Heat Budget of the Earth and Distribution of Temperature

Heat Balance or Heat Budget of the earth is the balance between the amount of shortwave insolation (incoming solar radiation) and the terrestrial longwave radiation that is received by the Earth-Atmosphere system.

Heat Budget of the Earth

• Out of the 100 units of insolation received by the Earth-Atmosphere system, 21 units are absorbed by the atmosphere, 48 units are absorbed by the earth (rocks, forests, seas, oceans, etc.) and 31 units are returned back by earth and atmosphere.
  
  
• Albedo of the Earth -
  
  
  • The amount of insolation in original shortwave form returned to cosmic space by earth-atmosphere system is called Albedo. So, Albedo of Earth is 31%.
    
    
  • Albedo of inner planets are less when compared to outer planets, e.g. Mercury has Albedo of 10% whereas Uranus has more than 60%.
    
    
  • Albedo values vary from place to place. Areas with fresh snow (like poles) will have high Albedo. More than 90% of insolation is reflected by the snow.
    
    
  • Albedo is lowest for oceans and seas (water bodies) and is around 5-10% whereas forests and rocky areas will have 15-35%.
  
  
• Out of the 100 units, 31 units are reflected as Albedo and the remaining 69 units are returned as long wave terrestrial radiation. Out of the 69 units, 62 units are returned by the atmosphere and 7 units by the earth.
  
  
• Out of the 48 units received by the Earth, 41 units are given by the earth to atmosphere. Earth gives energy to the atmosphere by evaporation or mechanical heat transfer.

Distribution of Temperature on Earth

Temperature on the Earth's surface depends on

• Latitude - From 0⁰ to 30⁰ latitude, there will be very high temperature. Beyond 30⁰ latitude, temperature decreases due to lower angle of incidence of sun rays and the duration of sun rays that lasts in the region.
  
  Lower the angle of incidence, lower will be the temperature. Beyond 23 1/2⁰ latitude, sun rays never hit the earth vertically. Within 23 1/2⁰ North - 23 1/2⁰ South, sun rays are higher in intensity.
  
  
• Altitude - Temperature decreases with increase in height from Earth's surface
  
  
• Location with reference to ocean - Interiors of the continents will have higher temperature when compared to the coasts
  
  
• Seasons of the year throughout the world
  
  
• Ocean currents around the world