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CarbonStory and complexities of online calculators

A few years ago I was trying to assess my carbon footprint, and had got conflicting advice on how big it actually was. I sat down on a rainy day and clicked my way through eight different online footprint calculators, giving me estimates of annual emissions between 1.5 and 9.4 tonnes. Clearly not all carbon calculators are created equal.

I wrote up my unscholarly observations for anyone else pondering the question, but I was pleased to find someone else addressing the problem properly. While studying sustainability and environmental management at Harvard, Andreas Birnik analyzed a range of online carbon calculators and came up with a set of 13 principles of best practice. He then ranked 15 online calculators and found that most of them aren’t up to scratch. And then he developed a better one.

There are a lot of questions to iron out – should it be CO2 alone, or a wider basket of greenhouse gases? How should those other gases be turned into a single figure? Should they include consumption of goods and services as well as energy and transportation?

When assessing most calculators, Birnik found that there were serious shortcomings. Most didn’t have proper documentation, so you couldn’t actually tell what was being measured or how things were being worked out. Many resorted to national averages on certain more complicated elements. Many were fundamentally incomplete. Six of the 15 didn’t include emissions from food, despite that accounting for 16-31% of our footprints. Government calculators are singled out for particular criticism. The EPA’s doesn’t include any public transport. The UK’s DirectGov calculator asks for great detail about computer peripherals and gadgets, but then forgets to mention food. Frustratingly, “a clear majority of calculators appear to systematically yield underestimated carbon footprints” he concludes.


Birnik built on this research to develop a better calculator called CarbonStory. It accounts for international differences, and is based on peer-reviewed findings as much as possible. Like all the better calculators, it demands specific usage information, rather than asking for the size of your house and whether or not you’ve got double glazing, like some of the others do. You can specify the number of trips you take, rather than just saying you have or don’t have a car. This is helpful, though it does require more of a commitment than the rough estimate calculators offered by the likes of Google or WWF.

Unfortunately, CarbonStory still suffers from a lack of detail elsewhere. It includes a host of categories around consumption, but these are rather general. So I can either tick the box to say I frequent hotels and restaurants, or untick it. They’re lumped together, so I have to tick it since I eat out from time to time, even though I can’t remember the last time I stayed in a hotel. Ticking it adds almost three tonnes to my total, more than my entire footprint on some other calculators. Likewise, I suppose I have to tick ‘alcohol, tobacco and drugs’, despite not smoking. These are also based on national averages, which is frustrating for those who might have made efforts to lower their consumption. I’m very selective about my purchases of clothing and footwear, but I get the national average regardless, adding almost a tonne for the contents of my wardrobe.

The calculator allows you to build a personal footprint or a household one. I attempted the household option, rather than divide everything up, but then there’s no way of specifying that two of the four of us in the house are little people. Eden isn’t even on solid food yet, but the calculator counts her as an adult eating at the national average. Presumably the ‘alcohol, tobacco and drugs’ box that I ticked assumes the consumption of four adults too.

One other hesitation is that, like many calculators, CarbonStory is geared towards offsets. It’s a social enterprise, but it still aims to sell you offsets at the end of the process rather than encourage you to cut your emissions. I’m not against offsets, and theirs are considerably more responsible and transparent than most, but the balance here doesn’t seem quite right.

In short, even by taking the time to learn from the mistakes of others, CarbonStory still hasn’t delivered a great carbon calculator.  It’s still in beta at the moment, so perhaps some of the problems will be ironed out in time and a bit more detail added. I hope so. It would be nice to have a carbon calculator that actually delivers a figure with confidence. As it is, I can still only really recommend George Marshall’s Carbon Detox as the best place to work out your footprint, and that’s a book.


  1. Nice to know others are scratching their heads on this topic. As someone who doesn’t live anywhere (nomadic) I find it impossible to have a calculation but I am very interested in knowing my carbon footprint with the flights I do… (scared to find out but important to find out).

    Anyone out there know a good flight emissions calculator? To offset I donate to organisations I know who are doing effective and sustainable environmental projects but would also be happy to know of other programs out there related to flight emissions as well…


  2. What about Quicksilver?

    seems to address most of the issues mentioned above, and you can tweak the settings to fine-tune for the nuances of your own behaviour. I still have some questions about it (for example, it rate my bus travel as about twice as bad as a single-occupant journey in an economical car, and i’d like to know what basis they use for these settings). But it is the best i’ve come across so far. I also like Carbon Detox; i think Quicksilver complements it.

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