It costs more energy to produce corn ethanol than it ultimately saves. Furthermore, it is a gasoline additive. Burning any kind of fuel contributes to global warming. This issues is only debated because politicians need to win the Iowa Caucus. Most Iowans are corn farmers and will only support politicians who agree with developing ethanol.
Corn ethanol may burn cleaner than petroleum fuels, but that doesn't change the fact that automobiles in the USA (the world's biggest polluter) require combustion engines to function. Corn ethanol still creates hazardous co2 emissions, endangering our planet. We need to decrease our dependance on combustible fuels to really slow global warming and save ourselves from disaster.