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What is a carbon footprint?

How many carbon emissions do you generate in your day-to-day activities?

What is a carbon footprint

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.

What are carbon emissions?

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’.

  • 1,000 g = 1 kg, so, for example, 150 g = 0.15 kg
  • 1,000 kg = 1 tonne

For example:

  • When you’re driving, your car engine burns petrol, and that creates carbon dioxide. The amount of CO2e generated depends on the car’s fuel consumption and how far you drive.
  • If you heat your home with gas, oil or coal, that will also create CO2e.
  • Whenever you use electricity, that also has a carbon footprint, as the electricity had to be generated at a power station, possibly using coal or oil, which produce more CO2e than hydroelectric, wind or nuclear power.
  • The food you buy created carbon emissions, during the growing process (unless it’s organic), and certainly when it was transported to the shop or market where you bought it.
  • In fact, everything you buy – clothes, furniture, toiletries – has its own carbon footprint, which is added to yours as a ‘secondary’ carbon footprint.
  • Even cycling has a secondary carbon cost because of the emissions generated at the factory where your bike was made, and the food you eat as fuel to give you the energy to cycle. So if you only eat bananas, the CO2e from cycling a mile would be 65 g (0.065 kg), but if you ate a cheeseburger for breakfast, it would be 260 g (0.26 kg)*.

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

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.

Measuring your carbon footprint

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:

  • Synthetic fabrics like nylon or fleece generally have a lower carbon footprint than natural fabrics. This is because they last longer and you use less water and electricity to wash and dry them.
  • Standard plastic carrier bags only have a CO2e score of 10 g (0.01 kg). So even if you used as many as five a week, the annual emission would be 2,500 g (2.5 kg) – about the same as a large cheeseburger*.

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*.

Working out your road travel footprint

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*.

Travelling by train or bus:

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 footprint of flying

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*.

The carbon footprint of your food

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:

  • 7.19 kg per day for high meat eaters.
  • 5.63 kg for medium meat eaters.
  • 4.67 kg for low meat eaters.
  • 3.91 kg for fish eaters.
  • 3.81 kg for vegetarians.
  • 2.89 kg for vegans.

Some examples of CO2e scores*

  • Less than 10 g: a text message, a pint of tap water, walking through a door.
  • 10 g - 100 g: ironing a shirt, cycling a mile, a banana, an hour’s TV.
  • 100 g - 1 kg: a mug of tea or coffee, a pint of beer, a toilet roll.
  • 1 kg - 10 kg: a loaf of bread, a bottle of wine, a litre of petrol.
  • 1 kg - 10 kg: a loaf of bread, a bottle of wine, a litre of petrol.

Easy ways to reduce your carbon footprint

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:

  • Re-use and recycle as much as you can – if one household recycles at least half of its waste, that can save around 1.2 tonnes of carbon dioxide each year.
  • Replace ordinary light bulbs with energy-efficient ones.
  • Unplug all appliances when you’re not using them.
  • Leave the car at home – walk or bicycle instead, take public transport or at least look into car-sharing opportunities.
  • Turn down your heating – put on an extra layer of clothing instead.
  • Insulate your home – install double or triple glazing, insulate your home’s roof and walls, and stop draughts under doors or through floorboards.
  • Eat less meat – see ‘The carbon footprint of your food’ above – and buy local or organic whenever you can.


*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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