You don’t need to look far to find convincing articles saying that plastic bags are the most environmentally friendly way to carry home groceries, but Consumer Ecology advocates that focusing on the bags themselves is far less important than what’s inside of them.
A recent Danish Government study (Bisenella et al., 2018) found that a cotton bag would need to be reused 7,100 times to equal all measured environmental impacts. With results like this, one might be inclined to think that Consumer Ecology is going to strike it rich with its new grocery bag fashion line, but this conclusion is misleading. When comparing very small impacts to impacts that are 7,100 times larger, the impact of a cotton bag is still very small. However, if you just look at carbon, it only needs to be reused 52 times.
Figure 1 shows the carbon footprints of different types of bags compared to different types of proteins. The Danish study states that the carbon footprint of the conventional cotton bag is 3.9 kg CO2e, which is equivalent to 0.44 gallons of gasoline. If your plastic bag is holding a pound of beef, it’s holding 14.31 kg CO2e (Clune et al., 2017), which is equivalent to 1.61 gallons of gasoline. If you decide to opt for a pound of split peas instead, which provides the same amount of protein, you’ll emit 0.72 kg CO2e (Clune et al., 2017), which is equivalent to 0.08 gallons of gasoline, and you can buy 3 cotton tote bags with your new environmental savings. Moving from a pound of chicken at 2.49 kg CO2e (Clune et al., 2017) to split peas saves 1.5 kg CO2e, so it would take 2.2 pounds of split peas to offset 1 cotton tote bag.
You can’t include multiple times the same chart.
To illustrate how much more important your food choices are for climate change than the bags you use, the comparison made in Figure 1 was for only 1 pound of protein compared to a year’s use of bags. The protein in 1 pound of peas/chicken/beef will only cover your protein needs for about 2 days. If the full year was used for protein in Figure 1, all the bags would look like 0 gallons in comparison. While 7,100 times may seem like a lot of reuse for a cotton bag, it would take 746 plastic bags to equal the climate impact of just 1 pound of beef.
While national policy makers and researchers might be interested in these comparisons, we can see in front of our eyes how damaging these bags are when they inevitably escape into the environment and end up in a bird or whale’s stomach. Being conscious of how much waste we create and setting examples for others is much more impactful than switching from a renewable resource to a nonrenewable resource, paradoxically in the name of sustainability.
Consumer Ecology’s take home message on grocery bags is that you should buy the bag that makes you feel the best about your purchase, and use it as many times as you can. You can equal the climate impact of the Danish high density bag standard if you use your cotton bag once a week for a year, and the recycled plastic reusable bags have even smaller environmental impacts than grocery bags, if used for a year. Before we start criticizing cotton bags, let’s take a look at what’s inside of them first.
Assumptions
- 24.2 g LDPE bag in Bisinella et al. (2018) is 4.4 times heavier than the 5.5 g American grocery bag (Hellman, 2009). The carbon footprint of 0.082 kg CO2e / bag in Bisinella et al. (2018) is divided by 4.4 to obtain the approximate emissions of an American grocery bag (0.019 kg CO2e). It is then compared to using a reusable bag once per week for 1 year, which is 52 grocery bags thrown away.
- Assumed 2 unbleached paper bags (double bagged) that were recycled at the end of life, as assumed in Bisinella et al. (2018).
- Carbon footprint of proteins is for cradle to grave. For more information, see: What is the Most Environmentally Friendly Protein?
References
Bisinella, V. Albizzati, P.F., Astrup, T.F., & Damgaard, A. (2018). Life Cycle Assessment of Grocery Carrier Bags.
Clune, S., Crossin, E., & Verghese, K. (2017). Systematic review of greenhouse gas emissions for different fresh food categories. Journal of Cleaner Production, 140, 766-783.
Hellman, A. (2009). Plastic Bags: To Recycle or Not: Essential Answer. See Link to Source
