On January 1st 1989 the nations of the world took action, via the Montreal Protocol on Substances that Deplete the Ozone Layer, to eliminate the production of certain atmospheric pollutants; the man-made chlorofluorocarbons (CFC’s) and hydrochlorofluorocarbons (HCFC’s), because they caused ozone depletion in the stratosphere. This depletion allows excessive ultraviolet-B (UV-B) from the Sun to reach the Earth’s surface where it increases the risk of skin cancer, cataracts, and suppresses the immune system for humans and also damages other life forms.
The action of ozone is to absorb the radiance from the Sun across a number of different frequency bands including the damaging UV-B band. An extensive database of the infrared absorption spectra for gases is maintained on the HITRAN Web site by the Harvard-Smithsonian Centre for Astrophysics, Cambridge, MA, USA, in conjunction with the V.E. Zuev Institute of Atmospheric Optics, Tomsk, Russia. It includes the absorption spectra for water vapour, carbon dioxide (CO2), methane, (CH4), nitrous oxide (N2O), and the halocarbons which the UN’s Intergovernment Panel on Climate Change (IPCC) has stated are, in order of importance, the main ‘greenhouse gases’ in the atmosphere.
While we have been told that ‘greenhouse gases’ are a cause of dangerous surface global warming, climate scientists have failed to tell us that they also absorbs radiation from the Sun in the upper atmosphere thereby protecting the Earth in a similar fashion to the protection given by ozone.For the case of absorption by CO2, the most prominent spectral line is at a wavelength of 4.3 microns.
Applying Planck’s Law this gives us a spectral radiance of no more than 0.73 Watts per (steradian metre squared) per micron. This is for an Earth emitting at a temperature of 288 degrees Kelvin, dependent on the emissivity at the time. For the incoming Sun’s spectral radiance at the Earth’s orbit, the figure is 2.24 W/(sr m^2)/micron for a Sun temperature of 5780 degrees Kelvin.
These numbers mean that at least THREE TIMES as much heat is radiated back into space by CO2 in the upper atmosphere as is ‘back-radiated’ to the Earth’s surface at this wavelength.
Clearly, absorption and re-radiation of the sunshine in the upper atmosphere at this wavelength cools the Earth and is going to cause additional cooling as the concentration of CO2 increases.