Carbon footprint

Greenhouse gases are gases that are relatively transparent to short-wave infrared radiation (such as heat from the sun). This means that they allow sunlight to enter the atmosphere and heat the Earth’s surfaces. These surfaces then re-radiate that heat as long-wave infrared radiation, which greenhouse gases tend to absorb rather than transmit.

The result is that the long-wave infrared radiation is ‘trapped’ and heat accumulates in the atmosphere causing a warming process. This process is known as the ‘greenhouse effect' because it is similar to the effect that glass has, trapping heat in greenhouses.

The four main greenhouse gases are:

• Water vapour.
• Carbon dioxide.
• Methane.
• Nitrous oxide.

For more information see: Greenhouse gases.

The term ‘carbon footprint’ refers to the total greenhouse gas emissions associated with a particular policy, individual, event, development or product.

It can be used as a measure of the impact that something has on climate change, or of the degree to which it consumes the Earth's resources. This can be used to help understand and reduce the impacts of activities, or to compare things so that lower impact alternatives can be selected.

Carbon footprints are very difficult to calculate accurately because of the complexity of the life cycle of the elements being analysed, which can include multiple components, comprising many raw materials, which have to be extracted, processed, transported, manufactured, operated, disposed of and so on. As a result, a number of carbon footprint calculators have been developed to help produce consistent, and so comparable, results.

Carbon footprints can be reduced by the careful selection, use and re-use of products, and by carbon offsetting, a process that offsets unavoidable carbon emissions by funding carbon dioxide saving projects.

The term ‘carbon footprint’ is similar in meaning to ‘embodied energy’ which refers to the total energy consumed by a building or product throughout its life, including; initial embodied energy, recurring embodied energy, operational energy and demolition energy. For more information see: Embodied energy.

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