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Date:2010/12/20 From: AetClose

The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric , and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere. As a result, the temperature there is higher than it would be if direct heating by solar radiation were the only warming mechanism.

This mechanism is fundamentally different from that of an actual , which works by isolating warm air inside the structure so that heat is not lost by .

The greenhouse effect was discovered by in 1824, first reliably experimented on by in 1858, and first reported quantitatively by in 1896.

If an ideal thermally conductive was the same distance from the Sun as the Earth, it would have an expected blackbody temperature of 5.3 °C. However, since the Earth reflects about 30% (or 28%) of the incoming sunlight, the planet's actual blackbody temperature is about -18 or -19 °C, about 33°C below the actual surface temperature of about 14 °C or 15 °C. The mechanism that produces this difference between the actual temperature and the blackbody temperature is due to the atmosphere and is known as the greenhouse effect.

, a recent warming of the Earth's surface and lower atmosphere, is believed to be the result of a strengthening of the greenhouse effect mostly due to human-produced increases in atmospheric greenhouse gases.

Greenhouse gases

Main article:

By their percentage contribution to the greenhouse effect on Earth the four major gases are:

, 36–70%

, 9–26%

, 4–9%

, 3–7%

The major non-gas contributor to the Earth's greenhouse effect, , also absorb and emit infrared radiation and thus have an effect on radiative properties of the atmosphere.

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