Energy Intensity

Like the IS92 scenarios before them, all of the SRES scenarios envision substantial improvements in technology. To illustrate the magnitude of the technological change assumed to occur over the course of the 21st century in the SRES scenarios, we compute the energy requirement for each scenario, given its population and gross world product, that would be associated with an energy intensity that remained unchanged from that of 1990 (see Figure 4.2).

World energy intensity is the ratio of energy to gross world product. Energy intensity improves in all SRES scenarios. That is, the amount of energy required to produce each dollar or yen or rupee of gross domestic product (GDP), after adjusting for inflation, is lower each decade than it was the decade before. Energy intensity declines as a result of many changes in the scenarios. These changes include improvements in the efficiency with which energy is used for a given process, shifts between processes, and the substitution of goods and materials with lower energy content for those with higher energy content.

Improvements in energy intensity are not new. They have been going on in some countries for a century. In the SRES scenarios, energy intensity improves at annual rates

Figure 4.3. Range of non-carbon-emitting energy supply (gray) in SRES illustrative scenarios. Also shown are the magnitudes of the 1990 global energy system (black) and the 1990 global oil and gas system (dotted).

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

Year

Figure 4.3. Range of non-carbon-emitting energy supply (gray) in SRES illustrative scenarios. Also shown are the magnitudes of the 1990 global energy system (black) and the 1990 global oil and gas system (dotted).

that range from less than 1 percent per year to more than 2 percent per year. By the year 2100 the cumulative effect is large. By the year 2100 primary energy demand in the SRES scenarios ranges from 55 percent to more than 90 percent lower than had no energy-intensity improvement occurred. Such is the effect of compounding.

Figure 4.2 shows the range of primary energy demands for the SRES illustrative scenarios and the corresponding range that would have been required assuming the same gross world product as in each of the SRES scenarios, but leaving energy intensity (energy per unit of gross world product) unchanged at 1990 levels. Without the improvements in energy intensity, it is hard to imagine how the global energy system could expand to produce the energy requirements of a constant-energy intensity-world. (This underscores the hypothetical nature of the constant-energy-intensity calculations and their purely illustrative character.)

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