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In its new report titled Guidance on Life-Cycle Thinking and Its Role in Environmental Decision Making, the Sustainable Materials Management Coalition (Coalition) takes a new look at how life-cycle assessment outcomes can and should be shaped by life-cycle thinking. In so doing, LCAs can be tailored to define the scope, the level of detail, the data required, and the questions that need answers.
A case in point is the widely held belief that buying food locally is the most environmentally friendly way to minimize transportation-related greenhouse gas (GHG) emissions associated with transporting food. In a 2008 life-cycle inventory performed by Carnegie-Mellon, researchers found that, in fact, “83% of the average U.S. household’s annual carbon footprint for food comes from producing the food (such as from the energy used to power farm equipment and the use of fertilizers that derive from natural gas).” In reality, transportation was responsible for only 11% of GHG emissions.
But the scope of this LCA was limited only to GHG implications related to food and buying local and did not address other potential environmental or health issues or the chronic problem of food waste. Several later studies did broaden the scope of the LCA to include food waste, and one performed in 2011 by Clean Metrics in Portland, Oregon, found that “for the U. S., ‘avoidable’ food loss accounted for nearly 29% of annual food production by weight” with 60% of the avoidable food loss taking place at the consumer stage. When calculating for GHG emissions related to avoidable food loss, the study concluded the life-cycle of the wasted food, from production through disposal, at distribution, retail, and consumer levels, was responsible for 2% of the nation’s total GHG emissions.
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According to the Coalition, these two examples demonstrate the importance of determining what questions an LCA is meant to answer so that the scope can then be defined. “The scope should be broad enough to address the question at hand, while avoiding analysis of factors that add work, but do not contribute to better understanding of the potential activity under consideration. You should acknowledge any limitations in scope, so that all limitations are clearly understood.”
Another important distinction made by the Coalition concerns the U.S. Environmental Protection Agency’s (EPA) waste hierarchy, which places source reduction and waste prevention at the top. According to the Coalition, while LCAs and life-cycle thinking do not replace the waste hierarchy, “the hierarchy was never intended … to provide prescriptive answers applicable to any particular situation or choice, and life-cycle thinking can provide significant insight for specific decisions.”
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As an example, the Coalition cited an LCA performed in 2000 by Proctor & Gamble to assess the life-cycle effects of their laundry detergents. After researching all life-cycle stages and a broad range of environmental impacts, the researchers discovered something that might have been missed if the scope had been different. This finding was that the greatest impacts occurred not in resource extraction, processing, manufacturing, transportation, or disposal but, again, at the consumer level, specifically as a result of heating water in residential washing machines. Just this one aspect of the product life cycle was found to be responsible for 80% of the energy used, 70% of the GHGs emitted, and more than 60% of the toxic emissions associated with the products. As a result of the findings, the company developed detergents that were as effective in cold water as earlier detergents were in hot water, leading an industrywide trend.
At the same time, however, keeping the waste hierarchy in mind remains a good idea because many LCAs show that the early stage of a product’s life cycle bears the burden of the most environmental impacts. Thus, finding ways to use less source materials or more preferable ones from the start may actually be a better idea than attempting to find a better disposal strategy.