> Why would growing corn for ethanol and burning it in an engine be any climate-friendlier than growing that same corn for food and burning an equivalent amount of gasoline in an engine? The carbon absorbed in the field wouldn’t change; neither would the carbon emitted from the car.

It would be worse because is food is also fuel. Whether motor vehicle fuel or animal fuel, the corn goes through pretty similar chemical change. Obviously, burning just the produce of fields that uptake as much carbon as their produce releases is better, in net carbon terms, than doing that plus burning fossil fuels.