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The greenhouse effect is a simile for the action of the Earth\'s atmosphere as a trap for energy which arrives as sunlight. Sunlight passes readily through the various layers of atmosphere and reaches the surface of the Earth to have a localized warming effect. The Earth\'s crust re-radiates much of this energy as infrared light, of a much longer wavelength than that of sunlight; various gases found in the atmosphere are opaque to infrared light so that the energy is absorbed rather than dissipated into space. The temperature of the atmosphere and the surface of the Earth are raised. This is the greenhouse effect and the gases which are responsible are called greenhouse gases: they include water vapour, carbon dioxide and methane. The levels of these gases in the atmosphere seems to be naturally regulated and the greenhouse effect is an important mechanism by which the temperature at the surface of the Earth is maintained within the fairly narrow limits suitable for life. It is thought that human activity has altered the atmospheric levels of certain greenhouse gases such as carbon dioxide and methane, and there appears to be a correlation between small increases in the level of atmospheric carbon dioxide and a slight increase in global temperatures over the past century. The consequences of continued increases in temperature could prove disastrous for human civilizations and, in the light of this there has been recent interest in the various options for reducing the upward trend in carbon dioxide levels. However, it is likely that the biosphere will be able to adjust to higher temperatures even if humans cannot. RB
See also conservation; Gaia hypothesis; global warming; pollution.Further reading Michael Gottlieb, Energy Policies and The Greenhouse Effect; , James Lovelock, Gaia: A New Look at Life on Earth; , Crispin Tickell, Climatic Change and World Affairs. |
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