Heat Budget of Earth

The Heat Budget of the Earth refers to the balance between the energy the Earth receives from the Sun and the energy it sends back into space. This balance is very important because it helps maintain the Earth’s average temperature at around 15°C, which is suitable for life.

• • Incoming energy comes from the Sun and is called solar insolation
  • Outgoing energy is released by the Earth in the form of heat

If this balance is disturbed, the Earth would either become too hot or too cold.

Heat Budget of the Earth and Atmosphere

The total amount of solar energy that reaches the Earth’s surface is called global radiation. It includes two parts:

• • Direct radiation: Energy that comes straight from the Sun to the Earth
  • Diffuse radiation: Energy that is scattered by the atmosphere (by dust, gases, and clouds) before reaching the ground

What happens to this solar energy?

• When solar energy reaches the Earth’s surface, it is absorbed and converted into heat
• This heat warms the land, water, and lower atmosphere
• After heating up, the Earth releases energy back into the atmosphere

Types of radiation involved

How it is calculated?

To understand the heat budget, scientists use a simple model. Let’s assume:

• • Total incoming solar energy = 100 units

Energy lost through reflection and scattering

• Some of this energy is reflected back into space without heating the Earth. This is called the Earth’s albedo.
• • Reflected by clouds = 27 units
  • Scattered by dust particles = 6 units
  • Reflected by ice caps and glaciers = 2 units
  • Total reflected energy = 35 units
• So, the energy that remains is:
  • 100 – 35 = 65 units
• This 65 units is the energy absorbed by the Earth and its atmosphere.
  

Heat Budget Of The Earth

• Out of the total solar energy, 51 units are directly received by the Earth’s surface.
• This can be divided into:
  • Direct radiation = 34 units
    
    • Energy reaching the surface directly from the Sun
  • Diffuse daylight = 17 units
    
    • Energy scattered by the atmosphere but still reaching the surface
  • Total received by Earth = 51 units

Heat Budget of Atmosphere

The atmosphere also plays an important role in absorbing and redistributing heat.

Absorption by atmosphere

• • • 14 units of solar energy are absorbed by atmospheric gases at different heights
    • So, total energy absorbed by Earth and atmosphere:
      
      • 51 (Earth) + 14 (Atmosphere) = 65 units

Re-radiation of energy

• • Out of the 51 units received by Earth:
    
    • 17 units are radiated back directly into space
    • The remaining 34 units are:
      
      • Absorbed by the atmosphere as longwave (heat) radiation

Final energy balance

• • Energy absorbed by atmosphere:
    
    • 14 units (direct absorption)
    • 34 units (from Earth’s radiation)
  • Total = 48 units

Simple summary

• • The Sun sends 100 units of energy
  • 35 units are reflected back (albedo)
  • 65 units are absorbed by Earth and atmosphere
  • Earth and atmosphere then release this energy back into space
  • This continuous exchange maintains the Earth’s temperature balance

This balanced system is what keeps our planet habitable and stable.