This article is based on the work of the SETAC-Europe LCA Working Group ‘Scenario Development in LCA’, which has started its work in April 1998. The goal of the Working Group is to focus on the use of scenarios in Life Cycle Assessment (LCA). This article presents the results of the first phase of the Working Group. The previous definitions of scenarios include three common basic elements: the definition of alternative future circumstances, the path from the present to the future, and the inclusion of uncertainty in the concept. We define a scenario in LCA as “a description of a possible future situation relevant for specific LCA applications, based on specific assumptions about the future, and (when relevant) also including the presentation of the development from the present to the future.’
On the basis of the scenario definition we distinguish between two basic approaches for scenario development in LCA studies: What-if scenarios and Cornerstone scenarios. What-if scenarios are used to gain operational information and to compare two or more alternatives in a well-known situation with a short time horizon where the researcher is familiar with the decision problem and can set defined hypothesis on the basis of existing data. The Cornerstone scenario approach offers strategic information for long term planning, new ways of seeing the world, and also guidelines in the field of study. Results of a study using the Cornerstone scenario approach often serve as a basis for further, more specific research where the scenarios can be defined according to What-if scenarios.
The frames of the scenarios are defined in the first phase of LCA, the goal and scope definition. Scenario development does, however, influence all of the following phases of LCA. The frames of the scenarios form the basis for modelling product systems and environmental impacts associated with products and services, which are not exactly known due to lacking information on parts of the life cycle.
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Metrics (potentials, potency factors, equivalency factors or characterization factors) are available to support the environmental comparison of alternatives in application domains like process design and product life-cycle assessment (LCA). These metrics typically provide relative insights into the implicit concern associated with chemicals, emissions and resource consumption in the context of human health, ecological health and resource depletion. The approaches used to derive the metrics range in their site-specificity, complexity, comprehensiveness, sophistication and uncertainty. It is therefore often necessary to consider the use of more than one approach within the context of a given impact category to help support a decision. In this paper we outline some of the strengths and weaknesses of available approaches in the commonly considered categories of global warming, tratospheric ozone depletion, tropospheric ozone (smog) creation, eutrophication/nutrification, acidification, toxicological impacts and resource depletion.
The main problem involved in valuing resource depletion is that the effect or damage occurs in the future and therefore our assessment depends on our assumptions on how this future looks like.
Resource depletion may not in itself be a problem if there is adequate time for humanity to develop technologies to deal with an imminent depletion, i.e.:
· technologies for harvesting adequate amounts of sustainable energy, and/or
· technologies (including societal arrangements) for a voluntary regulation of the size of the human population so that it becomes stable and adjusted to a size which can be sustained by the actual size of the resource basis.
The problem is that these technologies may not be developed in time to avoid damage during the transition period.
Market-based system delimitation may reduce the need for data collection in life cycle assessments (LCAs) without compromising reliability. Rather than including all potential suppliers and customers (e.g. in a weighted average), the market-based procedure allows the data collection to be reduced to those suppliers and customers, which are actually affected by a studied product substitution. Furthermore, the uncertainty on the market data will most often determine the level to which the overall uncertainty of the LCA can be reduced, thus providing a limit for what process data it is meaningful to collect.
The need for improvement of LCA performance is discussed with a starting point in the demands for comprehensiveness, reliability, simplicity, and integration into day-to-day management. It is argued that simplicity can be achieved without compromising comprehensiveness and reliability. The necessary improvements are discussed in a number of development areas: standard procedures, data verification, assessment techniques, understanding of uncertainties, software.
Two purposes for normalization in LCA are presented: resolving non-commensurate units, and assessing significance. Two families of approach for normalization in LCA are described: internal and external. The need for congruence between the normalization and valuation is illustrated by showing the nonsensical conclusions which can result from an approach that is common in North American LCA applications: internal normalization with external valuation. In order to achieve congruence with internal normalization methods, valuation in such instances must be case-specific. External normalization methods bring an added benefit not provided by internal normalization methods: an assessment of relative significance.
The private sector decision making situations which LCA addresses must also eventually take the economic consequences of alternative products or product designs into account. However, neither the internal nor external economic aspects of the decisions are within the scope of developed LCA methodology, nor are they properly addressed by existing LCA tools. This traditional separation of life cycle environmental assessment from economic analysis has limited the influence and relevance of LCA for decision-making, and left uncharacterized the important relationships and trade-offs between the economic and life cycle environmental performance of alternative product design decision scenarios. Still standard methods of LCA can and have been tightly, logically, and practically integrated with standard methods for cost accounting, life cycle cost analysis, and scenario-based economic risk modeling. The result is an ability to take both economic and environmental performance — and their tradeoff relationships — into account in product/process design decision making.
