Breaking down the Danish study on the environmental impacts of grocery carrier bags
By Parkpoom Kometsopha | April 18, 2019 | Parkpoom Kometsopha
Last weekend, I came across several viral news articles on Facebook discussing the environmental impacts of grocery carrier bags. They reported that organic cotton bags are much worse than plastic bags and that conventional cotton bags are better than organic cotton ones. All of them had those classic controversial headlines: “Your cotton tote is pretty much the worst replacement for a plastic bag” or “Bad news! Cotton bags have more impacts than plastic bags!!” and so on.
At first, I didn’t want to bother much about them since these articles tend to use invalid references (at least in my experience). However, when I saw that all of their sources came from a study published last year by the government of Denmark — a country that is seriously committed to sustainability — they certainly got my attention.
About the study
This particular study is about Life Cycle Assessment (LCA) of grocery carrier bags in Denmark, which assesses the environmental impacts of various carrier bag types used in the country and later compares the results between them. It considers the whole life-cycle of the products, starting from the raw material acquisition until their end-of-life.
Accordingly, one of its conclusions was that the conventional and organic cotton bags must be used at least 7,100 and 20,000 times respectively in order to meet the environmental performance of LDPE plastic bags. These figures were actually quite surprising, even for me; I know cotton bags need to be reused multiple times before they have lower impacts than plastic bags, but I did not expect the numbers to be THAT much. All of the articles I read so far presented both numbers.
However, was that conclusion accurate? Can cotton bags have such tremendous impacts over plastic bags?
After diving into the research paper, I’d say yes — AND no.
Yes, because the result of the study was presented indeed according to its methodological framework with full data disclosure. The authors also briefly discussed the limitations of their research method as well as the alternative result under a different assumption and scenario.
No, because I believe the framework and the result put the cotton bags at a disadvantage, especially the organic bag, and the authors failed to mention it. It would be difficult for readers without basic knowledge of LCA to make a correct interpretation of the research’s method and the result — hence, these controversial articles.