What is the Greenhouse Effect?

Posted on June 25, 2007 in About Global Warming

The greenhouse effect is nothing but a rise in the Earth’s temperature due to certain gases like carbon dioxide, methane, water vapor and nitrous oxide that trap solar energy. The term has its origins in the way plants grow in a greenhouse during winter by trapping solar heat. In the absence of these gases the Earth’s temperature would be several degrees lower as the solar energy escapes back in to the atmosphere. Since these gases warm the earth, they are termed green house gases.

The sun’s energy enters the Earth’s atmosphere and most of it is absorbed by the land and water. Radiation from the Earth is of two types, one in the form of reflected solar radiation and the other in the form of emitted thermal infrared radiation. Some of it escapes in to the atmosphere as the earth reflects it. A part of this radiation is again re-absorbed and re-emitted by the green houses gases. This cycle of absorption and reflection continues till there is no more radiation available. Solar energy that reaches the Earth’s surface is useful for evaporation of water, photosynthesis by plants and melting of snow.

Concern about rise in concentration of greenhouse gases
The greenhouse gases in the Earth’s atmosphere act like the glass panes in a greenhouse, trapping the heat and warming the earth. However an increase in the greenhouse effect will cause a rise in the Earth’s temperature making it unfit for human habitation. Therefore there is growing concern with the increase in the percentage of greenhouse gases in the Earth’s atmosphere. The percentage of greenhouse gases in the atmosphere has been on the rise since the Industrial revolution. Of these, carbon dioxide contributes more than fifty percent, followed by chlorofluorocarbons at 25%, methane at 15% and nitrous oxide at 5% to the increase in the greenhouse effect.

The increase in the levels of carbon dioxide in the atmosphere is due to rise in the number of automobiles, burning of fossil fuels, cutting of forests, and use of coal in electricity generation. Chlorofluorocarbons produced by humans are the densest gases, but their levels are on the decline after the signing of the Montreal Protocol in 1987 to phase them out completely. Increase in levels of methane is due to rice cultivation, grazing by domestic animals, oil and gas extraction, creation of landfills and coal mining.

The levels of nitrous oxide increase due to burning of biomass, deforestation and use of nitrate and ammonium fertilizers. Deforestation causes nitrogen that is stored in plants to be released in to the atmosphere and burning fuel releases nitrous oxide in to the atmosphere. It is not known if ozone enhances the green house effect. However there is a depletion of the ozone layer due to the buildup of chlorofluorocarbons. With the rising population and pollution levels, scientists believe that the green house effect will increase the earth’s temperature by almost one to three degrees by the next century, leading to global warming.

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