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Green House Effect









Green House Effect

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The greenhouse effect is the heating of the surface of a planet or moon due to the presence of an atmosphere containing gases that absorb and emit infrared radiation. Thus, greenhouse gases trap heat within the surface-troposphere system. This mechanism is fundamentally different from that of an actual greenhouse, which works by isolating warm air inside the structure so that heat is not lost by convection.

Convection is the movement of molecules within fluids (i.e. liquids, gases and rheids). It cannot take place in solids, since neither bulk current flows or significant diffusion can take place in solids.

The greenhouse effect was discovered by Joseph Fourier in 1824, first reliably experimented on by John Tyndall in 1858, and first reported quantitatively by Svante Arrhenius in 1896.

The black body temperature of the Earth is 5.5 °C. Since the Earth's surface reflects about 28% of incoming sunlight, the planet's mean temperature would be far lower - about -18 or -19 °C - in the absence of the effect. Because of the effect, it is instead much higher at about 14 °C.

Global warming, a recent warming of the Earth's surface and lower atmosphere, is believed to be the result of an "enhanced greenhouse effect" mostly due to human-produced increases in atmospheric greenhouse gases. This human induced part is referred to as anthropogenic global warming (AGW).

Basic mechanism
The Earth receives energy from the Sun mostly in the form of visible light and nearby wavelengths. About 50% of the sun's energy is absorbed at the Earth's surface. Like all bodies with a temperature above absolute zero the Earth's surface radiates energy in the infrared range. Greenhouse gases in the atmosphere absorb most of the infrared radiation emitted by the surface and pass the absorbed heat to other atmospheric gases through molecular collisions. The greenhouse gases also radiate in the infrared range. Radiation is emitted both upward, with part escaping to space, and downward toward Earth's surface. The surface and lower atmosphere are warmed by the part of the energy that is radiated downward, making our life on earth possible.

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