CO2 EMISSIONS FROM THE PRODUCTION AND COMBUSTION OF FUEL ETHANOL FROM CORN

Concern over the increasing concentration of CO2 in the Earth's atmosphere is causing us to re-evaluate how we use energy. In particular, we need to inquire if there are alternative energy systems which discharge less net CO2 per unit of energy service. This paper deals with the CO2 fluxes associated with the use of one biomass fuel, ethanol derived from corn. In a sustainable agricultural system, there is no net CO2 flux to the atmosphere from the corn itself but there is a net CO2 flux due to the fossil-fuel supplements currently used to produce and process corn. A comparison between ethanol from corn and gasoline from crude oil becomes very complex because of the variability of corn yield, the lack of available data on corn processing, and the complexity of treating the multiple products from corn processing. When the comparison is made on an energy content basis only, with no consideration of how the products are to be used, and at the margin of the current U.S. energy system, it appears that there is a net CO2 saving associated with ethanol from corn. This net saving in CO2 emissions may be as large as 40% or as small as 20%, depending on how one chooses to evaluate the by-product credits. This analysis also demonstrates that the frequently posed question, whether the energy inputs to ethanol exceed the energy outputs, would not be an over-riding consideration even if it were true, because most of the inputs are as coal and natural gas, whereas the output is as a high-quality liquid fuel.