Which source of ethanol is most effective at reducing emissions?

Ethanol is a simple chemical. It doesn't matter what the source is unless you are talking about efficiency. They are renewable so the last column didn't make any sense. How could they possibly get the 56% reduction in global warming. That is just stupid on so many levels. The real comparison should be to how much petroleum is used to manufacture it. Corn is very inefficient but sugar cane is very efficient, something like 90%. It gives 9 times as much energy as it take to create it. It is barely above break even for corn. Switch gr (cellulose) has the potential to be 90% efficient and it doesn't require burning food for fuel. If that technology can be developed, it would be wonderful for eliminating our dependence on foreign oil.