The Greenhouse Effect

Greenhouse gases let short-wavelength radiation come into the Earth’s atmosphere from the sun. However, they absorb and re-radiate Earth’s long-wavelength radiation back towards to Earth’s surface keeping the temperature on Earth warm enough to inhabit.
The Earth’s atmosphere is largely transparent to visible wavelengths. Sunlight which warms the Earth’s surface in the daytime is reradiated at night at longer infrared wavelengths.

Greenhouse gases in the Earth’s atmosphere absorb and scatter radiation at differing wavelengths. Notice the largest absorption band for carbon dioxide is in the infrared.


The greenhouse effect is not necessarily a bad thing. In the absence of Earth’s greenhouse gases the Earth’s climate would be on average 33˚ C colder, mostly frozen and uninhabitable. The recent concern about greenhouse warming is based on abnormal levels of greenhouse gases leading to climate changes unseen in human history.