In his intro to sustainable engineering classes at Northwestern University, professor Eric Masanet likes to set the tone for the semester by posing the once ubiquitous checkout question: “Paper or plastic?” For many of his eager young students, the answer seems obvious—paper breaks down fast in the environment, is easy to recycle, and comes from trees. Meanwhile, plastic is notorious for building up indefinitely in the environment, harming aquatic ecosystems and clogging drains, and being made from fossil fuel. With all that in mind, it’s easy to conclude that paper bags are the eco-winner.
But life cycle analysis—i.e., measuring an item’s cradle-to-grave impact—reveals a more complex picture. In terms of single use bags, “the science shows that moving from plastic to paper is not necessarily ‘greener,'” says Masanet. In a nutshell, here are the key categories he says are part of determining the environmental footprint of any bag:
- Production: For both plastic and paper, processing raw materials and manufacturing the final product causes pollution and requires energy and water. The numbers are too complex to get into here, but the UK’s Environment Agency’s life cycle analysis determined that the impact of paper production on human health and eco-toxicity is “significantly worse” than plastic’s.
- Distribution: Simply put, because a paper bag is five to seven times heavier than a plastic bag, transporting paper bags requires more resources to move it from point A to B. With more trucks, you need more fuel, and you get more greenhouse gas emissions.
- End of life: Paper definitely scores points for being easily recycled, or, if trashed, breaking down quickly. But worth noting, too, is the UK LCA’s estimate that 76 percent of plastic shopping bags are reused at least once, which can help reduce the purchase of new trash bags and pet waste bags.
Does biodegradability trump reuse? Does harming aquatic life outweigh distribution-related air pollution? Masanet cautions us from calling a winner, because there are so many variables involved…which is why, when he learned of the City of Chicago’s new bill to restrict plastic bags, he worried it might have the unintended consequence of making paper the de facto eco-hero in this story.
So, what’s a planet-appreciating person to do? You probably know the answer: BYOB. In terms of legislation, perhaps Chicago can take a cue from cities like Austin, Texas, which have banned businesses from providing single-use bags of any kind, instead recommending reusables.
Compared with both paper and plastic single-use bags, reusable bags are “an environmental slam dunk—if you reuse them,” says Masanet. If you need to buy a bag, opt for durable recycled plastic options over cotton, unless you plan to reuse the cotton bags hundreds of times.
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