FIGURE 5-2 Global SO2 emissions (million tons of sulfur per year) for the four SRES scenarios families and from each of the emissions models. Red lines correspond to the A1 family of scenarios, brown lines to A2, green lines to B1, and blue lines to B2. These emissions, along with the ozone precursor emissions of methane, carbon monoxide, nitrogen oxides, and volatile organic compounds, were also gridded onto 1° × 1° latitude-longitude maps for use in global climate, atmospheric chemistry, and air quality models. The grids were developed using simple scaling applied to a base-year 1990 map and using the projected four to six regional changes from the SRES emissions models. SOURCE: Nakićenović et al. (2000).

Workshop on GHG Stabilization Scenarios, 2004). Such targets can easily be inverted by carbon cycle models to determine the required emissions scenario for stabilization (e.g., Wigley, 1991). Cost-benefit scenarios are another approach. They are based on the premise that the most efficient policy intervention is that in which the marginal cost of reducing emissions is balanced by the marginal reduction in climate damages, measured in monetary terms (Cline, 1992).

Developing emissions scenarios is tantamount to asking how different societies will produce, transform, and consume energy; extract and use Earth’s resources; and modify the landscape for the next century. The possible answers to this vast and complex question are manifold. Uncertainties arise in all facets of the problem of building long-term scenarios. Moreover, unforeseen events, such as a revolutionary breakthrough in tech-

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