Carbon footprint calculators and their lessons

VSHRIS JONES from the University of California, Berkeley, was on 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 the amount of greenhouse gases associated with everyday activities – driving the car, heating the house – they could change their behavior and help in a small way to save the Amazon. Seventeen years and a proliferation of rival calculators later, trackers provide a wealth of often overlooked information on the carbon emissions of everyday life. They provide local data and micro-data that usefully complement the global conclusions of the Intergovernmental Panel on Climate Change.

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Trackers work by asking users to answer questions such as: how many miles per year do you travel; how much is your household’s annual electricity bill; how often do you eat meat? They then calculate a personal or family estimate of carbon dioxide equivalent emissions (CO2e) per year. Alex Beale, an Atlanta climate blogger who has studied them, estimates there are dozens of home carbon trackers and hundreds of specialists, including those who calculate emissions from food or other industries, as a new one from the Stockholm Environment Institute (UTE) to track emissions from shipping. For individuals, Beale believes, the most comprehensive are the Cool Climate tracker run by Dr Jones at Berkeley and the calculator set up by the World Wildlife Fund (WWF) and UTE. What are they telling us?

Dr Jones describes the main polluting household activities as “cars, coal, cows and consumption, roughly in that order”. By far the main source of emissions is the family vehicle. A car with average fuel efficiency driven 14,000 miles (22,500 km) releases 7 tonnes of carbon, according to Dr Jones’ tracker. Replacing it with 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 the electricity in the house is responsible for over 5 tonnes 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. Diet change costs less and US households consume meat for 2.7 tons of CO2each year, far more than most people. If Americans miraculously became vegetarians, that would equal half of an average solar roof.

These household averages, however, mask what might be the most important thing carbon tracers reveal: that seemingly similar households produce vastly 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 or five times more carbon than city centers or rural areas, a much larger multiple than might have been expected. Chicago households produce 37 tons of CO2every year ; the suburbs of Eola, about 35 miles (56 km) from Windy City, emit 96 tons. It’s not just because of travel. Return trips to work account for less than a fifth of the kilometers travelled; the rest is for shops, schools, etc.

What is even more striking is the difference air travel makes. The average household contribution by plane is 1.5 tonnes, less than a car. But half of Americans never fly. According to Cool Climate, traveling 100,000 miles per year (as some frequent flyers do) produces an additional 43 tons of CO.2. If jet-set households were to drastically reduce 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 are promising to go to net zero carbon, implying that household emissions will have to be reduced to next to nothing. Stephanie Roe, WWF, estimates that, at best, half of the reduction could be achieved through demand-side measures, such as changes in the behavior of individuals and households. And even that would require companies and governments to provide more incentives for change through supply-side investments to make low-carbon options cheaper and more widely available. Trackers, it seems, hold daunting lessons for public bodies and private households.

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This article appeared in the United States section of the print edition under the headline “Seeing footprints in the air”

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