University of Oregon chemistry professor David Tyler blew conventional environmental wisdom out of the water in Hillsboro last night.

He gave a talk that focused on life cycle assessments that tally the total environmental impacts of everyday choices: Which bag you use for your groceries, which milk container you buy, which cup you use for your coffee, which car you drive…

The assessments account for the impacts of a product throughout it’s entire life: from the first steps of obtaining the raw materials to the waste products leftover after it’s been used. They evaluate the total energy use, contributions to global warming, ocean acidification, air and water pollution, for example. They’re usually pretty expensive and time consuming.

And the conclusions aren’t what you’d expect. They show plastic bags are greener than paper bags, disposable plastic cups have fewer impacts than reusable ceramic mugs, and owning a dog is worse than driving an SUV.

Surprise! Apparently, we’re not as green as we thought.

“Most people I know want to do the right thing with regard to the environment,” Tyler said at the outset of his talk. “What is the right thing?”

One of the biggest surprises from the life cycle assessments he’s studied is that plastic often has fewer environmental impacts than paper, glass or cotton.

“There is no basis for believing that plastics are considerably more harmful to the environment than traditional materials such as paper, glass or cloth,” Tyler said. “In many cases, products made from plastic are more sustainable.”

Tyler isn’t under any illusions that plastic is good for the environment. He listed the problems it causes because it doesn’t readily biodegrade, it contains harmful chemicals such as Bisphenol A and phthalates that leach out and disrupt hormones in people and wildlife, and it takes non-renewable petroleum to make it.

However, he said, only 3 percent of the petroleum used in the U.S. is going toward making plastic while 87 percent goes toward energy and transportation.

“If we stop using plastics tomorrow, it would only have a small impact on our use of petroleum,” he said.

A life cycle assessment in Australia found single-use plastic bags have fewer impacts than paper grocery bags. They use less energy and resources and produce fewer pollutants.

The most sustainable grocery bag option, according to that assessment, is a reusable bag made of recycled plastic. The next best is cotton, then regular plastic bags and then paper.

“They found paper bags are the worst thing we can do for the environment,” he said. Yet in cities that have banned plastic bags, grocery stores are now offering paper bags instead.

The same counter-intuitive conclusion came out of another life cycle assessment that found ceramic mugs take so much energy to produce that we’re better off using disposable plastic cups. Paper cups actually require more process water and chemicals to make than styrofoam, the study found.

And your milk container? A life cycle assessment found biodegradable plastic produces almost twice as many greenhouse gases than regular plastic, which has fewer climate impacts than cardboard and glass.

The best option, he said, is actually the rectangular “tetrapack” that’s commonly used to package soy and rice milk.

But life cycle assessments don’t account for everything, said Tyler.

“In every category, the plastic bag looks pretty good,” he said. “But what about quality of life? People just don’t like the fact that the plastic does not degrade. It impacts our life in the form of litter.”

The life cycle analyses of grocery bags don’t account for what kind of food goes in the grocery bag either, Tyler noted. And that has a much bigger impact than any of your grocery bag choices.

“What goes into the bag is going to make the biggest impact,” he said. “If you eat a vegetarian diet, you have a much smaller impact.”

Life cycle assessments have produced some really interesting details about the impacts of everyday life, Tyler reported:

  • They’ve found that the impacts of food miles – the distance food has to travel to get to you – are negligible.
  • They’ve found one pint of beer, roughly 1 pound of liquid, produces the equivalent of 3.8 pounds of carbon dioxide.
  • One assessment determined that a six-pack of Fat Tire beer produces the equivalent of 11 pounds of carbon dioxide – the weight of a small bowling ball.
  • Another found that one pair of Levi’s 501 jeans produces the equivalent of 72 pounds of carbon dioxide and 3,500 liters of water.
  • They haven’t been kind to cotton. Growing cotton has major impacts in the form of pesticides. Roughly 25 percent of all the pesticides used in North America are used on cotton crops.
  • And they’ve found that having a dog is a bigger environmental impact than driving an SUV.

“Anything involving agriculture is hard on the environment,” Tyler said. “Food for the dog makes it a larger impact than a Toyota Land Cruiser.”

Tyler quoted one of his students asking him: “So you’re saying I should go home, shoot my dog, wear no pants and drive a sport utility vehicle?”

No, he said. The thing about life cycle assessments is they don’t consider cost, technical performance or the political and social acceptance of the items in question.

In the end, he said, society makes its own calculations.