CO2 emissions from fossil
tion range in 2100 varies between 687 and 719ppmv, while the 2100 concentration is 717ppmv for the reference case (dark gray area in Figure 45.2(b)).
Further experiments consider the uncertainties in the CO2 emissions from land-use changes (land-use sources and carbon sink uncertainties) by setting its scaling factor at maximum and minimum values (emissions during the 1980s between 0.6-2.6GtC/yr) (Table 45.2). The extreme upper and lower CO2 concentration projections are now achieved (662 and 794 ppmv, respectively, by 2100), by balancing the past carbon budget with only the CO2 fertilization effect, while the oceanic parameters are kept constant (light gray area in Figure 45.2(b)). Summarized, these experiments show that various balanced past carbon budgets in the model lead to a range in the 2100 atmospheric CO2 concentration for the IMAGE Baseline-A scenario of about 10 per cent above and below the central projection of ~717ppmv.
Figure 45.2 shows the temperature increase for the Baseline-A scenario using the CO2 concentration pathway from the reference case according to the meta-IMAGE climate model (solid line). In Figure 45.2(a), uncertainty of carbon cycle modeling is illustrated, given by uncertainty in terrestrial and oceanic carbon sink fluxes (dark gray), and in the sink and land-use sources (light gray). Figure 45.2(b) illustrates uncertainty in the climate system response as estimated by using different IRFs of AOGCMs. Dark gray: range of outcomes for IPCC's 'best guess' climate sensitivity of 2.5°C combined with the IRF time scale parameters of the AOGCMs. Grey: IRF time scale parameters combined with their respective climate sensitivities. Light gray: IRF time scale parameters arbitrarily combined with climate sensitivities in the full IPCC range of 1.5-4.5°C. The two uncertainty ranges represent the uncertainties in the terrestrial and oceanic carbon sink fluxes (dark gray), and in the sink and land-use sources (light gray).
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