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The Greenhouse Effect -- Re-examination of the Impact of an Increase in Carbon Dioxide in the Atmosphere
  • Trevor Underwood
Trevor Underwood

Corresponding Author:underwoodtrevor@bellsouth.net

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Examination of the radiation budget at the surface of the Earth shows that there are three factors affecting the surface temperature; the amount of solar radiation absorbed by the atmosphere and by the surface respectively, and the amount of leakage of infrared radiation emitted from the surface directly into space. If there were no leakage, the upwelling infrared radiation from the Earth’s surface would be equal to the incoming solar radiation absorbed by the atmosphere plus twice the solar radiation absorbed by the surface. This results from the summation of a sequence of equal upward and downward re-emissions of infrared radiation absorbed by the atmosphere following the initial absorption of solar radiation. At current levels of solar absorption, this would result in total upwelling radiation of approximately 398.6 W/m2, or a maximum surface temperature of 16.4°C. Allowing for leakage of infrared radiation through the atmospheric window, the resulting emission from the Earth’s surface is reduced to around 396 W/m2, corresponding to the current average global surface temperature of around 15.9°C. Absorption of solar and infrared radiation by greenhouse gases is determined by the absorption bands for the respective gases and their concentrations. Absorption of incoming solar radiation is largely by water vapor and ozone, and an increase in absorption would reduce not increase the surface temperature. Moreover, it is probable that all emitted infrared radiation that can be absorbed by greenhouse gases, primarily water vapor, with a small contribution from carbon dioxide and ozone, is already fully absorbed, and the leakage of around 5.5 % corresponds to the part of the infrared red spectrum that is not absorbed by greenhouse gases. The carbon dioxide absorption bands, which represent a very small percentage of the infrared spectrum, are most likely fully saturated. In these circumstances, increased concentrations of greenhouse gases, and carbon dioxide in particular, will have no effect on the emitted radiation. The surface temperature is probably at the thermodynamic limit for the current luminosity of the sun. Satellite based measurements since 1979 suggest that any global warming over the past 150 years may be due to an increase in total solar irradiance, which we are still a decade or two from being able to confirm.