I've heard that both paper and plastic shopping bags are pretty dreadful for the environment—the former because they require so many trees, the latter because they suffocate animals and last for centuries. I remember a lot of talk in the late 1990s about biodegradable bags composed of vegetable matter—whatever happened to those?
You can find them at a few tony stores, but they're still nowhere cheap enough for the local Piggly Wiggly. Standard polyethylene bags cost retailers around 2 cents each, while paper bags might be a penny or two more expensive. But so-called bioplastic bags, made from natural starches or oils, cost in the neighborhood of 7 or 8 cents—a lot for stores that hand out millions of bags per year. American shoppers are issued more than 100 billion polyethylene bags annually, so a nickel-per-sack premium would add up to an extra $5 billion in business costs.
But bioplastic bags are closing the gap, in part because people are coming to realize that the two reigning supermarket favorites are far from green. Polyethylene, for starters, is made from fossil fuels—it takes roughly 12 million barrels of oil a year to satisfy America's plastic-bag jones. And since discarded plastic bags don't break down for eons, they're free to wreak havoc on wildlife and ecosystems; there are, for example, 46,000 pieces of plastic floating in every square mile of ocean.
Given their arboreal origins, paper bags might seem the greener checkout-line option. But that just isn't the case—according to one Environmental Protection Agency estimate, producing a paper bag emits 70 percent more greenhouse gases than manufacturing a similarly sized polyethylene sack. Since paper bags are bulkier than their plastic counterparts, they require more fossil fuel to transport. And as any lobbyist for the Film and Bag Federation would be happy to point out, supplying the United States with paper bags requires chopping down 14 million carbon-soaking trees per year.
Bioplastic bags, by contrast, are made from resources like corn that are significantly more renewable than trees. (It takes a lot less time to set up a cornfield than it does to regenerate a forest.) In one common process, corn starch is fermented into lactic acid, which is then mixed with a variety of additives to give it polyethylene-like properties. The source material needn't be corn—potatoes are also popular, and Japan's Hitachi Zosen is experimenting with cassava. There are also processes that use microbes to ferment cane sugar and vegetable oils.
Bioplastics companies contend that producing their bags typically requires anywhere from 30 percent to 70 percent less fossil fuel than their polyethylene rivals. When discarded, bioplastic bags are designed to break down completely in a matter of weeks, leaving behind water and the carbon dioxide the corn or potatoes had absorbed before they were harvested. There have been complaints that this rapid decay can only take place under certain conditions, such as the intense heat of an industrial composting facility, but newer bags are designed to degrade more easily.
Bioplastics still have their problems. For example, they usually lack the strength of polyethylene, meaning that they're more readily used as simple food wrappers rather than as grocery bags. There is also a land-use component to the issue: It would take a lot of corn to replace 100 billion polyethylene bags per year, which means that a lot more land would have to be placed under cultivation. (While this problem could be ameliorated somewhat by using genetically modified corn, many environmentalists are opposed to that prospect, as well.) Finally, some researchers contend that bioplastic bags aren't as green as the proponents claim.
The bottom line on bioplastic bags is that they're not going to show up in mainstream supermarkets until prices come down significantly. The wild card, though, is government intervention—several American cities are debating whether they should follow San Francisco's lead and ban the use of nonbiodegradable plastic shopping bags. (San Francisco estimates that the ban will reduce its CO2 emissions by 4,200 metric tons per year, though it's not clear whether this figure takes into account emissions related to the unavoidable increase in paper bag use.)
Aware that polyethylene bags have become something of an environmental boogeyman—whether fairly or not—the plastics industry is striking back. It's touting the advent of polyethylene bags with additives that allegedly accelerate decay. Plastics companies are also supporting government efforts to establish bag recycling centers, most notably in California.
At the end of the day, however, the greenest choice is really "none of the above." Your best bet, instead, is to use and reuse a cloth satchel, one that you don't dispose of for several months. The Lantern has been meaning to do this for ages, but laziness has intervened—as it does for many shoppers. Plus, there's a fear of being lumped in with the pious folks who bought those "I'm Not a Plastic Bag" totes—you know, the designer bags that had to be shipped over from China.