The Earth has a natural temperature control system.
Certain atmospheric gases are crucial to this system and are known as greenhouse gases.
- On average, about one third of the solar radiation that hits the earth is reflected back to space.
Of the remainder, the atmosphere absorbs some but the land and oceans absorb the most.
The Earth's surface becomes warm and as a result emits infrared radiation.
Infrared light is heat energy.
Greenhouse gases are abbreviated GHG.
- The greenhouse gases 'trap' the infrared radiation, thus warming the atmosphere.
Technically, when the infrared rays hit a GHG molecule, it starts vibrating.
When this molecule vibrates, it makes adjacent gas molecules of any kind to vibrate as well.
Vibration is a form of energy that is converted to heat energy according to the physical laws of thermodynamics.
The GHG molecule vibrations makes evenings and early nights feel warm after a sunny day.
Without the GHG, the nights would immediately turn extremely cold at once the sunlight disappears.
An increased greenhouse effect therefore can be observed as increasingly warmer nights.
- Naturally occurring greenhouse gases include water vapor, carbon dioxide, ozone, methane and nitrous oxide, and together create a natural greenhouse effect.
The greenhouse gases have three or more atoms in their molecules.
CO2, H2O, CFC all have three atoms, while O2 (Oxygen) and N2 (Nitrogen) only have two.
The two last mentioned gases thus do not have any greenhouse effect,
- However, human activities are causing greenhouse gas levels in the atmosphere to increase.
The additional effect is called the anthropogenic (human) greenhouse effect, the 'enhanced greenhouse effect' or for those who like extra precision: 'the anthropogenically enhanced greenhouse effect'.
Note: Greenhouse gases are mixed throughout in the atmosphere.
For simplicity, they are depicted here as a layer.
Graphic: UNEP/GRID-Arendal: Vital Climate Graphics, 2001