Short-wave electromagnetic radiation from the Sun passes through the transparent atmosphere unhindered (except for the effect that albedo has on the mean reflectivity of a planet). On heating the planet's surface, long-wave radiation (i.e. Infrared radiation) is emitted into the atmosphere. Long-wave radiation will not escape into space if the atmosphere is dense enough, and contains greenhouse gases (such as carbon dioxide, water vapour, methane etc.) which reflect long-wave radiation back to the surface, heating the atmosphere further. This shortwave input, long-wave emission, long-wave reflection, atmospheric heating process is known as the Greenhouse Effect.
The Greenhouse Effect is an essential process to heat a planet's atmosphere to habitable temperatures. To make life sustainable on the surface of Mars, the process of terraforming would require a thickening of the tenuous Martian atmosphere and injection of selected greenhouse gases. Decreasing the planet's albedo would also be beneficial.
Artificial Greenhouse Effect
Greenhouses are artificial structures that harness heating from the greenhouse effect. Greenhouses will be an essential addition to future colonies on Mars if they are to be long-term and self-sufficient. Essential for growing food, greenhouses will also provide immense feelings of well-being for humans living away from Earth, so the psychological effects on colonists will be invaluable.
Examples of the Greenhouse Effect
- Venus has a very dense atmosphere, causing a runaway greenhouse effect. Temperatures on Venus' surface are increased by 400 degrees by this extreme heating creating a surface temperature of over 700 Kelvin and surface pressure of 90 times that of the Earth's atmosphere (about 1350 pounds per square inch).
- Earth's global warming is believed to be in direct correlation with carbon emissions from industrial burning of fossil fuels and other human activity. It is believed the planet will reach a "tipping point" where the heating cannot be sustained by the atmosphere causing a catastrophic collapse in weather systems and climate shift. Now Earth greenhouse effect is 33ºK.
- Mars global warming at present have very thin atmosphere producing only 6ºK greenhouse effect.
- Christopher P. McKay, Owen B. Toon & James F. Kasting - Making Mars habitable, Nature 352, pp. 489-496. DOI:10.1038/352489a0