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There has been a watershed in the UK鈥檚 attitude to global warming. The Stern Report, the popularity of Al Gore鈥檚 film An Inconvenient Truth and the government鈥檚 announcement that all new homes will be zero-carbon by 2016 marked the point when sustainability came of age. In both the public and private sectors, in government and the population at large, attitudes have shifted.

Carbon footprinting has become a hot topic. Our personal carbon footprint is a measure of how many tonnes of CO2 are emitted, directly or indirectly, as a result of our consumption of goods and services. In the UK, on average it鈥檚 about 12 tonnes, in America it鈥檚 roughly twice that amount, while in India it鈥檚 closer to 2 tonnes. How much should we be emitting? To meet the UK鈥檚 2010 20% CO2 reduction target, we need to reduce our footprint to 8 tonnes, but the true globally sustainable level of personal carbon emissions is thought to be about 2 tonnes per person. This means we have some big reductions to make if we鈥檙e going to do our bit for the planet.

To calculate a personal carbon footprint, emissions are typically divided into three areas: dwelling-related, transport and lifestyle. It鈥檚 possible to go into great depth when carbon footprinting, so this article makes some necessary generalisations to make the whole process quick and user-friendly. It is designed to be used with the calculator (see graphic attached), where you can fill in your personal emissions to calculate your own carbon footprint.

Dwelling emissions are fairly straightforward to calculate 鈥� all you鈥檒l need is a year鈥檚 worth of energy bills and a few handy conversion factors. First, total up the kilowatt hours of electricity you鈥檝e used in the year, and multiply the result by 0.527 to find how many kilograms of carbon were emitted to provide you with that quantity of electricity. Repeat the process for gas, using the relevant conversion factor. If you use a wood-burning stove, oil or coal, work out the annual quantity used (take a weekly average and multiply if you haven鈥檛 got records) and use the appropriate conversion factor to work out the related emissions. Add up all of these totals to find your dwelling-related emissions, and then divide the total by the occupancy of the house to determine your individual share.

In percentage terms, dwelling emissions are typically composed of space heating (53%), water heating (20%), cooking (5%) and lights and appliances (22%). When looking to make savings it makes sense to attack the biggest target 鈥� space heating 鈥� first. Injection-filling cavity walls with insulation will set you back about 拢260, but you can save about 拢150 annually. If your loft has low insulation levels (50mm), top it up to 270mm (拢240) and you can save about 拢50 a year. Surprising savings can also be made simply by draught-proofing your home 鈥� typically, about 20% of heat loss occurs in this area. Draught-proofing costs about 拢75 and pays for itself in savings within four years.

These kinds of fabric measures aren鈥檛 very glamorous and it may be tempting to cut to the chase and stick a renewable energy installation on the roof, but bear in mind that without first addressing the fundamental thermal performance of your house, your money could be spent more effectively elsewhere. If you decide to go for renewables, there is a multitude of options 鈥� for more information, and to learn more about the savings available, visit www.energysavingtrust.org.uk.

The second main footprint area is transport. First, you鈥檒l need to have an idea of your annual car mileage 鈥� check MOT certificates if you鈥檙e not sure. Multiply your annual mileage by 0.33, but then divide that total by the average number of people who use the car to determine an individual share of its emissions. You鈥檒l need to exercise a bit of judgment at this point; for example, if you share the car with another person half of the time, divide by 1.33 to obtain your 75% share. At this stage, work out your annual taxi usage and calculate it in the same way as your car emissions, using the same emissions factor.

Next, tot up your annual train and bus mileage and proceed as before, using their appropriate emissions factors. Finally, add up all of the flights you鈥檝e taken in the past year. For simplicity, these can be calculated using total hours鈥� duration or using distance (the calculation assumes an average speed of 500mph). Remember you鈥檒l need to account for the return trips too. Enter the data into the calculator in the usual way.

When it comes to transport emissions, the big offender is clearly air travel. This portion of the footprint can dwarf all other emissions, and can send otherwise very green individuals spinning off into carbon purgatory. Allowing for the exacerbated effect of high-altitude CO2 emissions, a return trip to a European destination such as Spain will emit well over half a tonne of CO2 per person, and a return flight from London to Australia may well emit about 5 tonnes. Unfortunately, this means that saying 鈥淚鈥檝e installed energy efficient light bulbs 鈥� now can I take that flight?鈥� won鈥檛 really wash, as any savings that you鈥檝e made are likely to be obliterated.

However, by switching your European flights to the rail network you can reduce your CO2 emissions by more than 50%. For informal advice on alternatives to air travel, visit www.seat61.com. Other reductions can be made by using more public transport, using a bicycle or even walking, switching to a smaller car, or car sharing 鈥� at full occupancy, most car emissions profiles will be comparable to public transport.

Lifestyle emissions are the final piece in the carbon jigsaw, and are the most difficult to quantify. They consist of emissions associated with the goods we buy (for example, food miles), as well as CO2 from our leisure activities, such as going to the gym. These emissions can be reduced by careful choices, but certain aspects of lifestyle emissions 鈥� for example, maintenance of national infrastructure such as defence and hospitals 鈥� loom in the background of even the greenest consumer As individuals, we are stuck with them. These 鈥渘on-negotiable鈥� emissions are estimated at about 1 tonne per person.

However, when it comes to the remainder, we can do our bit by combining a variety of approaches. First, by minimising waste: for every tonne of food sold, there is a quarter of a tonne of packaging associated with it, and for every bag of waste you throw away, further CO2 is emitted in its transport, handling and eventual landfill. To cut these emissions, compost all kitchen waste and buy unpackaged food when available.

Food miles 鈥� denoting the distance food has travelled before ending up on our plates 鈥� have been a hot topic for the a couple of years and can make up a big chunk of lifestyle-related CO2 emissions. The aim is to buy local and buy organic 鈥� look for the Soil Association logo. On a separate issue, although Fairtrade is a great scheme, it has nothing to do with energy.

In the garden, use your compost rather than buying from the garden centre and, instead of using fossil fuel-derived fertilisers and pesticides, try natural alternatives 鈥� see www.panda. org for more information. Avoid sprinklers, hedge trimmers and other electric aids and invest in a water butt and some hand tools 鈥� you鈥檒l save carbon and get fit. Finally, energy intensive leisure activities also contribute to lifestyle emissions, so instead of using electrically powered equipment at the gym, go for a jog, and ditch the jet ski for kite surfing. Going green doesn鈥檛 have to be dull.

Producing an accurate lifestyle emissions count is beyond the scope of this article, so the carbon calculator asks you to rate your emissions based on your own assessment of the energy intensity of your lifestyle. For example, if you鈥檙e a regular gym user who goes motor racing at the weekends and lives off ready meals, you鈥檙e likely to be at the top of the scale. This part of the calculator is approximate, so make a judgment as to where you stand.

Having completed the three sections, add up the totals to find your individual carbon footprint. Now you have a baseline, taking action to reduce your emissions can be surprisingly rewarding. In the December issue of BSj, we will be taking a similar look at how to reduce your workplace footprint.

Online carbon calculators:

• Try for a quick approximation of your footprint
• For a more accurate, in-depth calculation, go to Defra is producing a calculator that should combine the best elements of the above 鈥� check for the latest news