Carbon dioxide: a naturally-occurring gas, which is also produced when fossil fuels are burned. It is the main greenhouse gas, and is responsible for climate change.

Carbon footprint: the amount of CO2 produced by individuals and companies. Activities such as travel, heating and shopping all form part of your carbon footprint.

Carbon neutral: when a person or company - through energy efficiency, carbon offsetting and other techniques - contributes no net CO2.

Carbon offsetting: improving your impact on the environment by contributing to support projects which reduce CO2 production.

Climate change: a change in global weather patterns, including temperature and storms. Climate change is partly influenced by greenhouse gases.

CO2: the chemical name for carbon dioxide.

Fossil fuels: fuels such as coal, oil and gas, which are formed from the decomposed remains of plants and animals.

Greenhouse gases: these trap heat radiated from the earth, and contribute to global warming.

Parts Per Million (ppm): The amount of pollution in the air is usually measured by its concentration in air which may be defined in terms of the proportion of the total volume that it accounts for. Concentrations of pollutant gases such as CO2 in the atmosphere are usually measured in parts per million by volume (ppmv), parts per billion by volume (ppbv) or parts per trillion (million million) by volume (pptv). So 370 ppm means 370 parts of CO2 to one million parts of air.

Renewable energy: sources of energy (such as wind and solar power) which don-t rely on a limited supply of fuel.