Updates in assessing soil organic carbon and their implications for evaluating land use change emissions

Abstract Emissions from land use changes are relevant for environmental policy analysis. Since the late 1990s and early 2000s many of these analyses have examined induced land use changes (ILUC) from biofuel production and policy as well as their associated greenhouse gas (GHG) emissions. These studies have often used the Harmonized World Soil Data (HWSD) to evaluate the corresponding changes in soil organic carbon (SOC) as a part of their assessments. However, those modeling efforts that used this data set have not necessarily implemented its latest version, and therefore, their results may not represent the most recent available SOC data sources. As an example, the AEZ-EF model, which has been frequently used in assessing ILUC emissions, is using the oldest version of this data set. To improve the quality and accuracy of ILUC estimates, this paper creates a new global data set of SOC by combining the latest version of the HWSD (V.2.0) with newly available national soil maps for the USA and Australia. Using this new data set, we then calculate the average SOC for each land cover type (cropland, pasture, and forest) by country and by agro-ecological zones (AEZs). Furthermore, we revised AEZ-EF model to adopt the new SOC data by land types. Finally, the revised AEZ-EF model is used to assess ILUC emissions for a few biofuel pathways to demonstrate the extent to which the new SOC data may affect ILUC emissions. The results of this paper indicate that the newest version of the HWSD represents a lower level of SOC at the global scale compared to its older version. The results also show that the revised AEZ-EF model calculates relatively lower ILUC emissions for the examined pathways compared to its older version.