The level to which cumulative weighted emissions can be constrained depends on the date at which emission regulations are imposed and the stringency of the regulations. Figure 7 illustrates the effect of these factors. The initial base surcharge, ranging between zero and five dollars per weighted pound, is indicated along the abscissa. In this standard case, POD demand is assumed to grow at the median rates described in the previous section and the surcharge increases three percent per year. The three lines in the figure correspond to regulations beginning in 1988, 1995, and 2000. In the absence of regulations (that is, with a surcharge equal to zero), global cumulative weighted emissions from 1985 through 2020 total about 63.5 million metric tons (Mt). If regulations were to begin in 1988, limiting emissions to 50 Mt would require an initial world-wide surcharge of about $0.90/lb., limiting emissions to 40 Mt would require an initial surcharge of about $1.87/lb., and the minimum attainable level of cumulative emissions, if the initial surcharge were $5/lb., would be about 32.5 Mt. 1 If regulations were not initiated until 1995 larger surcharges would be necessary to limit emissions to the same levels: A 50 Mt limit would require a surcharge beginning at $1.22/lb.; a 40 Mt limit would require a surcharge beginning at $2.83/lb. The smallest attainable cumulative emissions, if regulations did not begin until 1995, would be about 37.2 Mt If regulations were not imposed until 2000, the range of attainable cumulative emissions is further reduced, and even higher surcharges would be required to hold emissions to any attainable level.