LCA Food 2012 in Saint Malo, France! - Manifestations et colloques ...

GROUP 6, SESSION B: METHODS, TOOLS, DATABASES 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
182. Analysis and propagation of uncertainty in agricultural LCA
Xiaobo Chen 1,2,* , Michael Corson 1,2
1 INRA, UMR1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France, 2 Agrocampus Ouest,
F-35000 Rennes, France, Corresponding author. E-mail: xiaobo.chen@rennes.inra.fr
The confidence in LCA results depends primarily on the quality of source data and their pertinence for the
system studied. However, the need for large amounts of data leads to much uncertainty in impact estimates
due to the data themselves: measurement, use in calculations, and final transformation into impact estimates.
The main sources of uncertainty in the data chain include not only statistical uncertainty (mean and standard
deviation) of the data, but also methodological choices in LCA, such as hypotheses made to represent the
system of interest, data representativeness, impact assessment methods, and allocation of impacts between
co-products. Therefore, consideration of uncertainty in LCA would provide more scientific information for
decision making. This topic is the focus of doctoral research recently begun at INRA that aims to (1) identify
sources of uncertainty in agricultural-production systems, (2) analyse their propagation, and (3) estimate
their relative contributions to the overall uncertainty in calculated impacts.
Although some texts describe uncertainty generally as a lack of knowledge, its definition may change depending
on the LCA steps in which it occurs (Huijbregts, 1998). Therefore, uncertainty is often classified
according to its nature and source (e.g., “natural” (i.e., variability) vs. “epistemic”; Van Asselt and Rotmans,
2002). Epistemic uncertainty has been subdivided into three sources: scenario, model and parameter (Fig. 1).
This first step allows uncertainties from each source to be evaluated by corresponding approaches.
Monte-Carlo analysis is used most frequently to evaluate uncertainty in LCA (Basset-Mens, 2009). With it
one can estimate the influence of uncertainties in input variables (using their probability distributions) on
predicted potential impacts. However, this approach suffers some methodological bias due to correlations
between variables and poorly-known response rules. For example, the selection of appropriate distributions
is usually based on literature, expert judgment, or empirical studies in other systems, which may increase the
complexity of model and parameter uncertainty. Moreover, Monte-Carlo simulation is commonly used for
assessing the influence of uncertainty in emission factors in LCIA, but it may not be appropriate for uncertainty
in other steps, such as the definition of scope or functional unit or the interpretation of results that consist
of both subjective and objective uncertainty (Fig. 2). Although it is not necessary or possible to consider
all uncertainties in LCA, subjective uncertainty should not be overlooked. More complex approaches (e.g.,
fuzzy logic) exist, but their use remains marginal. Currently, the methods used to describe uncertainty propagation
in LCA have not tried to differentiate the various types of uncertainty but rather to aggregate them.
Thus, more research is necessary to overcome barriers to analysing uncertainty in LCA.
Thesis work will begin by identifying and classifying uncertainty in each LCA step, especially uncertainties
frequently encountered when assessing agricultural systems. With case studies, the research will identify the
most important uncertainties, develop methods to categorise them, and work to estimate the contribution of
each source of uncertainty to the overall uncertainty in output. By considering uncertainty in agricultural
LCA, more complete information about environmental impacts can be given to decision-makers, who should
consider uncertainty as an important part of decision analysis.
References
Basset-Mens, C., Kelliher, F.M., Ledgard, S., Cox, N., 2009. Uncertainty of global warming potential for
milk production on a New Zealand farm and implications for decision making. Int. J.LCA 14, 630-638.
IPCS, 2008. Uncertainty and Data Quality in Exposure Assessment. Geneva, World Health Organization,
International Programme on Chemical Safety (Harmonization Project Document No. 6).
Huijbregts, M.A.J., 1998. Application of uncertainty and variability in LCA. Part I: a general framework for
the analysis of uncertainty and variability in life cycle assessment. Int. J. LCA 3, 273-280.
Van Asselt, M.B.A., Rotmans, J., 2002. Uncertainty in integrated assessment modelling. Int. J. LCA 54, 75-
105.
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