LCA Challenges As a young discipline, LCA faces many difficulties. There are problems with the amount and quality of data, problems in determining and weighting impact categories, and problems with generalizing LCA and making it practically relevant to those who should be using it. I have touched on some of these problems above: for example, the difficulty in establishing functional equivalence in comparing alternative materials and systems. Many discussions of LCA want to focus on the impact assessment stage, but probably the biggest challenges lay in the realm of the inventory, and the collection of raw data. This is crucial since garbage-in equals garbage-out. Different LCA tools use different sources. Some come from manufacturers, others from national averages derived from government estimates. Others use regional averages. When exact data is missing, assumptions have to be madefor example, in the transport distance between the mining and processing of certain ores. The lack of standardization of data sources presents real difficulties for users, and undermines the credibility of LCA in general. Another challenge in LCA is double-counting or the allocation of impacts. A windows environmental impact might be attributed to the window, the heating system, or a power plant. And when a company makes multiple products in the same process, resource and pollution flows have to be allocated among the products. Standards for LCA, such as those being developed through ISO, are trying to deal with these