Biofuels, cropland expansion, and the extensive margin

Background: Recently, several papers have assessed land use consequences of biofuel expansion. In the absence of empirical evidence, these papers assigned subjective values to extensive margin (productivity of new croplands over productivity of existing croplands). Methods: This paper fills the gap in this area and provides a new data set which estimates land productivity at 0.5° × 0.5° (longitude × latitude) grid-cell level using a process-based biogeochemistry model, the terrestrial ecosystem model (TEM) calibrated for a C4 crop. Results: The results obtained from the TEM can be used in connection with economic models which are designed to assess land use changes induced by economic factors. To show a real application, a set of regional extensive margins are calculated based on the new data set. The calculated regional extensive margins are then introduced in a computable general equilibrium (CGE) economic model which has been frequently used to assess the land use implications of ethanol production. Finally, land use changes due to US ethanol production are examined using the augmented CGE model with the new extensive margins. Conclusions: The approach developed here provides estimates of extensive margins disaggregated by the country and agroecological zone, replacing the earlier assumption of a globally uniform value. Using these new parameter values, the estimation of land required for ethanol production is 25% lower than earlier published results.