本人就这个问题思前想后很多日了。今日看到一篇文章和大家share.

总而言之，目前科学家搞不清究竟是纸袋还是塑料袋更污染环境，但我们可以从重新使用旧袋子开始。

另外，本人也希望朋友们share环保tips with me. I'd like to do something for mother nature everyday.

Paper or plastic? What's the environmentally correct choice?

By Aviya Kushner • Bankrate.com

Paper or plastic? Ever wonder which is actually the right choice?

Environmentalists, bag manufacturers and garbage specialists have all wondered the same thing, but they come up with different answers.

Plastic bags "end up in landfills, or on roadsides, or in lakes and streams, where they prove quite a hazard to wildlife, who choke on the bags," says Anna Peterson, co-chair of the Sustainable Consumption Committee of the Sierra Club, and a professor of environmental ethics at the University of Florida.

"The bags are like balloons," she explains. "Especially if there are crumbs in there. A raccoon might smell peanut butter and swallow the bag along with the crumbs."

But plastic-bag manufacturers and garbage experts say that in the long run, plastic wins over paper.

"Paper bags are easier to recycle, but they weigh 10 times as much," says Robert Bateman of Roplast Industries, a bag manufacturer. "They use more energy and cause more waste in the process of manufacturing."

A paper bag eats up almost three times as much energy in the manufacturing process, says Bateman, who's also a past president of the Plastic Bag Association.

That's not something usually emphasized by environmentalists trying to reduce plastic use.

"Plastic bags come out on the right side of the equation on everything except the recycling side," Bateman says.

Is paper better?

Ask a professor specializing in garbage whether paper is better than plastic, and he'll say the equation is relatively easy to solve.

"The answer is very simple and very straightforward," says garbologist Bill Rathje, a fellow at the Archaeology Center of Stanford University and director of The Garbage Project, and a leading authority on what is in America's garbage.

"It's not one that the paper-bag people like to hear. In a dry landfill, paper bags don't degrade any faster than plastic bags. In a normal, well-run landfill, paper bags do not biodegrade any faster over at least 40 years than plastic."

The problem with paper is that it's fatter, he explains.

"Paper bags are much bulkier than plastic, so they fill up more landfill space," Rathje says. "They're three to five times bulkier than plastic, and you can see that yourself at the grocery. Landfills are closing down because they're full. From that perspective, plastic is much better than paper."

Flying bags

Environmentalists insist that the problem with plastic is that plastic bags don't always go gently into the landfill.

They point out what any beachgoer notices -- that some bags have active, high-travel lives before they ever get tossed into a trash can.

"They go airborne after they're discarded -- getting caught in fences, trees, even the throats of birds, and clogging gutters, sewers and waterways," according to Brian Halweil, senior researcher at The Worldwatch Institute, an environmental group.

Bag manufacturer executive Bateman says that a lot of the wildlife-are-hurt argument is based on anecdotal evidence.

"A seal eating plastic is very rare," he says. "Plastics are durable and light and tend to float. As far as damaging other wildlife is concerned, the worst of it is sort of anecdotal and not representative of what's going on."

Bag nation

One thing manufacturers, environmentalists and garbologists agree on is the number of bags out there. You're not hallucinating if you think your house is drowning in free plastic bags from newspapers, restaurants and grocery stores.

According to Halweil of Worldwatch, "No one knows exactly how many bags Americans throw away, but it is easily in the billions."

The plastic bag is winning the global popularity contest, manufacturers say, and part of that is because plastic is cheap.

"The paper bag is a mass-commodity product and is dying because of the costs involved -- specifically, because of the energy costs," explains Bateman. "Paper is energy-intensive compared to plastic.

"That's why the plastic bag has taken over the market, except in the U.S., where there's more paper and it's cheaper."

Recycling, anyone?

For some consumers and environmentalists, the solution is to recycle.

"We take our bags to our local Publix supermarket and recycle them," says Peterson. "Most people don't do that -- most people throw them out."

