This is a brief overview of the manufacture of paper and of plastic, and is not intended to be comprehensive, or a chemistry class. It was original posted on the SWIFT blog of the James Randi Educational Foundation website (randi.org) several years ago, which is no long accessible.
Paper or plastic, Ma’am?
You can recycle your plastic bags into…a bag.
How do you answer? If you give what you think is the ‘correct’ answer, you say ‘paper’ or you’ve brought your own bags. Let’s examine that choice.
The paper bags used in grocery stores begin in the forest, with the timber industry. Even though trees are a renewable source, there is more to producing new paper than planting new trees. The paper industry is one of the dirtiest industries around. The chemicals used in the paper pulp process include sulfur, bleaches, and acids. The process uses huge quantities of water, which must be treated and cleaned, a process which also uses chemicals. According to a representative of the Texas Commission on Environmental Quality, paper manufacturing also receives a larger number of complaints than refineries or petrochemical plants on ‘nuisance odors ‘ which is a term meaning that the facilities emit very strong, disagreeable odors, as unpleasant to live near as a feedlot. Processing facilities must control odors to the same extent that they must control pollutant emissions. Odor is a non-trivial pollution problem.
Save the Trees!
Paper has a limited ability to be recycled. On each trip through recycling, paper must be chopped and shredded, which shortens the fiber length. Eventually, the fibers become too small to use and must be discarded into landfill, as do many of the manufacturing byproducts from paper manufacture. 
What about plastic? Grocery stores bags are made of polyethylene, which begins as the ethane component of natural gas. The primary emission from polyethylene manufacture is from natural-gas fired heaters, which supply heat or steam for the process. Natural gas is the cleanest burning fuel, and natural gas wells are clean and low-profile – a valve sticking up out of the ground as opposed to the ‘pumping units’ associated with oil wells. The conversion of ethane into polyethylene is close to 99% efficient. The feedstocks for ethylene are basically ethane – clean and odorless, and steam. Additionally, polyethylene can be recycled almost infinitely. Even though the molecular weight of the polymer chains will change with recycling, it’s still plastic and can be reused. It is also inert- in some locations, polyethylene has been chopped into sand-sized bits and incorporated into heavy clay soils, to lighten them as you would do with sand.
Bag flowers in bloom. Blue bag flowers are most commonly found near WalMarts. Source: creeklife.com
The manufacture of polyethylene requires about 6% of the water that paper manufacture requires. As our population grows and the supply of fresh water becomes increasingly scarce, industrial usage of water becomes an important consideration in the chain.
It costs to get the bags to you
Transportation adds more cost to the paper product than to plastic. Paper is heavier, so trucking costs, for a given ‘carrying capacity’ of the bag, are higher, as is the amount of pollution from the gasoline needed to transport the denser product.
Frequently, the public’s attitudes and beliefs about environmental consequences of our choices are shaped by sound bites and pictures from the media. Pictures of sea turtles with a plastic grocery bag stuffed into their throat, or a sea mammal with a set of six-pack rings caught around its head, are moving and emotional. These items do end up in the oceans, due to sloppy handling. However, legible newspapers from 70 years ago have also been mined from landfills. Searches on the EPA’s website will turn up studies showing that the TOTAL environmental impact from the manufacture and long-term landfill storage of paper bags exceeds that of plastic bags – from the mining of the raw materials (trees or natural gas), through manufacture including energy requirements, pollutants, water use, and hazardous wastes, to the volume of a bag in the landfill.
As skeptics, we must look at the entire picture. The issue is more complicated than I can discuss in a short blog post, but critical thinking skills can be used on these issues just as readily as they can on issues of quackery and pseudoscience. I posted this article in a slightly different format on a well-known skeptic website a few months ago, and was attacked for either being a shill for Al Gore or a shill for Big Oil. I’m not sure how I can be both at the same time, but it shows the knee-jerk reaction of people on hot-button issues. Although most people wanted to disagree with my statement that plastic is a better choice (as compared to paper), the only evidence given was that sometimes “bags end up in the ocean and get caught on bird beaks or swallowed by whales”. This is true, but the answer is not to ban plastic over paper, but to handle any bag properly through reuse, recycling, and proper disposal.
The option with the least environmental impact is to carry reusable shopping bags, or carry personal bags. However, if you are faced with a choice between paper or plastic, plastic is the environmentally responsible decision.
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Categories: Travel
Two Different Girls 
Thanks for reposting this here! A few months ago the city in which I live, Woowooville, passed an ordinance restricting the use of plastic bags and requiring stores to charge customers for bags. I remembered the talk you gave on this issue on one of the JREF cruises. When the Woowooville ordinance was pass, I thought, “Where’s Naomi when we need her?”
I’ve had to start carrying a reusable bag in my handbag so I’m not without a shopping bag. Matt refuses to use reusable bags for grocery shopping as there is a risk for disease as a result of bacteria in uncooked meat spreading to fresh fruits and vegetables. I gather we’re supposed to buy washable bags for grocery store use. I’m wondering what the environmental impact is of having to sanitize reusable grocery bags (particularly in Woowooville where we have major water restrictions).
Jeff had linked to a article about this topic, which made me think of reposting it. The piece calculated that you’d need to use a cotton bag over 100 times to break even, environmentally, with the production of a plastic bag.
We ship out water to China. Out in West Texas, they pump water like mad out of the aquifers, to water cotton in a area that gets maybe 10-12″ of rain each year. Then we ship all that cotton to China. Some comes back to us, most doesn’t.
I suppose at the same time that water is being shipped to China, Texans have water meters and are required to pay a fee for water usage. Is that the case?