The AGW community would have you believe that the science in favor of AGW is settled. As a professional scientist, a physicist with 40 years experience in aerospace and extensive knowledge of atmospheric physics, I can tell you that, indeed, the science is settled, but not the way the AGW extremists would have you believe. Atmospheric transmission measurements taken in the 1950s demonstrate conclusively that increasing CO2 concentration in the atmosphere cannot be the cause of global warming if global warming even exists.

A basic principle of science is that correlation does not prove causation. Climate scientists are working overtime fudging temperature related data showing global warming over many decades that correlates with the industrial revolution and increasing use of carbon-based fuels. Climate scientists are boldly asserting that this correlation proves global warming is caused by increased CO2 in the atmosphere.

Real scientists would demand to know the physics of how increased CO2 in the atmosphere causes global warming.  Is there any real physics behind this unsupported bold assertion?  As I am about to explain, based on test data from the 1950s, there is not.

There are three points I want to make that fall in the categories of physics and atmospheric physics. First, molecules in the atmosphere absorb lightwaves over what are called spectral bands. The spectral band can be narrow, as small as a single wavelength, or broad, covering a continuum of wavelengths or frequencies. This molecular absorption causes increased vibration within the molecule exciting certain vibration modes. The physics of each molecule determine which wavelengths can be absorbed to excite internal vibrations. Spectral band absorption in the atmosphere can be quantified based on measurements over a certain distance through the atmosphere such as “90 per cent absorption in this spectral band over a distance of 300 meters at sea level through the atmosphere”.

The second point is not really atmospheric physics, but more fundamental. Objects like the earth emit a spectrum, or wavelength continuum, of radiation that is completely described by “Planck’s Law” of black body radiation, derived in the 1900 by Nobel-winning physicist Max Planck. That curve predicts the peak intensity of light from the sun in the visible spectral band, and the peak intensity of light emitted by the earth in the LWIR spectral band. Planck’s curve has been validated by experimental data for over a hundred years, and was a huge breakthrough for the physics community in the 20th Century.

The third point is that there are two spectral bands in which the CO2 molecule absorbs infrared radiation. The first band is in what is called the Medium Wave InfraRed (MWIR) spectrum, and the second spectral band is in the LWIR spectrum. Both bands are created by absorption of energy in a CO2 molecule to excite stretching and/or bending modes of vibration within the molecule. The MWIR band of absorption excites stretching vibration modes, and the LWIR band of absorption excites bending vibration modes.

Of these two bands, the LWIR band is the most important in the absorption of infrared radiation from the earth because it is centered in the LWIR where most of the energy radiated by the earth is located, and is at least 5 times wider than the MWIR band. The center wavelength of the LWIR absorption band for the CO2 molecule is 15 microns with a width of about 1 micron.  By comparison, the center wavelength at which the maximum spectral radiant emittance occurs for the earth (based on Planck’s Law) is approximately 9.5 microns with significant amounts of energy contained in radiation with wavelengths that extend out to beyond 25 microns.

So, there is a spectral band centered at 15 micron where the CO2 molecules happily absorb radiating energy in the atmosphere to excite bending modes of vibration within each molecule. This band is in the LWIR where most of the radiation from the earth is contained, and has a spectral width of about 1 micron. This is a small but not insignificant portion of the more than 20 micron wide spectral band over which the earth radiates in the LWIR.

A reference book published by the Office of Naval Research, a department of the U.S. Navy, titled The Infrared Handbook was published in 1978 and is used as a bible by everyone I know in the IR community. Atmospheric transmission data at sea level is contained in this book based on measurements that were taken in the 1950 time frame, much before any recent increases in the concentration of CO2 in the atmosphere. These particular measurements are over a path length of 300 meters, and cover the IR spectrum from short-wave infrared out to beyond 20 microns in the LWIR (see “Field Measurements of Atmospheric Transmission”). In the LWIR absorption band of CO2 (center wavelength of 15 microns) the transmission measured is 0.0 due to CO2 absorption. That is, total 100% absorption over 300 meters at sea level in the spectral absorption band of CO2 that would capture the most energy, or “heat”, being radiated by the earth’s surface.

Increasing the concentration of CO2 in the atmospheric mixture of gasses present in the 1950s by burning fossil fuels or by bovine flatulence will not increase the measured absorption in the CO2 LWIR band above the 100% level that was measured and reported in The Infrared Handbook.  You cannot get more than 100% absorption. It is not physically possible. And yet that appears to be the basis of the theory of “man made” global warming

The science of anthropogenic global warming is settled, and has been for decades. Just not the way the AGW alarmists would have you believe.  Increased amounts of CO2 in the atmosphere cannot be the cause of global warming, if global warming even exists.