Biofuels can provide a number of environmental advantages over conventional fossil fuels—most notably a reduction in greenhouse gas (GHG) emissions. Since the transportation sector accounts for about a third of total U.S. emissions of carbon dioxide (an abundant GHG), cleaner transportation fuels can play an important role in addressing climate change.
The level of GHG emissions associated with a particular biofuel depends on the energy used in growing and harvesting the feedstock, as well as the energy used to produce the fuel (e.g., coal, natural gas, biomass). On a full fuel-cycle basis corn ethanol has the potential to reduce greenhouse gas emissions by as much as 52% over petroleum-based fuels. Even better, ethanol made from cellulosic feedstocks, such as switchgrass, or agricultural residues, such as corn stover, has the potential to reduce greenhouse gas emissions by as much as 86% compared to gasoline.
Biofuels have the added benefit of providing a "carbon sink." As crops grow to produce the feedstocks for making the biofuel they absorb carbon dioxide from the atmosphere.
Ethanol offers additional environmental advantages over fossil fuels. It naturally biodegrades in soil and water without leaving harmful residues in the environment. Because MTBE has been found carcinogenic in high concentrations, ethanol is now used as a replacement gasoline oxygenate. Ethanol provides the same oxygenate benefits, but poses little or no risk to drinking and groundwater supplies.
Reduced Fossil Fuel Inputs
When evaluating the life cycle from feedstock production to end use, production of ethanol fuel requires less fossil energy than its petroleum-based counterpart. For example, ethanol produced from corn requires about 30 to 35 percent less fossil energy to deliver a gallon of liquid transportation fuel, on an energy equivalent basis, than is used to deliver gasoline (about 0.76-0.78 million (MM) BTU for corn versus about 1.22 MM BTU for gasoline). Fuel efficiency is increasing with improved agronomic practices, increased crop yields, improved nitrogen and water utilization, and advanced conversion technologies.
The figures for ethanol produced from lignocellulosic feedstocks – or non-starch, non-food based biomass feedstocks – are even more impressive. Cellulosic ethanol requires only ten percent of the fossil energy required to deliver a gallon of liquid transportation fuel on an energy equivalent basis compared to gasoline.
For more information see the full web page at energy.gov/eere/transportation/bioenergy.