Carbon Footprint – A measure of all the greenhouse gases we individually produce, through burning fossil fuels and refrigerant gases expressed as tonnes. Carbon footprint is measured in tonnes of CO₂ per year

To remember the meaning of the term Carbon Footprint, use the following mnemonic:

On a car bonnet, a huge foot left a print (carbon footprint). They weighed the foot afterwards: it was one tonne (measured in tonnes). Making the foot green reminds you, too, that it is all about greenhouse gases.

CARBON FOOTPRINT = Number of tonnes of CO₂ per year.

Individual carbon footprints vary enormously – many tonnes in the US and generally very small in undeveloped countries. Bear in mind the term "carbon footprint" includes other gases such as methane, so it's not just CO₂.

2016
United Kingdom = 5.6 Tonnes of CO₂ per person per year
United States = 15 tonnes of CO₂ per person per year

• A carbon footprint includes all the different greenhouse gases that contribute to global warming: CO₂, methane, nitrous oxide and refrigerant gases.
• Carbon dioxide is produced when we burn fossil fuels for electricity and transport.
• In 2016, the world average was 4 tonnes of CO₂ per person per year released into the atmosphere.
• In 2019, 15 countries were responsible for almost three-quarters of the world's carbon emissions.
• In 2017, China was responsible for 27.2% of all the world's carbon emissions.

The Greenhouse Effect

Solar radiation heats up Earth's surface and is emitted back into the atmosphere as infrared radiation. Carbon dioxide is transparent to solar radiation and yet absorbs the infrared radiation that is reflected back up from the earth. So, the presence of carbon dioxide in our atmosphere allows sunshine to penetrate to Earth's surface but inhibits the emission of infrared radiation to space. This warms up the atmosphere and is known as the greenhouse effect.

CO₂ and other greenhouse gases trap heat in Earth's atmosphere.