The meaning of the heat budget of earth: The heat budget refers to the heat received by the Earth and the atmosphere and the balance of heat loss by the earth. The greater capacity of heating of the Earth, the greater is the amount of heat energy returned back into space by radiation.
The budget of heat: The Earth gets the solar radiation from the Sun in the form of short waves. After colliding with the Earth, reflection of the solar radiation takes place. The returning radiation from the Earth is called Terrestrial Radiation, which is in the form of long waves. Thus, the amount of solar radiation received by the earth and the terrestrial radiation released by the earth is almost the same.
Earth can receive only 1 part of the sun’s total energy from two billion parts of the incoming solar insolation. The rest is dissipated due to the absorption, reflection and scattering by the atmosphere. As long as the amount of solar radiation and earth’s natural radiation remains equal, it is called a balanced heat budget. Due to the increasing role of human action, the quantum of Terrestrial Radiation is gradually decreasing, due to which the temperature of the earth has started gradually increasing.
If we assume that 100 units is the heat received by the upper boundary of the atmosphere, then the budget formed will be:
Receipt of solar radiation by Earth: If there is 100 units of heat coming from the Sun, 27 units of them are reflected by the clouds and 2 units of heat are reflected by the surface whereas 6 units are dispersed by the atmosphere. Thus, there is no role of 35 units of heat in heating the earth. Of the remaining 65 units, 14 units are absorbed by thermal conductivity (water vapor, dust particles).
Thus, only 51 units of heat reaches on the Earth. Apart from this, only 34 units of heat are received directly by the earth, the remaining 17 units are received by the earth through atmospheric light. This form of solar radiation obtained by the Earth has been clarified with the diagram given above.
Earth’s process of Terrestrial Radiation: Earth receives 51 units of solar radiation which return as Terrestrial Radiation. Out of this 51 units of heat, 23 units are radiated in the form of long waves from the thermal surface, out of which 17 units of heat goes directly to space, while 6 units heat the atmosphere with effective radiation.
9 units are spent in the form of heat convection and disturbance and the remaining 19 units are spent in the process of earth evaporation and compaction. Thus the earth returns all the 51 units of heat. This form of terrestrial radiation is represented by the following diagram:
