Beer’s Law and climate change

Vincent J. Curtis

13 Nov 21

One of the best laws that chemists employ is Beer’s Law.  It’s used in analytical chemistry.  Anybody who has calibrated a humble Spectronic 20 or an atomic absorption spectrophotometer has discovered Beer’s Law.  But what has Beer’s Law got to do with climate change?

Beer’s Law states that the amount of light absorbed by a sample is proportional to the concentration of the sample.  The higher the concentration, the more light absorbed.  Up to a point.  Beyond that point, the calibration curve departs from linearity and flattens.  Eventually, the sample becoming more concentrated causes detectably no more light to be absorbed. The curve at that point is flat.

When the earth cools at night, it emits infra-red light in a spectrum known as blackbody radiation.  Carbon dioxide absorbs a narrow band of that light at 15 micron wavelength.  The amount of light absorbed by CO2 follows Beer’s Law up to a point.  Beyond that point, adding more CO2 to the atmosphere causes no more infra-red light of that wavelength to be absorbed.  Work recently published in the journal Atmospheric and Oceanic Physics showed that the light absorption, or greenhouse effect, of CO2 is maxed-out by 100 ppm, and the current concentration of CO2 in the atmosphere is well into the flat part of the light absorption curve.  Doubling the concentration of CO2 in the atmosphere will result in only a tiny increase in the amount of light absorbed.  CO2 is already maxed-out in its greenhouse effect.

Likewise, methane  Methane’s infra-red light absorption overlaps that of water vapor’s absorption, and doubling methane concentration causes an almost undetectable amount of more light to be absorbed.

Hence, the greenhouse effect is already maxed-out, and adding more CO2 and methane to the atmosphere is not going to cause a runaway greenhouse effect.  The earth isn’t going to get warmer and the world’s climate isn’t going to change if even if the amount of CO2 and methane in the atmosphere were doubled.

COP26 was a failure, but the world would be far worse off had it been a success.

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