Greenhouse Gas

Vincent J. Curtis

1 Jan 2019

The greenhouse gas theory of anthropogenic global warming hangs its hat on some pretty old science – of black-body radiation and atmospheric absorption of infrared light.

The problem of black-body radiation puzzled classical physics until German physicist Max Planck, in 1900, proposed the quantization of energy and then solved the problem exactly.  This marked the dawn of modern quantum physics.  The second part, infrared absorption, is related to the quantization of energy.  After World War II, infrared detection and guidance systems were invented, and the age of guided missile technology began.  The Office of Naval Research of the United States Navy sponsored a lot of fundamental research into infrared spectroscopy during the 1950s.

When we see an object glowing red hot, it means that the black-body radiation of that hot object extends into the range of visible light.  When cooler, the warm object will emit black-body radiation in the infrared region but no longer in the visible region.  The sun acts as a nearly perfect black-body radiator of a temperature of 5,777 K.  Because the earth is not of uniform temperature, it does not act as a perfect black-body radiator, but it acts so piece-wise.

A plot of radiant power versus wavelength produces the curve characteristic of black-body radiation (See curve in Figure 1.).  The shape is characteristic, but the area under the curve and where the curve’s maximum is on the wavelength axis depends upon the temperature of the radiating body.

The theory of “greenhouse” gases turns on the absorption by certain gases in the atmosphere of infrared black-body radiation that is emitted by the earth into space.  Greenhouse gases are supposed to absorb and trap some of that energy in the earth’s atmosphere.  The greenhouse gases are so-called after the heat trapping effect, not because they are used in a greenhouse.  “Greenhouse” gases include ozone, dinitrogen oxide, and natural gas, or, as it is known in New Zealand, “bovine flatulence.”  Nobody is going to fill a greenhouse with bovine flatulence unless the plan is to blow it up.  Carbon dioxide and water vapor are used in greenhouses, not for their heat trapping effect, but because plants convert carbon dioxide and water into plant matter through photosynthesis.  More carbon dioxide and water, the bigger the plant.

The major infrared absorption band of carbon dioxide occurs at a wavelength of 15 micros and is about 1 micron in width (depicted as post in Feg.1)  That absorption occurs in this manner is a consequence of the quantization of energy.  Research funded by the U.S. Navy in the 1950s measured the atmospheric absorption of solar irradiation in the infrared region, and discovered that over a distance of 300 meters at sea level all the radiation at 15 microns wavelength was absorbed.  Transmission was 0.0.  Atmospheric carbon dioxide of the 1950s level was sufficient to absorbing all 15 micron radiation over a distance of less than 300 miters.

What does this mean?  It means that more carbon dioxide in the atmosphere is not going to absorb any more 15 micron radiation, because all of it already is.  There is no more “greenhouse” effect to be had out of carbon dioxide.  Adding more carbon dioxide to the atmosphere is not going to result in the absorption of more heat.

So, how can more heat trapping occur?  Water vapor absorbs strongly in some parts of the infrared spectrum, and weaker in others.  Higher absolute humidity would increase marginally the heat trapping effect of water vapor.  Bovine flatulence absorbs in areas of the spectrum not covered by water or carbon dioxide, but there is not enough of the gas in the atmosphere for it to be of serious concern.  Otherwise, new gases of low molecular symmetry and large dipole moment would need to be introduced into the atmosphere to increase atmospheric absorption of the earth’s black-body radiation.

The greenhouse gas theory of anthropogenic global warming falls apart upon consideration of 1950s research.

Figure 1

Curve of Black-Body radiation at T=287 K (14°C)

Figure courtesy of Andre Lofthus.

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Cf. Figures 5-31 h, i, j of The Infrared Handbook  1978   Edited by William L. Wolfe and George J. Zissis.  Prepared by the Environmental Research Institute of Michigan for the Office of Naval Research, Department of the Navy.

Vincent J. Curtis is a research scientist and occasional free-lance writer.