Life Cycle Impact Assessment Weights to Support Environmentally Preferable Purchasing in the United States

Abstract

LCA is a quantitative method for understanding the environmental impacts of a product, yet all product purchasing decisions are ultimately subjective. Weights are the nexus between the quantitative results of LCA and the values-based, subjective choices of decision makers. In May 2007, NIST introduced a new optional weight set in Version 4.0 of the BEES software. Three key points about this new optional weight set are the basis for discussion in this paper: The new weight set was created specifically in the context of BEES. It is intended to support a practical method to assist environmentally preferable purchasing in the United States based on LCIA results. This is in contrast to the weight sets currently in BEES, which are based on generalist perspectives. The new weight set was created by a multi-stakeholder panel via the AHP method, and is a synthesis of panelists' perspectives on the relative importance of each environmental impact category in BEES. The weight set draws on each panelist's personal and professional understanding of, and value attributed to, each impact category. While the synthesized weight set may not equally satisfy each panelist's view of impact importance, it does reflect contemporary values in applying LCAto real world decisions, and represents one approach others can learn from in producing weight sets. The new weight set offers BEES users an additional option for synthesizing and comparing the environmental performance of building products and making purchasing decisions. In so doing, it strengthens the decision-making process, which is important when making product comparisons in the public domain. The Weight Set: Across all panelists and with explicit consideration of all time horizons, anthropogenic contributions to global warming, weighted at 29%, was judged most important, yet not so important that decisions can be made solely on the basis of this impact. A strong tail of other concerns include fossil fuel depletion (10%), criteria air pollutants (9%), water intake/use (8%), human health cancerous effects (8%), ecological toxicity (7%), eutrophication of water bodies (6%), land use (6%), and human health noncancerous effects (5%). Also of interest are the identified impact areas of concern assigned the lowest weights: smog formation (4%), indoor air quality (3%), acidification (3%), and ozone depletion (2%). Their low weights may indicate that there is not as much immediate concern or that the remedial actions associated with the impact for the most part are underway.

Interpretation of comparative LCAs: external normalization and a method of mutual differences

“…Given subjectivity concerns, and a general lack of information regarding decision-maker preferences, most LCAs truncate results at characterization, at external normalization, or apply Bequal weights^ (Prado-Lopez et al 2016). However, where analysis continues beyond these stages, weight values can be derived from a panel of experts in a professional field (Gloria et al 2007), through surveys (Schmidt et al 2002), monetization or willingness-to-pay techniques (Finnveden 1999), linear programming (Cortés-Borda et al 2013), and distance-to-target approaches (Seppälä and Hämäläinen 2001). Alternatively, in the absence of preference information, novel stochastic approaches in LCA provide a useful way to sample all possible weight values without favoring any single impact category thus enabling an inclusive view of the problem (Rogers and Seager 2009;Prado-Lopez et al 2014).…”

Environmental Decision-Making Using Life Cycle Impact Assessment and Stochastic Multiattribute Decision Analysis: A Case Study on Alternative Transportation Fuels

“…While completely disallowing compensation between criteria is not feasible, SMA-LCIA uses a partially compensa- (22).…”

Environmental LCA and Financial Analysis to Evaluate the Feasibility of Bio-based Sugar Feedstock Biomass Supply Globally: Part 2. Application of Multi-Criteria Decision-Making Analysis as a Method for Biomass Feedstock Comparisons

“…Environmental impact categories included are shown in Table 1. SMAA-LCIA (Rogers and Seager 2009;Prado-Lopez et al 2014) was conducted using midpoint impact values for each impact category and the Gloria et al (2007) weighting set for producers. Environmental preference probability distribution functions were developed for each alternative and a single score was calculated from this for ranking purposes.…”

“…These weighting values reflect a biorefiner's values with respect to the importance of various environmental impact categories. The LCIA impact category weight values used herein during SMAA were derived from weighting values developed by Gloria et al (2007) for producers (herein "biorefiners"). .…”

“…Thus, relative weighting of the TRACI impact categories for a biorefinery that was applied towards the environmental preference single score were converted to this +/-scale, as outlined in Table 4. No weights of "--" or "+ +" were assigned because weighting for each impact category for the biorefiner was relative to greater and lesser category weight values for LCA users and LCA experts (Gloria et al 2007). The coefficient of variation values for LCIA mean values for each impact category for each feedstock alternative are provided in Table 5.…”