Which is Greener, Paper or Plastic? The Answer is Gray

With a recent vote by the Chicago City Council to partially ban the use of plastic shopping bags starting in August 2015, Chicago becomes the latest American city to institute some sort of attempt to curtail the use of such containers.

The action once again brings focus to a hotly debated question in the environmental community: Which is greener – paper or plastic? The answer is complicated, according to Northwestern University recycling and sustainability expert Eric Masanet.

“Many of us instinctively assume that paper is better than plastic, but this is not necessarily true,” said Masanet, an associate professor of mechanical engineering and of chemical and biological engineering at the McCormick School of Engineering and Applied Science. “Paper versus plastic is a classic question in the life cycle assessment field, with many studies having been done. The science shows that moving from plastic to paper is not necessarily ‘greener.’”

Rather, he said, the worthy goal of reducing plastic litter may come at the expense of increasing societal energy use, water use and greenhouse gas emissions because paper bags can have higher production and transportation footprints.

Masanet said that the real opportunity is to use the plastic bag ban to encourage greater use of reusable shopping bags, which the science shows are the most environmentally friendly option as long as they are used frequently. He further adds, “Surprising to many, reusable bags made of durable plastics are better in many respects than cotton reusable bags due to the enormous environmental footprint of cotton production and its requirements for water, energy and fertilizers.”

Sustainability is a complicated field involving quantitative study and tradeoffs to make informed decisions about consumer behavior and consumption, Masanet said. 

“Improvements are vital for a clean planet and a healthy economy, but they need to be guided by sound science,” he said. “Hard data are required to change behavior, change mindsets and realign incentives in ways that truly lead to environmental benefits.”

After the Chicago City Council approved a partial ban on the use of plastic shopping bags in the city, some Evanston aldermen said they would like to see the suburb’s city council revisit the issue.