A review of LCA greenhouse gas emissions results for advanced biofuels: The use of meta-regression analysis

This article presents the results of a literature review performed with a meta-regression analysis (MRA). It focuses on the estimates of advanced biofuel Greenhouse Gas (GHG) emissions determined with a Life Cycle Assessment (LCA) approach. The mean GHG emissions of both second (G2) and third generation (G3) biofuels and the effects of factors influencing these estimates are identified and quantified by means of specific statistical methods. 47 LCA studies are included in the database, providing 593 estimates. Each study estimate of the database is characterized by (i) technical data/characteristics, (ii) author's methodological choices and (iii) typology of the study under consideration. The database is composed of both the vector of these estimates-expressed in grams of CO2 equivalent per MJ of biofuel (g CO(2)eq/Mn and a matrix containing vectors of predictor variables which can be continuous or dummy variables. The former is the dependent variable while the latter corresponds to the explanatory variables of the meta-regression model. Parameters are estimated by means of econometrics methods. Our results clearly highlight a hierarchy between G3 and G2 biofuels: life cycle GHG emissions of G3 biofuels are statistically higher than those of Ethanol which, in turn, are higher than those of BtL. Moreover, this article finds empirical support for many of the hypotheses formulated in narrative literature surveys concerning potential factors, which may explain estimates variations. Finally, the MRA results are used to address the harmonization issue in the field of advanced biofuels GHG emissions thanks to the technique of benefits transfer using meta-regression models. The range of values hence obtained appears to be lower than the fossil fuel reference (about 83.8 in g CO(2)eq/MJ). However, only Ethanol and BtL do comply with the GHG emission reduction thresholds for biofuels defined in both the American and European directives. (C) 2013 Elsevier Ltd. All rights reserved.