A number of gases in the atmosphere are known as greenhouse gases. This is because they trap heat from the sun that is normally reflected back into space from the Earths surface. By doing this they act like the glass panels in a greenhouse, which let light in and keep heat inside. Without them the world would be a lot colder, but recently, levels of some greenhouse gases have begun to increase. In the last 20 years, concern has grown that the increase of greenhouse gases and global climate change or global warming are, at least in part, associated with each other, which could have detrimental effects such as rising sea levels and the extinction of plant and animal species that cannot cope with the change. It is known today that the Earth has warmed up by about 0.6C in the last 100 years.

Carbon dioxide (CO₂) is an important greenhouse gas, and levels of it are slowly increasing. This occurs as a result of the burning of fossil fuels, which release a great deal of carbon dioxide into the air. Reducing carbon dioxide emissions is an important part of the United Nations Sustainable Development Programme. In the UK, emissions of carbon dioxide have not risen throughout the 1990s, partly through cleaner technology and also through the substitution of gas for coal in electricity generation. Natural gas gives off much less CO₂ than coal when it is burnt. It also gives off lower sulphur dioxide emissions, which results in less acid rain.