| Summary: | Time-dependent geographical distributions of surface–air temperature change relative to year 2000 are constructed for four scenarios of greenhouse gas (GHG) and sulfur dioxide (SO2) emissions, and are compared to the IS92a scenario. The four new scenarios have been developed by four different modeling teams. The four scenarios are noninterventionist, in that they do not include abatement of GHG emissions for the purpose of climate-change mitigation. The time evolution of the changes in global-mean surface-air temperature and sea level are calculated for each scenario by our energy-balance-climate/upwelling-diffusion-ocean model. The temperature changes individually and jointly for the radiative forcing by the GHGs and by the sulfate aerosol, which is formed in the atmosphere from the emitted SO2. These GHG- and SO2-induced global-mean temperature changes are used to scale in time the geographical distributions of surface–air temperature simulated by our University of Illinois at Urbana–Champaign (UIUC) atmospheric-general-circulation/mixed-layer-ocean model, respectively for a doubling of the CO2 amount and for a 10-fold increase in present-day SO2 emission—the latter from the entire earth as well as individually from Europe, Siberia, North Africa, Asia, North America, and the Southern Hemisphere—each geographical distribution having been normalized by its respective global-mean surface–air temperature change. It is found that: (1) the global-mean surface–air temperature changes are not distinguishable among the four scenarios presented here until near the middle of the 21st century; (2) in 2100, the warming and sea level rise range from 1.2°C and 27 cm for the B1 scenario, with a temperature sensitivity of ΔT2x = 1.5°C to 4.9°C and 72 cm for the A2 scenario, with ΔT2x = 4.5°C, with 62 and 69% of these 3.7°C and 45 cm ranges respectively resulting from the uncertainty in ΔT2x, and 38 and 31% from the scenario uncertainty; (3) the scenario uncertainty in future noninterventionist CO2 emissions translates into a large uncertainty about the geographical distribution of the warming, particularly in the Arctic; (4) the reduction in regional SO2 emissions of the four scenarios compared to IS92a results in a significant warming of Europe, Asia, and North America, as well as either a reduction or reversal of the cooling elsewhere, thereby showing that mitigation of the acid-rain problem exacerbates the greenhouse-warming problem; and (5) sulfate aerosol reduces the GHG-induced warming in the Arctic for IS92a, but increases the Arctic warming for the four scenarios.
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