The Carbon Footprint & Global Warming Explained (Part 1)

The Carbon Footprint

First came organic. Then came fair trade. Now makers of everything from milk to jackets to cars are starting to tally up the carbon footprints of their products. That’s the amount of carbon dioxide and other greenhouse gases that get coughed into the air when the goods are made, shipped and stored, and then used by consumers.

In the Gelsi household, reducing their carbon footprint is a family affair — they even wrote a musical about it. MarketWatch reporter Steve Gelsi offers tips for saving the environment and saving money while doing so.

So far, these efforts raise as many questions as they answer. Different companies are counting their products’ carbon footprints differently, making it all but impossible for shoppers to compare goods. And even if consumers come to understand the numbers, they might not like what they find out.

For instance, many products’ global-warming impact depends less on how they’re made than on how they’re used. That means the easiest way to cut carbon emissions may be to buy less of a product or use it in a way that’s less convenient.

So, what are the carbon footprints of some of the common products we use? How are they calculated? And what surprises do they hold? What follows is a look at six everyday items — cars, shoes, laundry detergent, clothing, milk and beer — and the numbers that go with them.

But first, here’s a number that will help you put all those carbon footprints in perspective. The U.S. emits the equivalent of about 118 pounds of carbon dioxide per resident every day, a figure that includes emissions from industry. Annually, that’s nearly 20 metric tons per American — about five times the number per citizen of the world at large, according to the International Energy Agency.

An Overview

The simplest statistic in the carbon-footprinting game may be this: For every mile it travels, the average car in the U.S. emits about one pound of carbon dioxide. Given typical driving distances and fuel-economy numbers, that translates into about five tons of carbon dioxide per car per year.

A study by the University of Michigan’s Center for Sustainable Systems found that, over its expected 120,000-mile life, an American-made midsize sedan emits the equivalent of about 63 tons of carbon dioxide. That number includes all emissions, from the making of the car’s raw materials, such as steel and plastic, through the shredding of the car once it’s junked.

The vast majority of those emissions — 86% — came from the car’s fuel use, the study found. Just 4% of emissions came from making and assembling the car. That means consumers can lower their footprint by buying a car with better fuel economy.

Sometimes, the differences between models can be substantial. For one overview of how cars stack up, consider a new computer model paid for by Toyota Motor Corp. that computes the lifetime carbon footprints of about 400 auto models from multiple manufacturers.

To narrow things down, consider a handful of Toyota’s own models. The Prius, a hybrid gasoline-and-electric car that averages 42 miles per gallon, has a lifetime carbon footprint of 44 metric tons, according to the updated computer model done for Toyota by Kreider & Associates, a consultant based in Boulder, Colo. The Corolla, a small sedan with a conventional gasoline engine rated at 29 miles per gallon, has a footprint of 64 tons. The Camry, a larger car rated at 23 miles per gallon, has a footprint of 95 tons. And the 4Runner, an SUV rated at 16 miles per gallon, has a footprint of 118 tons.

Gregory Keoleian, co-director of the Michigan center, says he used to advise people that the best way to minimize the carbon footprint of their driving was to keep their car as long as possible, since junking a car and manufacturing a new one produces pollution. But that was before hybrids hit the market and offered markedly better fuel economy. Now, he says, scrapping an old car in favor of a new model makes lots of sense.


The introduction of the hybrid “changes the whole dynamic,” Mr. Keoleian says. “Then, you replace.”


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