Emissions Scenarios

Other reports in this collection Land-Use Carbon Dioxide Emissions

Changes in land use are influenced primarily by the demand for cropland and grassland (to supply plant and animal food to the world population) and by the role of biomass energy. The uncertainty of emission estimates is reflected in the models used to quantify the SRES scenarios - in 1990 they range between 1.0 and 1.6 GtC and the spread at the regional level is even larger. In all the SRES marker scenarios, most emissions related to land use originate from the ASIA and ALM regions (Tables 5-13a-d). In the industrialized regions, the land-use change emissions in 2100 vary from -0.40 to +0.04 GtC. In the developing regions emissions from land-use change span a larger range (from -0.56 to +0.35 GtC).


Figure 5-16: Regional and global CO2 emissions in the four SRES markers scenarios A1B, A2, B1, and B2, shown as an index (1990 = 100). The numbers for the additional two illustrative scenarios for the A1FI and A1T scenario groups noted in the Summary for Policymakers can be found in Appendix VII. Total Carbon Dioxide Emissions

Figure 5-17: Anthropogenic CH4 emissions in the SRES
marker scenarios by region. The numbers for the additional
two illustrative scenarios for the A1FI and A1T scenario
groups noted in the Summary for Policymakers can be found
in Appendix VII.

Adding land-use CO2 emissions to the energy- and industry-related emissions does not make significant changes to the distribution of emissions across regions (Figures 5-14 and 5-15). Table 5-14 provides an overview of the relative shares of the industrialized and developing regions within global CO2 emissions. On average, the SRES marker scenarios project a shift in relative contribution in both energy- and industry-related and total CO2 emissions from the industrialized to developing regions. In general, the relative contribution of industrialized regions is the lowest in A1 and the highest in B2.

Shifts in the regional emission shares (Table 5-13a-d) result from different developments in regional emission trajectories. To illustrate this, the trajectories were normalized to the base year (1990 = 100 for each region) and are presented in Figure 5-16.

Figure 5-16 confirms that CO2 emissions in the ASIA and ALM regions in all the SRES markers grow much faster than in the industrialized regions. It also illustrates that the global pattern is strongly influenced by the developing region trajectories. Furthermore, reflecting different development perspectives in the four SRES families, CO2 emissions grow differently in ASIA and ALM. In the A1B marker, emission trajectories in ALM and ASIA are roughly parallel over the entire time horizon. In the B1 marker, this is only true in the earlier years. As the emission of ALM peaks and then declines later than that of ASIA, emission trajectories diverge strongly in the second half of the 21st century. In the A2 marker, emissions in ALM start to grow at a lower rate than in ASIA, but subsequently catch up and later the two are again fairly close. Finally, in the B2 marker, ALM emissions initially grow at a modest rate, close to those for the OECD90 region and the world average. In later years, the growth in ALM exceeds the global rate, but total carbon emissions remain far below those in the ASIA region (Figures 5-15, 5-16).

Figure 5-18: Anthropogenic N2O emissions in the SRES
marker scenarios by region. The numbers for the additional
two illustrative scenarios for the A1FI and A1T scenario
groups noted in the Summary for Policymakers can be
found in Appendix VII. Methane

The resultant CH4 emission trajectories in the four SRES markers are displayed in Figure 5-17. By 2020, regional differences between the four markers are minimal. In 2050, the largest difference is the relative share of the REF region in the A2 marker, attributable primarily to an increased coal and gas production in this region. By 2100, the A2 marker has the largest CH4 emissions in all the regions as compared to the other markers (Tables 5-13a-d, Figure 5-17). This arises from the "heterogeneous" nature of the A2 storyline, in which each region has to rely primarily on its own resources and progress in the renewable energy sector is quite limited. The second highest methane emissions are attained in the B2 marker, which also has a "regional" orientation, but with a more environmentally sustainable emphasis as compared to the A2 marker. Starting from 2100, both A1B and B1 markers have notably lower CH4 emissions in all the regions in comparison with the A2 and B2 markers (Figure 5-17). The regional emission allocation changes considerably from 1990 to 2100; all four markers project much greater percentages of emissions in the developing regions (ASIA and ALM). Nitrous Oxide

Figure 5-19: Halocarbons and other halogenated
compounds emissions in the SRES marker scenarios
by region. The numbers for the additional two illustrative
scenarios for the A1FI and A1T scenario groups noted
in the Summary for Policymakers can be found in
Appendix VII

The relative shares of the OECD90, REF, ASIA, and ALM regions in the base year N2O emissions are 39%, 9%, 34%, and 18%, respectively (Figure 5-18). The OECD90 emissions remain quite stable over the 21st century in all the markers, except A2 in which emissions increase from 2.6 MtN in 1990 to almost 4 MtN in 2100. Emissions in the ASIA and REF regions increase in the A2 marker, decline in the B1 marker (after an initial increase in ASIA), and do not change significantly in the A1 and B2 markers. Finally, the ALM N2O emissions grow quickly in the A2 marker and remain relatively flat in the other markers. The relatively small changes in the N2O emissions across regions and scenarios are explained, in part, by a limited capacity of the SRES models to capture drastic shifts in technologies and practices (e.g., new catalytic converters or new manure management systems) that directly impact emission levels. Halocarbons and Other Halogenated Compounds

In 1990, emissions of halocarbons and other halogenated compounds occurred almost exclusively in the OECD90 region, which contributed 95% to the world total (Figure 5-19). By 2020, OECD90 still remains a major emitter, but emissions in ASIA and ALM are increasing at much higher rates. The continued growth of the production and use of halocarbons and other halogenated compounds in the developing regions after 2020 makes them primary emitters of these substances in all the markers, except the B1 marker, in 2100 (Figure 5-19).

