FIGURE 6.21 Annual production of biofuels assumed for Case 3.

The reference case corresponds to about 10 percent ethanol by volume in gasoline by 2050. In Case 3 (Biofuels), this is expanded to include an additional 54 billion gallons of biofuels per year (beyond the reference case). This is roughly four times the biofuel use in the reference case or about 40 percent ethanol in gasoline plus some other advanced biofuels. It is important to note that the greenhouse gas and oil reductions shown for Case 3 are relative to a reference case that already includes biofuel use up to 10 percent of gasoline by volume.

In the Biofuels case, the assumed corn ethanol use is the same as in the reference case. The difference is that more cellulosic and other advanced biofuels are produced. The additional biofuels production assumed in the Biofuels case (compared to the reference case) is shown in Figure 6.22.

Gasoline displacement for Case 3 is shown in Figure 6.23. The total is about 12 billion gallons per year by 2020 and 39 billion gallons per year in 2050.

Greenhouse gas emissions reductions are given in Figure 6.24 for the Biofuels case. The total reduction in greenhouse gas emissions is about 8 percent from the reference case by 2020, rising to 23 percent by 2050. The committee has not estimated the costs of building biofuel production plants or changes in the fuel distribution infrastructure that might be needed.

FIGURE 6.22 Case 3: Added biofuel production relative to the reference case.

FIGURE 6.23 Case 3: Oil displacement relative to the reference

FIGURE 6.24 Case 3: Greenhouse gas emission reductions relative to the reference case.

Comparison of Scenarios

The estimated savings in gasoline use and greenhouse gas emissions for each case are plotted in Figures 6.25 and 6.26. In the near to mid term, improving the fuel economy of gasoline vehicles will be the most effective option for reducing oil use and greenhouse gas emissions. This is already incorporated in the reference case up to 2020, but continued improvements thereafter could match the savings from hydrogen until about 2035. Biofuels could begin to make a difference sooner than hydrogen, which takes more time to implement, assuming cellulosic ethanol comes online in 2010. After about 2032, however, Case 1 (Hydrogen Success) would lead to greater greenhouse gas reductions per year than Case 3 (Biofuels). By 2040, the Hydrogen Success scenario offers about twice the greenhouse gas reduction and oil savings per year as the Biofuels scenario, and by 2050, almost three times the reduction. This clearly illustrates the time frames for different technologies and the total contributions they might make by 2020 and beyond. Although efficiency and biofuels could contribute sooner, hydrogen would surpass the annual savings achievable with either after



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement