Earth’s Energy Budget

Earth’s Energy Budget can be discussed in terms of incoming heat energy and outgoing heat energy. These are as follows:

Incoming Heat Energy

This is made of :

• Solar radiation (99.97%)
• Geothermal energy (0.025%)
• Tidal energy (0.002%)
• Fossil fuel consumption (about 0.007%)
• Minor Sources: remains part

Outgoing Heat Energy

• The average albedo (reflectivity) of the Earth is about 0.3, which means that 30% of the incident solar energy is reflected into space, while 70% is absorbed by the Earth and reradiated as infrared. This 30% of the incident energy is reflected, consisting of 6% reflected from the atmosphere, 20% reflected from clouds and 4% reflected from the ground (including land, water and ice). The remaining 70% of the incident energy is absorbed, out of 51% is absorbed by land and water, and then emerges in the following ways:
• 23% is transferred back into the atmosphere as latent heat by the evaporation of water, called latent heat flux
• 7% is transferred back into the atmosphere by heated rising air, called Sensible heat flux
• 6% is radiated directly into space
• 15% is transferred into the atmosphere by radiation, then reradiated into space
• 19% is absorbed by the atmosphere and clouds, including:
• 16% reradiated into space
• 3% transferred to clouds, from where it is radiated back into space.

The above figures are the averages for the whole earth over a year’s time.

Balance in Earth’s Heat Budget

For any particular location, the factors discussed may not be balanced, and adjustments must be made within the entire earth system. Some places have a surplus of incoming solar energy over outgoing energy loss in their budget, while others have a deficit. The main cause of these variations is the differences in latitude, and the seasonal fluctuations.

We know that the amount of insolation received is directly related to the latitude. The tropical zone where insolation in high throughout the year; more solar energy is received at the earth’s surface and in the atmosphere than can be emitted back into space. In the arctic and Antarctic zones there is so little insolation during the winter, when the earth is still emitting long-wave radiation, that there is a large deficit for the year. Places in the midlatitude zone have lower deficits or surpluses, but only at about latitude 38° is the budget balanced. It is the heat energy transfer within the atmosphere that prevents a situation whereby the tropical zones get hotter and hotter and the arctic and Antarctic zone get colder and colder.