The use of fossil fuels for transportation represents one of the largest anthropogenic contributions to greenhouse gases (GHGs), and the need for clean, renewable, alternative fuel sources has become a global priority. It is no wonder that biofuel production has grown exponentially over the past 30 years; biofuels essentially contribute no additional GHG in their carbon life cycle and can be grown in almost any farming region in the world. However, the rapid expansion of the biofuel market has generated considerable controversy in the practice: many scientific studies have revealed significant variability in the GHG reduction efficiency of different biofuel production methods in relation to fossil fuel displacement, some of which actually result in net increases of GHG emissions.

To address this controversy, this paper reviews the policies behind past and current biofuel production and analyzes the relative efficiencies of different production methods around the world. By assembling and comparing such eclectic data one can identify the primary sources of GHG emissions within the different methods, as well as which general trends in biofuel production show the greatest potential efficiency. This information will be of great assistance to any future policies that plan for a self-sufficient biofuel market with fewer government subsidies.

The results of this study showed that within the wide spectrum of variance for different methods, the greatest factors affecting GHG reduction efficiency were the type of crop grown, the subsequent amount of nitrogen fertilizer required for cultivation, and the amount and type of land converted to farmland for production.

In most instances, second-generation biofuels showed clear superiority to first-generation biofuels, though current technological limitations prevent their production on a competitive scale.

Based on these conclusions, any future policies promoting biofuel production in the U.S. must include provisions to diversify the domestic market based on the most efficient crops and methods practiced in similar regions, preferably offering incentives towards responsible land and fertilizer use. Such policies must also promote the development of second-generation biofuel technology to further expand their role in the market.

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