The earth as a whole does not accumulate or lose heat. It maintains its temperature.

●  The amount of heat received in the form of short wave radiation insolation is equal to the amount lost by the earth through the short wave terrestrial radiation.

●  Consider that the insolation received at the top of the atmosphere is 100 percent.

●  Roughly 35 units are reflected space even before reaching the earth’s surface.  Of these, 27 units are reflected from the top of the clouds, 6 units are from the top of the atmosphere and 2 units are from the snow and ice-covered areas of the earth. The reflected amount of radiation is called the albedo of the earth.

●  The remaining 65 units reach the earth surface. 14 units within the atmosphere and 51 units by the earth’s surface. The earth radiates back 51 units in the form of terrestrial radiation.

●  Of these, 17 units are radiated to space directly and the remaining 34 units are absorbed by the atmosphere. Of these 34 units, 6 units are absorbed directly by the atmosphere, 9 units through convection and turbulence and 19 units through latent heat of condensation.

●  Totally 48 units absorbed by the atmosphere, 14 units from insolation and 34 units from terrestrial radiation. These 48 units are also radiated back into space. Thus, the total radiation returning from the earth and the atmosphere respectively is 65 units which balance the total of 65 units received from the sun.

●  This is termed the heat budget or heat balance of the earth. This explains why the earth neither warms up nor cools down despite the huge transfer of heat that takes place.

●  The Earth’s surface absorbs and radiates back the same amount of heat. Therefore, there is no net gain or loss by the Earth and the atmosphere.

Variation in the Net Heat Budget

●  When some parts of the earth have a surplus radiation balance while the other part has a deficit.

●  There is a surplus of net radiation balance between 40 degrees north and south and the regions near the poles have a deficit. The surplus heat energy from the tropics is redistributed towards the poles.

●  As a result, the tropics do not get progressively heated up due to the accumulation of excess heat or the high latitudes get permanently frozen due to excess deficit.