Calculating my Carbon Footprint?

Introduction

This unit seeks to explain what makes up a personal carbon footprint, and to identify alternative options in calculating one. For example, should footprints include emissions associated with goods and services purchased, or should they be restricted to directly attributable emissions, mainly from the use of energy and transport? There are many websites offering carbon footprint calculators, but the answers are almost always different. This unit will explain why this is the case, and allow you select the ones that you feel are most appropriate. Finally, a carbon footprint by itself achieves little; users need to be able to compare their carbon footprint with other people's, and to identify actions that might reduce the footprint to a desired level in the battle against global climate change.

Unit authored by Ian Byrne

Learning outcomes

By the end of this unit you should be able to:

• find out what carbon footprints are, and what is – and is not – included in a typical footprint;

• evaluate critically what should be put into a carbon footprint;

• understand how to calculate your own carbon footprint;

• place your own carbon footprint into the context of other UK and international footprints;

• identify how carbon footprints can used as a tool in the action against global climate change.

1 Explaining carbon and ecological footprints

1.1 Carbon footprints

A carbon footprint is a measure of how much someone is contributing to the gases that contribute to global climate change. More scientifically, it is the amount of anthropogenic carbon dioxide (CO₂) emissions (those resulting from or produced by human beings) attributable to an individual or a household or an organisation, generally resulting from their direct or indirect use of energy. Although we talk about a ‘carbon footprint’, it would be more accurate to talk about a ‘carbon dioxide footprint’. A carbon footprint is normally calculated in tonnes of carbon dioxide equivalent (tCO₂e) but occasionally footprints are calculated in tonnes of carbon equivalent (tC). You will need to multiply by 44 and divide by 12 to convert from tonnes of carbon to tonnes of CO₂ equivalent. In this unit we may talk interchangeably about carbon emissions, carbon dioxide emissions and CO₂ emissions.

Carbon footprints may also include other gases that contribute to global climate change – the socalled ‘greenhouse gases’ (GHGs). The most common of these is methane (CH₄), but they also include nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride (SF₆). These other gases tend to be produced from agriculture or industrial processes. Most are much more powerful contributors to global warming than CO₂. Water vapour (H₂O) is also a significant contributor to global warming but, as its concentration varies little with time, it is not considered to be an anthropogenic greenhouse gas, except from aircraft vapour trails (see section 2.3).

However, the largest contributor to global warming is carbon dioxide itself, which is produced from burning fossil fuels such as coal, oil or gas. As well as the direct use of fossil fuels, people's carbon footprints normally include the use of electricity (where CO₂ is emitted at the power station) and as a result of collective travel, such as on trains, buses and aircraft.

For more information on carbon footprints, look at greenhouse gases on Wikipedia.

1.2 Ecological footprints

A carbon footprint involves only the global warming effect of an individual's actions. The wider ecological footprint takes into account the use of other finite resources, such as metals, as well as water and food use. The calculator from Best Foot Forward calculates both a carbon footprint and the land area required (in hectares), to give the equivalent number of planets that would be needed if everyone had the same lifestyle.

For more on ecological footprints, look at the following web-based resources:

• explanation of ecological footprint by Best Foot Forward

• ecological footprint calculator

• the ten principles of sustainability developed by Bioregional and WWF under the name One Planet Living.

• charts showing how many planets are needed to support current global lifestyles, and how many planets based on the average inhabitants of different countries.

2 The scope of a carbon footprint

2.1 Boundary

Before calculating a carbon footprint, you have to decide on the boundary and the scope.

The boundary simply describes or limits what is being measured: it can be a single person, a household or an organisation. If you choose to calculate your carbon footprint on an individual basis, you may need to divide your home's energy consumption by the number of occupants. You may also want to bring in the CO₂ emissions associated with business travel. It is easiest to look at emission from cars on the basis of ownership. So, if you have a car, include all the fuel use (and associated emissions) from that car, but you could split emissions relating to a car that is shared with a partner, for example. It is often easier to look at the total carbon footprint of a household, but you will then need to bring in your partner's travel emissions, too.

At the domestic or individual level, people usually only consider carbon dioxide emissions, and not those from the other GHGs mentioned in section 1. But, even then, you will need to decide how to calculate indirect emissions arising from your use of services – notably electricity supply and public transport, including air travel. In the UK, DEFRA publishes a table each year showing CO₂ emissions associated with electricity. This gives two main values: an average for grid electricity; and a longer-term value for ‘marginal electricity’ – typical emissions per unit of electricity (kWh) for extra capacity brought online when demand rises or falls (that is, when people switch something on or off). However, it doesn't take into account differing emissions associated with different suppliers: for example, you may pay extra for a green tariff or buy your electricity from a company such as Good Energy or Ecotricity, which source most of their supply from renewable sources. Even among the main suppliers, some claim lower than average emissions because of purchases from nuclear power stations or a high proportion of efficient combined-cycle gas turbines. DEFRA's view is that you should use the grid average figure because it is not possible to differentiate the actual electricity that comes down the wires to your home or business.

