IPCC Special Report on Emissions Scenarios

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5.6. Regional Distribution and Gridding

Regional information on emissions serves at least two major purposes - to identify the contribution of world regions¹² to the global total and to track shifts in the relative weight of different regions. This information is especially relevant for the development of mitigation scenarios. For climate modeling, the regional distribution of emissions for well-mixed GHGs (CO₂, CH₄, N₂O, and halocarbons) may not be that important. However, short-lived gases such as SO₂ are radiatively important close to the point of origin only; their local and regional concentrations may significantly change the future climate outlook. The same is true for the group of ozone precursors (CO, NO_x , and NMVOCs). To be able to estimate tropospheric ozone concentration levels, regionalized information is indispensable.

The initial evaluation showed that the 40 SRES scenarios have a very substantial regional variability in emissions of all radiatively important substances. The detailed and rigorous analysis of this variability falls outside the scope of the current report. Therefore, this section merely illustrates possible regional patterns based on standardized regional emissions in the four SRES marker scenarios (see also Kram et al., 2000). Standardized regional outputs from the 40 SRES scenarios are provided in Appendix VII.

Subsection 5.6.1 describes emissions of GHGs and SO₂ in the four SRES macro-regions, followed by the description of "gridded" SO₂ emissions (distributed over a 1 � x1 � grid) in 5.6.2.

5.6.1. Regional Distribution

As Tables 5-13a to 5-13d clearly illustrate, the distribution of emissions over the four regions in the base year (1990) is very uneven. For example, while in industrialized regions (OECD90 and REF) fossil and industrial CO₂ emissions are dominant, in the developing regions (ASIA and ALM) the contribution of land-use emissions (deforestation) is also very important. In 1990, developing regions produced much lower volumes of CO₂ and high-GWP gases than the industrialized world, while their relative share of N₂O, CH₄ , and NO_x emissions was much more substantial (see Tables 5-13a to 5-13d).

5.6.1.1. Carbon Dioxide Emissions from Fossil Fuels and Industry

As suggested by Figure 5-14, in all the SRES scenario families the share of industrialized regions (OECD90 and REF) in global total becomes progressively smaller and by 2100 these regions emit from 23% to 32% of the total (Table 5-14, Figure 5-14).

In the OECD90 region, standardized fossil fuel and industrial CO₂ emissions in the A1B marker scenario (A1B-AIM) increase from 2.8 GtC in 1990 to 3.4 GtC in 2050, and subsequently decline to 2.2 GtC in 2100 (Figure 5-14). Compared to other scenarios, the growth in primary energy use in this region is relatively high, spurred by rapid economic development (see also Chapter 4). However, after 2050 the increases in the use of primary energy are accompanied by declining emissions through the combination of a lower use of fossil fuels and a switch from coal to gas. The share of non-fossil fuels in the OECD90 region of the A1B marker scenario also increases drastically. In 2100, the contribution of non-fossil energy amounts to 68% of the total primary energy use of the OECD90 countries, the largest non-fossil fuel share for this region of all the SRES marker scenarios.

The fossil fuel and industrial CO₂ emission trajectory of the REF region is even less linear than in the OECD90 region. Initially, emissions decline from the base year level of 1.3 GtC to 1.1 GtC in 2020 because of economic restructuring. After 2020, emissions increase, driven by an increased energy demand to support renewed economic growth (Figure 5-14). However, after 2050 emissions decline again primarily through a decrease in population and improved energy efficiency. By 2100, non-fossil fuels in REF contribute 58% of the total primary energy use and the share of natural gas reaches almost 40%.

The energy and industry CO₂ emission growth in the ASIA region of the A1B marker scenario is very high, reflecting rapid economic growth and high energy demand. By 2100 the total primary energy use in this region exceeds the 1990 level more than 10 fold. Standardized CO₂ emissions increase from 1.15 GtC in 1990 to 5.73 GtC in 2050 and then drop to 5.27 GtC in 2100 (Figure 5-14, Table 5-13c). By 2100 contributions from the two major energy sources, non-fossil fuels and natural gas, are 69% and 25%, respectively.

