Testing CO2 Assumptions

Are you, or do you know a college student who’s looking for a thesis project? Here’s one for you.

CO2 is purported to be the lynchpin surrounding the theory of manmade global warming.  According to the theory, CO2 is a very effective gas at absorbing IR radiation, causing the atmosphere to warm up.  Based on this theory, the more CO2 in the atmosphere, the more warming will occur. Computer climate models assume a constant correlation between CO2 levels and atmospheric warming (typically that a doubling of CO2 results in a 1°C change of temperature).  The question is whether that relationship is experimentally valid. Let's stop arguing about it and test it.

To warm the planet, changing CO2 levels must change the net heat balance between what the Earth receives from the sun and what it radiates back to space. 

CO2 is a chemically stable, colorless, odorless gas that is generally evenly mixed with and distributed among other atmospheric gases.  It is an essential gas for life, without which plants will die, collapsing the ecosystem that relies on plants to provide the base of the food chain.  High concentrations of CO2 can degrade respiratory performance and lead to death.

Hypothesis:  CO2 absorption is so efficient that atmospheric CO2 absorbs all the available IR energy in its absorption spectrum many times over before leaving the atmosphere.  Since all of the available IR energy in the absorption spectrum has been absorbed already, adding more CO2 to the atmosphere will have a negligible effect on global atmospheric levels. Without a source of additional heat, no amount of additional warming will occur by adding CO2 beyond the current levels, because all the available energy in the CO2 absorption levels has already been absorbed and contributed to warming the atmosphere

Please see my other article detailing the physics behind CO2 absorption.

The experiment:  On a controlled test range, measure the spectral loss due to CO2 absorption over a given distance.  Calculate from that how far an IR emission can propagate before there is no measurable energy in the CO2 absorption frequencies.

What you will need: 

1 FTIR spectrometer.  You can get these from E-bay for under $500, and they run up into the thousands

1 broadband IR source

1 CO2 level meter.

(optional) cannisters of compressed CO2 gas.

A suitable site for the experiment.  A large, empty climate-controlled warehouse, manufacturing facility or aircraft hangar would be ideal. A blimp hangar or gymnasium would be an excellent location. An open area test site outdoors would be acceptable, with a change to the test protocol.

For experimenting in doors, make the facility as cold as possible, with as low humidity as possible. Have as few people as possible in the facility during the experiment, as CO2 exhalations in a confined area can dramatically change the atmospheric CO2 concentrations in an enclosed space in a very short time. Experimenting indoors provides the opportunity to test varying levels of CO2 and observe the effects on the spectrum.

If experimenting out of doors, an arid climate area with extremely low humidity is preferable, and all measurements should be conducted after dark, preferably in winter or after a cool day, so that IR emissions from the Earth do not adulterate the measurements. Experimenting outdoors provides the opportunity for measurements at longer ranges than you would typically be able to achieve indoors.

Assumptions:

Only the direct propagation path will be considered.  Any given point of the Earth’s surface emits IR radiation in all directions, giving an infinite number of paths for IR energy to leave the atmosphere.  Since all points are emitting IR energy and contributing to the total energy leaving the atmosphere in any given direction, the vertical path from an emission point to the edge of the atmosphere will represent the integrated aggregate of all points contributing to the measurement.  In other words, what is lost because the emission is omnidirectional is recovered because all the other emission points are likewise omnidirectional and contribute their emissions to the radiation from any point in the atmosphere as if those emissions originated as a vertical column.

In any free space electromagnetic measurement, the antenna factors must be calibrated to accurately measure the signal loss over the transmission distance.  For the purpose of this experiment, we can dispense with antenna correction factors, because we can use the spectrum itself as a control. CO2 is transparent to IR radiation at 13µm and 17µm wavelengths. Range measurements at these frequencies can provide a range calibration factor for measurements taken across the CO2 absorption spectrum between these frequencies.

Based on data compiled by the National Institute of Standards concerning the absorption spectrum of CO2, I predict that we should see a loss of 10dB in the CO2 absorption spectrum at a distance of 166 meters with CO2 levels at 400 ppm.

Measurement 1: 

Place the FTIR spectrometer receiver close to the IR source, to minimize the amount of CO2 between the receiver and the source.  If possible, a transmittance path in vacuum would be ideal.  You should see no change in IR emission levels between 13µm and 17µm wavelengths.  Record the levels across this spectrum.  This is your reference baseline.

Measurement 2: 

Move the FTIR spectrometer to a set distance from the IR emitter.  Measure and record the CO2 levels of the test range and record the spectrum between 13µm and 17µm wavelengths.  You should see a drop between 14.5µm and 15.5µm.  This is due to CO2 absorption.

Make a variety of measurements at different distances, recording the distance, spectrum and CO2 levels at each measurement.

If operating indoors, establish a baseline measurement at ambient CO2 levels at the longest distance.  Release gas from the bottled CO2 to double the CO2 levels on the range and repeat the measurement.  Use fans to disperse the CO2 evenly throughout the room.  Pay attention to CO2 levels and the chart above for safety.

If operating outdoors, see how far the FTIR spectrometer needs to be placed from the IR source to achieve a 10dB loss in the CO2 absorption band.

After all the measurements have been taken you should be able to graph the signal loss due to atmospheric CO2 absorption by distance and be able to project the losses to greater distances than those measured. Typically, the loss in dB will double when you double the distance. Keep in mind that electromagnetic losses due to distance are logarithmic, not linear.  Determine the distance necessary to achieve a 60dB loss in the CO absorption spectrum vs your control frequencies, representing a measurement of 1/1,000,000 of the original power – effectively zero.  Since this will be well below the measurement threshold/noise floor of your FTIR spectrometer unless you have an exceptionally hot IR source, you could safely say that adding any more CO2 or distance will not measurably change your readings.

In your conclusions, be sure to acknowledge that your measurements were conducted horizontally, and so had a constant partial pressure of CO2 across the range.  Calculate and correct for this in the vertical atmospheric column, where pressure changes with altitude.  If the theoretical model is accurate, you should be able to draw conclusions well before you have to deal with the atmospheric pressure step that happens at the tropopause.

One criticism of this experiment will be that the effect of the nonlinear "skirts" of the CO2 absorption spectrum will get wider as CO2 levels increase.  This can be measured and put to rest by calculating the total power density received by the spectrum analyzer at various levels of CO2. Additional experimentation may be interesting using a tube between the IR emitter and receiver, and calculating the spectral density at a variety of levels of CO2.  I believe you will find that the assumption that doubling the CO2 levels causes the absorption bandwidth to be wider breaks down pretty quickly as CO2 levels rise.