The big ethanol picture

From a broader perspective, several studies have tried to clarify ethanol's value as an energy source and there remains some debate on the issue.

David Pimentel, a Cornell University professor of ecology and agricultural sciences, who served on a government committee that studied ethanol in the 1980s, says it takes almost 30 percent more energy to grow corn and turn it into ethanol than the ethanol contains.

However, Michael Wang, an Argonne National Laboratories scientist who has contributed to several government studies, estimates that ethanol produces 35 percent more energy than its production process consumes.

Most recent studies have shown a positive energy balance for ethanol of between 23 and 40 percent.

Another debate centers on ethanol's greenhouse gas emissions. Proponents say that ethanol use doesn't add to the world's balance of greenhouse gases because it simply puts back the same carbon dioxide that the source plants absorbed while growing. Some recent studies have disputed that assumption, however, saying that growing more corn in the United States causes farmers in other countries to clear more land to grow crops displaced by corn here. And in any case, harvesting crops such as switchgrass for ethanol that wouldn't be harvested otherwise releases extra carbon into the atmosphere.