Corn-Based Ethanol’s Effects on Global Warming

Corn-based ethanol has recently been touted as a readily available, carbon-neutral alternative to gasoline. Ethanol can be easily made and distributed by preexisting means, to ordinary cars. This makes it a more feasible alternative than, say, hydrogen fuel cells. For these reasons and more, US farmers now receive subsidies under the Energy Independence and Security Act of 2007. Recent research, however, suggests that corn based ethanol production isn’t what it was cracked up to be.
Corn-based ethanol is called carbon-neutral because, supposedly, any greenhouse gases emitted in the processing and use of the fuel are re-absorbed from the atmosphere by the next crop. There are problems with this theory, however. Much of the carbon dioxide sequestered by plants is in the soil beneath the plant, not the plant itself. This sequestered carbon dioxide is released when the ground is plowed for planting, which occurs each time a new crop of corn is planted. This extra carbon, depending on prior land use, may completely obscure the benefits of the biofuel created for 50 years.
If land used for a parking lot, a stripped mine, or any other plant-free area were converted to corn-based ethanol production, the reduction in greenhouse emissions over gasoline would be around 20%.2 This is because these areas have relatively little biological activity occurring within the soil, and so the soil has very little carbon sequestered in it. Economically, it’s cheaper to convert fallow fields into cornfields than it is to convert unproductive soils. Fallow fields sequester great amounts of carbon dioxide in the soil due to their productivity and lack of tillage. This carbon is released during cultivation, resulting in the situation described earlier. For a technical description of soil carbon sequestration, see the “Sequestration of C in Soil” and “Tillage” sections of “Emission of carbon dioxide from soil.”
For the short term, rather than giving subsidies for producing corn-based ethanol, subsidies should be given for practicing no-till farming, and to landowners who leave grassland and forest undisturbed, as these practices sequester more carbon than typical production of corn-based ethanol. In the long run, however, I recognize that gasoline use is environmentally unsound. Cellulosic ethanol, though not yet feasible, would produce ethanol without yearly tillage, allowing carbon to remain in soil while still providing a renewable liquid fuel source. Governmental plans for this are included in the 2008 Farm Bill.