5. Conclusion
The uncertainty in waste management LCA arising from uncer¬tainty in waste composition has been less extensively studied than uncertainty stemming from the choice of system boundaries, tech¬nology and energy replacement. In this paper we have systemati¬cally modified the average waste composition estimated from the waste composition of five Norwegian cities. We found that a ±15% change in selected fractions resulted in a greater than 10% change in global warming, nutrient enrichment and human toxic¬ity via water impact categories. Hence, such LCA impacts are highly sensitive to uncertainties in waste composition. If the quantities of source-separated material are known the uncertainty is low for most categories, but still 10% for global warming. A percentage change in the large fractions - paper, plastic and food waste - is of most importance, together with changes in the metal content. When comparing scenarios, the results are more robust. The anal¬ysis of the five cities showed wide variation in waste composition in the municipalities, and using a waste composition from another city or an estimated average can influence the result of a study. Having good data on the quantity of waste recycled, and the qual¬ity of this waste is of importance for the reliability of the results.