Heat Budget Notes | EduRev

Geography for UPSC (Civil Services) Prelims

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Heat budget of the Earth

Heat Budget of the Earth balances incoming solar insolation and outgoing terrestrial radiation which maintains the average annual temperature of the earth at 14-degree celsius.

Solar energy received by earth’s surface is called solar insolation.

Heat Budget of the Earth and Atmosphere

  • The total solar radiation reaching a horizontal surface on the ground is called global radiation
  • It comprises the direct shortwave radiation from the Sun + the diffuse radiation scattered by the atmosphere.
  • It may be pointed out that the solar energy received at the earth’s surface is converted into heat energy, which heats the earth's outer surface.
  • Thus, the earth, after being heated, also radiates energy in the form of long-wave radiation.
  • The Radiation from the sun towards the earth is called incoming shortwave solar radiation and from the earth towards the atmosphere is called outgoing longwave terrestrial radiation.
    Question 1:What is the average annual temperature of the earth?

➤ 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 of 35 units are reflected into space. (known as albedo of the earth) Now, the units received by earth and its atmosphere = 100 – 35 = 65units.

➤ Heat budget of the Earth

The earth receives 51 units of solar insolation as direct radiation which can be segregated as follows:

  • Received through direct Radiation = 34units
  • Received as diffused daylight =. 17units

Which comes out to be 51 units.

➤ Heat Budget of Atmosphere

  • Absorption by atmospheric gases in different vertical zones of atmosphere-14 units
    Now 51 units + 14 units= 65 units (total solar insolationreceived by earth andatmosphere)
  • Out of the solar radiation received directly by earth i.e. 51 units, 17 units are re-radiated back into outer space, and rest 34 units (51-17units) is absorbed by the atmosphere in the form of outgoing terrestrial radiation.
    Which comes out to be 48 units (14+ 34 = 48)

➤ Albedo

  • Albedo can be defined as measuring how much light that hits a surface is reflected without being absorbed.
  • It is a reflection coefficient and has a value of less than one.
  • When the solar radiation passes through the atmosphere, some amount is reflected, scattered, and absorbed.
  • The reflected amount of radiation is called the albedo of the earth.
  • Because of albedo's effect, highly developed areas such as urban cities can experience higher average temperatures than the surrounding suburban or rural areas, a phenomenon known as the Urban Heat Island Effect.
  • The higher average temperature can be attributed to less vegetation, higher population densities, and more infrastructures with dark surfaces (asphalt roads, brick buildings, etc.).


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