In fact, only 0.6 percent of bags are recycled nationwide, according to Worldwatch.

Some stores offer discounts for people who bring their own bags.

But America is only part of the bag market -- the rest of the world is definitely helping the numbers rise.

"Factories around the world churned out a whopping 4 trillion to 5 trillion of them in 2002, ranging from large trash bags to thick shopping totes to flimsy grocery sacks," Halweil says.

What plastic bags are made of

It's hard to tell by looking, but plastic bags are basically made of oil. "They're petroleum products," says Peterson of the Sierra Club.

The bags "start as crude oil, natural gas or other petrochemical derivatives, which are transformed into chains of hydrogen and carbon molecules known as polymers or polymer resin," says Halweil of Worldwatch.

"After being heated, shaped and cooled, the plastic is ready to be flattened, sealed, punched or printed on," Halweil explains.

Plastic bags for bread and vegetables first appeared in America in 1957, and plastic trash bags made their debut in the late 1960s. They've been practically everywhere since.

Paper or plastic?

If all you want is an environmentally correct answer to which free bag is best, forget about getting that from the experts.

"Paper or plastic? Neither option is best. The better option is to bring your own," says Peterson of the Sierra Club.

For Bateman, who represents a bag manufacturer, the real question is what to do with bags after they're used. "In France, they actually burn 30 percent of their bags for energy. Basically, you recapture the value of the bags by turning it into electricity.

"That's really the answer to a lot of the waste-disposal policies. Until now, it was much cheaper to buy coal, so you could waste plastic."

As far as his company's individual solution, it's to make plastic bags less free. "Our solution is to sell, so people value them," Bateman says. "We sell about 100 million bags a year, and we think that's the correct solution."

International bag laws

Some countries actually have a national plastic-bag policy.

In January 2002, South Africa began requiring bags to be more durable, and therefore pricier, to discourage disposal. The result? A 90 percent decline in use.

And in Ireland, a new 15-cent-per-bag tax has decreased use by 95 percent. Seven countries, including Canada and the United Kingdom, have plans to tax plastic bags -- or ban them altogether.

Meanwhile, Tesco, a supermarket chain in the United Kingdom, "just introduced a degradable additive to their bag so they break down quicker," says Bateman.

"It's still debatable whether that's good or bad. It will decrease its recyclability."

SUVs, fake food, and plastic bags

If you've experienced scathing looks in the supermarket after asking for plastic, it may help to know that there are worse things you can do.

"If you recycle your bags, but drive your SUV to the grocery store, the gas-guzzling vehicle is having a much larger impact," Peterson explains.

"And what you're buying there is important too. If it's artificial cheese product, that's not helping either.

"What you drive and what you eat are the two biggest decisions you can make, along with how much you drive," says Peterson. "The third biggest factor is your household -- how big your house is and how well-insulated it is."

"Your house is the biggest contributor to the environment," Peterson says.

So don't worry so much about your bags, in other words.

"These individual choices to take canvas grocery bags aren't something people should stay up at night tossing and turning over," says Peterson.

"On the other hand, it really does matter," she says. "Individual acts really do add up."

It's easy to use canvas bags, or reuse paper bags, she says. "I would not want to encourage people to look at plastic bags or any other consumption choices as either-or issues," Peterson says.

"There are good choices, bad choices and in-between choices," she says.

"Another thing is the power of example. Some people see me and think, there's the funny-looking lady and her bags, but other people might see me and think, that's easy, I can do that."

Just use it again

Garbologist Rathje says it's not your bag choice as much as what you do after you pick up that initial bag.

He strongly encourages reusing bags, and he doesn't care whether what you're reusing is plastic or paper, as long as you reuse.

"Take a bag when you go to the store that you can reuse for something else. The more you reuse it, the better it is. Even if you take your lunch in a paper or plastic bag, that's good. The goal is to use it again for something else.

"If it's easier for you to do that with plastic, take plastic. If it's easier with paper, take paper," Rathje says. "The bottom line is that paper takes up more volume in landfills, but you should use what you can reuse."