Are reusable bags green?

National Public Radio's "All Things Considered" is doing a series this month called "How green Is It?," which is taking a closer look at things Americans are doing because they believe they help the environment.

On Friday, the focus was on reusable bags, which some grocery chains -- and some communities -- are encouraging shoppers to use instead of the traditional paper or plastic.

To start, environmental consultant Catherine Greener points out the differences among reusable bags.

Last year, Wal-Mart started selling a black bag that was made entirely from recycled bottles. Now, it offers a cheaper blue bag that is thinner and uses less plastic. On the other hand, however, only a third of the plastic in the new blue bag is recycled. And, it lasts only about half as long as the black one.

"I think we are living in the land of confusion right now as we migrate through what is less bad into what is truly good," Greener says. "This is an evolving and a moving target."

That's a problem with lifecycle analysis. In the end, deciding what's best requires some assumptions. What should manufacturers optimize? Carbon footprint? Recyclability? Recycled content? Not everyone is going to agree.

In the end, deciding between paper, plastic and resusable bags isn't going to make a lot of difference for the environment, according to Bob Lilienfeld, editor of the Use Less Stuff report (which touts lifecycle impact studies on its home page).

In the big picture, he says, the big fuss around shopping bags is really just a distraction.

"The bag is not the environmental bogey-person that everybody thinks it is," he says. "If you look at the entire grocery package that you bought, the bag may account for 1 to 2 percent of the environmental impact.

"The other packaging may account for 7 percent. Ninety percent is accounted for by the products you buy. That's where all the environmental impact is."

Thanks to blog reader Andrew Peacock for pointing out the NPR story. He called the report "refreshingly balanced." Let's watch the "How Green Is It?" series for more plastics-related topics.