9-05: Mathematical Consistency and Validity in Indirect Land Use Change (iLUC): the Numbers Do Not Add Up

Both the United States Environmental Protection Agency and the California Air Resources Board are using life cycle assessment models combined with agro-economic models in an attempt to understand the impacts of biofuel production on potential greenhouse gas releases associated with indirect land use change. Global agricultural economic models comprise a multi-input/output system involving numerous economic activities.  To determine the consequence of each individual economic activity, such as the production of different types of biofuels, the activity of interest must be isolated from the whole economic system. This isolation process in iLUC is an attribution function: the consequence of each change is assigned or attributed to a specific economic activity. The same approach is used for allocation in life cycle assessment.  In most iLUC calculations, the amount of one type of biofuel is changed, either the one of interest to the particular study or all of the different biofuels but one at a time, to isolate its consequence, while other biofuel volumes remain constant. The sum of consequences (e.g., global harvested crop areas) when biofuels are shocked one at a time must be equal to the case in which all biofuels are shocked simultaneously. This is a simple mathematical consistency requirement.  However, we are not aware of any iLUC studies that have been tested or justified by applying this important, fundamental mathematical test. Models which do not satisfy this fundamental mathematical test should not be relied upon for policy and regulation: the numbers do not add up.