As proposed by United Nations Environment Programme (UNEP)-Society for Environmental Toxicology and Chemistry (SETAC) Life Cycle Initiative (MilA i Canals et al., Int J Life Cycle Assess 18:1265-1277, 2007 and Koellner et al., Int J Life Cycle Assess 18:1188-1202, 2013), the impacts of land occupation should be studied in comparison to a baseline. Regardless of these guidelines, a land use baseline is often ignored in agro-bioenergy life cycle assessment (LCA) studies. This paper tests the appropriateness and significance of applying natural regeneration as a land use baseline for assessing the greenhouse gas (GHG) balances of agro-bioenergy in Finland. In the land use baseline applied, the land is assumed to be left to regenerate toward its natural state, which, in Finland, would most probably be some sort of forest. The foregone carbon stock of the natural regeneration baseline was estimated based on the literature. The GHG balances were studied by comparing the cumulative warming impacts of the dynamic biomass carbon cycle of the agro-bioenergy production system and the defined baseline over a given time horizon varying from 0 to 100 years. The significance of the results is illustrated by comparing them to other GHG emissions related to bioenergy. The results depend significantly on the agro-bioenergy yields and the carbon sequestration rate assumed in the natural regeneration baseline scenario. The GHG balances may be of the same magnitude as GHG emissions due to indirect land use changes resulting from market-mediated impacts, life cycle emissions of fossil fuels, and relative reduction in carbon stocks due to forest harvesting for bioenergy. Ignoring a dynamic land use baseline results in misleading conclusions on the GHG balances of land occupation, including agro-bioenergy, due to ignorance of foregone carbon sequestration. Thus, the interpretation of the results and conclusions provided in the vast number of agro-bioenergy LCA studies relying on biomass carbon neutrality should be reassessed. Besides bioenergy, the issue of land use baseline is relevant for any provision service function of land occupation. The foregone carbon sequestration is, however, highly uncertain and thus speculative.