Collectively, the selection of which indirect emissions to measure is referred to as the scope. At a corporate level, there are three internationally recognised scopes under the Greenhouse Gas Protocol explained on their website. They are described in the next section.

2.2 Scope – travel on public transport

Travel on public transport poses similar questions. If a service is running anyway, is the marginal energy use (and hence CO₂ emissions) from you getting on that service close to zero? Or should you average the emissions across a typical load factor? Otherwise, we could all fly anywhere guilt-free on the assumption that the flight was not scheduled especially for us! Data on some forms of transport is quite hard to come by or surprisingly complex. For example, how can you compare emissions from a crowded electric commuter train with an almost empty diesel multiple unit on a rural branch line? And should you try to estimate the higher emissions associated with a high-speed intercity train, compared with a slower multiple unit? It is even harder as we don’t know where the train companies buy their electricity from.

2.3 Scope – aviation

Aviation adds an extra issue – the effect of water vapour ejected at high altitude (contrails) means that flights have a much greater contribution to global climate change than solely from their CO₂ emissions. This is sometimes called the radiative forcing effect, and some carbon footprint calculators take it into account. You will also need to consider the differing emissions from long- or short-haul flights, and for flying in different classes to provide an accurate footprint.

2.4 Scope – goods and services

The final element in setting the scope for a personal carbon footprint is to consider whether or not to calculate emissions attributable to bought-in goods or services. This area is still in its relative infancy, although the British Standards Institution (BSi), working with the Carbon Trust, has published a Publicly Available Specification (PAS2050) for calculating emissions. However, few products are labelled at present, which makes including estimates in a carbon footprint quite difficult.

2.5 Resources

The following web-based resources provide additional information:

• GHG Protocol, explains scope and boundaries in detail in an organisational context (free registration is needed for this website)

• DEFRA’s guidance for conversion factors to CO₂

• green suppliers’ (contradictory) guides to CO₂ emissions from electricity

• an independent listing of proportions of renewables for all UK electricity suppliers

• what the ASA thought about British Gas’s claims to be a lower-carbon supplier

• Eurostar’s claim to be greener than flying

• George Monbiot (Guardian blogger) meets the Chief Executive of easyJet

• PAS 2050 explained by BSi.

3 Calculating your carbon footprint

3.1 Getting prepared

You have already seen that there is no single way to define a carbon footprint, nor any consensus about what is best. In this section you will look at several freely available carbon footprint calculators. You may also want to consider how you would put one together yourself using (say) an Excel spreadsheet.

Not all of the sites in section 3.2 offer a disinterested estimate of your footprint. Some use the footprint calculator to offer to offset your emissions at the end of the process. Keep a note for each calculator you try (and there are far too many to try them all) of what data you were asked for, and how often they made assumptions about your lifestyle based on UK averages. You will note that most calculators work on driving distance, not actual fuel consumption, and not all adjust for differing sizes of engine or driving styles; some don't even include rail or bus travel as an option. Try comparing the results, especially for a common flight (such as London to New York) and then see if any assumptions are given that might explain differences, such as the effects of contrails or radiative forcing.

After you have worked through some of the calculators below, do you think that you could create a spreadsheet to do the calculation for you? Where would you need to go to get data on air travel distances?

3.2 Web-based footprint calculators

Here is a list of some web-based footprint calculators for you to try out.

• The UK government’s official carbon calculator with a highly graphical interface or a Flash version (for broadband only).

• WWF’s carbon footprint calculator has a wider scope, bringing in food and ‘stuff’.

• Google’s carbon calculator for the UK allows you to plot your footprint on a Google map.

• Warwick University has a carbon calculator.

• The National Energy Foundation has two carbon calculators, one aimed at consumers wanting to pledge to make reductions and one for conversion calculations from energy and distances: a consumer version with pledges and a simple carbon calculator.

• The Carbon Footprint Company is a carbon-offset company that has a carbon calculator.

• The Carbon Neutral Company is another carbon-offset company that has a carbon calculator.

• JP Morgan ClimateCare is another carbon-offset company that has a carbon calculator, which shows that big financial institutions see a profit in footprinting and carbon offsetting.

• Carbon Clear has simple driving and air carbon calculators as part of its carbon-offset product.

4 Comparing your carbon footprint with other people's

4.1 Average UK carbon footprints

As you worked through a selection of the calculators in section 3.2, you might have been given information about the UK or international average carbon footprints. Typically, they might have told you that per capita emissions are 5.5 tonnes a year, or 10 tonnes a year, or that the average UK household emits 13 tonnes a year. This is all very confusing!

