Net Carbon Emission
It should be noted, that GHG emissions over the full ethanol life cycle could vary dramatically depending on the energy sources used to produce the ethanol. For example, in Canada, the manufacturing plants that produce ethanol from corn and wheat are fuelled by natural gas and produce fewer GHG emissions than many American ethanol plants that burn coal or other fossil fuels. There can thus be significant variations in the overall environmental benefit of using ethanol compared with gasoline.
At present, replacing 5% of conventional fuels with biofuels would have a relatively minor impact on reducing GHG emissions across Canada. In fact, if 10% of the fuel used were corn-based ethanol (in other words, if the E-10 blend were used in all vehicles), Canada’s GHG emissions would drop by approximately 1%. Therefore, in order to have a real impact on a country’s total GHG emissions, certain types of biofuels must be targeted, such as biodiesel and cellulose-based ethanol.
Paul Crutzen, Nobel Laureate, says: The relationship, on a global basis, between the amount of N fixed by chemical, biological or atmospheric processes entering the terrestrial biosphere, and the total emission of nitrous oxide (N2O), has been re-examined, using known global atmospheric removal rates and concentration 5 growth of N2O as a proxy for overall emissions. The relationship, in both the pre-industrial period and in recent times, after taking into account the large-scale changes in synthetic N fertiliser production and deforestation, is consistent, showing an overall conversion factor of 3–5%. This factor is covered only in part by the 1% of “direct” emissions from agricultural crop lands estimated by IPCC (2006), or the “indirect” emissions cited therein. This means that the extra N2O entering the atmosphere as a result of using N to produce crops for biofuels will also be correspondingly greater than that estimated just on the basis of Intergovernmental Panel on Climate Change's (IPCC) (2006). When the extra N2O emission from biofuel production is calculated in “CO2-equivalent” global warming terms, and compared with the quasi-cooling effect of “saving” emissions of fossil fuel derived CO2, the outcome is that the production of commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn (maize), can contribute as much or more to global warming by N2O emissions than cooling by fossil fuel savings. Crops with less N demand, such as grasses and woody coppice species have more favourable climate impacts. This analysis only considers the conversion of biomass to biofuel. It does not take into account the use of fossil fuel on the farms and for fertilizer and pesticide production.