How Well Do Carbon Footprint Calculators Estimate Your Impact?
Comparing nine online surveys reveals some discrepancies
Katie Peek • January 26, 2010
Plenty of places are in the business of green guilt these days, especially the myriad web sites offering to assuage your travelers’ remorse with carbon footprint calculators and the corresponding carbon offsets. While there are many questions to ask about the accuracy of these sites, a basic one is: do they at least agree with one another?
To find out, I put a consistent life picture into ten online footprint calculators, and found a vast range in the outputs: the Climate Crisis calculator (from Vice President Al Gore’s Alliance for Climate Protection) estimates I emit 2.9 tons of carbon dioxide each year, while the Global Footprint Network thinks my impact is 23 tons — nearly an order of magnitude higher.
Part of the discrepancy comes from the different carbon-producing activities each calculator factors in. I included my life story at Brighter Planet and was tickled that Belgrave Trust (aimed at luxury consumers) inquired about my yachting habits. Some calculators, like the Nature Conservancy’s, declare my commute carbon-neutral just because I don’t use a car, but New York City’s subway produces about 60 percent as much carbon per person per mile as a Prius, so my train time ought to count.
More troubling, however, was finding different results for the same activity. Flying to San Francisco once and Buffalo twice created 5.8 tons of carbon dioxide according to the Nature Conservancy, but only 1.1 tons in the TerraPass calculator. The calculators aren’t forthcoming enough about their methods to figure out where the discrepancy comes from.
So maybe carbon offset calculators aren’t all they claim to be. They can be useful for identifying the places where lifestyle changes can have an impact — one fewer plane flight per year reduced carbon footprint substantially in every calculator — but I, for one, might look for other ways to ease my guilty greenhouse conscience.
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About the Author
Katie Peek
Katie Peek is an astronomer by training, with a Ph.D. from the University of California, Berkeley, where she discovered extrasolar planets and investigated the formation of the Milky Way’s heavy elements. Now she likes to write about nature and the environment. Visit her web site at www.katiepeek.com.
5 Comments
Well said!
I also find the push to include “carbon tons” (or lbs, or grams) on individual products a terrible mistake and a waste of time. It suggests a level of accuracy that is, as you point out, grossly exaggerated.
Nice post, Katie, and thanks for checking out our carbon calculator at Brighter Planet.
We agree that there’s much room for improvement in consistency among online footprint calculators. The discrepancies are largely due to two things — the level of personalization, and the categories of emissions that are included. Even for something as straightforward as a flight, your emissions depend on things like your seat class, your layovers, and your aircraft type, and they depend on whether non-carbon climate impacts like radiative forcing are included.
We’ve tried to design our calculator to be comprehensive but flexible, with the end goal being to give people perspective on their impact so they can start working to reduce it.
You might be interested in a post we did on this subject a while back, over at Carbon Offsets Daily: http://www.carbonoffsetsdaily.com/news-channels/global/rethinking-the-personal-carbon-calculator-31070.htm
Nice post, Katie, and thanks for checking out our carbon calculator at Brighter Planet.
We agree that there’s much room for improvement in consistency among online footprint calculators. The discrepancies are largely due to two things — the level of personalization, and the categories of emissions that are included. Even for something as straightforward as a flight, your emissions depend on things like your seat class, your layovers, and your aircraft type, and they depend on whether non-carbon climate impacts like radiative forcing are included.
We’ve tried to design our calculator to be comprehensive but flexible, with the end goal being to give people perspective on their impact so they can start working to reduce it.
You might be interested in a post we did on this subject a while back, over at Carbon Offsets Daily: http://www.carbonoffsetsdaily.com/news-channels/global/rethinking-the-personal-carbon-calculator-31070.htm
Oops, should have said great post! Can’t wait on the next post!
Interesting. Do similar issues plague carbon markets?
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