In this article, I want to walk you through the important concept of climatology i.e. Heat Budget Of the Earth for UPSC examination.
Heat budget of the Earth
Heat Budget of the Earth is the balance between incoming solar insolation and outgoing terrestrial radiation
which maintains the average annual temperature of the earth at 15-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 outer surface of the earth.
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.
How it is 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.
Heat budget of the Earth
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.
Heat Budget of Atmosphere
(i) 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)
(ii) 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)
Question
Consider the following statements
- The equilibrium between the terrestrial radiation and the insolation is called as the heat budget of the earth.
- If the incoming heat and the outgoing heat are not balanced, then Earth would be getting either gradually warmer or cooler.
Select the correct ones
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Answer: C
Albedo
- Albedo can be simply defined as a measure of how much light that hits a surface is reflected back 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 of it is reflected, scattered, and absorbed.
- The reflected amount of radiation is called the albedo of the earth.
- Because of the effect of albedo, 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.).
