40 Stabilization of Atmospheric Greenhouse Gases: Physical, Biological and Socio-economic Implications portfolio of actions addressing climate change and adjusting it over time in light of improved information. To implement a portfolio of actions to address climate change, governments must decide both the amount of resources to devote to this issue and the mix of measures they believe will be most effective. With regard to the former, the issue is how far to proceed beyond purely no-regrets options. As noted in SAR WGIII, "the risk of aggregate net damage due to climate change, consideration of risk aversion, and the application of the precautionary principle provide rationales for action beyond no-regrets". The decision on how much action to take depends on the "stakes", the "odds" and the costs of policy measures. The risk premium-the amount that a society is willing to pay to reduce a risk - ultimately is a political decision that differs among countries. 42 Stabilization of Atmospheric Greenhouse Gases: Physical, Biological and Socio-economic Implications backs to increased global temperatures. Climatic Change, 22, trial ecosystem responses to climate change and CO2 doubling. 293-303. Global Biogeochemical Cycles, 9, 407-438. United Nations, 1992: Earth Summit Convention on Climate VEMAP Participants, 1995: Vegetation/Ecosystem modelling and analysis project (VEMAP): Comparing biogeography and biogeochemistry models in a continental-scale study of terres Wigley, TML. and S.C.B. Raper, 1992: Implications for climate and sea level of revized IPCC emissions scenarios. Nature, 357, 293-300. Wigley, T. M. L., R. Richels and J. A. Edmonds, 1996: Economic and environmental choices in the stabilization of atmospheric CO2 concentrations. Nature, 379, 242-245. Appendix 1 Temperature and Sea Level Consequences of Stabilization of CO, Concentrations from 1990 to 2300 Section 2.3 discussed the temperature and sea level implications of greenhouse gas stabilization, focusing on the period 1990 to 2100. In order to give a longer term perspective, the temperature and sea level results shown in Figures 11 to 15 (and discussed in Section 2.3) are presented in this Appendix, extended out to 2300 (Figures A1 to A5). 3.5 5650 5450 Year 2150 2190 Year 5650 Figure A1. (a) Projected global mean temperature when the concentration of CO2 is stabilized following the's profiles and the WRESSO and 1000 profiles shown in Figure 4. CH4. N2O and SO, emissions are assumed to remain constant at their 1990 levels and halocarbons follow an emissions scenario consistent with compliance with the Montreal Protocol until 2100 and then remain constant thereafter (i.e.. the reference case); (h) As for (a), but for global sea level change and central ice-melt parameters. All results were produced using the Wigley and Raper simple climate/sea level model (see IPCC TP SCM Figure A2. (a) The effect of different non-CO2 gas emission profiles on global temperature change for the $450 and S650 concentration profiles (see Figure 2). The solid lines give the "reference" results; the short dashed lines the "CO, alone" results and the long dashed lines give results where CH4. N2O and SO2 emissions increase according to IS92a to 2100 and then stabilize (the "IS92a case"). The climate sensitivity is assumed to be the mid-range value of 2.5°C: (b) As for (a), but for global sea level change. Central values of the ice-melt parameters are assumed. See Figure 12 for results from 1990 to 2100. Stabilization of Atmospheric Greenhouse Gases: Physical. Biological and Socio-economic Implications 5650 5450 1990 2030 2070 2110 2150 2190 2230 2270 Year 5650 Global sea level change (cm) 100 €90 5450 Year Figure A3. (a) The effect of climate sensitivity uncertainties on global mean temperature for the $450 and $650 CO2 concentration profiles and the reference case for non-CO, gases. The range of climate sensitivity (AT) is 1.5 to 4.5°C with a mid-range value of 2.5°C; (h) As for (a), but for global sea level change. The low, mid and high values of climate sensitivity are combined with low, mid and high ice-melt parameters, respectively, to give extreme ranges. See Figure 13 for results from 1990 to 2100. Figure A4. (a) Sensitivity of global mean temperature change to CH emissions for the $450 and $650 concentration profiles (see Figure 4). The solid lines give the "reference" results; the "CH4 low"/CH, high" curves assume annual CH, emissions decrease/increase linearly by 100 Tg(CH4) over 1990 to 2100 and then remain constant (see Table 4); (h) As for (a), but for global sea level change. Central values of the ice-melt parameters are assumed. See Figure 14 for results from 1990 to 2100. Figure A5. (a) Sensitivity of global mean temperature change to SO2 emissions for the $450 and $650 concentration profiles (see Figure 4). The solid lines give the "reference" cases; the short dashed lines show the "high SO" cases where emissions increase linearly from 75 TgS/yr in 1990 to 112.5 TgS/yr in 2100 and then remain constant, and the long dashed lines show the "low SO" cases where emissions decrease linearly to 37.5 TgS/yr in 2100 and then remain constan: (h) As for (a), but for global sea level change. Central values of the ice-melt parameters are 5650 $450 |