Infrared (IR) active gases, principally water vapor (H2O), carbon dioxide (CO2), and ozone (O3), naturally present in the Earths atmosphere, absorb thermal IR radiation emitted by the Earths 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
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.
The AGU Council approved a position statement on Climate Change and Greenhouse Gases in December 1998. The statement and a short summary of the procedures that were followed in its preparation, review, and adoption were published in the February 2, 1999, issue of Eos (p. 49) [AGU, 1999, also at AGU's Web site: http://www.agu.org/sci_soc/policy/climate_change.html]. The present article reviews scientific understanding of this issue, as presented in peer-reviewed publications. This understanding serves as the underlying basis of the position statement.
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