In the A1B marker scenario, the increase in energy demand in the ALM region is even higher than in the ASIA region. The primary energy use of 47 EJ in the base year increases to a level of 802 EJ in 2100, with 72% of energy from non-fossil sources. The emission path in this region is in line with trends observed in ASIA. Emissions grow from 0.72 GtC in 1990 to 5.72 GtC in 2050. After this peak they decline to 4.81 GtC in 2100 (Figure 5-14, Tables 5-13d).

In the A2 marker scenario (A2-ASF), technological development is relatively slow and fossil fuels maintain their dominant position to supply the rapidly expanding population. By 2100, the contributions of coal to the total primary energy mix in the OECD90, REF, ASIA, and ALM regions are 52%, 38%, 61%, and 48%, respectively, the largest shares across all the SRES marker scenarios. Relatively slow rates of technological improvements in the A2 scenario family result in the lowest contribution of non-fossil fuels compared to the other scenarios. In the A2 marker, CO₂ emissions grow continuously in all SRES regions (except REF from 1990 to 2020; Figure 5-14, Tables 5-13a-d). The fastest growth occurs in the ASIA and ALM regions as a result of the fast population growth in these regions. The contribution of CO₂ emissions by ASIA increases from 19% to 38% of the global total, and that by ALM from 12% to 31%.

The strong trend toward more ecologically compatible consumption and production in the B1 storyline is reflected by structural changes that lead to fewer energy- and material-intensive activities and result in a relatively limited growth of energy requirements in the B1 marker scenario (B1-IMAGE). In all the regions the shift is away from fossil fuels. In 2100, non-fossil sources supply more than 50% of the global energy requirements, with regional shares ranging from 41% (REF) to 64% (ASIA). Drastic changes in energy systems lead to an eventual decline in OECD90 emissions starting from 2020; this starts from 2050 in other regions (Figure 5-14, Tables 5-13a-d). By 2100 emissions in all regions but ALM are smaller than they were in 1990. A decline in emissions is less pronounced in the developing regions - ASIA and ALM combine to produce around 70% of CO₂ emissions by in 2100.

In the B2 world (illustrated by the B2-MESSAGE marker), the regions exploit comparative resource and technology advantages to structure their energy systems. Combined emissions in the OECD90 and REF regions remain more or less stable, changing from 4.1 GtC in 1990 to 4.3 GtC in 2100. The relative share of these two regions decreases from 69% in the base year to 31% in 2100 (Figure 5-14, Tables 5-13a-d). In the B2 marker scenario, fossil fuel and industrial CO₂ emissions in the OECD90 region increase to 3.71 GtC by 2020. Thereafter, emissions decline to 3.3 GtC in 2050 and to 3.1 GtC in 2100. This dynamic is caused by a decline in the use of fossil fuels and by the replacement of oil with natural gas, as pressure on the oil resource base increases considerably after 2050. In the REF region, standardized fossil CO₂ emissions decline to 0.8 GtC in 2020, after which they return to the 1990 level by 2100 (1.2 GtC). Toward the end of the 21st century, primary energy use in this region decreases while emissions increase because of a switch to coal (mainly to produce liquid substitutes for oil). In ASIA, both primary energy use and carbon emissions increase during the 21^st century. Although the use of non-fossil fuels becomes more important, the contribution of fossil fuels to emissions remains high. The use of coal, oil, and gas increases until 2050, after which the use of oil and gas decreases, while the use of coal grows rapidly. Population, energy use, and emissions in the ALM region constantly increase during the 21st century. Again, the fossil fuels retain a dominant role and supply 47% of the energy requirements in 2100. Gas use increases until 2100, while the use of coal is rather stable until 2050 and shows a rapid increase afterward. Oil use drops sharply after 2050 as resources become depleted.