During the 1980s, the question “Paper or plastic"” became a common phrase heard at many grocery stores as customers were given a choice between having their groceries placed in a paper sack or a plastic bag. For years, it was believed that the environmentally correct answer was “paper.” Paper, after all, was biodegradable and could be recycled, while plastic filled up space in the landfill. But at the close of the twentieth century, the answer is not as clear as it once was.

Most paper is made from trees that are planted specifically to be made into paper and are thus a renewable resource. However, paper-making pollutes water supplies because it requires thousands of gallons of water to wash and bleach the wood pulp before it is made into paper. Once the paper is used and...