2. Heat Budget

The average temperature of the earth overall does not change in spite of continuous supply of sun rays. This is possible only when an equal amount of energy is sent back to space by the earth’s system. In the way there is balance between incoming solar radiation and outgoing

terrestrial radiations. This balance is known as the heat budget of the earth. Figure 4 depicts the heat budget of the planet earth. Consider that the insolation received at the top of the atmosphere is 100 per cent. While passing through the atmosphere some amount of energy is reflected, scattered and absorbed. Only the remaining part reaches the earth surface.

Roughly 35 units are reflected back to space even before reaching the earth’s surface. The

details of this reflected radiation are as under:

♤ Reflected from the top of clouds - 27 units

♤ Reflected by ice-fields on earth - 02 units

♤ Reflected by the atmosphere - 06 units Total - 35 units

The reflected amount of radiation is called the albedo of the earth. The above given radiation

does neither heat the atmosphere nor the earth’s surface.

The remaining 65 units are absorbed as:

♤ Absorbed by the atmosphere - 14 units

♤ Absorbed by the earth - 51 units (Scattered + direct radiation) Total - 65 units