FIGURE 2.3 (a) Illustrative atmospheric CO2 stabilization scenarios for 1,000, 750, 550, and 450 ppmv; SP1000 (red), SP750 (blue), SP550 (green) and SP450 (black), from Meehl et al. (2007). (b) Compatible annual emissions calculated by three models, the Hadley simple model (solid), the UVIC EMIC (dashed), and the BERN2.5CC EMIC (triangles) for the three stabilization scenarios. Panel (b) shows emissions required for stabilization without accounting for the impact of climate on the carbon cycle, while panel (c) included the climate impact on the carbon cycle, showing that emission reductions in excess of 80% (relative to peak values) are required for stabilization of carbon dioxide concentrations at any of these target concentrations.

FIGURE 2.3 (a) Illustrative atmospheric CO2 stabilization scenarios for 1,000, 750, 550, and 450 ppmv; SP1000 (red), SP750 (blue), SP550 (green) and SP450 (black), from Meehl et al. (2007). (b) Compatible annual emissions calculated by three models, the Hadley simple model (solid), the UVIC EMIC (dashed), and the BERN2.5CC EMIC (triangles) for the three stabilization scenarios. Panel (b) shows emissions required for stabilization without accounting for the impact of climate on the carbon cycle, while panel (c) included the climate impact on the carbon cycle, showing that emission reductions in excess of 80% (relative to peak values) are required for stabilization of carbon dioxide concentrations at any of these target concentrations.

suggested that slow reductions in emissions could lead to eventual stabilization of climate (e.g., Wigley et al., 1996). But recent studies using more detailed models of key feedbacks in the ocean, biosphere, and cryosphere, have underscored that although a quasi-equilibrium may be reached for a limited time in some models for some scenarios, stabilizing radiative forcing at a given concentration does not lead to a stable climate in the long run. Cumulative emitted carbon can more readily be linked to climate stabiliza-



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