The A1B marker has the largest emissions in all the regions in 2050, while in 2100 the largest emissions across all the regions are produced in the A2 marker. Emissions in all the regions are smallest in the B1 marker, which reflects its sustainability features (e.g., increased recycling and "dematerialization").

Figure 5-20: Anthropogenic SO2 emissions in the SRES
marker scenarios by region. The numbers for the additional
two illustrative scenarios for the A1FI and A1T scenario
groups noted in the Summary for Policymakers can be found
in Appendix VII. Sulfur

As noted in Section, even with a comparatively good agreement on global sulfur emission levels, important uncertainties remain at the sectoral and regional levels. The base-year uncertainties are especially important because regional sulfur emissions trends have changed drastically during the past decade. While declining strongly in the industrialized regions as a result of sulfur control policies in Europe and North America, and because of economic reforms in Russia and Eastern Europe, emissions increase rapidly in Asia with an increase in the energy demand and coal use.

As a general rule, in the SRES scenarios an increasing affluence causes energy use per capita to rise and leads to the substitution of solid fuels, such as coal and fuelwood, with energy forms of higher quality. This relationship determines the sulfur emission dynamics across the SRES markers and regions (Figure 5-20).

In "high income regions" (OECD90, REF) sulfur emissions have already passed their peaks and are actually declining at present. This trend is expected to continue in all the markers, except A2 in which an increased use of coal "counters" a decline in specific emissions in OECD90 (Figure 5-20). Emissions in ASIA grow in all the markers by 2020, and then decline by 2050, and further decline by 2100. The most dramatic decline is registered in the A1B marker; this is related to its aggressive assumptions on the introduction of low-sulfur technologies and fuel switching in the ASIA region (see Box 5-3 for more details). Unlike ASIA, the ALM region sees increases in emissions in all four markers from 2020 to 2050, because of the somewhat "mixed" nature of this region, which combines countries with substantially different affluence levels and development trends. However, by 2100, when low-sulfur technology becomes widely available everywhere, emissions in the ALM decline in all markers (Figure 5-20).

Figure 5-21: Distribution of SO2 emissions in 1990 (top), 2020, 2050, 2080 and in 2100 (bottom) in the A1B marker scenario. Low emission levels are indicated by shades of (bright) green; higher levels are indicated by shades of red and pink.

Box 5-5: Gridding of Emission Data

The climate effects of SO2 are intrinsically regional and emissions on a latitude-longitude grid are required as input to climate models. Emissions of SO2 were first standardized for four world regions as described above. Then, emissions from the marker scenarios for six regions (OECD90, REF, Centrally Planned Asia, Rest of Asia, Latin America, and Africa/Middle East, scaled to match the standardized emissions) were used for gridding purposes. For the Annex II countries, a value of 23 MtS was taken for 1990 emissions, a figure derived from a compilation of country-level emissions inventories (Smith et al., 2000).

These emissions were mapped to a global 1 x 1 emissions grid. For each region, the pattern of total SO2 emissions from the EDGAR database (Olivier et al., 1996) was scaled by the total emissions for that region and a time period. Emissions for OECD90 countries were first scaled individually to their country-specific values. The value of 3 MtS was added to reflect international shipping, with the pattern and magnitude of these emissions held constant.

Emissions of other short-lived gases (CO, NOx , NMVOCs, and CH4) also needed to be mapped to a global grid for use in atmospheric chemistry models. The approach taken was essentially the same, with the EDGAR database used to establish the spatial pattern. Standardization and subsequent gridding were carried out at the level of the original four world regions, and no specific adjustments were made for international shipping.

5.6.2. Gridded Sulfur Emissions

As discussed above, global sulfur emissions eventually decline in all SRES scenario families and associated groups. In addition, the regional distribution of emissions changes drastically over time. While in previous decades major sulfur emitters were located primarily in industrialized regions of the world, presently emissions for these sources are declining because of the introduction of cleaner fuels and the conversion to low-sulfur technologies to comply with environmental regulations. In the majority of SRES scenarios, this trend is expected to continue. Meanwhile, less-developed regions are anticipated to experience strong economic growth associated with an increased demand for energy. Especially in the short term, fossil fuels are likely to satisfy the major share of this new demand, which may lead to a steep initial growth in sulfur emissions. As mentioned earlier (see Section 5.5.2), at some point in time sulfur emissions will be controlled in all the scenarios and, together with shifts to essentially sulfur-free energy resources, they will decrease in the developing regions as they are decreasing now in the industrialized world. As a consequence of these complex dynamics, different countries and regions are bound to experience very different levels of sulfur emissions over the 21st century. To illustrate this, Figure 5-21 shows gridded sulfur emissions in 1990 and 2050 in the A1B marker (see Box 5-5)

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