Climate change mitigation efforts that involve land use decisions call for comprehensive quantification of the climate impacts of land use change. This is particularly imperative for analyses of the climate impact of biofuel production, as land use change is often the single most important factor in determining their sustainability. Land use change affects climate through both biogeochemical and biophysical forcings. Biogeochemical forcings—i.e., greenhouse-gas induced climatic changes—have been receiving increasingly comprehensive treatment in biofuel life cycle analyses; however, current analyses are not comprehensive in all aspects and often use improper accounting for the timing of emissions. Biophysical forcings—i.e., the effects of land use change on climate through perturbation of water and energy between the land surface and the atmosphere—are sometimes more influential than the biogeochemical forcings; however, they have largely been neglected in assessments of the impacts of biofuels-related land use change. We present a metric for quantifying the effects of land use change on radiative forcing from both greenhouse gases and changes in albedo, and we use this metric to assess whether biofuel life cycle analyses are accurately quantifying the climate impacts of biofuels-related land use change.
Results/Conclusions
Comprehensive and time-sensitive accounting for changes in ecosystem-atmosphere greenhouse gas exchange that would occur upon land clearing—including greenhouse gas release from stored organic material and displaced annual greenhouse gas fluxes—can substantially alter the perceived value of ecosystems. For example, the full greenhouse gas value of a tropical forest is approximately 20% higher than its value based on organic matter storage alone. In addition, changes in albedo contribute strongly to the climate value of ecosystems, sometimes impacting radiative forcing more strongly than greenhouse gasses. As a result, the full climate effects of land use change often differ substantially from estimates used by biofuel life cycle analyses. Effective analysis of the climate impacts of biofuel production must consider the integrated effects of biogeochemical and biophysical radiative forcings.