Greenhouse Gas  Impacts of
    Expanded Renewable  and
    Alternative  Fuels Use
         The increased use of renewable and alternative fuels can result in
         significant reductions in the use of petroleum-based fuels.  By
    displacing petroleum fuels, many, although not all, of these fuels can
    provide reductions in greenhouse gas emissions.  To estimate the
    impacts of increases in renewable and alternative fuels on greenhouse
    gas emissions, the entire fuel lifecycle including fossil fuel extraction
    or feedstock growth, fuel production, distribution, and combustion
    should be accounted for.  There are a variety of lifecycle models and
    analyses available to perform this type of work, the results presented
    here are based on one such model, Argonne National Laboratory's
    GREET model, and one specific set of assumptions.

    Lifecycle analyses must contend with the fact that the inputs and assumptions
    generally represent industry-wide averages even though energy consumed and
    emissions generated can vary widely from one facility or process to another.  Thus,
    greenhouse gas emissions can vary depending on each of these factors  and the
    assumptions made about those factors. For example, renewable and alternative
    fuel production plants can utilize different processes and be powered with biomass,
    natural gas, coal or a mix of these fuels. Similarly, greenhouse gas emissions from
    alternative fuels like hydrogen depend on the fuel used to make the hydrogen.
    The combustion, or use of these fuels in vehicles, is another factor that influences
    lifecycle greenhouse gas emissions. For example, electric vehicles can have a much
    higher fuel efficiency thereby improving the lifecycle greenhouse profile of electricity
    as a fuel.

    The chart below presents an estimate for the percent change in lifecycle greenhouse
    gas emissions, relative to the petroleum fuel that is displaced, of a range of alternative
    and renewable fuels. The fuels are compared on an energy equivalent or BTU basis.
    Thus, for instance, for every BTU of gasoline which is replaced by corn ethanol, the
    total lifecycle greenhouse gas emissions that would have been produced from that
United States
Environmental Protection
Office of Transportation and Air Quality
                          April 2007

           BTU of gasoline would be reduced by 21.8 percent. These emissions account not only for CO2,
           but also methane and nitrous oxide.
                                          Percent Change in GHG Emissions
             ^  -56.0%
                                                      D    D
                                                     -22.6%  -21.8%  -19.9%
           Assumptions on alternative fuels production are based on GREET defaults and the following
               -  Electricity: represents the national average CO2 output rate for electricity in 2004, based
                  on the EPA eGRID database, which assumes a U.S. average mix of fuel types. This
                  number also accounts for the higher per mile efficiency of electric vehicles.
               -  Hydrogen (gaseous and liquid): represents using natural gas to produce hydrogen and
                  accounts for the higher per mile efficiency of use of hydrogen in a fuel cell vehicle.
               -  Coal-to-Liquids: represents production of Fischer-Tropsch diesel fuel from coal.  The
                  carbon capture and sequestration case includes electricity needed for capture and storage.
               -  Natural Gas (compressed and liquefied): represents production from fossil sources (e.g.,
                  does not account for biogas potential).
               -  Methanol: represents fuel produced from natural gas feedstock.
               -  Liquefied Petroleum Gas: represents production from natural gas and crude oil
               -  Gas-to-Liquids: represents production of Fischer-Tropsch diesel fuel from natural gas.
                                                             Office of Transportation and Air Quality
           Greenhouse Gas Impacts                                                                   3