Using cellulosic ethanol instead of gasoline should reduce CO2 emissions
Cellulosic biofuels, of which cellulosic ethanol is one, hold the promise of providing transportation and other fuels that, unlike corn ethanol, yield much more energy than the amount in the fossil fuels used to make them.
Cellulosic biofuels have the further advantage that, because they can be made from waste products, they will not necessarily generate pressure farmers to clear or farm more land, the way that growing corn for fuel may. Extra clearing and farming can lead to increased CO2 emissions.
These two general factors — low energy inputs and low land requirements — mean that cellulosic fuels can be made and used with low net greenhouse gas emissions.
Even should farmers grow trees or grasses specifically for the purpose of making cellulosic biofuel, varieties could be selected that require little or no soil preparation and are able to thrive on marginal lands. Thus little or no cropland would need replacement, and little or no tilling would be required — two causes of carbon emissions.
However, it is very important to note that this is only a potential advantage — nothing would keep farmers from using active cropland to grow plants for cellulosic biofuels if it made sense economically. If farmers do use cropland to grow cellulosic biofuels, there could be unintended land-use consequences in other parts of the world, leading to boosted greenhouse emissions.