Ethanol and environment

Jan. 19, 2004
Ethanol and environment In his letter, "Ethanol's Net Energy Balance" (OGJ, Nov. 10, 2003, p. 10), Steve Plotkin seems to have some misconceptions not only of energy balances, but more importantly, of environmental costs and benefits. He argues that ethanol's negative net energy balance means very little and that petroleum fuels also have negative net energy balances.

In his letter, "Ethanol's Net Energy Balance" (OGJ, Nov. 10, 2003, p. 10), Steve Plotkin seems to have some misconceptions not only of energy balances, but more importantly, of environmental costs and benefits. He argues that ethanol's negative net energy balance means very little and that petroleum fuels also have negative net energy balances.

As Gavin Longmuir succinctly explained in his letter (OGJ, Sept. 22, 2003, p. 10), in the case of fossil fuels we invest some energy in development, extraction, transportation, and processing in order to obtain more energy than we expended in these processes.1 In the case of ethanol, even with the input of "free" solar energy, the energy content of the ethanol is no greater than the fossil energy input. Therefore, ethanol is not a "renewable" energy source.

So why should we use fuel ethanol? Plotkin says, "What does matter is cost and environmental impact, and net energy balance is one tool that helps us to estimate these." The fact that ethanol has a negative net energy balance is, of course, a major contributor to its high cost. Plotkin argues that ethanol's greenhouse gas emissions are less than those of gasoline, so its use as a gasoline substitute would be beneficial from the standpoint of climate change.

Let's look at some environmental impacts. In essence, corn ethanol is made by cycling fossil fuels (in the form of gasoline, diesel, fertilizer, pesticides, and propane for drying the grain) through cropland and then refining the corn. Over the past 4 years (1999-2002) US corn production has averaged about 9.5 billion bushels from about 70.3 million acres.2 About 23% of the US corn crop is produced in the Great Plains states of South Dakota, Nebraska, Kansas, Wyoming, Colorado, Oklahoma, Texas, and New Mexico. The acreage devoted to corn in these states is about 18 million acres or about 26% of the US corn acreage.3 Much of this land is easily erodable, and numerous studies have conclusively demonstrated that row crops—such as corn—result in much higher erosion rates than cereal grains or forage crops. For example, on a silt loam soil with a 12% slope and an average rainfall of 38.5 in. near Zanesville, Ohio, a continuous corn-cropping sequence resulted in an average soil loss of 99.6 tons/acre over a 9-year period. Wheat grown in a rotation sequence with corn yielded a soil loss of 11.4 tons/acre, while permanent pasture had a soil loss of only 0.2 tons/acre.4

Furthermore, 45% of the corn acreage in these Great Plains states, or about 8 million acres, is irrigated with water that is being overdrafted (mined) from the Ogallala aquifer.3 Since corn requires approximately 2 acre-ft of applied irrigation water per acre, the corn acreage in the Great Plains requires close to 16 million acre-ft/year of irrigation water. To put this in some perspective, the average annual flow of the Colorado River (measured at Lee's Ferry) is about 14 million acre-ft/year.

Growing a crop that results in soil erosion nine-fold greater than wheat or with overdrafted groundwater in order to produce ethanol that contains less energy than the fossil inputs to produce it hardly qualifies as either sustainable or environmentally beneficial. Basically corn ethanol is a nonrenewable energy source, and its environmental costs outweigh whatever meager benefits it may possess.

References

1. Gavin Longmuir, "Alternate energy," OGJ, Sept. 22, 2003, p. 10.

2. State level data for field crops, Agricultural statistics data base, National Agricultural Statistics Service, US Dept. of Agriculture [www.nass.usda.gov].

3. County level data by state for crops, Agricultural statistics data base, National Agricultural Statistics Service, US Dept. of Agriculture [www.nass.usda.gov].

4. J.P. Zublena, "Corn Cropping Sequences," NCH-50, National Corn Handbook, Purdue University Cooperative Extension Service, West Lafayette, Ind., 1987.