GHG are gases emitted from the majority of human activity which trap energy from the sun radiated off the earth's surface in a process similar to that of a greenhouse (hence the name).

The main GHG, collectively known as the “Kyoto Basket of Six” (after the international agreement that listed them as being of particular concern), are: Carbon Dioxide (CO2), Methane (CH4), Nitrous Oxides (N2O), Hydrofluorocarbons (HFC), Perfluorocarbons (PFC) and Sulphur hexafluoride (SF6).

The amount of energy different gases trap and radiate is known as global warming potential (GWP) and is expressed in relation to a known unit of carbon dioxide (usually a tonne).Increased concentrations of these gases in the Earth's atmosphere is leading to alterations in global weather and climate patterns in a phenomenon known as climate change.

What are the benefits of having a carbon footprint calculated?

Research by the Carbon Trust shows that there are four areas where businesses can gain a competitive edge from having a carbon footprint:

• Achieve cost savings by identifying inefficiencies and wastage in their processes and providing a framework for action to address and resolve these ‘hotspots'. Sequential carbon footprinting allows for benchmarking of company performance and can be an integral part of a continuous improvement process.
• Enhanced reputation by demonstrating their commitment to improving environmental performance in a measured and quantifiable way.
• Achieve legal compliance as the data collection process for carbon footprinting can reveal areas where the company may be in breach of existing environmental legislation, allowing the company to take prompt action and avoid potential penalties.
• Assist with employee recruitment and retention as research has shown that individuals generally prefer to work for environmentally responsible organisations.

How is a carbon footprint calculated?

At a simplistic level, a carbon footprint is the sum of total GHG emissions from all activities within an agreed boundary and multiplied by their respective GWP, with the result expressed as tonnes CO2 equivalents (t CO2e).

As a result of a vast body of research and international agreements, calculating carbon footprints benefits from well established methodologies and growing library of emission factors for different activities.

A key stage in the calculation of any carbon footprint is the definition of boundaries, as the decision of “where the line is drawn” both informs and expedites the subsequent data collection stages.

As the range of activities that can be included in a carbon footprint is potentially endless, it is important that appropriate boundaries are set, as these will aid data collection efforts. Ultimately, however, the range of activities included should be determined by the reason for calculating the footprint.

For example, if a footprint is to be used to foster efficiency improvements by indentifying “carbon hotspots” then only onsite activities need to be included. If a footprint is to be used to aid product marketing initiatives, then the boundary needs to include the wider supply chain.

However, the extent of the carbon footprint should ultimately be defined to support a concrete business objective, such as improving resource efficiency or explore a competitive advantage through product footprinting.

The methodology used in the UK and associated emission factors are available from DEFRA's website.