IPCC Special Report on Emissions Scenarios

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3.4.2. Energy Use and Emissions by Major Sectors

3.4.2.1. Overview

Sectoral energy use and GHG emissions changes are often discussed in terms of trends in the major end-use sectors (e.g., Sathaye et al., 1989; IEA, 1997c; Schipper et al., 1997a; Price et al., 1998). Trends reveal striking differences between sectors and regions of the world. The key sectors of the economy that use energy are industry (including agriculture), commercial, residential, and institutional buildings, and transportation. Key drivers of energy use and carbon emissions include activity drivers (total population growth, urbanization, building, and vehicle stock, commodity production), economic drivers (total GDP, income, and price elasticities), energy intensity trends (energy intensity of energy-using equipment, appliances, vehicles), and carbon intensity trends. These factors are in turn driven by changes in consumer preferences, energy and technology costs, settlement and infrastructure patterns, technical progress, and overall economic conditions.

Table 3-4 shows that global primary energy use grew from 191 EJ in 1971 to 307 EJ in 1990 at an average annual growth rate of 2.5% per year. This growth tapered off in all sectors after 1990, and total global primary energy increased to only 319 EJ by 1995, mainly because of the large declines experienced in the REF region (see Chapter 1 for definition of SRES world regions) as a result of the political and economic restructuring of the countries within it. Table 3-4 shows that the industrial sector clearly dominates total primary energy use, followed by the buildings sector (commercial, residential, and institutional buildings combined), transport sector, and agriculture sector.

Energy intensity is the amount of energy used to perform a particular service, such as to produce a ton of steel, power a refrigerator, or propel a vehicle. Technical progress generally leads to improved energy efficiency in technologies such as lights, vehicles, refrigerators, and manufacturing processes. Many studies show that considerable energy efficiency improvement can be realized (technically and economically) in the short term (10-15 years) with available technologies (Szargut and Morris, 1987; Ayres, 1989; Jochem, 1989; Lovins and Lovins, 1991; Nakicenovic et al., 1993; WEC, 1995b; Watson et al., 1996; Worrell et al., 1997).

In 1990, industry accounted for two-fifths of global primary energy use, residential and commercial buildings for a slightly smaller amount, and transportation for one-fifth of the total. These shares vary according to economic structures in each region (see below). Carbon emissions that result from energy use depend on the carbon intensity of the energy source. Changes in carbon intensity mainly result from fuel substitution, but can also arise from changes in technology or process. The largest shifts in carbon intensity over the long term are associated with changes in the energy sources used for power generation since 1850 (Nakicenovic and Gr�bler, 1996). Smaller but still significant shifts resulted from fuel switching in industrial, commercial, and residential energy consumption. The relationship between total sector energy use and economic drivers such as GDP per capita varies across countries depends upon the sector. In 1995, the relationship in the transport and buildings sectors was relatively strong and that in the industrial sector was moderate (Price et al., 1998). Income elasticities vary widely among the different types of energy services and the country or region under consideration. For example, the income elasticity of refrigerator ownership in most countries in the IND region (see Chapter 1 for definition of SRES world regions) is extremely low, as most households already own a refrigerator. The elasticity is much higher in medium-income countries in which refrigerator ownership is low. Other economic indicators, such as level of economic development in the industrial sector and personal consumption expenditures in residential buildings, are more closely correlated with energy use in these sectors.