9.1 Life cycle assessment  (Page 9/18)

Incommensurability

Sometimes LCA impact categories, such as those shown in Table Common Impact Categories and Their References , overlap in the sense that the same pollutant may contribute to more than one category. For instance, if a given assessment comes up with high scores for both aquatic toxicity and human toxicity from, say, pesticide use then one might be justified in using both of these categories to draw conclusions and make choices based on LCA results. However, more typically elevated scores are found for categories that are not directly comparable. For instance, the extraction, refining, and use of petroleum generate a high score for global warming (due to GHG release), while the product chain for the biofuel ethanol has a high score for eutrophication (due to nitrogen release during the farming stage). Which problem is worse – climate change or coastal hypoxia? Society may well choose a course of action that favors one direction over another, but in this case the main value of the LCA is to identify the tradeoffs and inform us of the consequences, not tell us which course is “correct.”

Risk evaluation and regulation

One of the inherent limits to LCA is its use for assessing risk. Risk assessment and management, as described in the Modules The Evolution of Environmental Policy in the United States and Modern Environmental Management , is a formal process that quantifies risks for a known population in a specific location exposed to a specific chemical for a defined period of time. It generates risk values in terms of the probability of a known consequence due to a sequence of events that are directly comparable, and upon which decisions on water, land, and air quality standards and their violation can be and are made. LCA is a method for evaluating the impacts of wastes on human health and the environment from the point of view of the product/service chain rather than a particular population. It can be used to identify the sources of contamination and general impacts on the environment – a sort of “where to look” guide for regulation, but its direct use in the environmental regulatory process has been, to date, rather limited. One application for LCA that has been suggested for regulatory use is for assessing the impacts of biofuel mandates on land use practices, in the United States and other regions, however no regulatory standards for land use have yet been proposed.

Tools for conducting lca

Fortunately a number of databases and tools, in the form of computer software, are available to assist in carrying out LCAs. This is an active area of development; in this section a few of the more well-known and widely used tools are described.

The greenhouse gases, regulated emissions, and energy use in transportation model (greet)

GREET is a spreadsheet-based database developed by Argonne National Laboratory that links energy use to emissions on a life cycle basis. Early versions were limited to greenhouse gases, but as the model has been refined many other types of contaminants have been added. Although it has been widely used for comparing transportation and fuel options (hence its title), GREET has been used for many other applications that have a significant energy component, including agriculture, material and product development, and strategies for recycling.