There are different types of gasses that are enabling the greenhouse effect and thus global heating. These are known as greenhouse gases. The most commonly known are carbon dioxide (CO2) and methane (CH4), but also water vapor (H2O) and ozone (O3) can trap heat in the earth’s atmosphere and thus contribute to its heating.

The different gases are differently effective in trapping heat, and some of them remain much longer in the atmosphere than others. These characteristics are summarised as the Global Warming Potential of a gas. To make it easier to quantify greenhouse gas emissions and discuss actions to reduce them, they are usually summarised as CO2-equivalent.

Greenhouse gas emissions can be measured on a national level, but also on a personal level. To do this researchers take into account the according level of greenhouse gas producing activities.

For a nation this would include things like energy and food  production, but also production of goods and transport. The level of activity in each area is measured or estimated based on data, like taxes, permits and so on. Each activity can then be matched with an according emission, for example a flight from Manchester to London emits a certain amount of greenhouse gasses as does the production of a kilo of beef. Matching these numbers with the tracked activity in a country allows to produce an estimate of its emissions.

Similarly for an individual their activities can be matched to greenhouse gas emissions: Depending on how much energy they use to heat their homes, or miles they travel by car, all of this contributes to what we call the ‘Carbon Footprint’: A measure of the amount of emissions created by an individual.