scenarios

Other models have (in most instances³⁵ with harmonized input assumptions) examined the uncertainties associated with the structural shift patterns described by the B1 scenario family. Whereas long-term trends all point in similar directions, considerable scenario variability remains, a function of differences in energy demand, resource availability, and technology assumptions (Table 4-16 and see Sections 4.4.6 and 4.4.7). Relatively robust patterns across all B1 scenarios include the continued importance of oil until about 2050 (15 to 28%) and a subsequent decline thereafter. Three scenarios (B1- ASF, B1-AIM, and B1-MESSAGE) indicate a more rapid decline to less than 10% market share by 2100, and three scenarios (the B1-IMAGE marker, B1-MARIA, and B1- MiniCAM) depict higher oil shares between 16% and 20% by 2100, largely as a function of higher oil resource availability assumptions (see Section 4.4.6). For gas, all scenarios suggest a relatively robust market share range of between 21% and 39% by 2050 and between 17% and 39% by 2100. Coal, biomass, and other non-fossil sources are largely substitutes for each other, depending on the specific cost assumptions used in the models. Whenever nuclear, renewable, and biomass costs are low, the share of coal declines (e.g., B1-AIM, B1-MARIA, B1-MESSAGE) and that of other sources increases, the degree of interfuel substitution being scenario (i.e. model) specific. Drastic shifts, however, are not anticipated before 2050. In most scenarios (except B1-MARIA and B1-MESSAGE) coal's share is around 20% by 2050, and declines to below 10% by 2100 as biomass and other non-fossil sources gain respective market shares. Their diffusion is described more conservatively in the B1-ASF scenario, in which coal maintains a market share of about 22% until 2100.

4.4.8.7. B2 Scenarios

The B2 (MESSAGE) marker scenario first follows a trend toward increasing shares of gas, followed by renewables, and finally - as oil and gas start to become scarce - increasingly returns to coal. By 2100, the B2 scenario ends up somewhere in the middle of the triangle in Figure 4-11 (i.e., it relies on a broad, diversified mixture of different primary energy sources). This global diversification results from heterogeneous trends at the regional level and is largely a function of the more modest assumptions concerning technology improvements and oil and gas resource availability (compared to other scenario families, in particular A1 and B1) that are characteristic of the B2 scenario family. By 2100, the main primary energy carriers are biomass (23%), coal (22%), oil and gas (29%), and other renewables and nuclear (26%). Countries with low income and high resource availability continue to rely on fossil fuels up to the end of the 21st century, such as China (mainly coal), Former Soviet Union (mainly gas), and Middle East (first oil and later gas). Regions with low resource availability, such as Africa and South America, rely on renewables and nuclear. The decreasing share of coal and oil in the primary energy structure of OECD countries is substituted by the growing share of renewables, gas, and nuclear. A major characteristic of the B2 scenario is the increasing importance of synthetic liquid fuels in the second half of the 21st century, because of a continuous phase out of conventional oil in all regions.

4.4.8.8. Harmonized and Other B2 Scenarios

Alternative B2 scenarios show a great diversity in changes in energy systems structures compared to the B2 marker. Common to all scenarios is their gradual transition away from conventional oil and gas, which are assumed to be comparatively scarce in the B2 scenario storyline. However alternative scenarios depict very different trends for this structural change, ranging from increased reliance on coal and coal-derived synfuels (B2-ASF, B2High-MiniCAM) to more biomass- and nuclear-intensive scenarios (B2-AIM, B2- MARIA, and B2-IMAGE). Generally, this reflects the considerable uncertainty as to direction and pace of technological change in the technologically more fragmented world described in the B2 scenario storyline. B2-MiniCAM anticipates a strong reliance on oil and natural gas as transitional fuels, with a share in primary energy of about 50% over the next 100 years to 2100 (i.e., gas shares in B2- MiniCAM are as high as in the A1G scenario group). In turn, B2-ASF suggests an increasing reliance on coal and coal-derived synfuels. A third group of scenarios tends to follow similar directions of structural change as those of the B2- marker - a gradual introduction of post-fossil alternatives (with different weights for nuclear and renewables as a function of technological progress), along with gas (or in some scenarios coal-derived synfuels) as transitional technology options. Structural changes in energy systems of the various B2 scenarios largely follow the main directions of the marker scenario developed with a particular model. That is, differences in alternative B2 scenarios appear to relate strongly to differences in model parametrizations derived from the respective marker scenario runs, most notably in the domains of resource availability and technology (see Sections 4.4.6 and 4.4.7). Thus, B2-ASF depicts structural changes in energy technologies and systems akin to the trends of the A2 marker scenario, whereas B2-AIM and B2-IMAGE largely follow the patterns of change of their marker scenarios (A1 and B1, respectively). Alternative patterns of change are illustrated by the B2-MiniCAM and B2-MARIA scenarios, which have also explored scenario sensitivities by developing alternative B2 scenario quantifications (B2C-MARIA, B2High-MiniCAM) that show a higher reliance on coal (and hence higher GHG emissions).

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