Greenhouse Effect

If Earth would not have the atmosphere, then all absorbed 160 Wm~ has to be irradiated into space in the form of LWR, since the temperature of the Earth's surface does not change. However, different atmospheric gases, transparent for SWR, may be weakly transparent for the LWR. For instance, the water vapor strongly absorbs LWR (in the cloudless atmosphere) in the spectral band (5-7.5 mm) and the carbon dioxide in the band (13-17 mm); absorption in the band (9-12 mm) is relatively small (see Figure 1). As a result, a part of the ground infrared radiation is detained, the atmosphere is warmed, and becomes in turn a source of LWR. Appearing here as a 'counter-radiation', Ecount = (EL )G = 102 Wm-2, it compensates a significant part of the ground LWR. A difference between the ground LWR and the counter-radiation is called an 'effective radiation' of the Earth's surface,

Eeff = (E°ut)G- (ELn)G = 58 Wm-2. Its spectrum is close to the blackbody one with T = 288 K, and namely this amount of LWR is irradiated by the Earth's surface into the space, the rest 180Wmis irradiated by the atmosphere. This is an essence of the 'greenhouse effect'.

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