Greenhouse Gases
- When shortwave radiation from the sun strikes the Earth’s surface it is absorbed and re-emitted from the surface of the Earth as infrared radiation
- Much of the radiation, however, is trapped inside the Earth’s atmosphere by greenhouse gases which can absorb and store the energy
- Carbon dioxide, methane and water vapour are gases that have this effect
- Increasing levels of carbon dioxide and methane, although present in only small amounts, are causing significant upset to the Earth’s natural conditions by trapping extra heat energy
- This process is called the enhanced greenhouse effect
Greenhouse gases trap some of the Sun's radiation causing the Earth to warm up
Carbon dioxide
- Sources: Combustion of wood and fossil fuels, respiration of plants and animals, thermal decomposition of carbonate rocks and the effect of acids on carbonates
Methane
- Sources: Digestive processes of animals, decomposition of vegetation, bacterial action in swamps and in rice paddy fields
Examiner Tip
It is important to understand the difference between the greenhouse effect and the enhanced greenhouse effect. The greenhouse effect ensures the mean global temperature is around 15 oC and without greenhouse gases the surface of the Earth would swing between extreme heat and extreme cold. The enhanced greenhouse effect, due an increase in greenhouse gas concentrations, most scientists believe, is leading to global warming.
