How to measure your personal carbon expenditure

February 23rd, 2010 by J-P Leave a reply »

When every kilogramme of carbon we produce contributes to climate change, then we each have a responsibility to minimize our own personal carbon emissions. While lots of media campaigns concentrate on the narrow field of just what we buy—stopping using plastic bags, buying certain produce—the majority of our personal carbon emissions actually comes from heating and lighting, cooking our meals, and travelling from place to place.

But it’s very hard to make moral choices when you just don’t have information about what impact you’re having. To do that you need to be able to measure your carbon emissions. And to do that, without being some sort of atmospheric scientist, you need to have a tool which translates meter readings and car odometers into relative carbon measures. There’s lots of sites out there that can take vague data about your lifestyle—how many people are in your house, how often you use the washing machine—and give you a similarly vague estimate of your “carbon footprint”. But what about if, say, you turn your heating up from 18C to 21C over Christmas? What does that mean in terms of the carbon your home emits?

Enter The Carbon Account, one of a few carbon calculators out there. It will collate your meter readings—gas and electricity—and work out how much carbon that represents based on how green your service providers are (so completely renewable electricity provision means zero carbon emissions.) It also translates car mileage, using available efficiency data for different car models, into fuel usage and hence emissions. Slightly more alarmingly, it takes any plane flight emissions and multiplies them by a “radiative forcing” factor—the estimate of the extra damage caused by emitting CO2 in the upper atmosphere—to compare them more fairly with your home and car’s emissions. You’ll find rather quickly that any plane flights you take will dwarf all but the most life-changing efforts you’d make elsewhere.

What does all this mean? Well, first and foremost, there’s a principle of “behavioural accountability” which suggests that anything measured will be almost automatically be reduced, if that’s what you want it to do. It’s a funny effect, but you’ll find your behaviour changes just from seeing those graphs going past. If you’re keeping a closer eye on your carbon emissions, and you spot the big blue lump that came from your road trip round Europe last year, then you’ll think twice about doing it next year. Conversely, if you’ve insulated your loft and you see your gas usage drop dramatically, you know a little bit more about the moral good of that decision, not just the financial good.

It also means that, while in the natural, ignorance-is-bliss course of things nobody can really excuse any plane flights anywhere, that if you can demonstrate that your carbon emissions are below the accepted per-capita global allowance by e.g. 0.2 tonnes for five years, then that means you can then justify a 1-tonne-equivalent plane flight. Carbon becomes a moral commodity, which you can save up over time and then spend on luxuries like aeroplane travel (if you really, really have to.)

In the interests of full disclosure, let’s start with a graph of my carbon usage from last year.

graph of carbon usage

What does this tell us? Well, let’s start by explaining the structure of the graph. On the vertical axis is kilogrammes of CO2 per month: that means that if the graph is at “200” for a whole month, then I’ve used 200kg of CO2. On the horizontal axis is of course months of the year. The three colours indicate the fractions of usage owing to electricity (mustardy green), car usage (blue) and gas (claret). Along the top are notes: when you submit a reading, you can also add a note to it, to remind you of anything important you did at that point (e.g. insulated the loft, or sold the car!)

The detail available is actually immense, and if you’re serious about cutting your carbon, for whatever reason, you can get a lot of information out of a graph like this. For example:

  1. We moved house in the latter half of 2009, from a leaky 3-storey cottage to a terraced house. You can see the effect on both electricity and gas readings if you compare either side of October. We didn’t turn the central heating on in the new place straight away either: hence the sharp dip.
  2. The car was used a lot in December 2008/January 2009 as I didn’t cycle, hence the wedge of blue on the left. The little note marks the point where I started cycling regularly and frequently again.
  3. We used the car to help us travel back and forth, redecorating, before we left and locked up the old property in October. There’s a large lump of blue around the summer that indicates that, with a note at the end of the period to indicate when we switched everything off at the old place.
  4. Our electricity usage is not seasonal: the height of the mustard-yellow component is almost constant at the old house, then it changes to another constant value at the new one. That means that e.g. increased lightbulb or oven use in winter baking has far less effect than the fridge being on all year round.
  5. Our gas usage is definitely seasonal: see how much the claret graph varies. It’s also the greatest single component of our carbon emissions, so if we want to do anything to improve the house’s efficiency rating then we have to look at draughts, insulation, a new boiler etc.

