Run, don’t walk, to Randall Parker’s place and read his excellent and thorough post on the science, economics, and politics of ethanol in Brazil and the US. Chock full of outstanding and informative links.
I also had not thought about what he mentions in his parting comment about ethanol from biomass:
But my guess is that coming advances in cellulosic technology will so lower the cost of biomass ethanol that ethanol usage will increase greatly in the next 10 years. I do not treat that as a happy prospect. Large scale biomass energy production will cause humanity to compete (too successfully) with nature and take habitat away from other species. Since I’m fond of other species I’m not happy about that. I’d much prefer we use nuclear, solar, and other energy sources that use much smaller ecological footprints.