The Greenhouse Effect
The air is comfortably warm because a blanket of air surrounds it. Meaning that temperatures on our globe are in the range between0( Celsius and 100( Celsius were water is liquid.
The moon surface temperature average is about -18( C. This temperature helps the balance of the sun heating, letting the earth with an averagetemperature of about 15( C. The blanket of air keeps our planet some 33( C. warmer than it would otherwise be.
This is achieve by the Solar Energy that is mainly radiated in the invisible partof the spectrum, in a band from 0.4 to 0.7 micrometers. This radiation passes through the atmosphere of the Earth without being absorbed although some of it is reflected back into space by clouds,and warms the surface of the land or sea.
This infrared energy is exactly the same as the radiant heat you feel when you warm your hands in front of a hot household radiator.
• Incomingsolar radiation
The sun has a surface temperature of about 6000( C, and this corresponds to the radiation in the invisible band. The surface of the Earth that is warmed by solar radiation has atemperature of a few tens of degrees Celsius, so therefore radiates in the infrared, mainly in the range of 4 to 100 micrometers.
Water vapour absorbs strongly in the band from 4 to 7micrometers, and carbon dioxide absorbs in the band of 13 to 19 micrometers. Between 7 and 13 micrometers there is a “window” through which more than 70% of the radiation from the Earth’s surface escapesinto the space.
Because of the absorption, the infrared heat radiated by the warm surface of the planet cannot escape freely into space, and warms the troposphere. Because the air in thetroposphere is warm, it radiates heat in turn still at infrared wavelengths. Some of this heat goes back towards the ground, and keeps it warmer that it would otherwise be--- the Greenhouse Effect.