Achievable Mitigation Levels

Figure 1.8 presents the recent IPCC [10] analysis relating projected warming from 1990 to 2100 to the following global impacts: fresh water availability, ecosystem damage, food supplies, seawater rise, extreme weather events, and human health impacts. The author has added projected warming ranges for a credible business-as-usual case and an aggressive global mitigation case. Note that for both ranges, it was projected that global annual emissions would grow at a 1.6% rate until 2030 or until mitigation starts, not the most recent (2000-2008) 3.25% growth rate. Figure 1.9 is a modified version of Fig. 1.8, and shows the potential impact of a 3% growth rate in emissions until mitigation. The mitigation option in this case also assumed 1% annual reductions that would start in 2025. Delayed mitigation amplifies the effect of the high growth rate, because it allows greater quantities of CO2 to be emitted before mitigation, over a longer time period.

For both base cases (Figs. 1.8 and 1.9) temperature increases in these range would result in potentially severe impacts, especially if the temperature increase is in the middle to upper end of the uncertainty range. Note that for the 3% growth case both the base and mitigation ranges are substantially greater with potentially more severe impacts. Also note, the upper end of the base case is off the IPCC chart, indicating the potential seriousness of impacts if warming is on the high end of the uncertainty range.

Using the MAGICC/SCENGEN model [9], Figs 1.10 and 1.11 projects 2100 warming for the 3% growth base and mitigation cases; and Figs. 1.12 and 1.13 project annual precipitation changes for the same two cases. The SCENGEN model generated these geographically explicit climate change projections using the MAGICC results, together with climate change information utilizing the four General Circulation Models listed on the figures. Projections are based on the default conditions inherent in the model.

As Figs. 1.10 and 1.11 indicate, warming is projected to be more severe over land and at highest and lowest latitudes. For example, Fairbanks, Alaska is projected to

2000 2050 2100

Fig. 1.7 Two global emission scenarios: original (green): IEA base case assumed 1.6% annual CO2 emission growth rate from 2000 to 2030; Revised (red): annual growth rate of 3.0% from

20020 to 2030

2000 2050 2100

Fig. 1.7 Two global emission scenarios: original (green): IEA base case assumed 1.6% annual CO2 emission growth rate from 2000 to 2030; Revised (red): annual growth rate of 3.0% from

20020 to 2030

see warming of 8.5°C for the base case and 5.1°C for the mitigation case. It is also apparent that despite mitigation, substantial warming is still projected. Figures 1.12 and 1.13 project major changes in precipitation patterns for base and mitigation cases. The models project that in, general, currently dry regions will get dryer, and


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Fig. 1.8 Projected impacts as a function of 2100 warming (0-5°C) from 1990; 1.6% early emission growth rate. Note: 1.6% growth rate to 2030. Entries are placed so the left hand side of text indicates approximate onset of impact, black lines link impacts, and dotted arrows indicate impacts increase with increasing warming relatively wet regions will see enhanced precipitation. For example, Los Angeles is projected to receive 48% less precipitation in 2100 for the base case, and 30% less for the mitigation case, whereas Chicago is projected to see substantial precipitation increases. Note that evaporation for all regions will increase due to warmer temperatures, exacerbating the potential for serious drought conditions for those areas with reduced precipitation.

Impacts associated with climate change [1] could include the following: water could become scarce for millions of people, wide-scale ecosystem extinctions, lower food production in many areas, loss of wetlands, infrastructure damage, storms and floods, and increased health impacts from infectious diseases. Although not included in Figs. 1.8 and 1.9, IPCC [1] also projects the potential for declining air quality in cities, due to warmer/more frequent hot days and nights over most land areas.

As noted, despite substantial CO2 emission mitigation, substantial warming is projected, especially if the high emission growth rate continues and serious mitigation is not initiated until 2025. Therefore, limiting warming to about 2.0°C (range of 1.3-2.7°C) from 1990 values is likely the best result achievable even with a major CO2 global mitigation program. Limiting warming to 2.5 ± 0.7°C is probably





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