Carbon-footprint calculators and their lessons

CHRIS JONES at the University of California, Berkeley, was in a river in the Amazon rainforest when he put the finishing touches on the world’s first online home carbon calculator. That was in 2005. He hoped that if he could show people how much greenhouse gas was associated with daily activities (driving the car, heating the house), they might change their behavior and do some small part in saving the Amazon. Seventeen years and a proliferation of rival calculators later, trackers provide a wealth of often-ignored information about the carbon emissions of everyday life. They provide local and micro data that usefully complement the global findings of the Intergovernmental Panel on Climate Change.

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The trackers work by asking users to answer questions like: how many miles do you drive per year; how much is your household’s annual electricity bill; how often do you eat meat? They then calculate a personal or household estimate of carbon dioxide equivalent (CO) emissions.twoe) per year. Alex Beale, a climate blogger in Atlanta who has studied them, acknowledges that there are dozens of home carbon trackers and hundreds of specialists, including ones that calculate emissions from food or other industries, like a new one from the Stockholm Environment Institute (MAYBE) to track emissions from shipping. For individuals, Mr. Beale believes, the most comprehensive are the Cool Climate tracker run by Dr. Jones in Berkeley and the calculator created by the World Wildlife Fund.WWF) and MAYBE. what do they tell us?

Dr. Jones describes the main household polluting activities as “cars, coal, cows, and consumption, roughly in that order.” By far the largest single source of emissions is the family vehicle. An average fuel-efficient car driven 14,000 miles (22,500 km) sheds 7 tons of carbon, according to Dr. Jones’ tracker. Swapping it out for an electric vehicle would save more than 6 tons, or one-eighth of the annual emissions of an average American household.

No other change would generate as much savings, although electricity in the home is responsible for more than 5 tons of carbon emissions per year, so generating it with solar panels would come close (see graph). Like electric vehicles, a roof full of solar panels doesn’t come cheap. Changing diets costs less and American households consume 2.7 tons of CO worth of meattwoeach year, much more than most people. If Americans miraculously became vegetarian, that would be about half of an average sunroof.

However, these household averages hide what may be the most important thing that carbon trackers reveal: that seemingly similar households produce very different emissions. By combining their tracker results with ZIP code data, the University of California team calculated average emissions by area. High-emitting places, mostly suburbs, produce four to five times more carbon than inner cities or rural areas, a much higher multiple than might have been expected. Chicago homes produce 37 tons of COtwoevery year; the suburbs of Eola, about 35 miles (56 km) from the Windy City, emit 96 tons. This is not just due to commuting. Trips to and from work account for less than a fifth of the miles driven; the rest are for shops, schools, etc.

Even more amazing is the difference air travel makes. The average domestic contribution for flying is 1.5 tons, less than a car. But half of Americans never fly. According to Cool Climate, flying 100,000 miles a year (as some frequent flyers do) produces an additional 43 tons of COtwo. If jet-setting households drastically cut back on their travel, it would have a disproportionate effect on emissions. They might even do something for the Amazon.

Over the next 30 years, many countries promise to go to net-zero carbon emissions, which means household emissions will have to be reduced to almost nothing. StephanieRoe, WWFThe leading climate scientist at , believes that, at best, half of the reduction could be achieved through demand-side measures, such as behavioral changes by individuals and households. And even that would require companies and governments to provide more incentives to switch through supply-side investments to make low-carbon options cheaper and more widely available. The trackers, it seems, have daunting lessons for both public agencies and private households.

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This article appeared in the US section of the print edition under the headline “Seeing Footprints in the Air.”

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