on transportation fuels.
Jacobson and Searchinger are considering ethanol as a replacement for ALL gasoline which is probably not very likely. Nonetheless, Ethanol can be a valuable technology even if it doesn't replace all our gasoline usage. Ford is going to soon offer an engine which will provide a 25% to 30% gain in gas mileage with only 5% ethanol vs 95% gasoline usage. This means that if all cars were using this engine you would get 25% to 30% reduction in total gas demand with ethanol supplying 5% of the total fuel supply. We currently produce an volume of ethanol that is about 5% of the total fuel supply.
NOnetheless, ethanol will most likely not replace gasoline use entirely. that will take plug-in hybrids. However, it will take a
two to three decades for hybrids to make an appreciable dent in gasoline demand and in that time ethanol will enable us to reduce our gasoline usage (and keep the price of gas down - it will go up again, you can count on it). We will need to save that money as investing in electric cars will not be cheap.
Even if electric cars averaged 200 mpg it would take 13 million electric cars costing
$180 Billion (without inflation and using GM's estimate of $37,500 for the volt) to reduce total gas consumption by 3%. This is assuming 200,000 units initial sales and sales growth of 20% per year. (note that the spreaadsheet at the link allows the user to change the assumed values for cost , mpg, initial sales and annual slaes growth and percent of total gasoline consumption saved. So if you don't like the assumptions I used try some of your own! The spreadsheet compares the Volt to a Corolla getting 30 mpg at the beginning rising to 39 mpg at end of period. The electric car goes from 200 mpg to 371 mpg)
http://www.transportation.anl.gov/pdfs/letter_to_science_anldoe_03_14_08.pdfSearchinger et al. had to decide what land use changes would be needed in Brazil, the United
States, China, and India to meet their simulated requirement for 10.8 million hectares of new
crop land. With no data or modeling, Searchinger et al. used the historical land use changes that
occurred in the 1990s in individual countries to predict future land use changes in those countries
(2015 and beyond). This assumption is seriously flawed by predicting deforestation in the
Amazon and conversion of grassland into crop land in China, India, and the United States. The
fact is, deforestation rates have already declined through legislation in Brazil and elsewhere. In
China, contrary to the Searchinger et al. assumptions, efforts have been made in the past ten
years to convert marginal crop land into grassland and forest land in order to prevent soil erosion
and other environmental problems.
In estimating the GHG emissions payback period for corn ethanol, Searchinger et al. relied on
the 20% reduction in GHG emissions that is provided in the GREET model for the current
ethanol industry. Future corn ethanol plants could improve their energy efficiency by avoiding
DGS drying (in some ethanol plants) or switching to energy sources other than natural gas or
coal, either of which would result in greater GHG emissions reductions for corn ethanol (Wang
et al. 2007). Searchinger et al. failed to address this potential for increased efficiency in ethanol
production.
In one of the sensitivity cases, Searchinger et al. examined cellulosic ethanol production from
switchgrass grown on land converted from corn farms. Cellulosic biomass feedstocks for ethanol
production could come from a variety of sources. Oak Ridge National Laboratory completed an
extensive assessment of biomass feedstock availability for biofuel production (Perlack et al.
2005). With no conversion of crop land in the United States, the study concludes that more than
1 billion tons of biomass resources are available each year from forest growth and by-products,
crop residues, and perennial energy crops on marginal land. In fact, in the same issue of
Sciencexpress as the Searchinger et al. study is published, Fargione et al. (2008) show beneficial
GHG results for cellulosic ethanol.
On the basis of our own analyses, production of corn-based ethanol in the United States so far
results in moderate GHG emissions reductions. There has also been no indication that U.S. corn
ethanol production has so far caused indirect land use changes in other countries because U.S.
corn exports have been maintained at about 2 billion bushels a year and because U.S. DGS
exports have steadily increased in the past ten years. U.S. corn ethanol production is expected to
expand rapidly over the next few years — to 15 billion gallons a year by 2015. It remains to be
seen whether and how much direct and indirect land use changes will occur as a result of U.S.
corn ethanol production.
The Searchinger et al. study demonstrated that indirect land use changes are much more difficult
to model than direct land use changes. To do so adequately, researchers must use general
equilibrium models that take into account the supply and demand of agricultural commodities,
land use patterns, and land availability (all at the global scale), among many other factors. Efforts
have only recently begun to address both direct and indirect land use changes (see Birur et al.
2007). At this time, it is not clear what land use changes could occur globally as a result of U.S.
corn ethanol production. While scientific assessment of land use change issues is urgently
needed in order to design policies that prevent unintended consequences from biofuel production,
conclusions regarding the GHG emissions effects of biofuels based on speculative, limited land
use change modeling may misguide biofuel policy development.
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NOte that by getting 25% to 30% better gas mileage with 1/20th as much ethanol, Ford will also be multiplying the performance of ethanol re GHG reduction 20 times.
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