What are the major greenhouse gases?
Carbon dioxide
About half the global warming problem during recent years has been caused by carbon dioxide, the most well-known greenhouse gas. Every year, the burning of coal, gas and oil — fossil fuels — to produce energy in power stations, factories, cars and homes adds over five thousand million tonnes of carbon to the atmosphere. The accelerating destruction of the world's forests adds at least another thousand million tonnes as trees are burnt or decay.
The halocarbons
The halocarbons, which includes the CFCs, are powerful greenhouse gases — molecule for molecule, 10,000 times as effective as carbon dioxide — as well as depleters of the ozone layer in the upper atmosphere. They accounted for fifteen per cent of the global warming problem during the 1980s. Halting production of these chemicals is one of the easiest ways to limit the greenhouse effect.
Methane
Methane, or swamp gas, is produced in waterlogged areas such as rice paddies, in the digestive systems of cattle and other ruminants and as a result of the production of fossil fuels. It is also released from waste disposal sites as organic matter breaks down. Accounting for about twenty per cent of the problem, the amount of methane in the air has doubled over the past couple of centuries.
Nitrous oxide
Nitrous oxide is also a cause of ozone depletion, and it is a powerful greenhouse gas with a lifetime of almost two hundred years. Produced during the breakdown of chemical fertilisers, when fossil fuels are burned and through land clearance, it accounts for around ten per cent of the greenhouse problem.
Ozone
While we need ozone in the upper atmosphere to protect us from ultraviolet radiation, ozone near the Earth's surface can be extremely harmful — damaging human health, crops and forests — and it is a greenhouse gas. Ozone is generated as sunlight causes chemical reaction amongst a range of pollutants such as the carbon monoxide and nitrogen oxides from car exhausts.