Allocating the environmental burdens of open-loop metals recycling is a polarizing and contentious issue for the life cycle assessment (LCA) community. LCA practitioners have developed numerous approaches, yet few studies have quantitatively evaluated their assumptions and compared their results. Consequential and systems-expansion approaches, which aim to quantify the indirect effects of recycling, have received very little scrutiny of their suitability for metals. These approaches most often rely on assumptions of market behavior and introduce layers of complexity not encountered in traditional LCA. We analyze the performance of four allocation approaches for calculating greenhouse gas (GHG) emissions for aluminum. Two of these approaches, value corrected substitution (VCS) and end-of-life recycling (EOLR) have been specifically advocated for aluminum. We find that the VCS approach, as well as the market-based approach, fails to capture the temporal nature of aluminum recycling and GHG emissions. More seriously, the EOLR approach is found to distort the timing of material flows and emissions relative to the recycled content (RC) approach in two case studies. The case study of a hypothetical fleet of aluminum automotive engine blocks finds that emissions associated with initial production account for over 99% of total GHG emissions using the RC approach and 36% to 50% using the EOLR approach. Estimated total GHG emissions in the same case study are 18% and 79% larger using the EOLR approach than the RC approach. The distortion of the timing of emissions has particular implications for climate change, as well as any other emission with time-dependent impacts. Additional analysis of the effects of emissions timing is performed using a time correction factor for carbon dioxide.
CSS Publication Number:
Colin McMillan and Gregory Keoleian. “Evaluating The Ability Of Recycling Allocation Approaches To Capture The Timing Of Material Flows And Emissions For Aluminum.” 6th International Conference of the International Society for Industrial Ecology (ISIE) Proceedings. Berkeley, CA, June 7-10 2011, Abstract #354.