It’s the decades-old question, which still hasn’t been adequately answered. These days when the environmental issue du jour is carbon emissions, the concerned citizen’s choice is a lot more complicated than earlier alternatives of saving trees or clogging landfills. Our assessment of “environmentally friendly” is constantly evolving; ironically, in the 1980′s “biodegradable” was the environmental buzzword, while now we are developing a more nuanced view because, for example, we are more aware of the environmental impacts of emissions which occur during biodegredation.
The Finnish Environmental Institute (SKYE) recently conducted a study on the complete life cycles of several different types of shopping bags in Finland. They estimated the total greenhouse gas emissions associated with use of paper, plastic and cotton bags, from production to disposal, and some of what they found may seem surprising.
Overall, it may come as good news that the impact of shopping bags on the larger universe of consumption-produced carbon emissions is relatively small. But within the context of that impact, it turns out that unless most paper bags are recycled (and most are not), recycled plastic is a better choice because it takes much less energy to produce.
But then the question arises: what is the proportion of plastic shopping bags in use that are recycled bags? This probably varies between Finland and the United States, but is a not easily answered. At present in the U.S. it seems that the majority of disposable shopping bags are produced directly from fossil fuel (usually natural gas), so this reduces the benefit of using plastic over paper.
It was clear from the study, though, that the bags to stay away from are “biodegradable” bags. This is because to increase their durability, fossil fuels are actually used in their production. This creates more emissions when bags are disposed of and they degrade, as opposed to regular plastic bags which do not degrade and thus do not add carbon to the atmosphere.
There has recently been increasing interest in the use of reusable shopping bags as a “pro-environment” choice. In Finland, the most common reusable bags are made of cotton, and it turns out that greenhouse gas emissions are so high for the production of the cotton to make the bags that a cotton bag must be used a minimum of 180 times before it becomes a better alternative to using a new recycled plastic bag each time. It was found in the study that “most” disposable plastic bags were reused as garbage can liners, which reduces the negative impact of a particular bag. This is certainly common practice, but one suspects it is more common in Finland than in the United States.
Interestingly, the reusable shopping bags rapidly coming into wide use in the United States are made of polypropylene, a type of bag not included in the study because it is not currently being promoted in Finland. Polypropylene bags are lightweight, strong, and often made of recycled plastic. In an interview, the authors of the study told me that these would certainly be the most sustainable option, requiring perhaps only 25 uses to be a better alternative to a disposable plastic bag. So the U.S. is ahead of Finland at least on that score.
The authors stress that even though the emissions impact of bags is low, there is demand by consumers to make more environmentally friendly choices, and thus the point of the study was to help to determine the direction in which further development of low-impact bags should go.
As a final note, even though we are now more aware of the impacts of emissions, and this awareness is beginning to affect consumer behavior, we should avoid repeating the same mistake that led to enthusiastic embrace of biodegradable products in the past: that one particular environmental impact (i.e. the current fad) is the only one that matters. Although this study was comprehensive in terms of emissions, it did not take into account other considerations such as the impacts of plastic litter on wildlife, and the broader implications of using a finite resource to produce a disposable product.
For now, the best option for the environmentally concerned is to forgo the paper vs. plastic question by buying a bunch of (preferably recycled) polypropylene bags at your favorite grocery store – many stores in the U.S. now carry the bags for about $1 apiece – and keep them in your car. Or, even better, keep them by your door and walk to your neighborhood market, thereby reducing emissions associated with shopping much more dramatically. One added advantage of reusable polypropylene bags is that they hold more and are easier to carry than either plastic or paper disposable grocery bags.
Then, say good-bye to those unruly wads of plastic shopping bags stuffed into kitchen drawers and cabinets, that you always planned to reuse but somehow rarely do.