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Conclusion
The use of ethanol as a substitute for gasoline proved to be neither a sustainable nor an environmentally friendly option, considering ecological footprint values, and both net energy and CO2 offset consideration seemed relatively unimportant compared to the ecological footprint. As revealed by the ecological footprint approach, the direct and indirect environmental impacts of growing, harvesting and converting biomass to ethanol far exceed any value in developing this alternative energy resource on a large scale.
In the Brazilian case, for carbon sequestration, it seems to be more effective to reduce the rate of deforestation than to plant sugarcane. According to Fearnside and colleagues (2001), the amount of CO2 released to the atmosphere because of forest burning in the Amazon is about 187 Mg per ha. The current Brazilian energy scenario contrasts with that of the 1970s. Currently, Brazil produces 90% of the oil it consumes, and so the national security argument for substituting ethanol no longer applies. Furthermore, the argument for electricity cogeneration is meaningless, since the energy surplus is minimal.
IN the US Case, the use of ethanol would require enormous areas of corn agriculture, and the accompanying environmental impacts outweigh it's benefits. Ethanol cannot alleviate the United States dependence on petroleum.
However, the ethanol option should not be wholly disregarded. The use of a fuel that emits lower levels of pollutants when burned can be important in regions or cities with critical pollution problems. Also, in agricultural situations where biomass residues would otherwise be burned to prepare for the next planting cycle, there would be some advantage in using the residues for alcohol production. However, further research should be done to improve the conversion process. Considering that, eventually, petroleum may no longer be available in the amounts currently consumed, one must conclude that substitution of alternatives to fossil fuel cannot be done using one option alone. It will prove more prudent to have numerous options (e.g., ethanol, fuel cells, solar energy), each participating with fractional contributions to the overall national and global need for fuel energy. Finally, it is important to notice that no option comes free from significant environmental problems.
