The eco-conscious community has embraced certain sustainable practices as unquestionably beneficial: walking to work in lieu of driving, composting food scraps or recycling instead of tossing waste in landfill. Using reusable bags in place of single-use plastic bags is one such dictum that is all but universally accepted.
“Of course, bagging groceries in a charming, rustic cotton tote is more sustainable than carrying them home in a flimsy petroleum by-product,” we reason.
But is that assumption really correct?
A number of studies have revealed that reusable bags can be less eco-friendly than their single-use plastic counterparts when considering the environmental impact of the full life cycle, including production, use and disposal.
According to a 2011 life cycle analysis conducted by the Environment Agency of the United Kingdom, a cotton bag’s carbon footprint is nearly 600 pounds of carbon dioxide, compared with more than three pounds for a standard plastic bag made from high-density polyethylene, or HDPE (these are the thin, flimsy bags most common at grocery stores; thicker plastic bags are made from low-density polyethylene, or LDPE). Non-woven polypropylene bags — the stiff, fibrous material that comprises many of the reusable bags available at grocery stores — had a carbon footprint of about 47 pounds.
The study found that cotton bags needed to be used 131 times and non-woven polypropylene bags needed to be used 11 times before the global warming impact was similar to that of HDPE plastic bags used only once. Depending on the make, LDPE plastic bags would have to be used at least four times to compensate for the more substantial upfront production costs.
“Whenever we do any of these big-picture type assessments, it is really thinking of the full life cycle of products,” said Shelie Miller, director of the program in the environment at the University of Michigan School for Environment and Sustainability. “Not just thinking of our visceral gut reactions to one product to another — that reusable is always necessarily better — but [taking] a systematic approach to environmental impacts and how they can be measured.”
The results from a 2018 study from Denmark’s Ministry of Environment and Food were even more grim. They found that non-woven polypropylene bags would have to be reused 52 times to match the total environmental impact of a single LDPE plastic bag. Conventional cotton bags would have to be reused 7,100 times, and organic cotton bags would need to be reused 20,000 times because of the crop’s lower yields.
Should we trust these studies?
Life cycle analysis experts say yes — but it’s complicated.
“From a life cycle perspective, I think the studies were very well conducted,” Miller said. “I think their results are valid and reasonable.”
Besides the fact that such studies buck assumed eco-truisms, sustainability-minded consumers may find other reasons to be skeptical. Other life cycle analyses that have reached the same conclusion as these government studies have been conducted on behalf of plastic industry groups.
However, Miller said that this does not necessarily rule out the results if the studies are conducted under the standards outlined by the International Standards Organization, or ISO, which requires specific methodologies and third-party certification.
“There are very specific life cycle assessment standards these particular reports have followed,” Miller explained. “Even if it is an industry group, if they are able to [show] that they are ISO certified or following ISO guidelines, I would not say it’s immediately disqualifying.”
The limitations of life cycle analysis
Even if there is no foul play, the methods of conducting life cycle analyses themselves may be flawed.
Rachel Meidl, fellow in Energy and Environment, Rice University’s Baker Institute for Public Policy, said that even the most thoroughly vetted life cycle analyses come with a certain amount of bias.
“Overall, I think the corporate and government perspective of [life cycle analyses] are narrow and limited,” Meidl said. “Just because a particular action, policy or solution is economically, technologically or environmentally feasible in the U.S. or Europe doesn’t mean it’s transposable in other economies.”
For example, the studies considered the recyclability of plastic bags as a point in their favor. Meidl countered that large countries like China and India generally lack the infrastructure, technology and capacity to effectively manage plastic waste in this way.
They are not the only countries that struggle, though. The U.S. Environmental Protection Agency says that most plastic bags do not wind up getting recycled — only about 13 percent of the 4.3 million tons generated every year. Most (though not all) recycling centers do not even take plastic bags because they clog machinery. Even plastic that is recycled can only go through the process a few times before it is no longer usable.
“When it comes down to choices, it’s not necessarily paper [versus] plastics,” Meidl said. “It’s really about incentivizing and encouraging reuse and proper disposal.”
Though the studies looked at a number of environmental impacts, including greenhouse gas emissions from manufacturing, water use in producing materials and the toxicity of the production processes, some less easily quantifiable (but equally important) factors were left out — namely, damage to marine wildlife and ecosystems, for which plastic bags are notorious.
“Physical harm to marine life is very difficult to capture as far as a measurable, quantifiable metric,” Miller admitted.
“There are efforts to capture this indicator in future assessments, but we first have to reconcile some knowledge deficiencies and data gaps before we can get a clearer picture on marine debris impacts,” Meidl added.
So, what’s an eco-friendly shopper to do?
Miller said, fundamentally, the answer goes back to the “three Rs:” reduce, reuse and recycle. And these three Rs are ranked in order of importance.
“First and foremost, reduce what you are consuming: think about whether or not you need a bag in the first place,” Miller said. “If you can’t reduce, reuse as much as possible. If those first two options fail, then recycle.”
“Every person who uses single-use products has the obligation to ensure these items are recycled or disposed of appropriately,” Meidl added.
Though the studies are not perfect, they do make one thing clear: if you are going to buy a reusable bag, you really need to use it.
“Just because something is built for reuse doesn’t mean it’s going to be environmentally better,” Miller said. “It really comes down to the idea of how people interact with products.”