Environmental Science 102
Global Energy System


A system is defined as:

Closed System

A system that does not interact with other systems of items outside of the closed system.
The closest example to a closed system is a terrarium; however, this is only a closed system where matter is concerned - energy still enters and exits a terrarium (sunlight in, heat out)

Open System

A system that does interact with other systems or items outside of the system.
Examples include: Atmosphere, hydrosphere, lithosphere, biosphere, the Earth, the Solar System

Global Energy System

The Earth's global energy system is an open system - energy from the Sun enters, energy from the Earth is lost to space.

The following discussion refers to pg. 43, Figure 2.13

FIGURE 1- Incoming Solar Radiation
FIGURE 2 - Longwave Energy Flow

Incoming Radiation

100 units - energy recieved from the sun (not important what type of units are used - could be joules, watts, calories, etc.)

Albedo is the percent of radiation scattered and reflected from a surface.

Of the 100 units of incoming radiation, 3 units are reflected back by the atmosphere, 19 units by the clouds, and 9 units by the ground. Total reflected = 31 units

Notice that the amount reflected by the clouds is two times greater than the amount reflected by the ground.
Light colored materials reflect more radiation than dark colored materials.
Dark colored materials absorb more radiation than light colored materials.

It should be noted at this point that "ground" is used here to indicate the surface of the Earth - land and water surfaces.

Of the 100 units of incoming radiation, 17 units are absorbed by the atmosphere, 3 units are absorbed by the clouds, and 49 units are absorbed by the ground. Total absorbed = 69 units

69 units + 31 units = 100 units

Outgoing Radiation

Starting with the radiation from the ground - the ground absorbs 49 units from insolation - it absorbs another 95 units of energy from counterradiation that has been re-emitted from the atmosphere.
49 units + 95 units = 144 units total absorption by the ground.

Radiation is then re-emitted from the ground as 114 units of infrared radiation. Of this 114 units, 102 units are absorbed by the atmosphere and 12 units are lost directly to space.
144 units - 114 units = 30 units remaining

23 units are moved from the ground to the atmosphere through Latent Heat Transfer (Heat is removed from the surface during evaporation)
7 units are moved from the ground to the atmosphere through Sensible Heat Transfer (the air is in contact with the ground and heat is transfered directly from one material to the other)
23 units + 7 units = 30 units

The Atmosphere directly absorbs 20 units of insolation, 102 units are absorbed from the ground, 23 units absorbed from latent heat transfer and 7 units from sensible heat transfer. Total = 152 units absorbed by the atmosphere.

Of this 152 units, 95 units are re-emitted to and absorbed by the ground, and 57 units are lost directly to space.

Of the total outgoing radiation lost to space, 31 units are reflected insolation, 12 units are radiated from the ground and 57 units are radiated from the atmosphere.
31 units + 12 units + 57 units = 100 units.

The amount of incoming radiation equals the amount of outgoing radiation. Global Radiation Balance

This equation is not constant and is not always balanced.
Variations in the amount of energy recieved, energy lost, ground cover, composition of the atmosphere can all affect the this equation.
The Earth's energy system is dynamic and is always changing and adjusting to new conditions.
As a result the global is either warming up or cooling down.

Net Radiation

The Global Energy Balance does not imply that all areas of the Earth recieve energy equally.
It looks at the Earth as an entire system.
Variations occur in given locations.
For example, radiation is only being recieved from the sun on one half of the globe at any one time.
Energy is being lost, however, on all parts of the globe whether it is night or day.
Equatorial regions recieve more radiation than polar regions.
Polar regions loose more radiation than they recieve.
Therefore, excess energy from the equator must be moved to the polar regions in order to maintain the global energy balance.