Some greenhouse gases, like carbon dioxide, appear naturally in the atmosphere. But CFCs (short for chlorofluorocarbons) are a direct result of industrial processing and chemical engineering. CFCs are found in aerosols, refrigerator coolants and air conditioners. They are much more harmful than other greenhouse gases.

CFCs are believed to be responsible for destroying a part of the atmosphere known as the ozone layer. At an altitude of around 10km (6 miles), the ozone is a protective layer that reduces the amount of ultraviolet light emitted by the sun reaching the Earth. Besides being harmful to our skin, increased UV light also contributes greatly to global warming.

Despite the threat of CFCs, carbon dioxide still causes the most damage to our environment. That's because there's so much more of it being produced. In fact, carbon levels in the Earth's atmosphere have risen by over 30% since man began relying on fossil fuels during the industrial revolution 160 years ago. Motor vehicles are now responsible for around 15%, or 400m tonnes, of our total carbon output. Scientists know that if car numbers increase at the present rate there will be more than a billion on the road in 2025.