The discrepancies are largely about boundaries and scope, as hinted at in section 2. Some websites take total UK emissions (531,735,718 tonnes CO₂e, according to the National Atmospheric Emission Inventory in 2005/6) and divide it by the UK population (60,587,900 from the same source) to reach a total estimate of UK emissions (8.78 tCO₂e if you do the maths, but this tends to be reported as about 10 tonnes!). Other websites look at directly attributable emissions – household energy use including electricity and personal travel – to come up with the household figure, and then divide that by average occupant numbers to come up with the lower figure for individuals. It can be argued that the total UK figure is seriously understated, as it omits the carbon embodied in goods imported into the UK (and the UK is a significant net importer). The value of 8.78 tCO₂e also omits emissions from aviation and shipping because of the vagaries of international accounting for carbon. On a more personal level, the Carbon Account website allows you to compare your footprint with other people’s in the UK. It allows you to compare your footprint with others and to plot its movement on a monthly basis. It includes a basic calculator, based on gas and electricity use, miles driven and flights taken.

The National Atmospheric Emissions Inventory allows you to download various datasets, including CO₂ emissions for local authorities.

4.2 International carbon footprints

International comparisons are easy to make but sometimes difficult to explain. They almost always start with the simple per capita average (the 8.78 tCO₂e value) and compare this with other countries. On this measure the worst performers are usually the USA and the Gulf States. The common factors are cheap energy (especially coal or oil), widespread use of air conditioning and limited public transport systems.

In Europe, Luxembourg is the worst performer but this is due to a large steel industry using coal, relative to a low resident population. According to the Carbon Dioxide Information Analysis Center (Oak Ridge National Laboratory), per capita statistics for 2006 (the latest available), the UK ranks 38th globally, with the USA 9th and China 82nd, with emissions around half those of the UK. (China is now believed to be the largest emitter in absolute terms, with the USA second and the UK 8th.) It is salutary that the countries with the lowest emissions are failed states such as Afghanistan and Somalia.

You can find a map showing global per capita CO₂ emissions by country, with brief explanations of some of the differences on the National Energy Foundation website.

4.3 Setting a personal target – contraction and convergence

If you are concerned about global climate change, you should set yourself a target. However, it is far from clear how to fix the right level. One school of thought, based around ‘contraction and convergence’, suggests that if everyone moves globally towards 2 tCO₂e, the CO₂ concentration in the atmosphere might stabilise around 550 ppm (parts per million), which could lead to a 2 °C rise in average temperatures. By all countries having the same target, this would be inherently fair. But, increasingly, this figure of 550 ppm is seen as too high, with the instability of climate caused at that level unacceptable. A new figure of 350 ppm has been proposed, but this would mean eliminating substantially all anthropogenic carbon dioxide emissions by 2030.

The Global Commons Institute has information on contraction and convergence.

The 350.org campaigns for a lower target concentration of atmospheric CO₂.

5 Acting on your carbon footprint

By this stage, you have seen plenty of ideas for reducing your carbon footprint, when you visited some of the resources. There is even an online game to provide ideas about what you can do (see below). But if you are finding it hard to prioritise what to do, among all the conflicting suggestions, you might like to consider the energy (or carbon) hierarchy:

Under this hierarchy, carbon offsetting is seen as the last step for unavoidable emissions. This is because it is usually much easier to salve your conscience by paying for an offset than to take the more difficult actions yourself. The whole question of carbon offsetting is too complex for this unit.

Finally, don't forget to share your ideas with other people. Look into actions such as joining a Carbon Rationing Action Group (CRAG), or seeing whether your community can become part of the Transition Towns network.

Here are some other resources to explore that may assist you in changing your carbon footprint.

• Online computer game: Logicity is set in a 3D virtual city with five main activities where you are set the task of reducing the carbon footprint of an average resident.

• A click-through low-carbon house showing how the bloggers on the Guardian’s ‘Green your home’ website cut their energy bills with solar panels, insulation, wood-burning stoves and more.

• The Home Energy Check from the Energy Saving Trust identifies key energy-saving measures at home.

• Guardian columnist George Monbiot likens carbon offsetting to selling papal indulgences.

• The UK government’s Quality Assurance Scheme for Carbon Offsetting.

• The Gold Standard is a rival international quality assurance scheme backed by WWF.

• Voluntary Carbon Standard (VCS) is another international quality assurance scheme used by some UK carbon-offset comp anies.

• Transition Towns Network is a social movement that seeks to support communities to reduce their carbon footprint.

Acknowledgements

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Text

Unit authored by Ian Byrne

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Links

All links accessed 27 November 2009.