Climate change and greenhouse gases

Infrared (IR) active gases, principally water vapor (H_2O), 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 reradiation of IR energy [Kellogg, 1996; Peixoto and Oort, 1992; Henderson-Sellers and Robinson, 1986].

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 rapid increase in concentrations of greenhouse gases since the industrial period began has given rise to concern over potential resultant climate changes.