Figure 5-7:(a)The required
rate of decrease in energy intensity (energy per unit GDP) in order to meet given
CO2 concentration stabilization targets is within the range of historically
achieved rates for stabilization above 550 ppm, and possibly even at 450 ppm,
but (b) the required rate of improvement in carbon intensity (carbon emissions
per unit energy) to stabilize at levels below about 600 ppm is higher than the
historically achieved rates.As a consequence, the cost of mitigation
rises as the stabilization level decreases, and does so more steeply below a target
of about 600 ppm than above (see Figure
7-3).
