Earth’s heat budget and its radiation balance
Earth’s Heat Budget Defined
- Earth's heat-budget or Earth's radiation balance refers to the net flow of energy into Earth in the form of shortwave radiation and the outgoing infrared long-wave radiation into space.
- Incoming heat is absorbed by the Earth, and outgoing heat escapes the Earth in the form of radiation and both are evenly balanced. In case of their being not balanced, Earth would become either warmer or cooler with the passage of time.
- This balance between incoming and outgoing heat is known as Earth’s heat budget.
- In other words, the heat budget at the top of the atmosphere must be in balanced state which in turn, is called Radiative equilibrium. It is note –worthy that the 29 percent of the solar energy that reaches the top of the atmosphere is reflected back to space by clouds, atmospheric particles, or earth surfaces like sea ice and snow.
How the Heat Budget is achieved?
- This heat or energy plays no role in Earth’s system. Besides, about 23 percent of incoming solar energy is absorbed in the atmosphere by water vapour, dust, and ozone, and 48 percent passes through the atmosphere and is absorbed by the surface. Thus, in totality, 71 percent of the total incoming solar energy is absorbed by the Earth.
The Three Levels for the Process to Occur
- This process occurs at the three levels: 1) the surface of the Earth, 2) the edge of Earth’s atmosphere and 3) the atmosphere in between. At each level, the amount of incoming and outgoing energy must be equal and balanced.
- The atmosphere and the surface of the Earth together absorb 71 percent of incoming solar radiation, so it is necessary that to maintain the balance of energy, they must radiate that much energy back to space to keep the earth ’s average temperature stable.
- The atmosphere radiates heat equivalent to 59 percent of incoming sunlight; the surface radiates only 12 percent. In other words, most solar heating happens at the surface, while most radiative cooling happens in the atmosphere.
Role of evaporation convection and thermal infrared radiation
- For the energy budget at Earth’s surface to balance, processes on the ground must get rid of the 48 percent of incoming solar energy that the ocean and land surfaces absorb. Energy leaves the surface through three processes: 1) evaporation, 2) convection, and 3) emission of thermal infrared energy.
The surface absorbs about 48% of incoming sunlight. Three processes of evaporation (25%), convection (5%), and thermal infrared radiation, or heat (net 17%)] remove an equivalent amount of energy from the Earth’s surface.