Mitigation of climate change through reduced greenhouse gas (GHG) emissions is a primary motivation for developing biofuels. We delineate the terms necessary to provide a complete accounting of the GHG effects of direct and indirect land use change associated with biofuels, and find that current life cycle analyses of liquid biofuels do not account for many of these terms. To quantify the full GHG effects of biofuels-related land use change, we assemble estimates of CO₂, CH₄, and N₂O emissions that would occur upon land clearing, along with annual CO₂, CH₄, and N₂O fluxes, for pertinent ecosystem types.

Results/Conclusions

We show that GHG emissions or savings from land use change are substantial, and present several notable findings: (1) there would be substantial benefits (>3 Mg CO₂-eq/ha/yr) of replacing row-crop agriculture with perennial biofuel crops, largely through reduction of N₂O flux; (2) the costs of directly or indirectly replacing native ecosystems with biofuel crops has been underestimated by approximately 25-35% through failure to account for displaced net ecosystem productivity (NEP) and trace GHG fluxes;  and (3) there are substantial, previously unrecognized costs (~ 7-17 Mg CO₂-eq/ha/yr) to growing biofuels on “abandoned” land that would otherwise succeed to forest as a result of NEP displacement. Thus, at present, no biofuels life cycle analyses thoroughly account for the GHG contributions of land use change, which are significant enough to determine whether or not GHG emissions can be reduced with the use of biofuels instead of fossil fuels.