Greenhouse effect

Believe that most of you have already heard about the term "greenhouse effect", as taught by your teacher in school.
Here I would like to discuss this topic in a more detail way.

Why the Earth can be warmed up?

The sun emits radiation in a band of wavelengths from ultraviolet to infrared. The radiation passes through the atmosphere of the earth with little absorption. When the radiation reaches the earth, it warms the ground and sea. The warm surface of the earth will, in turn, radiate energy outwards at the longer infrared wavelengths.

The infrared radiation, however, is not travel as freely as the radiation from sun in the atmosphere. They are absorbed by water vapour, ozone, carbon dioxide and other *gases (They are known as greenhouse gases) in the lower atmosphere. As these substance absorbed the energy and is heated up, they can warm up the lower layers of the atmosphere. They radiate some heat back to the surface of the ground, while some will out into the space.

Water vapour, ozone, carbon dioxide etceteras thus act as an insulating layer of the earth to the space, which trap part of the heat in the Earth.

Greenhouse Effect

The warming effect of carbon dioxide, water vapour and other gases has been named the greenhouse effect. There is more water in the atmosphere than carbon dioxide, so most of the greenhouse heating of the earth's surface is due to water vapour. However, there is a gap in the absorption by water vapour (i.e, certain wavelength of infrared radiation cannot be absorbed by water vapour), which is partly plugged by carbon dioxide. If the amount of carbon dioxide increase, more heat will be trapped, and the earth will be warmed up more. This overheating problem is known as global warming.

The water vapour content in the atmosphere, on the whole, is kept into a roughly constant level, while the carbon dioxide content in the atmosphere of the earth has been raising since the Industrial Revolution in Europe. Before the Industrial Revolution, the carbon dioxide concentration was about 280-90 part per million; in 1990, it was about 340 part per million.

The warming up of the earth is not only due to the increase in the amount of carbon dioxide in the atmosphere, but also due to other gases. Since carbon dioxide's influence contribute most to this global warming, so, when we talking about Greenhouse effect, we will mainly discuss about carbon dioxide. Though the concentration of other greenhouse gases are present in a much lower level than carbon dioxide, they are much more efficient at absorbing infrared radiation, and have a potentially greater influence on the greenhouse effect.

Apart from warming up the earth, it may also cause flooding to the low-lying land. Although greenhouse effect may cause flooding, without its influence, the earth's surface will at an average of -18°C rather then 15°C .

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