Heat Budget of the Earth-Atmosphere System| by K_Siddhartha

Heat Budget of the Earth-Atmosphere System| by K_Siddhartha:
In order to maintain its temperature pattern, the Earth must lose heat as well as gain it. On the global scale, the Earth must reradiate as much heat back to the space as it receives from the Sun. These gains and losses in heat by way of incoming and outgoing radiation is known as
Radiation budget or Heat budget.
The Sun emits energy in the form of electromagnetic radiation travelling at the speed of light. The

  • Earth receives only two-billionths (0.000000002) portion of Sun’s energy. Some of this energy received is:
    • Reflected,
    • Absorbed,
    • Radiated,
    • Reradiated
  • that is how it makes up energy budget.

100 units of solar energy are incoming to the Earth’s atmosphere:

  • 31 units reflected back to the outer space
    • This reflected radiation does not accomplish any heating of the Earth or its atmosphere.
  • Of the 69 units left:
    • 4 are reflected by the Earth’s surface through the atmosphere to the outer space and these also do not take any part in the heating of the Earth.
  • Out of the rest 65 units:
    • 47 units are absorbed by the Earth’s surface
    • 18 units are absorbed by the Earth’s atmosphere.
  • To balance the budget, 65 units must be lost to the space by reradiation of long wave radiation.
    • 5 units are reradiated by the Earth’s surface
    • 60 units are reradiated from the atmosphere.
  • Although the Earth absorbs 47 units, it loses only 5 units to space for a gain of 42 units,
  • The atmosphere absorbs 18 units and loses 60 units to space for a loss of 42 units.

Under these circumstances, the atmosphere cools and the Earth heats.
In order to maintain the near constant average temperatures of the Earth’s surface, 42 excess units gained by the Earth must be transferred to the atmosphere to make up for the 42 units the atmosphere has lost.
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