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Carbon calculators abound, but which ones measure up?

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Users can customize this carbon calculator from Zerofootprint and use it to track their emissions. (Courtesy of Zerofootprint.net)

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Zerofootprint's carbon calculator asks users to answer questions ranging from travel habits to the food they eat. (Courtesy of Zerofootprint.net)

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GreenIQ.com's calculator focuses on how everyday habits, such as unplugging appliances when not in use, affect a user's carbon footprint. (Courtesy of GreenIQ.com)

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The Nature Conservancy's carbon calculator compares its users' carbon footprints to the U.S. and world averages. (Courtesy of The Nature Conservan)

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GreenIQ.com's calculator focuses on how everyday habits, such as unplugging appliances when not in use, affect a user's carbon footprint. (Courtesy of GreenIQ.com)

Laurel House always considered herself environmentally friendly, so she knew that flying roundtrip a half dozen times a year between her home in Kansas City, Mo., and Los Angeles for business interests wasn’t helping global warming.

But when she tried a couple of carbon calculators to gauge how her lifestyle was affecting the environment, House wasn’t satisfied with the results. “They didn’t take into account my daily choices,” she said, noting that many of them asked only about her travel habits.

So, with the help of a scientist, she designed her own carbon calculator.

Along with tracking use of electricity and carbon emissions from flying and driving, House’s GreenIQ.com Web site, which launched in October, asks for information about everyday habits like whether you run the dishwasher only when full or reuse bags at the supermarket.

“We feel you can offset carbon emissions through environmental choices,” she said. “It takes the esoteric concept of green and takes it down to Earth.”

With GreenIQ, House has joined the growing ranks of environmental groups, government agencies and private companies that offer users the chance to tally their carbon footprint, the amount of carbon dioxide an individual emits through daily activities.

“This issue has really taken off,” said Zoë Kant, the manager of carbon finance for The Nature Conservancy, a conservation organization. “As far as the environmental movement goes, there’s been a renaissance.”

But for people who want to not only understand their environmental impact but also want to do something about it, they need to do some work to find the right carbon calculator. As seen from House’s experience, they vary widely in detail and complexity.

On one end, there is the “One Minute Calculator,” created by the Toronto-based Zerofootprint Web site to provide what its CEO and founder, Ron Dembo, calls a “quick and dirty” tool for getting a sense of carbon emissions. Dembo said the results given by his company’s model, based on information about the type of home one lives in, how much meat one eats and one’s travel habits, is all about 80 percent of the population wants to know.

And while quick and simple, this calculator, he says, is more accurate than many others out there.

“Everyone and their grandmother can put up a carbon calculator, but very few can do it well,” he said. “Knowing how software works, some of them are probably dead wrong.”

Zerofootprint also provides a more comprehensive, customizable calculator. It can get as detailed as assessing the number of sheets of paper you use weekly. Entire communities can measure and track their carbon footprint through the site.

Like Zerofootprint, The Nature Conservancy has experienced a boom since it launched its carbon calculator last April. A little less intense than Zerofootprint’s personalized calculator, the site asks about activities ranging from driving (How often do you check your tire pressure?) to waste (Do you compost food scraps?).

But inputting the same information in both the Zerofootprint and Nature Conservancy calculators might leave users with vastly different answers.

While it might be hard to tell if a calculator is giving you accurate results, experts said there are some signals that you’ve hit a reliable site. Good calculators, according to Daniel Scott, an assistant professor in the geography department at the University of Waterloo in Ontario, ask users where they live, as emissions vary depending on the type of power supply used in a particular region. The calculators should also say what data is being used.

Kant at The Nature Conservancy agrees that the more detailed the questions, the more accurate the calculator. But she warns that calculator providers must balance accuracy with ease of use. If they ask too many questions that require rooting through old electric bills, she said, some people might lose patience.

The importance of the level of accuracy also depends on what organizations, and their Web sites’ users, expect to do with their information. If the goal is to simply make people more aware of their role in the world, a simple calculator might do. Some take it a step further and offer tips on reducing certain types of carbon emissions, like unplugging appliances when they’re not in use.

But most sites running calculators offer carbon offsets--a chance for users to make a contribution to an environmentally friendly project or product based on the size of their carbon footprint. The Nature Conservancy, for example, uses money to plant trees, while other organizations collect funds to support renewable energy like wind power.

If people are making donations based on what they are told their carbon emissions amount to, some experts say, those calculations had better be accurate.

“The risk is that if consumers do become skeptical, they’re not even going to go to the good ones,” Scott said. “It would be nice if there were some standard, but who’s going to set that up?”

And there are a growing number of consumers who take the information they glean from carbon calculators very seriously. . In December, Shannon Moore started the first U.S. branch of the U.K.-based Carbon Rationing Action Group (CRAG). Moore, who has a background in environmental science, says 30 members of her Maryland group regularly track their carbon emissions using a spreadsheet she designed. The group has set a goal of reducing its emissions to 10 percent below the national average.

“It’s a social problem so why not have social solutions?” she said.

Still, some scientists worry that too few Americans are taking this kind of action. Anthony Leiserowitz, director of the Yale Project on Climate Change at the university’s School of Forestry and Environmental Studies, said carbon calculators need to go farther. People are more aware of global warming, but he said there’s not enough attention to what can be done.

“If your purpose is just to make people aware, almost any of them are reasonably effective,” Leiserowitz said, but he added that not all of them really get at the scope and scale of the problem.

But for House at GreenIQ, awareness is the natural first step. Her team is working on a Facebook application that would allow people to post their GreenIQ on the social networking site.

“We’re trying to create a consciousness,” she said, “so people think about their choices throughout the day.”

E-mail: esk2007@columbia.edu