عادی سازی در ارزیابی چرخه عمر محصول: ارزیابی چرخه عمر سیستم اقتصادی جهانی و اروپا در سال 2000 

In the methodological context of the interpretation of environmental life cycle assessment (LCA) results, a normalisation study was performed. 15 impact categories were accounted for, including climate change, acidification, eutrophication, human toxicity, ecotoxicity, depletion of fossil energy resources, and land use. The year 2000 was chosen as a reference year, and information was gathered on two spatial levels: the global and the European level. From the 860 environmental interventions collected, 48 interventions turned out to account for at least 75% of the impact scores of all impact categories. All non-toxicity related, emission dependent impacts are fully dominated by the bulk emissions of only 10 substances or substance groups: CO2, CH4, SO2, NOx, NH3, PM10, NMVOC, and (H)CFCs emissions to air and emissions of N- and P-compounds to fresh water. For the toxicity-related emissions (pesticides, organics, metal compounds and some specific inorganics), the availability of information was still very limited, leading to large uncertainty in the corresponding normalisation factors. Apart from their usefulness as a reference for LCA studies, the results of this study stress the importance of efficient measures to combat bulk emissions and to promote the registration of potentially toxic emissions on a more comprehensive scale.

Life cycle assessment of products (LCA) has become a widely recognised method for quantifying the environmental performances of products (c.f. EC, 2001 and Curran, 2006). Numerical scores make it possible to compare product alternatives on the aspects of climate change, ozone depletion, acidification, eutrophication, toxicity, fossil energy resource depletion, and more environmental impact categories. All environmental releases, fossil energy resource extractions and land use activities that belong to a product life cycle are translated and aggregated in the right proportions to deliver an environmental profile in terms of the overall contribution of the product to a limited number of impact categories (Guinée et al., 2002). A comparison of environmental profiles reveals the relative environmental performance of product alternatives in the context of every single impact category. Despite their apparent simplicity, however, LCA profiles are not in every respect interpreted so easily. Impact scores are expressed in complex units, and reflect environmental impacts in a way that does not correspond directly to perceptible problems or prevailing threats. Their absolute value as an assessment measure remains difficult to interpret as long as it is not placed in an adequate environmental context. This is what LCA normalisation aims at. LCA normalisation offers a reference situation of the pressure on the environment for each environmental impact category. Normalisation makes it possible to translate abstract impact scores for every impact category into relative contributions of the product to a reference situation. This reference situation exists of an environmental profile on a higher scale — that is, the environmental profile of an economic system that the product life cycle is considered to be part of. The fact that the normalisation results are expressed in the same unit for each impact score makes it easier to make comparisons between impact scores of different impact categories (Norris, 2001). Since product life cycles often have a global coverage – e.g. including resource extractions in diverse geographic regions – the global system is the most promising candidate to act as a reference situation (Guinée et al., 2002). A number of normalisation methods have appeared during the past 10 years. An overview is given in Table 1. Some methods are shown to be specific for a limited region or for a limited number of impact categories. This study can be considered as a follow-up of the study by Huijbregts et al. (2003), in which 1995 was used as the reference year, and which distinguished economic systems on three levels: the world, Western Europe, and The Netherlands. A follow-up was considered necessary for three reasons: ■ Acquiring more up-to-date emission and extraction data (year 2000 instead of 1995) and more up-to-date boundaries for the European region (28 instead of 15 countries); ■ Extending the number and improving the quality of emissions and extractions (although the availability and quality of the data for toxic emissions appeared to be still limited); ■ Including more up-to-date impact assessment models in the normalisation factor calculations for many impact categories, including global warming, ozone depletion, toxicity and acidification. The outcomes of this normalisation study can be interpreted as an LCA study of the economic systems as a whole on both the European and the global level. LCAs of economic systems can also be used in a broader context than normalisation, for instance by comparing the impacts of different economic systems with each other and by identifying the most important emissions or extractions within a specific impact impact category or economic system. Both aspects will be discussed and quantified.

This study has been performed in the context of LCA methodology, but the relevance of the results ranges much further. For LCA, this normalisation study is not only an update in the sense that it refers to a time step of 5 years in comparison to our former study (Huijbregts et al., 2003). Much more important is the fact that a large reduction in uncertainty could be reached by the increased data availability, resulting from a growing international awareness of the urgency of emission data reporting. Another important feature of these updated normalisation data is in their correspondence to up-to-date LCA midpoint characterisation factors. Although intended as a methodological step in LCA, this normalisation study can also be considered as an LCA case study in itself — with the economic system as the functional unit. The results of this study clearly indicate that the environmental profile of the global and European economic systems appears to be dominated to a large extent by only a small number of substances, released in bulk quantities. Large uncertainties remain to exist with respect to toxic substances. Current toxic release inventories are available for developed countries only. Releases in developing countries are very difficult to estimate, even by approximation. Moreover, characterisation factors are still lacking for many toxic chemicals, most probably because no or insufficient toxicity data is available. This combination makes it impossible to assess the magnitude of overall toxicity of chemicals, released to the environment, and thus to construct reliable normalisation factors for toxicity-related impact categories in LCA. An update of this normalisation study is recommended as soon as either supplemental emission information or new characterisation factors have become available. With a fast growing world economy, new, strictly controlled procedures for the abatement of bulk releases and the inventory of toxic releases, coupled to the identification of key toxic substances, are recognised to be of prior importance for global environmental management in the context of sustainability.