Since taking this image I’ve added more data to my Carbon Account, including our increased power usage over winter, and a car journey to see family at Christmas. Our house move’s effect on gas usage looks considerably less impressive since the cold snap, but that in itself gives us pointers about what we can do next.

The Carbon Account isn’t perfect: none of the tools out there are. It doesn’t include rail, bus or ferry journeys; it doesn’t account for well-tuned, ecodriven cars using far less fuel than badly maintained ones; and it doesn’t measure carbon from the produce you buy, or the carbon that the state—NHS, governmental departments, city maintenance—emits on your per-capita behalf. But it can help to change your lifestyle, and hopefully change your life, for the better.

If you’re interested in trying out the Carbon Account, you can do so straight away: register on the site now. It’ll ask you for a few details so it can calculate an initial estimate but that’s it. Alternatively, come and say hello this weekend at the Fair Trade Market. I’ll be on the Sustainable Witney stall from 10.30 till at least lunchtime, laptop in hand, to help demonstrate the Carbon Account.

(Even fuller disclosure: I work for the company which originally built The Carbon Account. But this isn’t really a plug, as we handed over ongoing development and support to a government-supported organization. I just happen to still use it loads.)



  1. jonathan says:

    The carbon calculator is a useful tool.
    Unfortunately the language we have learned to use when discussing global warming is a bit loose. It is understandable why this has come about but can cause confusion

    We do not actually emit carbon but by burning fossil fuels cause the emission of carbon dioxide which is a greenhouse gas.

    Carbon is a chemical element made up of just carbon atoms whereas carbon dioxide is a compound made up of 1 carbon atom and 2 oxygen atoms bonded together.

  2. Kevin says:

    I’ve registered with The Carbon Account and found the bills out to get some initial readings. Took readings for today and entered those – the most difficult part was finding the triangular key for the gas meter!
    Had a play around with flights to see what they look like which was interesting. It’s very easy to do a what if – enter a flight, see what it does to the graph, and then just delete it afterwards. Great for putting things in perspective.
    I reckon if anyone’s signed up for the 10:10 campaign pledge this will be a great tool to monitor how they’re getting on.
    Presumably there’s a figure for the per capita emissions for services provided on our behalf?

  3. J-P says:

    The usual figure quoted is that 50% of the average per-capita UK carbon emissions are a result of the national infrastructure burning fuel on your behalf. This information is notoriously hard to get a hold of in capsule form, although lots of raw data sets do exist out there for the not-so-faint-hearted.

    I never know whether to call them carbon or CO2 emissions: they both hide the fact that methane is often treated as a CO2-equivalent gas and added to the final measure. “Carbon” is less clumsy in conversation than “CO2”, although less strictly accurate.

    The masses are related by a constant: C*3.7=C02 . So as long as you know what you’re aiming for — say a 10% reduction of your total as part of the 10:10 campaign — in whatever units, it doesn’t matter too much unless you’re comparing them to other statistics.

  4. Kevin says:

    Is the constant gas usage from May though September water heating?

    It’s a fair chunk of the summer emissions that could presumably be excised by solar water heating?

  5. Sally says:

    Really interesting Blog J-P. I liked seeing the personal graph and reading about what the graph was telling you. I’m going to register next week.

  6. J-P says:

    Is the constant gas usage from May though September water heating?

    Hard to tell: cooking and non-CH water heating are the two year-round constants. But that constant gas usage is actually from our last house, where you had to run the water in the kitchen for literally two minutes before it would be hot enough.

    Sally: let us all know how you get on. I think Kevin’s been successful in putting historical data in using utility bills. If any car repairs or services record your mileage then you could do the same for that, to get some idea beyond the CA’s initial estimates.

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