Monday, September 21, 2015

Paper or Plastic?

Most consumers used to think the environmentally friendly option at the grocery store checkout was paper bags. Paper bags are made out of natural materials after all, whereas plastic bags are made from non-renewable petrochemicals. But this decision doesn’t matter much in the context of all the purchases that consumer make. And in general, some people focus too much on product-level decisions when they should focus on product-category decisions.
A product-level decision usually means deciding between two brands of a product (e.g., a Honda Accord versus a Toyota Camry). A product-category decision means deciding between entirely different ways of getting a product or service. For example, all of the following are different ways of getting transportation: driving a personal automobile, biking, walking, and mass transit. Driving a Camry won’t change your overall environmental impact nearly as much as biking to work would.
An assessment in Finland compared various types of grocery bags, including plastic bags, recycled plastic bags, paper bags, and biodegradable (starch) bags, and it found that recycled plastic bags actually had the lowest life cycle CO2-eq. emissions1 (Mattila et al. 2011). But the more important finding is the range of CO2-eq. emissions per bag: at least −7 g CO2-eq./recycled plastic bag and at most 60 g CO2-eq./biodegradable bag. For context, the per capita emissions of CO2-eq. in Finland are somewhere in the range of 9.0 tonnes to 12.5 tonnes (Heinonen and Junnila 2011). So if you purchase, say, 50 bags of groceries per month, and you switch from the most polluting bag to the least polluting bag, you save
(60gCO2eq.bag7gCO2eq.bag)×50bagsmonth×12monthsyear=40,200gCO2eq.year \left( \frac{60 g CO_{2} eq.}{bag} - \frac{{-7} g CO_{2} eq.}{bag} \right) \times \frac{50 bags}{month} \times \frac{12 months}{year} = \frac{40,200 g CO_{2} eq.}{year}
If we take 10 tonnes CO2-eq. as a nice, even number for annual per capita emissions of CO2-eq., the savings from this one decision amount to about
(40,200gCO2eq.year×kg1000g)×(year10tonnesCO2eq.×1tonne1000kg)=0.00402 \left( \frac{40,200 g CO_{2} eq.}{year} \times \frac{kg}{1000 g} \right) \times \left( \frac{year}{10 tonnes CO_{2} eq.} \times \frac{1 tonne}{1000 kg} \right) = 0.00402
or 0.402%.
This is a rough calculation, but I used generous assumptions, and choosing a different grocery bag still only makes less than half a percent difference in per capita greenhouse gas emissions.
Plastic grocery bag

What Decisions Matter

It turns out that three broad areas of consumption are responsible for the bulk of people’s environmental impact, at least in developed countries:
  • construction and housing (e.g., heating and air conditioning),
  • food (especially eating meat), and
  • transportation (especially driving and flying).
When researchers study the broad areas of consumption that cause environmental impacts, these three sectors are at the top of the list, again and again (e.g., Brower and Leon 1999; Spangenberg and Lorek 2002; OECD 2002). One study found that these three sectors account for roughly 70% of consumers’ annual greenhouse gas emissions (Jones and Kammen 2011). So why worry about paper-versus-plastic when it’s far more important whether you rode your bike to the store and whether you’re buying meat or not?
I am not arguing that people and companies should stop caring about product-level improvements. Environmentally friendly laundry detergent, for example, helps, but the benefits are more obvious for the company that sells the product than for consumers who purchase the product. And it’s often difficult for consumers to know which detergent is better, in any case.

Confusing Messages

Messages about products that are better for the environment are dangerously close to becoming like messages about foods that are more healthy. Are eggs actually healthy? Should I really make an extra effort to drink the occasional glass of wine? Is the low-fat alternative actually better for me?
All of these questions have had different answers in recent years, and as the confusion mounts, the general public decides that health experts don’t really know what’s best. Or if they do, they’re not communicating it well, so the average person eventually says, “Forget it: I’m eating eggs, bacon, and buttered toast for breakfast and washing it down with a cup of coffee. It can’t be that bad if there’s this much confusion.” Similarly, those of us who tell consumers what’s best for the environment need to make sure that our messages are clear, accurate, and (ideally) easy to implement.
In my example about grocery bags, you might have been surprised to read that the bag with the highest greenhouse gas emissions was the biodegradable one. This type of bag has been developed specifically to be environmentally friendly, and I’m sure it’s marketed as such. Wouldn’t you be annoyed if you spent extra on the environmentally friendly option, only to find out later that it’s the least environmentally friendly option? And wouldn’t that make you less likely to purchase “environmentally friendly” products in the future? That would certainly be my reaction. So researchers and marketers need to be extra careful about their messages to consumers; otherwise, consumers will just stop caring.

Clear Messages

The best recommendation that I can give consumers is to trying making changes in the big three areas of consumption (housing, food, and transportation), and don’t worry so much about other decisions. Ride a bike when you can. Take public transit. Eat less meat (or at least less beef and pork). Turn up the thermostat in the summer. This list is not exhaustive, but these are examples of recommendations that are clear and will definitely reduce your environmental impact, even if they aren’t always easy to do.

I originally wrote this post for Aaron Redman’s Achieving Sustainability blog.


Brower, Michael, and Warren Leon. 1999. The Consumer’s Guide to Effective Environmental Choices: Practical Advice from the Union of Concerned Scientists. New York: Harmony.
Heinonen, Jukka, and Seppo Junnila. 2011. “A Carbon Consumption Comparison of Rural and Urban Lifestyles.” Sustainability 3 (12): 1234–49. doi:10.3390/su3081234.
Jones, Christopher M., and Daniel M. Kammen. 2011. “Quantifying Carbon Footprint Reduction Opportunities for U.S. Households and Communities.” Environmental Science & Technology 45 (9): 4088–95. doi:10.1021/es102221h.
Mattila, Tuomas, Marjukka Kujanp√§√§, Helena Dahlbo, Risto Soukka, and Tuuli Myllymaa. 2011. “Uncertainty and Sensitivity in the Carbon Footprint of Shopping Bags.” Journal of Industrial Ecology 15 (2): 217–27. doi:10.1111/j.1530-9290.2010.00326.x.
OECD. 2002. “Towards Sustainable Household Consumption? Trends and Policies in OECD Countries.” Paris: OECD Publishing.
Spangenberg, Joachim H., and Sylvia Lorek. 2002. “Environmentally Sustainable Household Consumption: From Aggregate Environmental Pressures to Priority Fields of Action.” Ecological Economics 43 (2): 127–40.

  1. CO2-eq. (or carbon dioxide equivalents) is a measure of greenhouse gas emissions. CO2 is the most well-known greenhouse gas but not the most potent. In order to describe global warming impact in a single unit of measurement, researchers often convert all greenhouse gas emissions associated with a particular activity into the equivalent amount of CO2 emissions.