The Truth about Ethanol
Ethanol has a promising role to play in helping to solve many of the problems associated with gasoline use. While improving fuel economy is the most cost-effective, near-term solution for reducing global warming pollution, U.S. oil dependence, and Americans' pain at the pump, there's no one single cure for our problems. We'll need cleaner fuels, more efficient vehicles, and smarter growth to truly clean up the transportation sector.
What is Ethanol?
Today's Use of Ethanol
Global Warming Benefits and Impacts
Sustainable Production
What is Ethanol?
Most of the ethyl alcohol, or ethanol, used in vehicle fuel is produced by the fermentation of a sugar solution. In the United States, most ethanol is derived from the starches in corn kernels. Other types of plant material such as grasses, wood, and agricultural wastes can also be used to make "cellulosic" ethanol (named for the long chains of sugars that are the main component of plant cell walls).
Today's Use of Ethanol
Nearly all of the ethanol used in the U.S. is blended into conventional gasoline. Ethanol use is on the rise in the U.S. According to the Renewable Fuels Association, demand for ethanol more than tripled between 2002 and 2007, from about 2 billion gallons per year in 2002 to over 6.5 billion gallons per year in 2007. In 2007, ethanol displaced about three percent of our gasoline use.
All of today's gasoline-burning cars and trucks can use a blend of 10 percent ethanol (known as E10) more or less without any engine modifications. However, E10 can cause an increase in smog-forming pollution relative to conventional gasoline. To ensure no backsliding in air quality, gasoline specifications must be modified to burn clean on E10. Flexible-fuel vehicles (FFVs) can run on a fuel blend of up to 85 percent ethanol (known as E85).
Global Warming Benefits and Impacts
Because a gallon of ethanol contains less energy when burned than a gallon of gasoline, ethanol yields lower fuel economy than gasoline. But the lifecycle emissions of the ethanol – from seed to tailpipe, depend upon how the ethanol is made, and what it is made out of. The best ethanol can have lower lifecycle global warming pollution than gasoline. But the worst ethanol can significantly increase lifecycle global warming pollution compared to gasoline.
Accurate lifecycle emissions accounting requires that all of the energy and inputs associated with growing, producing, delivering, and using any biofuel are tracked, including emissions associated with changes in land use. Most analyses conducted before 2008 indicate that corn ethanol delivers a 10 to 20 percent reduction in global warming emissions over its lifecycle compared with gasoline, but these analyses did not include land use changes. The reduction is modest because corn production requires a significant amount of fossil fuel inputs for farm operations, processing and distilling, and fertilizer production (generally natural gas). Fertilizers used for corn production also generate a substantial amount of nitrous oxide, a potent global warming pollutant, as unused fertilizer breaks down in the field. In addition, many corn ethanol production facilities operate on natural gas; if new production facilities use coal instead, the emission benefits of corn ethanol could be reduced or eliminated.
Several new studies have focused on the contribution of land use changes to lifecycle global warming pollution. If land is converted from forest to cropland, there can be a significant increase in global warming pollution. Recent estimates suggest that the emissions from these changes in land use may be huge and could dramatically shift the balance of risks and rewards for some kinds of ethanol. For example, when lifecycle analysis of corn ethanol includes land use changes caused by using corn for ethanol rather than food or animal feed, the lifecycle emissions can end up as high as gasoline or potentially much higher (see the UCS Land Use Fact Sheet for more details).
Cellulosic ethanol can reduce lifecycle global warming emissions by as much as 80 to 90 percent compared with gasoline. Cellulosic materials require less fertilizer to grow and require less land in order to produce an equivalent amount of fuel. Additionally, the non-fermentable parts of the plant can be used as combustible fuel in place of fossil fuels. However, if cellulosic ethanol is made from crops that compete with food crops for land, indirect changes in land use can reduce or eliminate the benefits of cellulosic ethanol. In order for cellulosic ethanol to achieve its potential, we need to make good choices about how and where the cellulosic materials are grown.
Sustainable Production
If done wrong, the production of biomass for biofuels like ethanol could destroy habitats, worsen water or air quality, limit food production and even jeopardize the long-term viability of the biomass resource itself. The environmental impact of biofuels is comparable to certain agricultural crops. For example, the growing of corn has similar consequences whether the corn is grown for food, animal feed, or as a biofuel feedstock.
The environmental impact is particularly high when forestland is cleared for monocrop farming of current generation feedstocks like corn. If done right, next generation feedstocks, such as mixed prairie grasses, may offer a lower-impact alternative, especially if grown with smart farming practices, such as no or low-till, plant diversification, and lower pesticide and fertilizer use. This potential for displacing some of our fossil fuel use makes next generation biomass feedstocks a worthwhile target for research and development. As we expand our biofuels production, there must be adequate safeguards in place to ensure that fuels are produced in a manner that safeguards the environment.
