3 How heavy is your footprint?
You’ve seen that individual and household carbon footprints vary widely both within and between countries. So, in this section you’ll be measuring your individual (i.e. personal) carbon footprint using a computer-based calculator.
The carbon calculator was specially developed for the Open University by drawing upon some of the studies and reports discussed in previous sections. The data from these were then updated using the latest available statistics.
In Section 2, you saw that household income and the number of people occupying the household usually have a big effect on individual carbon footprints. That’s why these questions are included in the carbon calculator.
The calculator will show you which consumption activities make large and small contributions to your carbon footprint. But because the calculator is a model of reality, a simplified representation of the real world, it can give you only an approximate measure of your carbon footprint and how it is broken down into: emissions arising from the energy you use for room and water heating; your travel by car and air; your typical diet, usual spending habits, and so on.
The results the calculator produces are only as good as the accuracy of the data, assumptions, equations and options within the model and the information you enter into it. For example, if you drive a medium-sized petrol-engine car, the calculator works out the carbon footprint of your personal car travel by multiplying your approximate annual car mileage (chosen from a drop-down list of options) by the mean CO2 emissions per kilometre for medium (1.4 to 2 litre) petrol engines from official statistics adjusted for the number of people who typically occupy a household car when in use. The accuracy of the car footprint depends on how close your actual car mileage is to the options offered by the calculator, how close your actual car emissions are to the mean for 1.4 to 2 litre petrol-engine cars, and how typical your car occupancy actually is.
The calculator could, of course, provide a more accurate car travel footprint if it asked you for more detailed information, such as the make and model of your car, how many people usually travel in the car and your typical annual car mileage. But it could be time-consuming and laborious if this amount of detail were required for all the questions in the calculator. Carbon calculators therefore make compromises between the time and effort required to use them and their accuracy. This one tries to make the process fairly quick and easy, and focuses on the information that has the biggest effects, in order to provide an approximate, but realistic, individual carbon footprint.
The carbon calculator also enables you to try out the effects on your footprint of making changes; for example, to your home’s energy efficiency. Testing different changes without having to make them in reality is a form of computer modelling. In Section 4 you’ll be asked to reduce your footprint by modelling the effects of changes allowed by the calculator – such as driving or flying less or more, or changing your car, diet or spending behaviour. Because it uses the consumption-based perspective, the calculator assumes that most of the nation’s footprint arises from consumer demand and behaviour. The emissions generated by public services, business and non-governmental organisations are allowed for to some extent, but the main responsibility for reducing the footprint is given to individuals and households. However, in Section 5 you can try out the effects on your footprint of making changes beyond the household level, such as spending some of your income on ‘voluntary carbon offsets’ for carbon-saving projects overseas or agreeing to tax increases for national investments in low-carbon technologies.