The surprising answer is plastic. What’s even more surprising is that plastic is often more environmentally friendly than reusable cloth bags as well.
According to a report by the Washington Post:
- “It takes more than four times as much energy to manufacture a paper bag as it does a plastic bag.”
- “The production of paper bags generates 70 perent more air and 50 times more water pollutants than production of plastic bags.”
- “It takes 98% less energy to recycle a pound of plastic than it takes to recycle a pound of paper.”
Plastic bags are still harmful in other ways, however, because they are not biodegradable and “an estimated 4 billion end up as litter each year” worldwide, resulting in a number of adverse effects including the deaths of multiple animal species (turtles, for instance, often think the bags are jellyfish and can die from choking).
The article recommends substituting reusable cloth bags, but it turns out that too may be foolhardy. A report by UK’s Environmental Agency finds that, here again, plastic is superior. Here is an article detailing the report before its release.
Here was the experimental setup of the study:
“The following types of carrier bag were studied:
- a conventional, lightweight carrier made from high-density polyethylene (HDPE);
- a lightweight HDPE carrier with a prodegradant additive designed to break the
- down the plastic into smaller pieces;
- a biodegradable carrier made from a starch-polyester (biopolymer) blend;
- a paper carrier;
- a “bag for life” made from low-density polyethylene (LDPE);
- a heavier more durable bag, often with stiffening inserts made from non woven
- polypropylene (PP); and
- a cotton bag.
These types of carrier bag are each designed for a different number of uses. Those intended to last longer need more resources in their production and are therefore likely to produce greater environmental impacts if compared on a bag for bag basis. To make the comparison fair, we considered the impacts from the number of bags required to carrying one month’s shopping in 2006/07.” One month’s shopping turns out to be an average of 483 items (wow!).
“We then calculated how many times each different type of carrier would have to be used to reduce its global warming potential to below that for conventional HDPE carrier bags where some 40 per cent were reused as bin liners. Finally the carriers were compared for other impacts: resource depletion, acidification, eutrophication, human toxicity, fresh water aquatic ecotoxicity, marine aquatic ecotoxicity, terrestrial ecotoxicity and photochemical oxidation (smog formation).”
The study found that: “The paper, LDPE, non-woven PP and cotton bags should be reused at least 3, 4, 11 and 131 times respectively to ensure that they have lower global warming potential than conventional HDPE carrier bags that are not reused.” This is because the production processes—and not transport, secondary packaging, or end-of-life management—dominated the environmental impact.
The article was peer-reviewed, but did not look at the entire effects of the bags. As mentioned above, for example, the study did not look at the problem of litter outlined in the Washington Post article. Certainly, this would change the outcome of the study though its important to remember that many of the other types of bags could cause similar litter problems. As the study tersely put it, using a cotton bag 173 times “seems ambitious,” yet this is the amount needed to equal the environmental impact of just one regular plastic bag. My most recent cotton bag broke after about 20 uses or so and now must be disposed of. If more people switched to these sorts of bags its easy to imagine that they too could become a litter problem, though with different consequences (I don’t think they’re on a turtle’s diet).