FIGURE 6.25 Oil consumption for Cases 1-3 compared.

FIGURE 6.26 Greenhouse gas emissions for Cases 1-3 compared.

2035. This result highlights the long time constants inherent in changing the energy system, as well as the need to develop long-term, very low carbon options.

The previous section looked at the potential impact of implementing one technological measure at a time. In the future, reducing oil use and greenhouse gas emissions probably will be increasingly important, and it is likely that a combination of approaches would be implemented. However the reductions for each approach cannot simply be added because they affect each other. This section considers several combinations.

This case combines higher gasoline vehicle efficiency with introduction of hydrogen fuel cell vehicles (Case 1 and Case 2). The results are shown in Figures 6.27 and 6.28. Comparing Figure 6.27 and 6.25, gasoline consumption in 2035 is about 18 billion gallons per year lower for the combined case than for HFCVs alone. By 2020, efficiency reduces greenhouse gas emissions by about 1.8 percent relative to the base case. Beyond 2030, HFCVs lead to deeper cuts in emissions than would be possible with efficiency alone.

Combining higher gasoline vehicle efficiency with biofuels yields much greater reductions in oil use and greenhouse gas emissions than are possible with biofuels alone. This is shown in Figures 6.29 and 6.30, which combine Cases 2 and 3. By 2020, biofuel use alone could reduce annual oil use by about 8 percent, with efficiency bringing the total to 10 percent. In the longer term, the effect of efficiency improvements dominates, with biofuels saving 23 percent of gasoline use or greenhouse gas emissions in 2050 and efficiency an additional 41 percent. This strategy “stretches” limited biomass resources to fuel more vehicle miles traveled per acre of land.

FIGURE 6.27 Oil use for Cases 1 and 2 combined.

FIGURE 6.28 Greenhouse gas emissions with HFCVs for Cases 1 and 2 combined.