RESEARCH AND ANALYSIS Uncertainty and Sensitivity in the Carbon Footprint of Shopping Bags Tuomas Mattila, Marjukka Kujanp¨ a¨ a, Helena Dahlbo, Risto Soukka, and Tuuli Myllymaa Keywords: climate change industrial ecology life cycle assessment (LCA) Monte Carlo simulation plastic waste treatment Address correspondence to: Tuomas Mattila Finnish Environment Institute (SYKE) Mechelininkatu 34 a 00251 Helsinki Helsinki 00251 Finland tuomas.mattila@ymparisto.ﬁ c  2011 by Yale University DOI: 10.1111/j.1530-9290.2010.00326.x Volume 15, Number 2 Summary Carbon footprints for several shopping bag alternatives (polyethylene, paper, cotton, biodegradable modiﬁed starch, and recycled polyethylene) were compared with life cycle as- sessment. Stochastic uncertainty analysis was used to study the sensitivity of the comparison to scenario and parameter uncertainty. On the basis of the results, we could give only a few robust conclusions without choosing a waste treatment scenario or limiting the parameter space. Given the scenario of current waste infrastructure in Finland, recycled polyethylene bags seem to be the most preferable (−7 to 24 g CO 2 eq./bag) and biodegradable bags the least preferable (38 to 60 g CO 2 eq./bag) option. In each analyzed waste treatment scenario, a few parameters dominated the uncertainty of results. Most of these parameters were downstream of the shopping bag manufacturing (consumer behavior, landﬁll conditions, method of waste combustion, etc.). The choice of waste treatment scenario had a greater effect on the ranking of bags than pa- rameter uncertainty within scenarios. This result highlights the importance of including several scenarios in comparative life cycle assessments. www.wileyonlinelibrary.com/journal/jie Journal of Industrial Ecology 217