Nakicenovich et al. (1998) discuss in great detail six scenarios ranging from a "high growth" case (A1) that is somewhat similar to the IPCC BAU scenario to cases C1 and C2, which the authors characterize as "ecologically driven". Case C incorporates a variety of different possible ways to reduce CO2 emissions to one third of current values by 2100. The difference between cases C1 and C2 involves the role of nuclear energy. In case C1 nuclear energy is phased out, while in case C2 a new generation of safe and acceptable nuclear energy is assumed to come on line.
Case B incorporates more modest estimates of economic growth and technological development, particularly in the developing countries. It contains features that are less attractive for developing coutries, though perhaps more realistic, than characteristics in the other cases.
Scenario A is devolved into three cases. Case A1 is a future dominated by natural gas and oil, while in A2 it is assumed that the greenhouse debate is resolved in favor of coal, which is assumed to be extensively used. In case A3 there is increasing reliance on both nuclear energy and renewables.
In all cases the population is assumed to reach 10.1 billions by 2050 and 11.7 billions by 2100. The primary energy intensity, defined as the primary energy needed to produce a unit of economic output, in watts per $US (1990), decreases by 0.8% per year (case B) to 1.4% per year (case C). Gross world product increases dramatically in all scenarios (but less so in C1 and C2), so that the globally averaged per capita income increases even in developing nations to somewhat near the value in developed countries today. However, there will still be quite large disparities between developed and developing countries. According to the IIASA scenarios the GDP per capita in North America will be $US 60000 or more by 2100, while in Latin America and the Caribbean it would be about $16 000 to $20 000 and in sub-Saharan Africa only $10000, even assuming stable governance, no major regional conflicts, and high social capital (education, the empowerment of women and other conditions conducive to reducing fertility). In centrally planned Asia in only the high growth scenario (scenario A) does the per capita income exceed the OECD 1990 income of $19000 by 2100.
Unlike in the WRE scenarios, all of the IIASA scenarios depart from current trajectories beginning in 1990. In cases A1 and A2, the CO2 loading of the atmosphere reaches 650 and 750 ppmv respectively and continues to increase thereafter. Even so, of the 33 TWt (terawatts thermal) of primary energy use in 2050, 11.3 TWt comes from nuclear and renewables in case A1 and 9 TWt comes from this combination in case A2. In case C2 world primary energy consumption in 2050 is 18.6 TWt, of which 9.1 TWt comes from nuclear and renewables. Other scenarios produce similar results. These are remarkable numbers, given that current world primary energy consumption stands at approximately 14 TWt . They are in substantial agreement with values that we have derived from a detailed analysis of the IPCC BAU scenario, which we discuss in some detail in the next section.
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