Phenomenon in which solar radiation absorbed by a planet is re-emitted from the surface as long-wave infrared radiation that is prevented from escaping by various gases in the atmosphere. These greenhouse gases trap heat because they readily absorb long-wave infrared radiation. As the energy cannot escape, it makes the planet warmer than it would otherwise be. The process is progressive and the heating effects rise with the concentration of greenhouse gases in the atmosphere. The most well-known greenhouse gas is carbon dioxide.
On the planet Venus, which is blanketed with a dense atmosphere of almost pure carbon dioxide, the greenhouse effect creates an average surface temperature of over 460°C/860°F. In comparison the Earth, which has an atmospheric content of only 0.0398% carbon dioxide, has an average temperature of around 14°C/57°F. The Earth's more moderate greenhouse effect makes life on our planet possible. However, increases in greenhouse gases due to human activity are thought to be producing a harmful additional heating effect that is a primary factor in global warming.
Although the greenhouse effect in itself would not produce an alarming amount of warming, it would produce alterations in the amount of cloud and ice cover that potentially could alter the balance between the amount of energy absorbed by the Earth and the amount radiated back into space. These changes are complex and difficult to predict, although the present consensus among climate scientists is that this change in energy balance would constitute a positive feedback that could dangerously amplify the warming.
The main greenhouse gases are carbon dioxide, methane, and chlorofluorocarbons (CFCs) as well as water vapour. Fossil-fuel consumption and deforestation are the principal causes of carbon dioxide build-up; methane is a by-product of agriculture (rice, cattle, sheep).
Dubbed the ‘greenhouse effect’ in 1896 by the Swedish scientist Svante Arrhenius, the phenomenon was first predicted in 1827 by the French mathematician Joseph Fourier.
The concentration of carbon dioxide in the atmosphere is estimated to have risen by 37% since the Industrial Revolution, and 10% since 1950; the rate of increase is now 0.5% a year. Chlorofluorocarbon levels are rising by 5% a year, and nitrous oxide levels by 0.4% a year.
The Earth: Structure and Atmosphere
Forests: The Hunt for Sustainability
Global Warming and the Greenhouse Effect
Influence of people on weather and climate
Sources and effects of pollutants
Effects of changing seal level on coastline
The World's Changing Climate
The Greenhouse Effect
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