• The Heat Budget of the Earth is a balance between incoming solar insolation and outgoing terrestrial radiation.
• This balance maintains the average annual temperature of the Earth at 15 degrees Celsius.
• Solar energy received by the Earth’s surface is called solar insolation.

Heat Budget of the Earth and Atmosphere

• The solar radiation reaching the ground is called global radiation and is composed of direct shortwave radiation from the Sun and diffuse radiation scattered by the atmosphere.
• The solar energy received by the earth’s surface is converted into heat energy and heats the outer surface of the earth.
• The heated earth radiates energy in the form of long-wave radiation.
• The radiation from the sun towards the earth is called incoming shortwave solar radiation.
• The radiation from the earth towards the atmosphere is called outgoing longwave terrestrial radiation.

How is it calculated?

• Suppose incoming solar insolation is = 100 units Amount lost through scattering and reflection.
  • a) Through Clouds- 27units
  • b) By dust particles – 6units
  • c) By Ice Caps and Glaciers- 2units
• Total 35 units are reflected back into space. (known as albedo of the earth) Now, the units received by earth and its atmosphere = 100 – 35 = 65units.

​​

• 51 units of solar insolation are received by the earth as direct radiation which can be segregated as follows:
  • (i)Received through direct Radiation= 34units
  • (ii)Received as diffused day light= 17units
• Which comes out to be 51 units.