Infrared (IR) active gases, principally water vapor (H2O), carbon dioxide (CO2) and ozone (O3), naturally present in the Earth’s atmosphere, absorb thermal IR radiation emitted by the Earth’s surface and atmosphere.
The atmosphere is warmed by this mechanism and, in turn, emits IR radiation, with a significant portion of this energy acting to warm the surface and the lower atmosphere.
As a consequence the average surface air temperature of the Earth is about 30° C higher than it would be without atmospheric absorption and re-radiation of IR energy.
This phenomenon is popularly known as the greenhouse effect, and the IR active gases responsible for the effect are likewise referred to as greenhouse gases.
The Greenhouse Effect
The rapid increase in concentrations of greenhouse gases since the industrial period began has given rise to concern over potential resultant climate changes
Greenhouse Gases and Global Climate Change
The principal greenhouse gas concentrations that have increased over the industrial period are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs).
The observed increase of CO2 in the atmosphere from about 280 ppm in the pre-industrial era to about 364 ppm in 1997 has come largely from fossil fuel combustion and cement production.
Of the several anthropogenic greenhouse gases, CO2 is the most important agent of potential future climate warming because of its large current greenhouse forcing, its substantial projected future forcing, and its long persistence in the atmosphere.
