LETTER pubs.acs.org/est
New Paradigm or Old Distance to Target? n the Viewpoint “Do we need a paradigm shift in life cycle impact assessment?” by Huijbregts, Hellweg, and Hertwich (Environ. Sci. Technol. 2011, 45, 3833 3834) Huijbregts, Hellweg, and Hertwich (HHH) question whether the marginal approach typically applied in life cycle impact assessment (LCIA) “is truly representing what we are looking for in LCA” and “advocate to further explore the benefits of following an average approach in the derivation of characterization factors”. What HHH propose is using characterization factors per unit of emission, which “represents the average distance between the current and the preferred state of the environment.” This is in fact not a new paradigm for impact assessment, but a simple normalization relative to a target, as we know it from some of the early LCIA methods such as EDIP (Hauschild & Wenzel 1998, ref 2) and the Swiss ecoscarcity method (Frischknecht et al. 2006, ref 1). One problem with distance-to-target methods is the inherent arbitrariness of political targets. Large problems that are difficult to handle are often not receiving due political attention, while ambitious targets are set for small and easily manageable problems. Targets are often set in roughly the same distance relative to the current situation. In this way, distanceto-target methods disregard the actual severity of the individual issues and the societal value of improvement in environmental conditions as measured by the marginal willingness-to-pay for the benefits of the improvements. In the LCIA methods that use distanceto-target, the distance-to-target is used as a valuation factor on the characterized midpoint results, that is, at the level of environmental problems such as global warming, acidification, etc. Now, HHH suggest using distance-to-target already in the characterization. This is at odds with the intention of characterization in ISO 14040 which stresses the “ability of the category indicator to reflect the consequences of the LCI results on the category end point(s).” It is also difficult to see how HHH intend that this should work in practice: If you only have a target for GWP (radiative forcing), what is the distance of CO2 and CH4 from this
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target? And if you set individual targets for CO2 and CH4, for example, based on their preindustrial levels, this would mean that substances that have been emitted in relatively smaller quantities (CH4) would get a smaller characterization factor than those emitted in large quantities (CO2), disregarding their radiative forcing (because radiative forcing is then not the target)? Using normalization as a substitute for characterization according to severity results in exactly the effect warranted by HHH: • Impacts above the target are valued relative to the distance-to-target (leading to high values also for negligible impacts on already destroyed environments, leading to more effort to revert the situation for these farfrom-target impacts, and relatively lower values for impacts that lead to large changes in the environment and can be avoided at less effort, and thus an overall lower efficiency in reducing the overall impacts). • Impacts at the target are ignored (because they are accepted by the target-setting authority). I fail to see that this should amount to a new paradigm, and even more that these results should be desirable. Bo P. Weidema* Aalborg University, 9220 Aalborg East, Denmark
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ REFERENCES (1) Frischknecht, R.; Steiner, R.; Braunschweig, A.; Egli, N.; Hildesheimer, G. Swiss Ecological Scarcity Method: The New Version. 2006. (2) Hauschild, M.; Wenzel, H. Environmental Assessment of Products: Scientific Background; Kluwer Academic Publishers: Boston. Hardbound, 1998; Vol. 2, ISBN 0-412-80810-2.
r 2011 American Chemical Society
Received: November 13, 2011 Accepted: November 15, 2011 Published: December 01, 2011 570
dx.doi.org/10.1021/es204049x | Environ. Sci. Technol. 2012, 46, 570–570
