The influence of the 15μ carbon-dioxide band on the atmospheric infra-red cooling rate


  • This paper was completed while the author was on leave of absence at Michigan State University. At present with Systems Research Corporation, Van Nuys, California.


The upward and downward radiation flux and cooling rate are calculated for the 15μ band of carbon dioxide. Results are obtained for three different carbon-dioxide concentrations from the surface of the earth to 75 km, and for six frequency intervals covering the band. The infra-red absorption measurements of Cloud (1952) are used for calculations, on a high-speed electronic computer, by a method which takes account of the pressure and Doppler broadening, the overlapping of the spectral lines, and the variation of the intensity and half-width of the spectral lines with temperature and pressure. The numerical integration is performed over intervals that are never larger than 1 km and average values over layers are not used. The cooling rate for the present atmospheric carbon-dioxide concentration is greater than 1°C/day from 24 km to 70 km and is greater than 4°C/day from 38 km to 55 km. The sum of the ozone and carbon-dioxide cooling rates is greater than 4°C/day from 33 km to 57 km and agrees reasonably well with the heating due to ozone absorption. The results for different carbon-dioxide concentrations indicate that the average temperature at the surface of the earth would rise by 3.6°C if the carbon-dioxide concentration were doubled and would fall by 3.8°C if the carbon-dioxide concentration were halved, on the assumption that nothing else changed to affect the radiation balance.