Some electromagnetic radiation from the Sun passes through Earth's atmosphere. This includes infrared radiation, visible light and ultraviolet radiation. This warms the Earth.
The warm Earth emits infrared radiation. Some gases absorb this radiation and re-emit it in all directions.
Gases which can absorb the infrared radiation are called greenhouse gases. These include carbon dioxide, water vapour and methane.
More energy is absorbed than is radiated back into space. This creates a warming effect that is called the greenhouse effect.
The diagram gives more details about this process.
- electromagnetic radiation at most wavelengths passes through the Earth's atmosphere
- the Earth absorbs most of the radiation and warms up
- the Earth radiates energy as infrared radiation
- some of the infrared radiation goes into space
- some of the infrared radiation is absorbed by greenhouse gases in the atmosphere
- the lower atmosphere warms up
Without the greenhouse effect, Earth would probably be too cold for life.