Abstract
In order to understand the climate effects of a bioenergy system, a comparison between the bioenergy system and a reference system is required. The reference system describes the situation that occurs in the absence of the bioenergy system with respect to the use of land, energy, and materials. The importance of reference systems is discussed in the literature but guidance on choosing suitable reference systems for assessing climate effects of bioenergy is limited. The reference system should be chosen to support appropriate comparisons between the studied bioenergy system and the reference system. Transparency of reference system assumptions is essential for proper interpretation of bioenergy assessments. This paper describes options for selecting suitable reference systems. Particular attention is given to aligning the land reference system with the goal of the study. If the goal is to study the climate effects of bioenergy as a part of total anthropogenic activity the reference system should illustrate what is expected in the absence of human activities, and suitable land reference is natural regeneration. If the goal is to assess the effect of a change in bioenergy use, the reference system should incorporate human activities and suitable land reference system describes the most likely alternative use of the land. It can be instructive to consider how alternative reference systems influence the results and conclusions drawn from bioenergy assessments.
