Overview of the Scenarios

The study's six scenarios are divided into three cases. The principal focus for all cases is on the period up to 2050, but results are also presented out to 2100. In brief, Case A presents a future of impressive technological improvements and consequent high economic growth. Case B describes a future with less ambitious, though perhaps more realistic, technological improvements, and consequently more intermediate economic growth. Case C presents an ecologically driven future. It includes both substantial technological progress and unprecedented international cooperation centered explicitly on environmental protection and international equity. Key characteristics of the three cases are given in Table 1.

Table 1: Summary of the three cases in 2050 and 2100 compared with 1990.

	A	B	C
	High growth	Middle course	Ecologically driven
Population, billion
1990	5.3	5.3	5.3
2050	10.1	10.1	10.1
2100	11.7	11.7	11.7
Global primary energy intensity improvement, percent per year
	Medium	Low	High
1990 to 2050	0.9	0.8	1.4
1990 to 2100	1.0	0.8	1.4
Primary energy demand, Gtoe
1990	9	9	9
2050	25	20	14
2100	45	35	21
Resource availability
Fossil	High	Medium	Low
Non-fossil	High	Medium	High
Technology costs
Fossil	Low	Medium	High
Non-fossil	Low	Medium	Low
Technology dynamics
Fossil	High	Medium	Medium
Non-fossil	High	Medium	High
Environmental taxes
	No	No	Yes
CO2 emission constraint
	No	No	Yes
Net carbon emissions, GtC
1990	6	6	6
2050	9-15	10	5
2100	6-20	11	2
Number of scenarios
	3	1	2

All three cases provide for substantial social and economic development, particularly in the developing world. They provide for improved energy efficiencies and environmental compatibility, and thus for associated growth in both the quantity and quality of energy services. Across all three cases, the structure of final energy develops in the same way and energy intensities improve steadily. To facilitate comparisons among the three cases, all share the same central demographic baseline assumption in which global population grows to 10 billion (10⁹) by 2050 and to nearly 12 billion by 2100. All have been checked for internal consistency with the aid of formal models and through a lengthy regional expert review process.

Case A includes three high-growth scenarios that address key developments in energy supply. They vary principally in the future they envision for coal, on one side, and nuclear and renewables, on the other. In Scenario A1, there is high future availability of oil and gas resources. Dominance of oil and gas is perpetuated to the end of the 21st century. At the other end of the spectrum, Scenario A2 assumes oil and gas resources to be scarce, i.e., limited to known reserves, resulting in a massive return to coal. Finally, in Scenario A3 rapid technological change in nuclear and renewable energy technologies results in a phaseout of fossil fuels for economic reasons rather than due to resource scarcity.

Case B has a single ``middle-course" scenario. It incorporates more modest estimates of economic growth and technological development, and the demise of trade barriers and expansion of new arrangements facilitating international exchange. Compared with the Case A scenarios (and the Case C scenarios), it is more ``pragmatic,'' which is its main appeal. Case B manages to fulfill the development aspirations of the South, but less uniformly and at a slower pace than in the other cases. For regions such as Africa, progress is painfully slow.

Case C is the most challenging. It is optimistic about technology and geopolitics, but unlike Case A, it assumes unprecedented progressive international cooperation focused explicitly on environmental protection and international equity. It includes substantial resource transfers from industrialized to developing countries, spurring growth in the South. These resource transfers, which recycle funds from the OECD to developing countries, reflect stringent international environmental taxes and incentives to reduce carbon emissions in 2100 to 2 gigatons of carbon (GtC) per year, one-third of today's level. In Case C, nuclear energy is at a crossroads. Two scenarios are included. In Scenario C1 nuclear power proves a transient technology that is eventually phased out entirely by the end of the 21st century. In Scenario C2 a new generation of nuclear reactors is developed that is inherently safe and small scale - 100 to 300 megawatts electric (MW $\!_{\rm e}$ ) installed capacity - and finds widespread social acceptability.

Across the three cases, the primary energy needs increase up to threefold by 2050 and up to fivefold by 2100. The six scenarios diverge in terms of the contributions of individual primary energy sources - what percentage of primary energy is supplied by coal, what percentage by oil, and so forth. That divergence is shown in Figure 2. Each corner of the triangle in the figure corresponds to a hypothetical situation in which all primary energy is supplied by a single source: oil and gas at the top, coal at the left, and non-fossil sources (renewables and nuclear) at the right. In 1990 their respective shares were 53% for oil and gas (measured against the grid lines with percentages shown on the right), 24% for coal (measured against the grid lines with percentages on the left), and 23% for non-fossil energy sources (measured against the grid lines with percentages at the bottom).

**Figure 2:** Evolution of primary energy structure, shares of oil and gas, coal, and non-fossil sources, in percent, historical development from 1850 to 1990 (triangles) and in scenarios to 2020 (open circles), 2050 (diamonds), and 2100 (closed circles). For an explanation of the figure see text.

Because of the long lifetimes of power plants, refineries, and other energy investments, there is not enough capital stock turnover in the scenarios prior to 2020 to allow them to diverge significantly. But the seeds of the post-2020 divergence in the structure of energy systems will have been widely sown by then based on RD&D efforts, early market deployment, intervening investments, and technology diffusion strategies. It is these decisions between now and 2020 that will determine which of the diverging post-2020 development paths will materialize.

After 2020 all scenarios move away from their current reliance on conventional oil and gas. This transition progresses relatively slowly in Scenario A1 where oil and gas are plentiful. In Scenario A3 and Case C, it progresses more rapidly due to faster technological progress (Scenario A3) or because of energy and environmental policies favoring non-fossil fuels (Case C). In Scenario A2 and Case B, the transition away from oil and gas includes an important contribution from coal, whose long-term market share after 2050 ranges between 20 and 40%. Nonetheless, little of this coal is used directly. It is instead converted to the high-quality energy carriers (electricity, liquids, and gases) demanded by the high-income consumers of the second half of the 21st century.

Despite the divergence in primary energy structures, the pattern of final energy use is remarkably consistent across scenarios, showing a continuing trend toward energy reaching the consumer in ever more flexible, more convenient, and cleaner forms. Figure 3 shows the small variation among Cases A, B, and C. Variations among the three Case A scenarios, and the two Case C scenarios, are even smaller.

As shown in the figure, all three cases reflect a continuing pervasive shift from energy used in its original form, such as traditional direct uses of coal and biomass, to elaborate systems of energy conversion and delivery. This shift continues in all cases, leading to ever more sophisticated energy systems and higher-quality energy carriers. A second profound transformation is the increasing degree to which energy is delivered by dedicated transport systems, such as pipelines and networks. This development enhances trade possibilities and promotes similar end-use patterns across regions with fundamentally different primary energy supply structures. Finally, changes in final energy patterns reflect the changes in economic structure presented in the scenarios. As incomes increase, the share of transport and residential and commercial applications also increases.