Greenhouse gases are gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared radiation emitted by the earth’s surface, the atmosphere, and clouds. There are two types of greenhouse gases; primary gases in including; water vapour, carbon dioxide, nitrous oxide, methane, and ozone in the earth’s atmosphere. Secondary greenhouse gases are human-made residences in the atmosphere such as; halocarbons, chlorine, and bromine described under the Montreal Protocol (Velders, 2007). The Kyoto Protocol deals with greenhouse gases including sulphur hexafluoride, hydrofluorocarbon, and perfluorocarbons (Velders, 2007). The two dominant gases in the atmosphere are nitrogen (78%) and oxygen (21%) but are not classified as greenhouse gases because neither can trap outgoing longwave radiation—they are not sensitive to infrared radiations emitted from the earth. The three most important greenhouse gases include water vapour, methane, and carbon dioxide. The role of these gases as climate regulators is initially articulated by the faint young sun paradox.

The Faint-Young Sun Paradox suggests the earliest sun shone 30% more faintly than the present radiation which presupposes earth’s climate should be colder. The earth has maintained a moderate temperature range throughout recent times though solar flux increases. The alternating sun output is controlled by a control knob that serves as a thermostat over geologic timeframes. The CO2 reaction to the carbon cycle has been the mechanism that functions to moderate the earth’s climate—as a result, its concentration has changed over time (Ruddiman, 2014).