The Earth as a whole neither accumulates nor loses heat. It maintains a thermal balance, which is possible only if the amount of heat received as insolation equals the amount lost via terrestrial radiation. This balance is known as the Heat Budget of the Earth.
Mechanism in Heat Budget:
- Short Wave Solar Radiation:
Out of 100 units of solar radiation:
- 35 units are reflected back (Earth’s albedo).
- 65 units are absorbed:
- 14 units within the atmosphere.
- 51 units by the Earth’s surface.
- Long Wave Earth Radiation:
The Earth radiates 51 units back as terrestrial radiation:- 17 units go directly into space.
- 34 units are absorbed by the atmosphere.
- The atmosphere, in total, absorbs 48 units (14 from insolation + 34 from terrestrial radiation) and radiates these back into space.
Total outgoing radiation = 17 (direct from Earth) + 48 (from atmosphere) = 65 units, which balances the 65 units received, thus maintaining Earth’s heat balance.
Factors Controlling Temperature Distribution on Earth’s Surface:
- Latitude:
Regions near the equator are hotter as the sun’s rays are more vertical, unlike the oblique rays near the poles, which reduce insolation. - Altitude:
The Earth is heated from below; hence, low-altitude areas are warmer than higher altitudes due to proximity to terrestrial radiation. - Continentality:
Land heats and cools faster than water. Thus, inland areas show greater temperature variation compared to coastal regions. - Air Masses and Ocean Currents:
- Warm air/ocean currents raise temperatures.
- Cold air/ocean currents lower temperatures.
- Other Factors:
Include winds, soil type, slope and aspect of land surfaces.
Example: Dark-coloured soil absorbs more heat than light-coloured soil.
Conclusion:
Understanding the heat budget reveals the dynamic equilibrium of Earth’s climate system. However, events like global warming and the greenhouse effect can disrupt this balance, necessitating urgent corrective action to preserve climate stability.