A carbon footprint is defined as the total amount (or the nearest estimate we can achieve of that figure) of greenhouse gas caused by an organisation, event, product, country or person over a set period.
The main greenhouse gas is carbon dioxide (CO2), but there are others, including methane and ozone. These would also be included when working out the carbon footprint of an individual, activity, item, business, lifestyle or country, so the result is usually shown as CO2e – where ‘e’ stands for ‘equivalent’ and shows the effect of all these gases together. As a group, the output of these gases is known as ‘carbon emissions’.
Driving a car, taking a flight and heating our homes all have an impact on the environment, because these activities create carbon emissions, which scientists believe are a major driver in climate change.
Adding together the carbon emissions of all your daily activities, from shopping at your local greengrocer to flying round the world, will give the amount of greenhouse gas you cause over your lifetime. This is what’s meant by the term ‘carbon footprint’.
The production process of building your car in the factory also created greenhouse gases, so it’s greener to buy a used car and then keep it for as long as possible, even if the actual model is less eco-friendly than some new cars.
In fact, according to The Guardian, if you can make a car last for 200,000 miles rather than 100,000, the emissions for each mile the car does in its lifetime may drop by as much as 50%, as you’re spreading its manufacturing emissions over a longer time. You can find out about different makes of car and their carbon emissions at http://www.dft.gov.uk/vca/fcb/index.asp.
It’s practically impossible to calculate a total carbon footprint accurately because you would need so much data and you would have to exclude any random CO2e produced by natural events. However, you can get a rough idea of your basic carbon footprint over a year for various activities, such as travel. You can then add them together to calculate a single figure for the amount of CO2e that enters the atmosphere because of the fuel and electricity you’ve used during that time.
Your carbon footprint is measured in tonnes (or tons in the USA). A ‘carbon calculator’, will give you a rough idea of your carbon footprint for selected activities like flying and driving, and you can then add them together for an approximate total.
It can be fun – and quite shocking – to use a carbon calculator, and it’s an effective reminder of how much CO2e we generate with the simplest, most innocuous activities.
For example, even when working out your ‘secondary’ carbon footprint (from items you buy and use rather than activities like heating your home or driving), it’s practically impossible to get a zero score. To do so, you would need to be a vegan, grow all your own food organically, buy everything second hand and unpackaged, recycle or compost all your waste, never drive a car and not even have a bank account.
Some figures are quite surprising:
Carrier bags create other environmental problems, of course: they don’t biodegrade for hundreds of years, and in the meantime they sit in landfill or, worse, waft out to sea and kill seals, fish and seabirds.
However, animal products tend to be extremely carbon intensive. Of the 2.5 kg of CO2e scored by the cheeseburger, 1.91 kg is due to producing the 108 g of beef, 0.25 kg is due to the cheese, and around 0.2 kg is generated by the cooking and transport. The rest is the bun (50 g), the salad (10 g) and the condiments (80 g)*.
So when the average person in the developed world carries a plastic bag of food out of the supermarket, that bag probably represents about one thousandth of the the total carbon footprint of the food inside it*.
If you ignore secondary items like the cost of producing your car at the factory, road travel is one of the easiest aspects of your carbon footprint to evaluate.
Using 1 litre of petrol creates 3.15 kg of CO2e*.
Driving 1 mile in an average car at 33 mpg creates 7.1 kg of CO2e.
Commuting in heavy traffic can cause three times as many carbon emissions as driving on a clear road*.
1 mile on a typical London bus or an Intercity standard class train creates around 150 g (0.15 kg) of CO2e*.
1 mile by London Underground is 160 g*.
The carbon emissions of flying depend on whether it’s a short hop or a long-haul flight.
One person flying from London to Glasgow and back (405 miles each way) would generate around 500 kg of CO2e.
The same person flying economy class from London to Hong Kong and back (5,969 miles each way) would cause around 3.4 tonnes*.
A 2014 study by Scarborough et al** looked at the real-life diets of people in the UK and estimated their dietary greenhouse gas footprints. The average daily CO2e emissions were:
In general, the ways you can reduce your greenhouse gas emissions are the same as the ways recommended for making your home more energy efficient and saving money on your energy bills. So they’re good for you as well as for the planet:
*Mike Berners-Lee ‘How bad are bananas?’ Profile Books Ltd 2010
**Peter Scarborough, Paul N. Appleby, Anja Mizdrak, Adam D. M. Briggs, Ruth C. Travis, Kathryn E. Bradbury, and Timothy J. Key, 'Dietary Greenhouse Gas Emissions of Meat-eaters, Fish-eaters, Vegetarians and Vegans in the UK', Climatic Change, July 2014, Volume 125, Issue 2, pp. 179-192, DOI:10.1007/s10584-014-1169-1.
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