Originally Posted by 85

[edit] Life cycle impact of E85 on greenhouse gas emissions
Use of E85 results in reductions of greenhouse gas emissions and energy use for each gallon burned, compared to the emissions and energy use for the gasoline it replaces.[1][2]

Using corn based fuel ethanol production, E85 has a significant effect on total fossil fuel / energy usage and greenhouse gas (GHG) emissions. As process efficiency increases over the coming years, these benefits are expected to continue to improve. A recent study by University of California at Berkeley estimates it cuts greenhouse-gas emissions by 13% over gasoline.[citation needed]

E85 produces less energy per gallon than gasoline, which means fewer miles per gallon. Until the price of E85 drops to 72% the price of gasoline, consumers may not see any savings in fuel costs per mile. But, as noted earlier in this article, the "energy penalty" per gallon of liquid fuel may not be the entire 28% differential in energy content of that gallon of liquid. In other words, a FFV may use the energy content (measured in BTUs) of E85 more efficiently than the energy content in gasoline. For example, if a Ford Taurus FFV with a highway fuel economy of 27 miles per gallon on gasoline gets 23 miles per gallon on E85, that "penalty" per gallon of E85 is only 15%, not 28%. Viewed from the other perspective, 23 miles per gallon on E85 is a "gasoline-equivalent" energy efficiency of 32 miles per gallon (23/0.72), compared to only 27 miles for the same number of BTUs if using gasoline.

Using dry milling process technology (circa 1999) each gallon of E85 burned reduced petroleum usage by an estimated 0.949 gallon (0.949 L/L). Reduced GHG emissions by 23.8%, compared to burning a gallon of gasoline, and reduced life cycle fossil energy consumption by 44.4% compared to gasoline.

On a per-mile-driven basis, using 1999 technology, dry milling process derived E85, reduced petroleum usage by 74.9%, GHG emissions by 18.8%, and total fossil energy consumed by 35%. Wet milling derived E85 with 1999 technology would net reductions of 72.5% in petroleum usage, 13.7% in GHG emissions, and 34.4% in fossil energy used.

Using more recent state of the art (circa 2005) the energy usage figures improve slightly, with an appreciable decrease in GHG emissions. Dry mill current technology reduces petroleum usage by 75.6%, GHG emissions by 25.5% and fossil energy use by 40.7%. Wet mill current technology reduces petroleum usage by 73.7%, GHG by 23.8% and fossil energy by 42.5%.

Using cellulose based processes, the reductions in petroleum, GHG, and fossil energy are expected to reach the following levels in a mature production environment. Cellulose based ethanol production is nearing commercial viability at this time (2006). Woody biomass process (near future technology) petroleum reduction 69.9%, GHG emissions 102.2% (taking GHGs out of the atmosphere) and fossil energy usage 79%. Herbaceous biomass process (near future technology) petroleum usage reduction of 71.4%, GHG emissions 67.6% and fossil energy 70.4%.

Skeptics caution, however, that these potential benefits are balanced, and possibly offset, by a significant cost in the form of farmland. It has been estimated that the land area required to operate a motor vehicle for one year on pure ethanol, 11 acres, could feed 7 people over the same timeframe.[2] The logical consequences of these competing land uses are that widespread use of ethanol would lower food production from existing agricultural land, potentially inflating food prices due to less supply. Alternatively, the agricultural industry could maintain existing levels of food production and create more farmland — through deforestation — upon which to grow crops for energy production. Ironically, this could lead to the acceleration of the greenhouse effect as well as the loss of biodiversity.

It should be pointed out though, that many of these concerns are derived from studies by a single author (Pimentel) which have been rebutted by several reports.[3][4] Pimentel's argument, for example, is based on long-outdated technology, understates the energy costs of refining and transporting petroleum fuels, and neglects to account for the energy value of the byproducts of the ethanol production process, including that of the high protein cattle feed.

Their conclusion is these series of assumptions may not be entirely appropriate. For example, if the use of ethanol is extended to 100% usage to cover today's fuel energy needs, using exclusively corn derived ethanol, the obvious conclusion is that too much farm land will be required for this usage. This is not likely given current events. Likewise corn used in ethanol production does not remove human food crops from the food chain, as the nutrients are retained and reintroduced to the human food chain through high quality livestock feed. [5]

Ethanol can be brewed from any organic source that contains sugar or starch using current technology. This includes other crops besides corn, such as rice, wheat, barley, potatoes, sugar beets, and sugar cane. At the moment the most cost effective crop in the USA is corn. There is however no reason to assume that will continue into the future. Alternate feed stock streams are already coming on line as producers and manufactures realize that their waste can be converted to a product with market value. For example, Coors Brewing Company is producing 1.5 million gallons per year of fuel ethanol from waste beer and is expanding that output an additional 1.5 million gallons per year in the near future.[6] Others have discussed using otherwise waste crops like freeze damaged fruit, over ripe produce like apples and even out of date bakery goods like stale bread and cakes as possible feed stock streams for ethanol plants.

If cellulose becomes a cost effective feed stock for ethanol, it will become economic to use waste products from other processes or discards, such as waste paper from trash, or stalks and stemmage from crops. Certain high-yield plants grown expressly as a source of cellulose may thrive in climates where food and timber crops do not.